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Basics - Poster 10

Biological Effects of Ionising Radiation

_ energy to atoms within that material . Most of the energy appears as heat , but a small percentage causes ionisation : the ejection of an electron from the atom , leaving the atom as a positively charged ion . Other forms of radiation do not have sufficient energy to do this .

The positive ion , the atom , will then combine with other atoms to alpha ( α ), beta ( β ) or gamma ( γ ) form a chemically reactive molecule . These can cause biological damage within the body , by reacting with other atoms and molecules . For example DNA in the cell . If the chromosomes cannot divide then the cell will die . At low doses the body can replace cells and recover .

Another possible effect is to produce changes in the DNA coding and functionality of the cell . Again the body has defence mechanisms but over time there is a small possibility of this leading to cancer or leukaemia .

Arrows pointing to damage points in the chromosomes .

Radiation Effects

• Stochastic effects - Cancers and Leukaemia

Risk factors Cancer risk factors are derived from epidemiological follow-up studies of exposed groups of people , such as the Japanese atomic bomb survivors . Most of these groups received high doses in short periods of time . Whereas for workers and the population most radiation exposure involves low levels of radiation over long periods of time .

A precautionary approach is used in deriving risk factors , one element of which is the assumption that there is a proportional

relationship between dose and risk . The risk factor for contracting

-5 fatal cancer is 5x10 per millisievert ( mSv )

- Low probability and latency period before onset - No threshold - Greater the dose , greater the probability

• Acute tissue reactions - Localised skin effects e . g . erythema & blisters - Hair loss - Acute Radiation Syndrome ( ARS ), possible death - Threshold for each type of effect - Greater the dose , greater the severity of effect

Typical Threshold Doses for Acute Effects

• Whole Body Doses Detectable chromosome changes

0.1 Sv Blood count changes 1 Sv Radiation sickness ( ARS ) Death

1 Sv 10 Sv

• Localised Doses to Skin Reddening ( erythema ) Hair loss Blistering

5 Sv 7 Sv 20 Sv

Erythema and blistering on the hands of an industrial radiographer who directly handled a very active radiation source .

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