P6 - Revision Summary

Seite 1

The three particles found in an atom

are protons, neutrons and electrons. Of these, protons and neutrons are found

in the nucleus.

An unstable atom is an atom which, due

to the amounts of protons, and neutrons, is radioactive.

Isotopes contain the same amount of

protons and electrons but contain different amounts of neutrons. Oxygen-16 has

two less neutrons than Oxygen-18 meaning it has less mass.

The

rate of radioactive decay is not affected by chemical processes. Radioactive

decay is a nuclear process; it happens in the nucleus and only involves

neutrons and protons.

Alpha radiation involves the release

of an alpha particle from a nucleus. An alpha particle contains only two

protons and two neutrons. This gives it a charge of +2 and a large mass of 4. Beta radiation involves the release of

an electron from

the nucleus. A beta particle is

an electron. This gives it a -1 charge and a very small mass. Gamma radiation involves the release

of gamma radiation from the nucleus. Gamma radiation is a high energy wave (or

photon) which is electromagnetic radiation and so is part of the

electromagnetic spectrum. Alpha is the least penetrating and

most ionising. Gamma is the most penetrating and least ionising. Beta is

intermediate in ionisation power and penetration power between alpha and gamma.

a) Alpha can be stopped by paper & skin b) Beta can be stopped by thin aluminium & any metal c) Gamma can be stop by thick lead & very thick concrete.

a) 131 & 54 b) 148 & 64

Half life is the time taken for half of the radioactive nuclei now present to decay.

840, 420,210,105 4x60=240 240/3=80 minutes

In this experiment, alpha particles were fired at gold

atoms. Alpha particles have a charge of +2. Most particles passed straight

through which indicated most of the atom is empty space. Some particles were

largely deflected or bounced straight back. This indicates that there must be a

large repulsion (from something with a large positive charge). This suggested

that all the positive charge is held in small space. This is where the idea of

a positive nucleus was suggested.

The positive protons repel each other.

However, in the nucleus there is an attractive force between protons and

neutrons called the strong force. This force is much stronger than the

repulsive force (at short distances only) and holds the nucleus together.

This equations shows that mass and

energy are interchangeable and in fact mass is a form of energy. This means

that mass can be converted into other forms of energy.

A neutron is the particle which is

released during fission reactions. This neutron can also initiate nuclear

reactions and so a chain reaction is sustained.

Nuclear reactions are initiated by

firing neutrons into the radioactive sample. This causes a nuclear reaction

which is a chain reaction and releases large amounts of heat. This heat is

absorbed by water which creates steam. The movement of the steam then turns a

turbine which turns a generator. The generator produces electricity.

Low level waste is slightly radioactive and can be buried in secure

landfill sites. Intermediate level waste is quite radioactive and some of it

will stay radioactive for tens of thousands of years. It is often sealed in

concrete blocks and then placed in a steel containers for storage. High level

waste is so radioactive that it actually gives off a significant amount of

heat. This waste is sealed in glass and steel then cooled for 50 years before

being moved to permanent storage.

Ionising radiation can break up

molecules into ions (charged molecules). These ions are very reactive and can cause damage in cells. High doses will

outright kill cells and low doses will cause damage to cells which may turn

them cancerous.

A dose of radiation is measured in sieverts (Sv), but it is often more appropriate to use milli sieverts (mSv). It takes into account the type of

radiation the subject has been exposed to and the amount of radiation (length

of time the subject has been exposed to it).

Uranium

miners and processors, workers in nuclear power plants, miners, nuclear

researchers, airline staff are at higher risk of exposure to radiation.

Radiation from rocks, radioactive gases (radon), cosmic

rays are sources of background radiation.

a)Treating cancer: Since high levels of gamma radiation

kill living cells, it can be focused onto cancerous cells to kill tumours.

Inevitably some may damage living cells and make the patient ill, but if it

removes the cancer then it is worth it. b) Sterilising medical

equipment: Gamma radiation can be used to kill microbes or bacteria on surgical

equipment to make it safe. It is better than heating as heating may damage

certain equipment.c)Sterilising food: As previously, gamma kills living

cells and so can be used to kill microbes in food meaning it will take longer

to spoil. It does not make food radioactive. d) Medical

treatment: Radioactive sources

can be used as tracers in medicine. This is when radioactive chemicals are

injected into patients and then the patient is scanned to see where the

chemical went. This can help diagnose several conditions. There needs to be a

short half-life so that it quickly disappears.