1976, British Journal of Radiology, 49, 974

Short communication Neutron beams generated by protons on beryllium By S. W. Johnsen, M.A., Ph.D., and N. F. Peek, M.A., Ph.D. Crocker Nuclear Laboratory, University of California, Davis, California G. O. Hendry, M.S.E.E., and J. L Tom, M.S.M.E. The Cyclotron Corporation, Berkeley, California W. M. Quarn, M.S. E. G. & G., Inc., Goleta, California andP. H. Heintz, M.S., Ph.D. Radiation Oncology Center of Sutter Community Hospitals, Sacramento, California. {Received June, 1976) On May 7 and 8, 1976, we made preliminary measurements to determine certain physical properties of neutron beams produced by protons incident upon lithium and beryllium targets.* Measurements were made using the 76-inch isochronous cyclotron at the University of California, Davis, at proton energies of 26 MeV, 35 MeV, and 45 MeV. A benelexf (pressed wood) collimator, 66 cm long, was employed to define a 10 cm X 10 cm field at 125 cm from the target. The complete results of these measurements will be reported in a forthcoming paper. We believe, however, that the 26 MeV data may be of immediate interest as several cyclotrons capable of producing protons of this energy are in operation. The tissue kerma rate in air of neutrons plus gamma rays *Work supported by N.I.H. contract 1 PO1 CA17419-01. f Masonite Corporation.

at 125 cm from the target was measured with a tissueequivalent ionization chamber filled with tissue-equivalent gas. For 26 MeV protons incident upon a thick (1.27 cm) beryllium target, we obtained 0.47 rad/minute/microampere of beam current. Depth dose was measured using a phantom filled with tissue-equivalent fluid (density =1.07 g/cm3) with the front window of the phantom 125 cm from the target. Using a 0.1 cc tissue-equivalent ionization chamber, we measured the depth for one-half maximum dose to be 10.2 cm corrected to unit density. A second measurement of kerma rate and depth for one-half maximum dose was made with a 6.0 cm polyethylene filter (density = 0.92 g/cm3) between the target and the collimator. With the addition of the polyethylene, the kerma rate was reduced to 0.21 rad/ minute/microampere of beam current. The depth for onehalf maximum dose was increased to 11.9 cm corrected to unit density. This depth dose compares favourably with a similar field size for cobalt-60 y radiation at 80 cm SSD.

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Neutron beams generated by protons on beryllium.

1976, British Journal of Radiology, 49, 974 Short communication Neutron beams generated by protons on beryllium By S. W. Johnsen, M.A., Ph.D., and N...
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