Rain-Induced Increase in Background Radiation Detected by Radiation Portal Monitors
- ORNL
A complete understanding of both the steady state and transient background measured by Radiation Portal Monitors (RPMs) is essential to predictable system performance, as well as maximization of detection sensitivity. To facilitate this understanding, a test bed for the study of natural background in RPMs has been established at the Oak Ridge National Laboratory. This work was performed in support of the Second Line of Defense Program's mission to detect the illicit movement of nuclear material. In the present work, transient increases in gamma ray counting rates in RPMs due to rain are investigated. The increase in background activity associated with rain, which has been well documented in the field of environmental radioactivity, originates from the atmospheric deposition of two radioactive daughters of radon-222, namely lead-214 and bismuth-214 (henceforth {sup 222}Rn, {sup 214}Pb and {sup 214}Bi). In this study, rainfall rates recorded by a co-located weather station are compared with RPM count rates and High Purity Germanium spectra. The data verifies these radionuclides are responsible for the dominant transient natural background fluctuations in RPMs. Effects on system performance and potential mitigation strategies are discussed.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1045235
- Report Number(s):
- ORNL/TM-2012/229; NN5005011; MDGA516; TRN: US1203657
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
61 RADIATION PROTECTION AND DOSIMETRY
BACKGROUND RADIATION
BISMUTH 214
COUNTING RATES
DEPOSITION
DETECTION
FLUCTUATIONS
GERMANIUM
LEAD 214
MITIGATION
MONITORS
RADIATIONS
RADIOACTIVITY
RADIOISOTOPES
RADON 222
RAIN
SENSITIVITY
SPECTRA
TRANSIENTS