An Integrated Photon, Neutron and Beta Calibration Phantom and Storage System for Thermoluminescent Detectors (TLDs)
K.J. Kearfott1; L.W. Parker1; and D.A. Cusumano2 (1University of Michigan; 2Advance Group, LLC)
For TLD calibrations, phantoms that assure repeatability while resulting in appropriate radiation scatter conditions mimicking the human torso are needed. ANSI N13.11 2001 specifies that acrylic phantoms with dimensions that depend upon the radiation type of interest be used. A single size meets the requirements for photons, neutrons, and betas: namely 15 cm thick with a 40 cm by 40 cm face. Such a phantom was constructed in three 5 cm thick pieces joined by four plastic screws to aid in handling. ANSI N13.11 2001 also specifies that TLDs must be contained within a 15 cm by 15 cm phantom center and, for neutrons, dosimeters cannot by within 10 cm of the edge. Based on these requirements, 40 cm by 40 cm enclosed plates were constructed to hold TLDs within a 15 cm by 15 cm center on the phantom's front so that both of these conditions will always be satisfied. Different enclosures were designed to hold the TLD cards and loose chips for attachment to the front of the phantom plates. These plates are designed to fit the maximum number of TLDs in the central area (15 cards or 100 chips). The plates have a 6 mm thick backing, and are held together with a front piece by plastic screws. The cards may be slipped in and out of the slots on the plate with no material in front of their elements. For the chips there is a 3 mm thick front piece attached by screws. The plates act as storage for TLD chips and have numbered compartments so each chip can be easily identified and associated with a unique calibration. Alternative front pieces corresponding to the equivalent of 1 cm and 0.07 cm tissue were also manufactured for use during irradiation if desired. The thin cover is achieved by machining indentations in the faceplate in front of each TLD location so that the bulk of the faceplate material remains in place for stability. To connect the plates and phantom, four countersunk plastic screws and wing nuts are fastened through holes in each corner of the plate and phantom, so that the TLD plate fits smoothly against the phantom. This integrated phantom and storage system markedly increases the efficiency and organization of experiments and calibrations.