Table of Contents
Dose & Radiation Protection
What is Dose?
Dose is a measure of the amount of radiation a person is exposed to. There are three main ways in which dose can be calculated:
Absorbed Dose
Absorbed Dose = the energy deposited per unit mass.
- Absorbed Dose is measured in Gray, Gy (1 Gy = 1 J/kg).
- Absorbed dose considers only energy and does not account for the differing extents of damage that may be caused by different forms of ionising radiation on different parts of the body.
Equivalent Dose
Equivalent Dose = Absorbed Dose x Radiation Weighting Factor (WR).
- Equivalent Dose is measured in Sieverts, Sv.
- A radiation weighting factor is used to account for the different ionising abilities of different radiation, due to their differing particle sizes and penetration.
| Radiation Type | Energy | Radiation Weighting Factor |
|---|---|---|
|
Alpha (α) |
All |
20 |
|
Beta (β) |
All |
1 |
|
Gamma (γ) |
All |
1 |
|
Neutron (n) |
Varies (keV – MeV) |
5 – 20 |
Effective Dose
Effective Dose = Equivalent Dose x Tissue Weighting Factor (WT).
- Effective Dose is measured in Sieverts, Sv.
- A tissue weighting factor is used to account for differences between the susceptibility of different parts of the body to radiation.
| Tissue Type | Tissue Weighting Factor |
|---|---|
|
Genitals |
0.20 |
|
Bone Marrow, Colon, Lung, Stomach |
0.12 |
|
Bladder, Breast, Liver, Oesophagus, Thyroid |
0.05 |
|
Bone, Skin |
0.01 |
- Where are different types of radiation found?
- Smoke Detectors - Americium-241 is used as a sealed alpha-emitting (α) source in smoke detectors. Under normal conditions, the alpha particles ionise air and generate an electric current which can be detected. This can’t happen if smoke gets in the way – no electric current and an alarm sounds!
- Radiotherapy – Beta-emitters (β), such as lutetium-177 and yttrium-90, are used in radiotherapy and brachytherapy to destroy damaged or diseased cells – treating illnesses such as cancer and arthritis.
- Food Irradiation – Gamma-emitters (γ), such as caesium-137 and cobalt-60, are used to sterilise food and food packaging as well as medical and dental implements. This kills bacteria, helping to reduce the 25-30% of food that is spoiled and wasted before consumption.
- Electricity Generation – Neutron sources, commonly polonium-210 with beryllium, are used in new nuclear fission reactors to start-up the reactor by instigating the first fissions.
How is dose measured?
The measurement, calculation and assessment of radioactive dose is known as dosimetry.
Radiation Detectors are used to measure the amount of radioactivity in an area. There are three types of these:
We also need to be able to measure the dose absorbed by any person working in a radiation-controlled area – this is called Personal Dosimetry and there are two types. Both are sensitive to beta (β) and gamma (γ) radiation; Passive Detectors also absorb x-ray (X) radiation.
Radiation Protection
Radiation Protection aims to protect people from the harmful effects of exposure to ionising radiation. It is enshrined in law. These effects may be deterministic (i.e. they occur above a given threshold) or stochastic (i.e. a statistical probability that increases with dose).
There are three principles of radiation protection:
There should be a net benefit to receiving a radioactive dose.
Doses should be kept As Low As is Reasonably Practicable (ALARP), to reduce the probability of stochastic effects (probabilistic events that occur by chance, such as cancer).
Exposure should be below dose limits, to prevent deterministic effects (which relate to the quantity of radioactive dose received).
The three principles of radiation protection are used throughout the entirety of the nuclear industry and are inherent in plant design. Such designs aim to reduce exposure to dose by considering:
Adam Piatt
Graduate Awareness in Nuclear (GAIN) Course, NSAN
Justification & Optimisation, IAEA
Monitoring our Environment, Sellafield Ltd.
Neutron Detection & Counting, Mirion
Nuclear Power Reactors, World Nuclear Association
Personal Dosimetry Management, Nuclear Institute
Radiation & Health Effects, World Nuclear Association
Radioisotopes in Consumer Products, World Nuclear Association
Radioisotopes in Food & Agriculture, World Nuclear Association
GM Counter, Marco Plassio – Licence CC BY-SA 3.0 DEED
Surface Contamination Scan, Dean Calma / IAEA – Licence CC BY 2.0 DEED
Cask Radiation Profiling System, Dean Calma / IAEA – Licence CC BY 2.0 DEED
Dosimeter at CROCUS, Rama – Licence CC BY-SA 2.0 FR DEED
Thermoluminescence Dosimeter Card, Dean Calma / IAEA – Licence CC BY 2.0 DEED
Pocket Watch, Dietmar Rabich – Licence CC BY-SA 4.0 DEED
20m Tape Measure, W. Carter – Licence CC0 1.0 DEED
Concrete Cells of Celler Cooperatiu d’Igualada, Jordiferrer – Licence CC BY-SA 4.0 DEED
