External dosimetry

Radiation Dosimetry. Radioactive materials cause damage to tissue by the deposition of energy via their radioactive emissions. Thus, when they are internally deposited, all emissions are important. When external, only those emissions that are capable of penetrating the outer layer of skin pose an exposure threat. The biological effects of radiation exposure and dose are generally credited to the formation of free radicals in tissue as a result of the ionization produced (17). 

The models for external dosimetry consider only the photon doses to organs of individuals who are immersed in air or are exposed to a contaminated object. 

Irradiations and Dosimetry. Dilatometers are irradiated in one of several dry cobalt-60 y-ray facilities, which are viewed through periscopes. Temperature control is maintained by using either appropriate freezing mixtures or externally controlled constant temperature baths, from which the fluid is circulated into and out of the bath in the irradiation cell. 

General. Dosimeters measure the total dose of external radiation to which the device is exposed. Dosimeters are usually worn by personnel thereby measuring the external dose to that individual. Dosimetry is necessary since the medical effects of radiation may not manifest themselves for days, years, or even decades. There are several types of dosimeters. 

Each radiation safety program should have an established survey program to monitor the radiation and contamination levels in the laboratory so that the individual user can maintain a safe working environment. The measurements can identify and measure individual radionuclides or measure radiation dose. The dosimetry program should monitor exposures to individuals from external radiation or internal—ingested or inhaled—radionuclides, and also in areas of the laboratory. 

The internal dosimetry program generally relies on in vitro (outside) or in vivo (inside) monitoring capabilities. In vitro programs use an external radiation... 

ICRU 1997. International Commission on Radiation Units and Measurments, Report 56. Dosimetry of External Beta Rays for Radiation Protection. Washington, DC ICRU. 

A.26. Records of occupational radiation doses. Inspection personnel should selectively review records of individual occupational doses, including internal and external doses. Activities should be observed to ensure that procedural and management controls are effective. This includes controls for radiation areas and contamination areas as well as inspection of activities for internal and external dosimetry. Exposures of personnel that result in the operator s reference levels for effective doses or intakes being exceeded should be noted. Records of radiation protection training and retraining should be assessed. 

Radiation dosimetry is the measurement of a person s exposure, usually on an individual basis. USNRC licensees are required to individually monitor the occupational radiation exposure to any individual likely to exceed 10% of the dose limits from external or internal dose considered separately. Altiiough, typically most licensees perform such individual monitoring for anyone classified as a rad worker regardless of the dose they are expected to receive. The discussions of external and internal dosimetry that follow are focused on the evaluation of doses to individuals. 

An individual s external dose is commonly directly measured with personal dosimetry. There are several devices that can be used to accomplish this, and they are generically divided into two categories those that document the dose of record and direct-reading dosimeters that are used for real-time or near real-time measurement of radiation doses being received. 

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