Microdosimetric basis for exposure limits
Consideration of the energy deposited by ionizing radiation in microscopic volumes has led to new insights into dosimetric concepts at the levels of interest in radiation protection. Large amounts of energy are deposited by the passage of low linear-energy-transfer (LET)-charged particles through small volumes. If a typical cell nucleus is considered to be about 7 micron, at an exposure rate of 2.5 X 10(-1) C kg-1 h-1 (1 mR hr-1) from a 60Co irradiation, the average cell nucleus receives one energy deposition event every 12.5 d. Biological processes, which modify radiation damage, typically occur in a few minutes to a few hours. Thus, at occupational exposure levels it is probably the irreparable or misrepaired effects of irradiation that determine the biological consequences. One goal of dosimetry is to measure the incident radiation, making it possible to predict biological risk and set meaningful exposure limits. These measurements must relate to the energy depositions that are responsible for radiation effects at low dose rates, yet the dosimetry system must not be excessively complex to allow use by operational health physicists. Furthermore, our description of the irradiation should be directly measurable. The use of quality factors based upon the energy deposition in a 1-micron-diameter volume of tissue as prescribed in International Commission on Radiation Units Report No. 40 (Joint Task Group 1986) satisfies these requirements. Instrumentation based upon measurement of lineal energy has already been successfully used in health-physics applications. Future changes in the quality factor can be accommodated by changing the algorithm in these microprocessor-based instruments.
- Research Organization:
- Pacific Northwest Lab., Richland, WA (USA)
- OSTI ID:
- 6729732
- Journal Information:
- Health Phys.; (United States), Vol. 55:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
LET
RBE
MICRODOSIMETRY
MAXIMUM PERMISSIBLE EXPOSURE
COBALT 60
DOSE-RESPONSE RELATIONSHIPS
RADIATION DOSES
RADIATION MONITORING
RADIATION PROTECTION
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
COBALT ISOTOPES
DOSES
DOSIMETRY
ENERGY TRANSFER
INTERMEDIATE MASS NUCLEI
INTERNAL CONVERSION RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MINUTES LIVING RADIOISOTOPES
MONITORING
NUCLEI
ODD-ODD NUCLEI
RADIOISOTOPES
SAFETY STANDARDS
STANDARDS
YEARS LIVING RADIOISOTOPES
560151* - Radiation Effects on Animals- Man