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SU‐E‐T‐299: Verification of High Density Concrete Transmission Characteristics under User Beams
Author(s) -
Yang C,
Dieck G,
Edwards J,
Liu T,
Rajaguru P,
He R,
Mobit P
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612250
Subject(s) - electromagnetic shielding , electrometer , transmission (telecommunications) , optics , beam (structure) , range (aeronautics) , materials science , radiation , linear particle accelerator , physics , composite material , telecommunications , computer science
Purpose: To verify transmission factors of the high density concrete (HDC) used in modification of an existing radiation shielding for a new linear accelerator and to measure transmission factors of other types of HDC under user beams before shielding construction started. Method and Materials:Six HDC 300 PCF (Pounds per Cubic Feet) blocks in size of 6″×6″×12″, randomly picked up from a shipment for radiation shielding at the user site, in addition to one sample of each 288 PCF, 250 PCF and 240 PCF were measured for their transmission factors using a 0.6 cc Farmer chamber and the Dose 1 electrometer. User beams used for measurement includes 6MV, 10 MV and 18 MV photon beams from an Elekta Synergy machine. Transmission factors are measured under both narrow (3×3 cm2)(NBG) and broad beam geometry (40×40 cm2)(BBG) with a close condition to a real shielding geometry. Results: Weight measurement indicates that the actual PCF is higher than stated: 313.3±4.5 (one SD) in the range from 306 to 318 PCF for 300 PCF and 291 PCF for 288 PCF, 251 PCF for 250 PCF, 247 PCF for 240 PCF. Transmission measured at seven spots under NBG (18 MV) for one 300 PCF sample is 0.087±0.002 (Min: 0.084 and Max: 0.089). Transmission measured under NBG (18 MV) for six 300 PCF sample blocks is 0.089±0.004 (Min: 0.086 and Max: 0.096). The first tenth value layer under BBG (18 MV) is determined as 7.4″, which is smaller than 8.5″ used in the shielding design calculation. Conclusions: We have confirmed that the HDC blocks used in constructing the radiation shielding meet and actually succeeded the transmission requirement in the shielding calculation. We provided the commercial company with updated measurement of its shielding materials under our user beams.