Nuclear Processes

In chemical reactions, electrons in atoms are responsible for

bonds forming and being destroyed.

The identity of the atoms involved does not change

This is not true for nuclear processes because;

These reactions involve the protons and neutrons in the

nucleus – too large or too small of a ratio between protons and

neutrons

There are two types of nuclear reaction

Fission and Fusion Reactions

Fission Reactions

• Involve a nucleus collapsing to form a smaller nucleus

• Usually involve atoms with large nucleii such as the Lathanides and Actinides

• They produce , and emissions.

Fusion Reactions

• These involve nuclei joining together to make larger ones.

• These type of reactions are what go on inside stars and provide the energy that causes them to shine.

The particle

• Consists of 2 protons and 2 neutrons

• Is emitted from a nucleus during radio active decay

• Is the most destructive radiation because it ionizes atoms it bumps into

The particle

• Has a relative mass of 4 amu• Low penetration ability (stopped by paper

or skin)• Harmful if ingested or inhaled (can’t get

out)• Decreases atomic number by 2 • Decreases mass by 4

The particle

• The particle is the same as a Helium atom with the electrons removed.

• It is often written as He 4

2 in nuclear equations

An decay reaction

The Uranium atom U23892 decays by particle emission

U 238

92 He 42 + ? 234

90

What is represented by ?

An decay reaction

The Uranium atom U23892 decays by particle emission

U 238

92 He 42 + Th 234

90

Th is thorium – we can work it out by using the periodic table and looking up the atom with atomic number 90. The mass number does not matter – it is simply an isotope of Th.

More decay reactions

The Thorium atom Th22790 decays by particle emission

Th 227

90Complete the equation

More decay reactions

Th 227

90 He 42 + Ra 223

88

More decay reactions

The Actinium atom Ac22589 decays by 3 particle emissions

Ac 225

89Complete the equation

More decay reactions

Ac 225

89 3He 42 + Bi 213

83

Particle emissions

Particles are electrons but they do not come from the electron shells which surround the nucleus – they come from the nucleus itself.

The electron is emitted when a neutron sheds its negative chargeand becomes a proton.

N10 p1

1 0-1

Tritium decay (beta)

Particle emissions

The effect of Particle emission is to increase the proton count by 1 whilst leaving the overall mass unchanged.

Th231

90 0

-1 + ?What is ?

Pa231

91

Decay Series

When a radioactive nucleus such as U23892 decays it

often produces another radioactive isotope which goes on to decay further.

We are going to construct a decay series on graph paper for the element U238

92 to show how it eventually forms a stable isotope of lead Pb206

82

GET A PIECE OF GRAPH PAPER

• Draw a vertical axis representing atomic mass. It will need to run from 200 to 240

• Draw a horizontal axis representing atomic number. It will need to run from 78 to 93.

• Position the isotope U23892 on your graph

and mark it clearly.

240

20078 93

Mass

Number

* U23892

Plotting an decay

• The nucleus gives off an alpha particle first to form a new nucleus

• Work out what the new nucleus is• Find the nucleus on your graph and add it in• Join the points with an arrow

240

20078 93

Mass

Number

* U23892

Th23490 *

Plotting a beta emission

• The Thorium next loses a Beta particle• Work out what would be formed• Add the nucleus onto your chart

240

20078 93

Mass

Number

* U23892

Th23490 * * Pa234

91

Building up the decay series

Continue to build up the series using the following emissions. Each alpha emission is shown as a diagonal to the left and each beta emission is a horizontal line to the right.

If you are successful you should end up with Pb20682

Good Luck !

Emission sequence (including the first two example emissions)

1. 2. 3. 4. 5. 6. 7.

8. 9. 10. 11. 12. 13. 14.

Electron Capture

• Some times a nucleus will capture an electron and a proton converts to a neutron.

• This decreases the atomic number but does not change the mass

• 201Hg80 + 0-1e 201Au79 + γ0

0

Positron Emission

• A positron has the mass of an electron and the charge of a proton – it’s kind of like a “positive electron”

• It may be emitted when a proton turns into a neutron

• Atomic number decreases and mass stays the same.

• 22Na11 0+1e + 22Ne10