Date of Award

12-1995

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Engineering Physics

First Advisor

Jeffrey Martin, PhD

Abstract

The purpose of this thesis was to model a computerized tomography device (CT) using Monte Carlo methods to determine the scattered radiation spectrum inside and the dose outside the suite at Wright-Patterson Medical Center and at a generic suite to non-occupational personnel. This was driven by the recent inclusion of the most recent NCRP recommended dose limits into 10CFR20 of 50 mSv, occupational; 1 mSv; non-occupational continuous exposure; and 5 mSv, infrequent exposure. The rotating fan beam of the CT was modeled for MCNP, a general-purpose Monte Carlo n-particle transport modeL The CT target was a standard human phantom defined in MIRD Pamphlet 5. The source and phantom were rotated 27° with respect to the walls. A head scan and an abdomen scan were simulate% CT usage factors were set equal to average WPMC values. The suite walls were modeled alternately with 1/16" and 1/8" lead shielding between gypsum drywall for the occupational and non-occupational dose, respectively. With CT isocenter as problem origin, test detectors were placed 30 cm outside the walls on two sets of axes defined by (a) the walls and (b) the source-body axes. Film badges placed in the CT suite at WPMC agreed with MCNP modeling results by a factor of two, vaiidnng the method. The analysis showed that outside both the WPMC CT suite and the generic room the continuous-exposure non-occupational dose limit was exceeded below the floor and above the ceiling; the infrequent exposure non-occupational dose limit was exceeded below the floor. Modeled results exceeded the occupational and non-occupational dose limits outside two walls of the generic suite. Modeled dose was below the occupational limit at all test locations. The scattered radiation spectrum is a softened source spectrum minus the 60 and 68 keV X-ray tube bremsstrahlung peaks.

AFIT Designator

AFIT-ENP-GAP-95D-3

DTIC Accession Number

ADA303595

Download

Share

COinS