Document 26jVm59w08vq0aE9v6woRzy5

IONIZING RADIATION be calculated If the exposure rate is 2.5 mR/hr, 40 hours will result m 100 rads (neglecting the conversion factor that arises from the fact that exposure to one roentgen results in a dose of 98 ergs/gm, while 1 rad equals 100 ergs/gm). If the exposure rate is 10 fames higher, then the tune must be reduced to one-tenth for the same dose (in the example, 100 rads) (See the earlier section on "Radioactive Decay" for discus sion of definitions ) In practice, the dose received in getting a task done can be spread over several em ployees so that no one person will exceed the guide levels Only necessary exposures should be planned for a work task The available cumulative exposure can be calcu lated from the formula (Age-18)5 rem, with a maximum of 5 rem per year if none is received in a particular year, then that 5 rem is earned forward m that em ployees "bank," and can be reserved for a future need But the RPG (radiation pro tection guide) limits its use to a maximum of 3 rem in any 13 consecutive week period, providing no more than 5 rem is used in a year In practice, the exposure rate (roent gens/hour) would be measured with an in strument Direct reading dosimeters are available, as are those that emit sound (a chirp) at a preset exposure rate Detecting and measuring external radiations instruments Instruments for monitoring and survey work to detect external radiation are avail able from many commercial sources In struments must be checked frequently for operation and calibration, and a dependable source of maintenance service must be available, especially for portable instruments Instruments may be used to detect or lo cate sources of radiation or to measure radiation Selection from the variety of choices of type and manufacture is based not only upon the lands of radiation to be encountered but also upon the reliability, operating characteristics, and vendor's serv ice capabilities Some instruments are designed to detect only one type and level of radiation, such as low-level alpha radiation Others will detect several types and levels of radiation Several air samplers are available These may be purchased complete, or the fans (vacuum pumps) may be ordered separate ly and then equipped with a specially.con structed, filter paper holder and an air-flow indicator The filter media must then be counted with a system for alpha or betagamma counting, such as a sealer, alpha probe, or beta-gamma tube Gas flow pro portional counters are also available If no prior experience exists in selection, obtain help from an experienced person as there are many types of specialized equip ment Detectors can be ionization cham bers, Geiger counters, proportional counters or scintillation counters. Portable survey in struments may consist of ionization chamber rate meters,, beta-gamma ionization cham bers, Geiger counters, beta-gamma Geiger counters, beta-gamma scintillation counters, alpha survey meters, or tritium sniffers Fixed monitors may consist of beta-gamma detectors, anr monitors, or area monitors Neutron monitors are available for slow, in termediate, and fast neutrons Specialized equipment is available for counting with counters and scalers Personnel monitoring systems exist for contaminated hands, shoes, or clothing. For further information see Health Phystes Instrumentation, J S. Handloser (Pergamon Press, 1959); Safe Handbag of Radunsotopes--Health fhysicta AddendumSafety Senes No 2, International Atomic Energy Agency (Vienna, 1960), especially pp. 34-46, Radiological Monitoring Meth ods and Instruments, NBS Handbook 51 (1952), pp 7-18, and Nuclear Instruments and Their Uses, A H Snell (ed ) (John Wiley, 1962), pp 425-442 Monitoring, surveying, and personnel monitoring The extent and type of monitoring for detection of external radiation are deter mined largely by experience and the nature of the source of radiation For example, if the radiation field is limited by the nature of the source of the radiation and the protective devices low, film badges or dosimeters worn by the ex posed employees may be completely ade quate. Some operations emit radiation at levels which would be excessive for 40-hr exposure On these operations, fixed moni toring equipment of the recording and 42-39