| Popis: |
The energy absorbed by aluminum, carbon, or tissue-equivalent (TE) material when exposed to gamma rays, fast neutrons, or 900-Mev alpha particles was measured with a microcalorimeter. The instrument has an ethylene glycol bath in stead of water. Spaced mylar sheets about 6-1/2 in. in diameter were mounted on one side of the absorber inside the evacuated cylindrical chamber in order that the detector could be thermally insulated in the direction beam without the presence of bath solution. Gamma-ray absorbed dose rates as low as 2 rads/ min were measured with the instrument. The dose rates obtained from the exposures to Co-60 and Cs-137 sources at this Laboratory (NRDL) agreed with the output of the sources as measured with a National Bureau of Standards secondary standard cavity ionization chamber. Thirteen 10-min exposures of the TE absorber in the microcalorimeter to fast neutrons from a 60-in cyclotron resulted in absorbed dose measurements varying from 24 to 40 rads. The average absorbed dose value was 5% higher than the NRDL determination based on flux and spectrum measurements. Microcalorimeter exposures to the 900-Mev alpha particle beam from a 184-in. synchro-cyclotron gave absorbed doses that agreed reasonably well with ionization chamber determinations. |
