7 2 radioactivity uses and dangers

The activity of a radioactive source is the rate at which the unstable nuclei decay.

1 becquerel (Bq) is equivalent to 1 nucleus in a radioactive source decaying in 1 second.

The activity of a radioactive source decreases over time.

Activity is the rate at which radiation is emitted, whereas count rate is the rate at which radiation is detected.

The randomness of radioactive decay can be observed by

Half-life is the time taken for half the nuclei of a particular isotope in any sample to decay.

True. Half-life is constant for any particular isotope.

The activity of a radioactive sample will have halved after one half-life

True. Half-life is different for different isotopes.

The value of the activity of a radioactive sample after two half-lives is of its original value.

To determine the half-life of an isotope on a graph of activity over time:

After three half-lives, the proportion of original nuclei remaining in the sample will be .

Alpha radiation is used in smoke detectors.

Beta radiation is used in measuring and controlling the thickness of materials.

Gamma radiation is used for irradiating food to kill bacteria.

Gamma radiation is used for sterilising equipment.

A smoke alarm works as follows:

Alpha particles are stopped by paper, so they would not penetrate the material to reach the detector.

Gamma radiation can penetrate packaging and objects so all surfaces of the food or equipment can be irradiated. Gamma radiation is ionising enough to kill any microorganism, therefore it is used for sterilisation.

Beta particles can penetrate materials such as paper and aluminium foil, so the number of beta particles detected by a sensor can be used to measure and control the thickness of the substance.

Gamma radiation is used in the treatment of cancer in the process of radiotherapy. Gamma radiation can damage cells and tissues so this can be used to target cancer cells. Gamma rays can penetrate the body to reach the cancer cells, but the beams must be emitted from different angles to reduce the damage to healthy tissues.

Contamination is the accidental transfer of a radioactive substance onto or into a material.

Irradiation is the process of exposing a material to ionising radiation.

False. A substance can only become radioactive by contamination.

The main difference between irradiation and contamination is that contamination makes an object radioactive whereas irradiation does not.

True. Surgical equipment is sterilised by irradiation.

The risk of irradiation can be reduced by using shielding made from materials such as lead or by increasing distance from the source.

The risk of contamination can be reduced by

True. Contamination poses a greater risk to health than irradiation, especially if the radioactive material gets inside the body.

The effects of ionising radiation on living organisms are:

Ionising radiation can remove electrons from the atoms that make up DNA and therefore change the structure of the molecule. A structural change in DNA can lead to mutated cells. Mutated cells usually either die or get destroyed by the immune system, but some mutations can cause cells to replicate uncontrollably and lead to cancer.

Radioactive waste is disposed of by:

Radioactive samples can be handled safely by:

People working with radiation monitor their exposure by wearing a badge containing photographic film (dosemeter). The photographic film darkens when exposed to radiation.