Radiology. Ionizing radiation- measurements. Units. Effects- determinative, stochastic
Written by Anam Hussain
Definition:
Ionizing radiation is the energy which radiates and is capable of changing the medium as well as causing the formation/emission of non-charged particles of rays.
Sources of ionizing radiation:
- Natural background ionizing radiation:
- Cosmic rays
- Terrestrial radiations
- Internal radiations
- Artificial sources
- X-ray examinations
- Crushed rocks used in building materials
- Phosphate fertilizers
- Nuclear plant emissions
Effects
- Deterministic effects (effects are proportional to IR activity, exposure, AD and EqD) and threshold doses as absorbed does are:
- Skin erythema: 2-5 Gy
- Irreversible skin damage: 20-40 Gy (gray)
- Hair loss: 2-5 Gy
- Sterility: 2-3 Gy
- Cataracts (opacity of the lens): 2-10 Gy average 5 Gy
- Lethality (affecting the whole body): 3-5 Gy
- Fetal abnormality: 0.1-0.5 Gy
- Stochastic effects:
- Of ionizing radiation are chance events
- Their occurrence and type of side effects are not known and are not related to the absorbed dose or type and power of radiation
- Assumed that stochastic effects have no threshold
- Effects are mainly linked to mutations in cells, induced by radiation
- If mutated cells are not identified and eliminated as ‘foreign’ by the immune system, this could lead to increase in risk of primary neoplasms
- Germline mutations could be passed on to offspring and cause congenital defects or increase in hereditary disorders in general
Measurements and units:
- Activity:
- defines the potential of the radioactive element to emit ionizing radiation
- Ionizing radiation is a product of the energy emitted during radioactive decay
- Hence to measure activity, need to measure how many nuclei are decomposed within a period of time
- SI unit is Becquirel (Bq)
- Activity is 1 Bq when one nuclear decays per 1 second (n/s)
- Exposure dose:
- Measures the amount of energy that ionizes the air
- SI unit is Coulomb (energy) per kg (mass of affected air)
- C/Kg
- Absorbed dose:
- Measures the energy deposited in a medium by ionising radiation
- It is equivalent to the energy deposited per unit mass of a medium so unit is Joules per kilogram (J/Kg)
- Adopted units are Gray (Gy)
- AD 1 Gy = 1 J/Kg
- Measuring biological effect of ionizing radiation:
- Different units are required because for example 1 Gy of alpha radiation would be more damaging than 1 Gy of gamma radiation
- Biological effects related to type of radiation measured in: Equivalent dose (EqD)
- EqD measured in Sievert
- EqD= AD x Kir (Kir is coefficient specifying the type of radiation)
- Measuring biological damage on particular tissue