Nuclear Chemistry Only one element has unique names for its isotopes … Deuterium and tritium are used in nuclear reactors and fusion research

Nuclear Chemistry

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.

Man-made Isotopes

Cobalt-59 occurs naturally. When a neutron “sticks” to the nucleus,

cobalt-60 is formed.

Man-made isotopes are usually made by bombarding atoms with protons or neutrons.

Uses for Isotopes

Radioisotopes are used as tracers in chemical reactions.

Radioisotopes are used in “imaging” living and nonliving systems.

Radioisotopes are used to kill cancer cells. (Co-60, Bi-212)

Properties of alpha, beta and gamma

radiation

Subatomic particles

H1

1 e0

-1

n10proton

neutronelectron

What do the numbers represent?

Mass number /Atomic number

U235

92

Mass number

Symbol of Element

Atomic number

protons + neutrons

Protons in nucleus

Mass number

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

What is the atomic number

of an particle?2 He4

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

How many times heavier is an alpha particle than

a hydrogen atom?4

Beta () particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.What is the mass number of a particle?

-1e0

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

No protons or neutrons in an electron. -1e0


NoneWhat is the difference between a particle and a “regular” electron?


LocationLocationLocation

What is the difference between a particle and a “regular” electron?

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

No protons, neutrons or electrons.

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

Gamma rays have short wavelengths

… and high energies.

Increasing energy

Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +

Electric field from electrically charged plates

What is the effect of an electric field on

Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +


Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +

Are , and rays deflected by magnetic fields?


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

Radiation Project

Create a table listing information for each of the three kinds of radiation:

Alpha, beta and gamma

Properties to include in your table:

(1) Greek letter

(2) symbol

(3) actually is

(4) atomic number

(5) mass number

(6) relative mass

(7) relative. charge

(8) penetrating ability

(9) shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter

Symbol

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding

Stop!Complete the chart on notebook paper,

then continue.


Greek Letter

Symbol

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding


Greek Letter Symbol

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding


Greek Letter Symbol

2He4-1e0 NA

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding


Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding


Greek Letter Symbol

2He4-1e0 NA


Atomic number 2 -1 NA

Mass number

Relative mass

Relative charge

Penetrating

Shielding


Greek Letter Symbol

2He4-1e0 NA



Mass number 4 0 NA

Relative mass

Relative charge

Penetrating

Shielding


Greek Letter Symbol

2He4-1e0 NA



Mass number 4 0 NA

Relative mass 4 1/1837NA

Relative charge

Penetrating

Shielding


Greek Letter Symbol

2He4-1e0 NA



Mass number 4 0 NA


Relative charge +2 -1 NA

Penetrating

Shielding


Greek Letter Symbol

2He4-1e0 NA



Mass number 4 0 NA



Penetrating Low Medium High

Shielding


Greek Letter Symbol

2He4-1e0 NA



Mass number 4 0 NA



Penetrating Low Medium High

Shielding 2.5 cm of air;anything else

Metal, plastic or wood

Lead or concrete

Protection from radiation1. Shielding 2. Distance

How do you protect yourself from …

Alpha

Beta

Gamma

2.5 cm of air, paper, skinaluminum, lead, other metals, wood, plastic, etc.up to a foot or two of lead, many feet of concrete

There are some kinds of radiation you can not

protect your self from.

Gamma rays and high energy cosmic particles from space.

But there is one kind of radiation hazard that you

can protect against.

Radiation

That hazard comes from the uranium beneath your feet.

Uranium in the ground decays according to …

Uranium-238 decays through

many steps to make stable

lead-206

The uranium decay series

http://library.tedankara.k12.tr/chemistry/vol1/nucchem/trans90.htm

The uranium decay series

Radon is the only gas in the series.

http://library.tedankara.k12.tr/chemistry/vol1/nucchem/trans90.htm

Hazards from radon

Since radon is the only gas in the decay series of uranium …

…it can work its way up through the ground and into your

basements and crawl spaces.

You breathe radon into your lungs.

Hazards from radon

And when radon is in your lungs…

…it can decay and release 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.

Protecting against radon

Get a test kit to see if there is a problem. Charcoal canisters, which are sent off for analysis.

Abatement:Seal places where gas gets in.

Ventilation – bring in fresh air.

Half life

What is half life?

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

Suppose you start with 100.0 grams of a radioisotope that has a half life

of exactly 1 year.

What is half life?

How much will be left after 1 year?


of exactly 1 year.

What is half life?

After one year there will be 50.0 g left.


of exactly 1 year.

After a second year there will be 25.0 g left.

What is half life?

After a third year there will be 12.5 grams left.

After one year there will be 50.0 g left. After a second year there will be

25.0 g left.

After a fourth year there will be 6.25 grams left.

Half life project1. 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 project5. 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?

Half life projectm

ass

time

10

52.5

t1/2 t1/2

Half life projectm

ass

time

2.5

t1/2 t1/2

10

5

Half life projectA

ctiv

ity

(cou

nts/

min

)

Time (min)

200

10050

t1/2 t1/2

Exponential decay

A = A0e-kt

Half life project

Time (min)

10050

t1/2 t1/2A

ctiv

ity

(cou

nts/

min

)

background

Radiation is “not a problem” when it falls below background level.

200

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

Decay equations

Alpha decay

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

The alpha particle carries away two protons and two neutrons.

Alpha decay

92U238 2He4 + 90Th234

alpha particle

decay product

Alpha decay

92U238 2He4 + 90Th234

The atomic number decreases by 2.

The mass number decreases by 4.

Alpha decay

These must add up to 238

These must add up to 92

92U238 2He4 + 90Th234

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

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

What does this suggest about the composition of neutrons?

Beta decay occurs because of the instability of a neutron.

Beta decayScientists used to think that neutrons might be a combination of a proton and an electron.

We know that neutrons decay into protons, which stay in the nucleus,

and electrons, which are ejected from the nucleus as beta particles.

Beta decay

0n1 1H1 + -1e0

neutron proton electron

The electron ejected from the nucleus is a beta particle.

Decay of a neutron:

Beta decay

0n1 1H1 + -1e0 + 00


Technically, the decay of a neutron also involves a neutrino.

anti-neutrino

Beta decay

0n1 1H1 + -1e0 + 00


Actually, an anti-neutrino.

anti-neutrino

The word “neutrino” comes from Enrico Fermi, meaning “little neutral one” in Italian.

Beta decay

0n1 1H1 + -1e0 + 00


A neutrino is a particle with no charge and almost no mass.

anti-neutrino

Beta decay

0n1 1H1 + -1e0 + 00


A neutrino carries off some of the energy in the decay of the neutron.

anti-neutrino

Beta decay

0n1 1H1 + -1e0 + 00


When predicting the products of beta decay we will ignore neutrinos.

anti-neutrino

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

The number of neutrons

The number of protons

The mass number

The atomic number

A neutron decays to make a proton.

decreases by 1

increases by 1

stays the same.

increases by 1

Beta decay

6C14 7N14 + -1e0

beta particle

decay product

Beta decay

6C14 7N14 + -1e0

The atomic number increases by 1.

The mass number stays the same.

Beta decay

6C14 7N14 + -1e0

Notice that these add up to 6

These add up to 14

Beta decay

Zn-69 decays by beta emission. What is the decay product?

30Zn69 -1e0 + ??? 31Ga69

Beta decay

Write the beta decay equations for:

1. 82Pb214

2. 27Co62

-1e0 + 83Bi214

-1e0 + 28Ni62

3. ??? -1e0 + 48Cd11347Ag113

Review: decay equationsAlpha:

Go down two on periodic tableAtomic number decreases by 2Mass number decreases by 4

Beta:Go up one on periodic tableAtomic number increases by 1Mass number stays the same

Nuclear energy

All have enough energy to ionize atoms.

Gamma rays are electromagnetic energy.

Alpha and beta particles have high kinetic energies.

All nuclear decay is accompanied by a release of energy.

Nuclear energy

This can result in damage to your body.

Ionization occurs when electrons are removed from

atoms by or radiation.

An ion is a “charged atom” or group of atoms.

cancer

Nuclear energy

Forms of ionizing radiation are:

Alpha Beta Gamma X-rays

Cosmic rays

Ultraviolet light (UV) can cause cancer, but it is not ionizing radiation.

Neutrons Positrons

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Nuclear Chemistry Only one element has unique names for its isotopes … Deuterium and tritium are used in nuclear reactors and fusion research