M.S. Thesis Presentation by Jeffery K. Tays
Friday, March 29, 2002

(Dr. Nolan Hertel, advisor)

"Shielding Effectiveness of an 18 MV Medical Accelerators Hanging Door"


The Crawford W. Long Hospital Oncology Department, in Atlanta, Georgia, uses a Varian 2100C 18- MV medical accelerator to produce photons for the treatment of cancer patients.  Photoneutrons are an unavoidable byproduct of an x-ray machine of this energy and represent a radiation component that cannot be ignored from a radiation protection viewpoint.  A thick-hanging door, approximately 23 inches thick, as opposed to the traditional maze entrance used at many similar facilities shields the therapy room.  This discussion will interpret physical measurements taken with moderating neutron detectors at the facility.  LiF 600 and 700 TLD’s as well as an active LiI(Eu) scintillation detector will be the main detection components used. Supporting transport calculations and detector calibrations were performed in support of this research.  Detector calibrations were made using a 252Cf source, which has a similar neutron spectrum to that of the photoneutrons produced at the accelerator.  The accelerator has the ability to rotate 360 degrees, therefore data was taken in 90-degree increments to judge the position that causes the highest flux at the doorway.  Results found the door to reduce neutron fluence by 94%.  The calculated effective neutron dose at the door’s outer surface was well below applicable regulations.