CALIBRATION OF THE DELAYED-GAMMA NEUTRON-ACTIVATION FACILITY

The delayed-gamma neutron activation facility at Brookhaven National L aboratory was originally calibrated using an anthropomorphic hollow ph antom filled with solutions containing predetermined amounts of Ca. Ho wever, 99% of the total Ca in the human body is not homogeneously dist ributed but contained within the skeleton. Recently, an artificial ske leton was designed, constructed, and placed in a bottle phantom to bet ter represent the Ca distribution in the human body. Neutron activatio n measurements of an anthropomorphic and a bottle (with no skeleton) p hantom demonstrate that the difference in size and shape between the t wo phantoms changes the total body calcium results by less than 1%. To test the artificial skeleton, two small polyethylene jerry-can phanto ms were made, one with a femur from a cadaver and one with an artifici al bone in exactly the same geometry. The femur was ashed following th e neutron activation measurements for chemical analysis of Ca. Results indicate that the artificial bone closely simulates the real bone in neutron activation analysis and provides accurate calibration for Ca m easurements. Therefore, the calibration of the delayed-gamma neutron a ctivation system is now based on the new bottle phantom containing an artificial skeleton. This change has improved the accuracy of measurem ent for total body calcium. Also, the simple geometry of this phantom and the artificial skeleton allows us to simulate the neutron activati on process using a Monte Carlo code, which enables us to calibrate the system for human subjects larger and smaller than the phantoms used a s standards. (C) 1996 American Association of Physicists in Medicine.