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Radioactivity notes

Extracts from this document...

Introduction

RADIOACTIVITYimage00.png

SUMMARY

Radioactivity

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

The mass number of an atom is the total number of protons and neutrons in the nucleus.

The atoms of an element have the same number of protons in their nuclei but the number of neutrons can vary.

Atoms with the same number of protons but different numbers of neutrons are called isotopes.

An atom is radioactive if its nucleus has an unstable proton to neutron ratio.

An unstable proton to neutron ratio causes an elevated energy level in the nucleus.

When a nucleus undergoes radioactive decay it lowers its energy level by giving off radiation.

The radiation given off by atoms that are naturally radioactive can be either alpha particles, beta particles or gamma rays.

Alpha particles are helium nuclei - two protons and two neutrons.

When an alpha particle is released, a new nucleus is formed with two less protons and two less neutrons.

Beta particles are electrons formed when a neutron in the nucleus changes to a proton and an electron.

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Middle

The number of nuclei remaining in unstable form after time t is equal to the number when timing started times e to the power minus the decay constant times t.

                                                        2.

Doses

Doses are measured by determining the number of joules of energy absorbed per kg of the body by radiation that has been absorbed.

If ionizing radiation transfers 1 Joule of energy to 1 kg of body tissue, the Absorbed Dose is 1 Gray.

Doses are usually around millionths of Grays.

The amount of damage to the body depends on the type of radiation.

The Absorbed Dose Equivalent equals the Absorbed Dose in Gray times the Quality Factor of the radiation absorbed. e.g.  particles  x 20         particles  x 1

The unit of Absorbed Dose Equivalent is called the Sievert Sv.

1,000,000Sv                Nausea, vomiting, not lethal but cancers likely in future years.

5,000,000Sv                Serious illness and 50% chance of imminent death.

10,000,000Sv        All people die.

Organs vary in the way they are affected by ionizing radiations. Each organ has a risk factor.

The Effective Absorbed Dose Equivalent an organ receives equals the Absorbed Dose Equivalent times the Risk Factor of the organ. e.g. bones  x 0.03 lungs  x 0.12

Nuclear Transformations

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Conclusion

3.

Nuclear Force

The nuclear force of attraction is the same for proton/proton, neutron/neutron and neutron/proton combinations.

The force acts over very short distances. A particle in the nucleus is only attracted to its immediate neighbours.

The nuclear force is about 100 times stronger than the repulsion between protons at the same distance apart, and holds the nucleus together.

Fusion

Fusion is the joining together of the isotopes of hydrogen called deuterium 2H1 and tritium 3H1.

A deuterium nucleus has one proton and one neutron. A tritium nucleus has one proton and two neutrons.

The fusion reaction is 2H1 plus  3H1  gives 4He2  plus  1n0 .

More energy is released in this process than in the fission process because more mass is lost.

To get the deuterium and the tritium nuclei to stick together, the nuclei must come very close so the nuclear force overcomes the repulsion between the protons.

The nuclei must be moving very fast if they are to get close enough to stick together and this means the temperature has to be as high as in the sun.

In the fusion reactors being developed, the super high temperature gas is held away from the walls of the container by a very strong magnetic field.

...read more.

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