Relative Dose Ranges from Ionizing Radiation

Relative Dose Ranges from Ionizing Radiation... 

RELATIVE DOSE RANGES FROM IONIZING RADIATION... 

Alanine dosimeters are based on the ability of 1-a alanine (a crystalline amino acid) to form a very stable free radical when subjected to ionizing radiation. The alanine free radical yields an electron paramagnetic resonance (EPR) signal that is dose dependent, yet independent of the dose rate, energy type, and relatively insensitive to temperature and humidity. Alanine dosimeters are available in the form of pellets or films and can be used for doses ranging from 10 Gy to 200 kGy. A reference calibration service using the alanine EPR system was developed and the scans were sent to the service center by mail. Currently the available system allows transferring the EPR scan to a NIST server for a calibration certificate. This way the procedure has been shortened from days to hours. ... 

Figure 3 illustrates rough dose-response model fits with human data for ionizing radiation and leukemia incidence from atomic bomb survivors (24). Data exist down to about the 10-5 lifetime risk per person exposed. This value is close to the region of regulatory interest, and relatively small risk differences are predicted by the three illustrated models in the dose range up to two orders of magnitude below the last observed dose value (ca. 5 rad). 

The radionuclide needs to be a gamma emitter (long-range ionizing radiation) that can be monitored from outside the patient s body. It should have a relatively short half-life to limit the radiation dose to the patient. The radionuclide most commonly used is technetium-99m, Tc. The m indicates that this is a metastable isotope, that is, that its half-life is considerably longer than most isotopes that undergo gamma decay. 

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