NEUTRON MODERATION IN ICE AT 90 K

The neutron spectrum in ice at 90 deg K was investigated. In order to avoid this usual systematic sources of error in differential measurements of the spectra, an integral method was used. An effective neutron temperature T/sub n/, was defined by the transmission of a 1/2-absorber; this was measured by means of activation of a dysprosium probe, which was screened with an indium filter. The result at 90 deg K ice temperature was T/sub n/= 212 plus or minus 15 deg K and at 273 deg K T/sub n/ = 335 plus or minus 23 deg K. The ratio of the neutron density was determined to be n-bar(90 deg )K)/n-bar(273 deg K) = 1.20 plus or minus 0.05, in good agreement with theoretical estimates. Likewise, a general rela tion was derived for the yield of slow neutrons by means of the cooling of the moderator and the connected cooling off'' of the neutrons to T/sub n/. The experimentally determined yield for subthermal neutron energies was about 2.4. For complete adjustment of the thermal equilibrium between neutrons and moderator it was 6.4. The results were compared with other authors. (tr-auth)