Radiation Protection Glossary

A radiation protection glossary for Radiation Protection Supervisors (RPS) and anyone interesting in radiation safety terminology. The glossary is a mixture of health physics terms, and phrases related to radiation legislation, transport, practical safety and similar.

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G

    Gamma Rays

    Gamma Rays are a type of high energy radiation the form of Photons which have no mass. They are part of the electromagnetic spectrum. In Radioactive Decay they originate from changes in the structure and energy levels of the Atomic Nucleus, or, through electron-positron annihilation or by nuclear fission. Gamma rays travel greater distances than either Alpha Particles or Beta Particles and are much more difficult to shield. Whilst their mode of formation is different, they are identical to X-rays.

    Gamma-ray Constant (Specific)

    The (specific) Gamma-ray Constant is a useful numerical quantity which can be used to predict exposure in terms of Equivalent Dose per unit activity per unit distance for gamma emitters. As the term is a constant, exposure (in terms of dose rate) will vary proportionally with distance and activity values, making approximate calculations (especially from Point Sources) quite easy.

    For example, the gamma-ray constant for Caesium-137 is 76 micro Sv/h per GBq at 1m from an unshielded point source. From this we can see that:

    • the dose rate will be 152 micro Sv/h at 1m from a 2GBq Cs-137 source.
    • the dose rate will be 19 micro Sv/h at 2m from a 1GBq Cs-137 source (using the inverse square law).

    It is important to note that the gamma-ray constant is specific to a particular radionuclide.

    Geiger counter

    A Geiger Counter (G-M Counter) is a type of detector used to measure levels of Radiation or Contamination. The counter is relatively simple to make and is quite robust so it is used regularly in the field to take quick measurements. Due to its mode of operation, the output of the Geiger Tube is independent of the incident energy or the incoming Ionisation event. Thus it is strictly a 'counter' rather than an energy spectrometer. Whilst the geiger counter will respond to Gamma Rays they are particularly suited to medium and high energy Beta Particles (e.g. C-14, S-35, P-32) and alpha emitters if fitted with a think window (e.g. Po-210, Am-241).

    Genetic effects

    Genetics effects (with respect to Radiation Protection) are those effects present in the offspring of those exposed to Probabilistic / Stochastic levels of Ionising Radiation.

    Glove Box

    The glove box is a type of enclosure used to completely contain Radioactive materials, thus separating them from the operator who needs to manipulate them. They are normally constructed from either a fibre glass material or stainless steel and incorporate extraction systems to maintain a negative pressure relative to the general working environment. They are particularly useful for Alpha emitting radioactive materials which can otherwise present a significant internal hazard if inhaled. If high energy Gamma emitters are also present the box may be shielded by lead sheet or bricks (with leaded glass viewing windows).

    Gray

    The Gray (Gy) is the SI unit of Absorbed Dose. 1Gy is equivalent to an energy of 1 Joule / Kg of absorbing medium. 1 Gy is also equal to 100 Rads (the rad being the older unit of absorbed dose, still used in the US).

Physics is, hopefully, simple. Physicists are not

– Edward Teller -