Nuclear chemistry

Nuclear Chemistry

P Squires

Basic Chemistry

2005-2006

Isotopes …

…have the same number of protons and electrons but different numbers of neutrons.

Isotopes …

…have different mass numbers but the same atomic number.

Symbols for Isotopes

UU23523592

Symbol Symbol of of ElementElement

Mass Mass numbernumber

Atomic Atomic numbernumber

Symbols for Isotopes

EA

Z

Symbol of Element

Mass number

Atomic number

A is the symbol for mass number

Z is the symbol for atomic number

Isotopes

Consider an atom of aluminum with 13 protons and 15 neutrons. What is Z and A?

A = #p+ + #n

13 + 15 = 28

How are isotopes of the same element alike and different?

Alike:

1. Number of protons and electrons

2. Atomic number

3. Chemical properties

Different:

1. Number of neutrons

2. Mass Number

3. Atomic weight of the isotopes

Isotopes

See Illustrated Isotope example

Finding the number of Protons, Neutrons, and Electrons

The atomic number is the number of protons in the nucleus.

The number of electrons in a neutral atom equals the number of protons.

# of neutrons = A - Z# of neutrons = A - Z



U-235U-235

A = 235A = 235protons + neutrons = 235protons + neutrons = 235

Z = 92Z = 92protons = 92protons = 92electrons = 92electrons = 92

Q. Find the number of neutrons in Q. Find the number of neutrons in the Ba-137 isotope.the Ba-137 isotope.



Element Symbol Z A #p #n #eZinc 66

In 6885 38

82 210Rn 136

35 47


Element Symbol Z A #p #n #eZinc Zn 30 66 30 36 30

In 6885 38

82 210Rn 136

35 47



Indium In 49 117 49 68 4985 38

82 210Rn 136

35 47



Indium In 49 117 49 68 49Strontium Sr 38 85 38 47 38

82 210Rn 136

35 47




Lead Pb 82 210 82 128 82Rn 136

35 47




Lead Pb 82 210 82 128 82Radon Rn 86 222 86 136 86

35 47




Lead Pb 82 210 82 128 82Radon Rn 86 222 86 136 86

Bromine Br 35 82 35 47 35

Only one element has unique names for its isotopes …

tritium H

deuterium H

hydrogen H

31

21

11

Deuterium and tritium are used in nuclear reactors and fusion research.

Some isotopes are radioactive

• Radioactive isotopes are called radioisotopes.

• Radioisotopes can emit alpha, beta or gamma radiation as they decay.

• Radioisotopes are important in a number of research fields.

Protection from radiation

1. Shielding

2. Distance

Protection from radiation

How do you protect yourself from …

Alpha

Beta

Gamma

2.5 cm of air, paper, skin

aluminum, lead, other metals, wood, plastic, etc.

up to a foot or two of lead, many feet of concrete

Properties of Alpha Particles

• Alpha () particles are the nuclei of helium atoms and have the symbol 2He4

Properties of Beta Particles

Beta () particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.

Properties of Gamma Rays

• Gamma () rays are high energy electromagnetic waves, not particles.

• Gamma rays have short wavelengths and high energies and travel at the speed of light.

Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +

Electrically charged plates

What is the effect of electrically charged plates on

Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +

Electrically charged plates

Why do the , and rays take the paths that they do?

Alpha, Beta, Gamma

Radioactive Source

Paper

Aluminum foil

Lead

Alpha, Beta, Gamma

Radioactive Source

Paper

Aluminum foil

Lead

Alpha, Beta, Gamma

Radioactive Source

Paper

Aluminum foil

Lead

Alpha, Beta, Gamma

Decay equations

Alpha Decay

In alpha decay, an alpha particle (2He4) is released from the nucleus.

Alpha decay

92U238 2He4 + 90Th234

alpha particle

decay product

Alpha decay

86Rn220 2He4 + ???

Radon-220 decays by alpha emission. What is the decay product?

84Po216

Alpha decay

Write the alpha decay equations for:

1. 95Am241

2. 84Po216

3. 88Ra226

2He4 + 93Np237

2He4 + 82Pb212

2He4 + 86Rn222

Beta Decay

Beta decay occurs because of the instability of a neutron.

Neutrons are a little more massive than protons; and neutrons are neutral.

Beta decay

0n1 1H1 + -1e0

neutron proton electron

The electron ejected from the nucleus is a beta particle.

Decay of a neutron:

Beta decayStart with a Li atom with

3 protons and 4 neutrons.

Suddenly a neutron decays!

Now there are 4 protons

and 3 neutrons.

A beta particle goes zipping out of

the nucleus.

Beta decay

6C14 7N14 + -1e0

beta particle

decay product

Beta decay

Zn-62 decays by beta emission. What is the decay product?

30Zn62 -1e0 + ??? 31Ga62

Beta decay

Write the beta decay equations for:

1. 82Pb214

2. 27Co62

-1e0 + 83Bi214

-1e0 + 28Ni62

3. ??? -1e0 + 48Cd11347Ag113

Gamma Decay

•Gamma rays are neutral and thus no change is made in the equation.

6C14 6C14 + ¥

Half life

What is half life?

Half life is the time needed for one half of a radioisotope to decay.

Half Life

• Take 100 pennies and throw them on the floor.

• Remove those that are heads up.

• Count remaining pennies.

• Continue until only one penny remains.

What can this tell us about Half Life?

What is half life?

• Suppose you start with 100.0 grams of a radioisotope that has a half life of exactly 1 year.

How much will be left after 1 year?

How much will be left after 2 years?

Half life projectQuestions:

1. A radioisotope has a half-life of 100 years. How long will it take for the radiation to decrease to 1/16 of its original value?

400 years

Half life projectQuestions:

2. A radioisotope has an activity of 560 counts per minute. After 16 hours the count rate has dropped to 35 counts per minute. What is the half life of the radioisotope?

4 hours

Nuclear Fission

Nuclear fission

Fission – the splitting of an atom after being struck by a neutron.

Nuclear Fission

U-235U-235

U-235

Nuclear fission

NeutronNeutrons

Fission fragment

Fission fragment

Nuclear fission

To picture a chain reaction, imagine 50 mousetraps in a wire cage.

And on each mousetrap are two ping-pong balls.

Now imagine dropping one more ping-pong ball into the cage …

Detail of ping-pong balls on mousetraps.

http://www.physics.montana.edu/demonstrations/video/modern/demos/mousetrapchainreaction.html



Nuclear fission

This heat energy can be harnessed to boil water,

creating steam,

that can turn a generator,

creating electricity.

Nuclear Fusion

Nuclear fusion

A day without

sunshine is a day without

fusion.

Nuclear Fusion

How do we detect radiation?

Mica window (fragile)

Wire (+ side of circuit)Metal shield (- side)Low pressure Ar gas

Counter 2435

Geiger-Mueller Tube

GM Tube

Rays leave the sourceSome hit the GM tube

Most do nothing

One ray may cause a discharge…

Source and the detector clicks

GM Tube

Filled with low pressure argon gas

About 1% efficiency

About 1 in 100 rays causes an electric spark between the case and the wire

Each spark registers as a count or click on the counter

Nuclear Fuel Cycle

Nuclear Fuel Cycle

• The Nuclear Fuel Cycle consists of sequence of steps in which uranium ore is mined, milled, enriched, and fabricated into nuclear fuel and then irradiated in a reactor for several years.

• The entire fuel cycle lifetime from mining to discharge is about 8 years.

Where is Nuclear Waste Kept?

• After irradiation the fuel is cooled in the spent fuel pit for several years and then moved to dry cask storage on the reactor site.

Spent Nuclear Fuel Pool

• Keep spent fuel rods under at least 20 feet of water to provide adequate shielding from the radiation for anyone near the pool

• Spent Fuel Pools were designed as TEMPORARY storage for fuel while short lived isotopes decay (<1 yr)

NUCLEAR REACTOR CORE

US Nuclear Power Plants

Radioactive Decay

Uranium-238 decays through

many steps to make stable

lead-206

The uranium decay series

Nuclide Half-Life Radiation *

U-238 4.468 · 109 years alpha

Th-234 24.1 days beta

Pa-234m 1.17 minutes beta

U-234 244,500 years alpha

Th-230 77,000 years alpha

Ra-226 1,600 years alpha

Rn-222 3.8235 days alpha

Po-218 3.05 minutes alpha

Pb-214 26.8 minutes beta

Bi-214 19.9 minutes beta

Po-214 63.7 microseconds alpha

Pb-210 22.26 years beta

Bi-210 5.013 days beta

The uranium decay series

Radon is the only gas

present in the decay process.

Mas

s nu

mbe

r

Symbol and Atomic number

U-238

Pb-206

The uranium decay series in NC EOC reference pages

StartStart

EndEnd

Alpha

Beta

Hazards from radon

• Radon gas works its way up through the ground and into your basements and crawl spaces.

• You breathe radon into your lungs.

Hazards from radon

• When a radon atom decays it releases an alpha particle …

…which travels only a short distance before it is absorbed by

your lungs, and transfers its energy.

Hazards from radon

This ionizing radiation in your lungs can cause lung cancer.

Smoking cigarettes and breathing radon really increases your

chances of getting lung cancer.

Half Life Project

Half life project

1. Pick a mass between 10g and 50g.

2. Decide on a half life – any time.

3. Scale your graph – mass on y-axis and at least six (6) half-lives on the x-axis.

4. Plot the masses after intervals of one half-life.

Half life project

5. What shape is the graph?

6. When will the mass of the radioisotope fall to zero?

7. When is the radioactivity no longer a problem?

8. What mathematical function describes radioactive decay?

Technology

Nuclear chemistry