The evaluation of a gas mixture having an atomic composition similar to that of A-150 TE-plastic has been extended to a high energy neutron therapy beam."A-150" gas, air and methane-based TE gas were each flowed through A-150 plastic-walled ion chambers of different sizes and irradiated with p(66)Be (49) neutrons. A tentative value for W(A-150) of 27.3 +0.5 J c-l was derived for this beam. The W value of the A-150 gas mixture is compared to those of methane-based TE gas and of air for the p(66)Be(49) neutron beam as well as to corresponding values found in similar experiments using 14.8 MeV monoenergetic neutrons.

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