Half Life

How long does radiation last

Book page 212 ndash 214

Syllabus 711 ndash 713

16032016

Half-Life 2 - I am the Freeman [3D Trailer] - YouTube [720p]mp4 copycgrahamphysicscom 2016

Starter

bull Radium Toothpaste

bull Whatrsquos the problem with this

16032016

copycgrahamphysicscom 2016

Starter Complete the Table Radioactive Decay αβɣ

Property α Alpha β Beta ɣ Gamma

Relative Charge

Relative Mass

Nature

Range in Air

Stopped By

Deflection in an Electric Field

16032016

copycgrahamphysicscom 2016

Radioactive Decay αβɣ

Property α Alpha β Beta ɣ Gamma

Relative Charge

+2 -1 0

Relative Mass 4 000055 0

Nature He nucleus (2 protons + 2

neutrons) Electron

High frequency electromagneti

c radiation

Range in Air Few cm Few m Very far

Stopped By paper Aluminium foil Lead

Deflection in an Electric Field

low high nil

16032016

copycgrahamphysicscom 2016

Aim bull Can we predict when radiation is emitted from

atoms

bull What is a half-life

Keywords bull Decay 쇠퇴

bull Half-life 반평생

bull Spontaneous 자연히 일어나는

bull Random 닥치는 대로의

bull Probability 개연성

16032016

copycgrahamphysicscom 2016

WHY16032016

copycgrahamphysicscom 2016

The big picture

Does radioactivity last for ever

Have you ever wondered

16032016

copycgrahamphysicscom 2016

What is half-life Radioactive decay is a spontaneous process that cannot

be controlled and is not affected by temperature

The half-life of a radioactive isotope is the average time

that it takes for half the nuclei in a sample to decay

For example the half-life of the isotope

iodine-131 is eight days

However every radioactive element has its own particular decay rate This is called its half-life

bull After eight days half the nuclei in a sample of iodine-131 have decayed

bull Eight days later half the remaining nuclei have decayed and so on

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Starter Complete the Table Radioactive Decay αβɣ

Property α Alpha β Beta ɣ Gamma

Relative Charge

Relative Mass

Nature

Range in Air

Stopped By

Deflection in an Electric Field

16032016

copycgrahamphysicscom 2016

Radioactive Decay αβɣ

Property α Alpha β Beta ɣ Gamma

Relative Charge

+2 -1 0

Relative Mass 4 000055 0

Nature He nucleus (2 protons + 2

neutrons) Electron

High frequency electromagneti

c radiation

Range in Air Few cm Few m Very far

Stopped By paper Aluminium foil Lead

Deflection in an Electric Field

low high nil

16032016

copycgrahamphysicscom 2016

Aim bull Can we predict when radiation is emitted from

atoms

bull What is a half-life

Keywords bull Decay 쇠퇴

bull Half-life 반평생

bull Spontaneous 자연히 일어나는

bull Random 닥치는 대로의

bull Probability 개연성

16032016

copycgrahamphysicscom 2016

WHY16032016

copycgrahamphysicscom 2016

The big picture

Does radioactivity last for ever

Have you ever wondered

16032016

copycgrahamphysicscom 2016

What is half-life Radioactive decay is a spontaneous process that cannot

be controlled and is not affected by temperature

The half-life of a radioactive isotope is the average time

that it takes for half the nuclei in a sample to decay

For example the half-life of the isotope

iodine-131 is eight days

However every radioactive element has its own particular decay rate This is called its half-life

bull After eight days half the nuclei in a sample of iodine-131 have decayed

bull Eight days later half the remaining nuclei have decayed and so on

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Radioactive Decay αβɣ

Property α Alpha β Beta ɣ Gamma

Relative Charge

+2 -1 0

Relative Mass 4 000055 0

Nature He nucleus (2 protons + 2

neutrons) Electron

High frequency electromagneti

c radiation

Range in Air Few cm Few m Very far

Stopped By paper Aluminium foil Lead

Deflection in an Electric Field

low high nil

16032016

copycgrahamphysicscom 2016

Aim bull Can we predict when radiation is emitted from

atoms

bull What is a half-life

Keywords bull Decay 쇠퇴

bull Half-life 반평생

bull Spontaneous 자연히 일어나는

bull Random 닥치는 대로의

bull Probability 개연성

16032016

copycgrahamphysicscom 2016

WHY16032016

copycgrahamphysicscom 2016

The big picture

Does radioactivity last for ever

Have you ever wondered

16032016

copycgrahamphysicscom 2016

What is half-life Radioactive decay is a spontaneous process that cannot

be controlled and is not affected by temperature

The half-life of a radioactive isotope is the average time

that it takes for half the nuclei in a sample to decay

For example the half-life of the isotope

iodine-131 is eight days

However every radioactive element has its own particular decay rate This is called its half-life

bull After eight days half the nuclei in a sample of iodine-131 have decayed

bull Eight days later half the remaining nuclei have decayed and so on

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Aim bull Can we predict when radiation is emitted from

atoms

bull What is a half-life

Keywords bull Decay 쇠퇴

bull Half-life 반평생

bull Spontaneous 자연히 일어나는

bull Random 닥치는 대로의

bull Probability 개연성

16032016

copycgrahamphysicscom 2016

WHY16032016

copycgrahamphysicscom 2016

The big picture

Does radioactivity last for ever

Have you ever wondered

16032016

copycgrahamphysicscom 2016

What is half-life Radioactive decay is a spontaneous process that cannot

be controlled and is not affected by temperature

The half-life of a radioactive isotope is the average time

that it takes for half the nuclei in a sample to decay

For example the half-life of the isotope

iodine-131 is eight days

However every radioactive element has its own particular decay rate This is called its half-life

bull After eight days half the nuclei in a sample of iodine-131 have decayed

bull Eight days later half the remaining nuclei have decayed and so on

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

WHY16032016

copycgrahamphysicscom 2016

The big picture

Does radioactivity last for ever

Have you ever wondered

16032016

copycgrahamphysicscom 2016

What is half-life Radioactive decay is a spontaneous process that cannot

be controlled and is not affected by temperature

The half-life of a radioactive isotope is the average time

that it takes for half the nuclei in a sample to decay

For example the half-life of the isotope

iodine-131 is eight days

However every radioactive element has its own particular decay rate This is called its half-life

bull After eight days half the nuclei in a sample of iodine-131 have decayed

bull Eight days later half the remaining nuclei have decayed and so on

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

The big picture

Does radioactivity last for ever

Have you ever wondered

16032016

copycgrahamphysicscom 2016

What is half-life Radioactive decay is a spontaneous process that cannot

be controlled and is not affected by temperature

The half-life of a radioactive isotope is the average time

that it takes for half the nuclei in a sample to decay

For example the half-life of the isotope

iodine-131 is eight days

However every radioactive element has its own particular decay rate This is called its half-life

bull After eight days half the nuclei in a sample of iodine-131 have decayed

bull Eight days later half the remaining nuclei have decayed and so on

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

What is half-life Radioactive decay is a spontaneous process that cannot

be controlled and is not affected by temperature

The half-life of a radioactive isotope is the average time

that it takes for half the nuclei in a sample to decay

For example the half-life of the isotope

iodine-131 is eight days

However every radioactive element has its own particular decay rate This is called its half-life

bull After eight days half the nuclei in a sample of iodine-131 have decayed

bull Eight days later half the remaining nuclei have decayed and so on

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Half Life

When radioactive sources give out radiation they DECAY

This means that the number of radioactive particles in a sample DECREASES

Any source contains billions of radioactive atoms As time goes by the atoms decay and become less radioactive

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

16032016

Half life

The decay of radioisotopes can be used to measure the materialrsquos age The HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decayhellip

At start there are 16 radioisotopes

After 1 half life half have

decayed (thatrsquos 8)

After 3 half lives another

2 have decayed (14 altogether)

After 2 half lives another

half have decayed (12 altogether)

= radioisotope = new atom formed

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Calculating half-life 16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

An Example

bull The activity of a source is 800kBq and its half life is 2 days What is the activity after 6 days

bull We know the half life is 2 days so how many half lives after 6 days

6

2 = 3 half lives

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Example contrsquod

Number of Half Lives Activity

o 800kBq

1 (after 2 days) 400kBq

2 (after another 2 days 4 days total)

200kBq

3 (after another 2 days 6 days total)

100kBq

As we can see from the table the final activity is 100kBq ALWAYS set out Half life calculations like this it helps keep track of where you are

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

16032016 Dating materials using half-lives

Question Uranium decays into lead The half life of uranium is 4000000000 years A sample of radioactive rock contains 7 times as much lead as it does uranium Calculate the age of the sample

8

8

Answer The sample was originally completely uraniumhellip

hellipof the sample was

uranium

4

8

2

8

1

8 Now only 48 of

the uranium remains ndash the

other 48 is lead

Now only 28 of uranium remains ndash the other 68

is lead

Now only 18 of uranium remains ndash the other 78

is lead

So it must have taken 3 half lives for the sample to decay until only 18 remained (which means that there is 7 times as much lead) Each half life is 4000000000 years so the sample is 12000000000 years old

1 half life laterhellip

1 half life laterhellip

1 half life laterhellip

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Another example

bull The activity of a source is 120MBq 12 years later the activity is 15MBq What is the half life of the source So how many times does the activity half in these 12 years

16032016 copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Another Example (2)

Number of Half Lives Time Taken (years) Activity

0 0 120MBq

1 4 60MBq

2 8 30MBq

3 12 15MBq

bullThe first calculation to do here is to see how many times 120MBq halves to make 15MBq bull120 gt 60 gt 30 gt 15 There are 3 half lives bullNow divide the total amount of years by the half life to find the time scale of a half life

bull 12

3 = 4 years 16032016 copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Dices as radioactive atoms

bull Flip the dices If it falls on an odd number it has decayed

bull We will count how many radioactive atoms (dices) are left each minute (throw)

bull Draw a decay curve of your results

Still radioactive

Time (mins) amp no half lives

Activity (Bq)

o 50

1 (after 1 min)

2 (after another 1 min 2 mins total)

3 (after another 1 min 3 mins total)

4 (etc)

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

The MampM Experiment Start with 64 MampMs 1 Give them a shake and pour onto a tray

bull If the M is face up it has not undergone radioactive decay and must be counted

bull If the M is face down it has undergone radioactive decay and must be removed and disposed of

2 Repeat for 6 half-lives recording your results

Number of half-lives

Number of MampMs

0 64

1

2

3

4

5

6 Still radioactive

decayed

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Keywords

bull Decay - the process by which a nucleus of an unstable atom loses energy by emitting radiation

bull Half-life - the average time that it takes for half the nuclei in a sample to decay

bull Spontaneous - a process or event occurring without apparent external cause

bull Random ndash happening without method bull Probability - is the measure of the likelihood that an event

will occur

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

Plenary

A _________substance is one that emits_______ due to having an ________nucleus Half-life is the ____for half the _____of an isotope to decay

radioactive

radiation

unstable

time

nuclei

Nuclei radiation radioactive time unstable

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

What is your opinion 16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016

16032016

copycgrahamphysicscom 2016