level safe for humans. The shielding materials are concrete and lead shield which is 0.25mm thick for secondary radiation and 0.5mm thick for primary radiation Internal dose uptake Internal dose, due to the inhalation or ingestion of radioactive substances, can result in stochastic or deterministic effects, depending on the amount of radioactive material ingested and other biokinetic factors. The risk from a low level internal source is represented by the dose quantity committed dose, which has the same risk as the same amount of external effective dose. The intake of radioactive material can occur through four pathways: inhalation of airborne contaminants such as radon gas and radioactive particles ingestion of radioactive contamination in food or liquids absorption of vapours such as tritium oxide through the skin injection of medical radioisotopes such as technetium-99m The occupational hazards from airborne radioactive particles in nuclear and radio-chemical applications are greatly reduced by the extensive use of gloveboxes to contain such material. To protect against breathing in radioactive particles in ambient air, respirators with particulate filters are worn. To monitor the concentration of radioactive particles in ambient air, radioactive particulate monitoring instruments measure the concentration or presence of airborne materials. For ingested radioactive materials in food and drink, specialist laboratory radiometric assay methods are used to measure the concentration of such materials. Recommended limits on dose uptake The ICRP recommends a number of limits for dose uptake in table 8 of ICRP report 103. These limits are "situational", for planned, emergency and existing situations. Within these situations, limits are given for certain exposed groups; Planned exposure – limits given for occupational, medical and public exposure. The occupational exposure limit of effective dose is 20 mSv per year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv. The public exposure limit is 1 mSv in a year. Emergency exposure – limits given for occupational and public exposure Existing exposure – reference levels for all persons exposed The public information dose chart of the USA Department of Energy, shown here on the right, applies to USA regulation, which is based on ICRP recommendations. Note that examples in lines 1 to 4 have a scale of dose rate (radiation per unit time), whilst 5 and 6 have a scale of total accumulated dose. ALARP & ALARA ALARP is an acronym for an important principle in exposure to radiation and other occupational health