Determination of photon backscatter from several calibration phantoms

Journal Article · Sat Jun 01 04:00:00 EDT 1996 · Health Physics

OSTI ID:393946

McDonald, J C; Murphy, M K; Traub, R J ^[1]

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1. Pacific Northwest Laboratory, Richland, WA (United States)

American National Standards Institute (ANSI) and International Organization for Standardization (ISO) standards recommend the use of different phantoms for the calibration and proficiency testing of personnel dosimeters. The ANSI N13.11 standard describes a polymethyl methacrylate (PMMA) phantom measuring 30 x 30 x 15 cm. ISO draft standard 4037, part 3, recommends the use of a 30 x 30x 15-cm water-filled phantom with PMMA walls. An additional phantom with dimensions identical to the other two, but constructed of a tissue-equivalent plastic mixture, RS-1, was also used in these studies. The photon backscatter factor for these phantoms was compared to the International Commission on Radiation Units and Measurements (ICRU) reference phantom that has the same dimensions as the above mentioned phantoms, but has the elemental composition of ICRU four element tissue. Calculations of the photon backscatter over the range from 10 to 2,000 keV were performed using the MCNP 4A code for each of the phantoms. Measurements of the backscatter were carried out using thin-walled ionization chambers and thermoluminescent dosimeters that were exposed to x-ray beams With narrow energy spectra, either free-in-air or placed on the surface of the phantoms. The measurements and calculations were consistent and demonstrated that the ISO water filled phantom and the RS-1 plastic phantom generate photon backscatter that is nearly the same as that produced by the ICRU tissue reference phantom, but the backscatter from the PMMA phantom was up to about 8% higher. The conclusion drawn from these measurements is that either an ISO water-filled phantom or one constructed of RS-1 plastic would provide photon backscatter more comparable to an ICRU tissue reference phantom than a PMMA phantom.

• DOE Contract Number: AC06-76RL01830
• OSTI ID: 393946
• Report Number(s): CONF-9607135--
• Journal Information: Health Physics, Journal Name: Health Physics Journal Issue: Suppl.6 Vol. 70; ISSN HLTPAO; ISSN 0017-9078
• Country of Publication: United States
• Language: English

Related Subjects

44 INSTRUMENTATION
INCLUDING NUCLEAR AND PARTICLE DETECTORS
56 BIOLOGY AND MEDICINE
APPLIED STUDIES
66 PHYSICS
99 GENERAL AND MISCELLANEOUS
BACKSCATTERING
CALIBRATION
ENERGY SPECTRA
ICRU
IONIZATION CHAMBERS
M CODES
PERSONNEL DOSIMETRY
PHANTOMS
PMMA
RADIATION DOSES
STANDARDIZATION
THERMOLUMINESCENT DOSEMETERS