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TRUE OR FALSE

1. As the sample of radioactive

decays, it half life decreases.

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TRUE OR FALSE

2. As the half life increasers the mass of the radioactive material increases

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TRUE OR FALSE

3. The time required for half a radioactive sample to disintegrate is called half life.

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TRUE OR FALSE

5. Half life is constant to all

radioactive substance

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TRUE OR FALSE

4. Decay constant defined as the fraction of the number of atom decay in a unit time.

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Nuclear Decay

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The Atom- Review•The atom consists of two parts:

1. The nucleus which contains:

2. Orbiting electrons.

protons

neutrons

•Atom of different elements contain different numbers of protons.

•The mass of an atom is due to the number of protons and neutrons.

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XAZ

Mass number

Atomic number

Element symbol

= number of protons + number of neutrons

= number of protons

Isotope Symbol Review

A = number of protons + number of neutrons

Z = number of protons

A – Z = number of neutrons

**Number of neutrons = Mass Number – Atomic Number**

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U235

92U

238

92

Fill in the chart for each isotope

A

Z

Number of protons

Number of neutrons

A

Z

Number of protons

Number of neutrons

235

92

92

143

92

92

238

146

Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

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•Most of the isotopes which occur naturally are stable.

•A few naturally occurring isotopes and all of the man-made isotopes are unstable.

•Unstable isotopes can become stable by releasing different types of particles.

•This process is called radioactive decay and the elements which undergo this process are called radioisotopes.

•The products of this decay are called daughter isotopes

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Radioactive decay results in the emission of either:

• an alpha particle (),

• a negative beta particle (electron) (),

• or a gamma ray

Radioactive Decay

• a positive beta particle (positron) (),

In a nuclear reaction the MASS and ATOMIC NUMBER must be the SAME on both sides of the equations

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An alpha particle is identical to that of a helium nucleus.

It contains two protons and two neutrons.

Alpha Decay

XA

ZY

A - 4

Z - 2+ He

4

2

unstable atom

more stable atom

alpha particle

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Alpha Decay

Ra226

88Rn

222

86 He4

2+

Loss of 2 protons & 2 neutrons: Atomic # decreases by 2Mass # decreases by 4

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XA

ZY

A - 4

Z - 2+ He

4

2

Write your own Alpha Decay

Rn222

86+Y

A

ZHe

4

2

What is Y?

Rn222

86He

4

2+Po

218

84He

4

2

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U234

+

Write the equation for the alpha decay of Uranium-234

He4

2U

234

92+Th

230

90He

4

2

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X A

Z+Pb

214

82He

4

2

Find the missing starting material

He4

2+Pb

214

82He

4

2Po

218

84

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Beta EmissionA beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.

Beta emission occurs when a neutron changes into a proton and an electron.

XA

ZY

A

Z + 1+ e

0

-1

beta particle (electron)

proton stays in nucleus

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Beta Emission

Po218

84e

0

-1At

218

85+

Neutron splits emitting negative particle leaving a proton.•Atomic # increases by 1 •Mass # stays the same

(electrons have no mass)

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XA

ZY

A

Z + 1+ e

0

-1

Write your own Beta Emission

What is Y?

Th234

90Y

A

Z+ e

0

-1

Th234

90Pa

234

91+ e

0

-1

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C 14

+

Write the equation for the betaemission of carbon-14

C14

N14

7+ e

0

-1

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X A

ZBi

214

83+ e

0

-1

Find the missing starting material

Pb214

82Bi

214

83+ e

0

-1

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Electron Capture is the opposite of Beta Emission

Electron Capture

XA

Ze

0

-1+ Y

A

Z-1

The capture of the electron allows a proton to turn into a neutron

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Electron Capture

Po218

84e

0

-1

At218

85+

Capture negative particle, forming a neutron from a proton•Atomic # decreases by 1 •Mass # stays the same

(electrons have no mass)

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Write your own Electron Capture

What is Y?

XA

Ze

0

-1+ Y

A

Z-1

Ar37

18e

0

-1+ Y

A

Z-1

Ar37

18e

0

-1+ Cl

37

17

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Ni 59

+

Write the equation for electroncapture of nickel-59

Ni59

28e

0

-1+ Co

59

27

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Find the missing starting material

XA

Ze

0

-1+ C

14

6

N14

7e

0

-1+ C

14

6

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Positron EmissionA positron is like an electron but it has a positive charge.

During positron emission a proton changes into a neutron and the excess positive charge is emitted.

XA

ZY

A

Z - 1+ e

0

+1

positronmass stays in nucleus

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Positron Emission

Po218

84 e0

+1

At218

85+

Proton splits emitting positive particle leaving a neutron.•Atomic # decreases by 1 •Mass # stays the same

(positrons, like electrons, have no mass)

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XA

ZY

A

Z - 1+ e

0

+1

Write your own Positron Emission

What is Y?

B8

5Y

A

Z+ e

0

+1

B8

5Be

8

4+ e

0

+1

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O 16

+

Write the equation for the positronemission of oxygen-16

O16

N16

7+ e

0

+1

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X A

ZCu

66

29+ e

0

+1

Find the missing starting material

Zn66

30Cu

66

29+ e

0

+1

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Gamma Decay

•Gamma rays are not charged particles like and particles.

•Gamma rays are high energy radiation

•When atoms decay by emitting or particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. These atoms will emit gamma rays to release that energy.

•There is no change in mass or atomic number

XA

ZX

A

Z + 0

0

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SummaryReaction What happens? Mass # Atomic #

Alpha Decay

Lose Helium Nucleus -4 -2

Beta Decay -

Lose electron from nucleus(neutron turns into proton)

No change +1

Electron Capture Gain electron in nucleus (proton turns into neutron)

No change -1

Positron Emission

Lose positron (proton turns into neutron)

No change -1

Gammy Decay

Emit high energy gamma ray No change No change

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Nuclear Stability The strong nuclear force holds all nuclei together

Otherwise protons would repel each other Neutrons space out protons and make nucleus stable

Not all isotopes are radioactive

Only unstable nuclei decay

In smaller atoms stable isotopes have equal numbers of protons and neutrons

In larger atoms stable isotopes will have more neutrons than protons

Too many or too few neutrons makes the nucleus unstable

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Nuclear Stability Graph

Dark band = stable nucleusAreas off line = radioactive

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Fission

Fission is when a nucleus splits This is what happens in nuclear

power plants

Neutrons emitted during fission reactions can cause other fission reactions This is a chain reaction

In a nuclear reactor the chain reaction is controlled with control rods

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Chain Reaction

Each reaction allows multiple other reactions to occur

Controlled vs Uncontrolled

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Fusion

When two or more elements fuse (combine) to form one new heavier element

The energy released by the sun and all stars is due to fusion reactions in the core

This process releases more energy than fission

Fusion reactions are hard to contain because the reactants are a plasma and at very high temperatures, no solid material can contain a plasma

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Fission Fusion

Nuclei combineNucleus splits

End product is heavier than reactants

End product is lighter than reactants

Energy is released

LOTS of energy released

Can’t contain reaction

Reaction can be harnessed

Nuclear Change