An Introduction to Radiation Safety 2014. Ian Williamson / Steve Clipstone. Alle Ding' sind Gift, und nichts ohn ' Gift; allein die Dosis macht , daß ein Ding kein Gift ist .
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Ian Williamson / Steve Clipstone
"All things are poison and nothing is without poison, only the dose permits something not to be poisonous."
(Paracelsus, 1493 - 1541)Restricting Exposure
The aim of the session is to
General and specific duties & rules about safe working practices, control measures, assessments, roles and responsibilities;
Health and Safety Executive (HSE) enforcement
Regulates the holding, storage, accumulation and disposal of radioactive material;
Environment Agency (EA) Enforcement
Replaced the RSA93 Act
Women of reproductive capacity - exposure of abdomen limited to 13 mSv in any consecutive 3 month period. Women are legally obliged to inform their employer
DistanceRadiation Dose rate
Double Reduced to ¼
Treble Reduced to 1/9
Quadruple Reduced to 1/16
- Helium nucleus
Not all of the atoms of a radioisotope decay at the same time, but they decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life.
The half-life of a radioisotope describes how long it takes for half of the atoms in a given mass to decay. Some isotopes decay very rapidly and, therefore, have a high specific activity. Others decay at a much slower rate– so decay at an “average rate”
After two half-lives, there will be one quarter the original sample, after three half-lives one eighth the original sample, and so forth.
It is an exponential decay process
= stable, although not a precise figure
After 1 half life half have decayed. There are 8 remaining
At start there are 16radioisotopes
After 2 half lives another half have decayed. There are 4 remaining
After 3 half lives another 2 have decayed. There are 2 remaining
How can we work out the half-life of a radioisotope?
We can plot a graph of activity against time
Whole body dose
The most massive of the radioactive emissions – alpha particles – have the shortest range. Due to their size they interact strongly with matter (lots of collisions with atoms) causing large amounts of ionization. This makes them very harmful to living tissue.
Beta particles being smaller have a weaker interaction but can still cause ionization as they interact with the electrons surrounding atoms.
Since gamma radiation is electromagnetic waves it is the most penetrating and least ionizing. However the deep penetration makes it dangerous to living tissue.
High Radiosensitivity - Lymphoid organs, bone marrow, blood, testes, ovaries, intestines
Fairly High Radiosensitivity- Skin and other organs with epithelial cell lining (cornea, oral cavity, esophagus, rectum, bladder, vagina, uterine cervix, ureters)
Moderate Radiosensitivity - Optic lens, stomach, growing cartilage, fine vasculature, growing bone (note optic lens may move up to high radiosensitivity)
Fairly Low Radiosensitivity - Mature cartilage or bones, salivary glands, respiratory organs, kidneys, liver, pancreas, thyroid, adrenal and pituitary glands
Low Radiosensitivity - Muscle, brain, spinal cord
Effects can take between 5 – 30 years
Takes place over a short period of time
Usually high exposures
Takes place over a long period of time
Usually low level exposures
Effect, e.g. malignancy and hereditary effects
Not immediately observable
probability increase as dose received increases
Effect, e.g. cataracts, fetal damage, skin effects
Large dose can be fatal
Degree of cells killed increases with dose impairing organ function
Design – fail to safety and cannot be bypassed
Engineered – shielded, fail to safety (interlocked), warning lights
Administrative – Local Rules, supervision, disposal
PPE – gloves , lab coats
All work requires a risk assessment where the risk is significant and foreseeable.IRRs require:
Nature and source of ionising radiation to be used
Estimated dose rates to anyone exposed
Likelihood of contamination arising and being spread
Results of previous monitoring if relevant
Control measures and design features
Requirement to designate areas and personnel
Planned systems of work
Estimated levels of airborne or surface contamination likely to be encountered
Possible accident situations, potential severity
Consequences of failure of control measures
Steps to limit consequences of accident situations