The effects that ionising radiation produces in living matter result from energy transferred from radiation into ionisation (and excitation) of the molecules of which a cell is made. The primary effects start with physical interactions and energy transfer, after which changed molecules interact by chemical reactions and interfere with the regulatory processes within the cell.
The resulting radiobiological effects in man can be divided into two different types:
• stochastic effects, where the probability of manifestation is a function of dose rather than the magnitude of the radiobiological effect, and
• deterministic effects, where the severity of the effect depends directly on dose, with a lower threshold dose below which no response occurs.
Symptoms of radiation exposure are classified as either early or late effects, with early effects relating to symptoms that occur within 60 days of exposure, and late effects usually becoming manifest many months or years later.
This chapter summarises the radiation quantities used to define the environment relevant to radiation effects in biological materials, and specifies the requirements for quantifying radiobiological effects for space missions.
Note that the discussions in this chapter are aimed at radiation effects on man. Effects on other biological materials (e.g. animals or plants flown as test subjects for experiment) on unmanned or manned missions can also be assessed, based on the principles discussed here.