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Normalization of Energy-Dependent Gamma Survey Data

Whicker, Randy*; Chambers, Douglas

doi: 10.1097/HP.0000000000000226
Operational Topics
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Instruments and methods for normalization of energy-dependent gamma radiation survey data to a less energy-dependent basis of measurement are evaluated based on relevant field data collected at 15 different sites across the western United States along with a site in Mongolia. Normalization performance is assessed relative to measurements with a high-pressure ionization chamber (HPIC) due to its “flat” energy response and accurate measurement of the true exposure rate from both cosmic and terrestrial radiation. While analytically ideal for normalization applications, cost and practicality disadvantages have increased demand for alternatives to the HPIC. Regression analysis on paired measurements between energy-dependent sodium iodide (NaI) scintillation detectors (5‐cm by 5‐cm crystal dimensions) and the HPIC revealed highly consistent relationships among sites not previously impacted by radiological contamination (natural sites). A resulting generalized data normalization factor based on the average sensitivity of NaI detectors to naturally occurring terrestrial radiation (0.56 nGy h−1HPIC per nGy h−1NaI), combined with the calculated site-specific estimate of cosmic radiation, produced reasonably accurate predictions of HPIC readings at natural sites. Normalization against two to potential alternative instruments (a tissue-equivalent plastic scintillator and energy-compensated NaI detector) did not perform better than the sensitivity adjustment approach at natural sites. Each approach produced unreliable estimates of HPIC readings at radiologically impacted sites, though normalization against the plastic scintillator or energy-compensated NaI detector can address incompatibilities between different energy-dependent instruments with respect to estimation of soil radionuclide levels. The appropriate data normalization method depends on the nature of the site, expected duration of the project, survey objectives, and considerations of cost and practicality.

*SENES Consultants, 8310 South Valley Highway, Suite 135, Englewood, CO 80112; †SENES Consultants, 121 Granton Drive, Unit 12, Richmond Hill, Ontario, Canada L4B 3N4.

The authors declare no conflicts of interest.

Randy Whicker is a Certified Health Physicist with a M.S. degree in the Radiological Health Sciences and 18 years of radiological assessment experience including a combination of applied research and environmental consulting projects. Specialties include project management, licensing support, remedial design, analytical techniques, radiological measurements and data analysis. Randy’s career efforts have supported entities both public and private in areas of academic research, radiological assessment, regulatory compliance and general radiation protection. His email is rdwhicker@yahoo.com.

© 2015 by the Health Physics Society