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.

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 Usually involve atoms with large nucleii

such as the Lathanides and Actinides They produce , and emissions. Involve a nucleus collapsing to form a

smaller nucleus

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 Is emitted from a

nucleus during radio active decay due to too many protons

Consists of 2 protons and 2 neutrons (a helium nucleus)

Decreases mass by 4 and atomic # by 2

241Am95 237Np93 + 4He2 4.0 cm of air Low penetration -protected by skin Is the most destructive radiation

because it ionizes atoms it bumps into Relative danger is low unless

ingested Used in smoke detectors

An decay reaction

The Uranium atom U23892 decays by particle emission

U238

92 He 42 + ?

234

90

What is represented by ?

An decay reaction

The Uranium atom U23892 decays by particle emission

U238

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

Th227

90Complete the equation

More decay reactions

Th227

90 He 42 + Ra

223

88

More decay reactions

The Actinium atom Ac22589 decays by 3 particle emissions

Ac225

89Complete the equation

More decay reactions

Ac225

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. Due to neutron to proton ratio being too great.The electron is emitted when a neutron sheds its negative chargeand becomes a proton. (Bet you didn’t know it could do that!)

10N 1

1 p 0-1

Tritium decay (beta)

Particle emissions

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

Th231

90 0

-1 + PaNotice how particle emission raises the atomic number by 1

231

91

Particle emissions Can penetrate 6-300 cm of air Blocked by clothing and paper Moderate danger Excessive exposure can be harmful Used in many medical diagnostic tests

and treatments

Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon known as a gamma radiation.

Gamma Ray Emission

Gamma rays have no mass and no charge – may accompany and/or emissions

High energy and very penetrating May be stopped with very thick (6 ft. or so

of concrete) or 3-5 cm of lead (think about the dentist)

γ00 or 0

0γ Used for medical tests and treatments Sterilization of equipment & foods

Electron Capture Sometimes 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

Decay Series

When a radioactive nucleus such as 238U92 decays it often produces another radioactive isotope which goes on to decay further.

You are going to construct a decay series on graph paper for the element 238U92 to show how it eventually forms a stable isotope of lead 206Pb82

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

Atomic Number

* 238U92

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

Atomic Number

* 238U92

234Th90 *

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

Atomic 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.