Final Task Report on NRF Measurements of Photon Scattering Resonances in Plutonium at the High Voltage Research Laboratory of MIT Page: 4 of 8
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1/2", 3/4", and 1") to reduce dead time at various end-point energies. The
data rate for a 1" absorber at an end-point energy of 2.8 MeV was about 600
Hz for each detector and a dead time rate of 1-2%. With 3/4" absorbers the
data rate increased to 5~kHz with a dead time of 17%. The data were collected
in histogram mode with DSPEC electronic acquisition machines by ORTEC.
We explored the optimization of signal to background by taking
measurements at end-point energies of 2.1 and 2.8 MeV. We found the 2.8-
MeV endpoint to be best for two reasons. First, even at 2.8 MeV, the setup
was found to be sensitive to strong NRF transitions down to 1.0 MeV.
Second, the only states observed in the initial runs were at energies above 2
The results for 239Pu are shown in Fig. 1. The Pu histogram in Fig. 1
includes data from both target configurations and the dispersion is about 0.75-
keV/channel.. The background peaks, which can be seen in the lower
(background) histogram of Fig. 1, are y-ray transitions from NRF states in
ssMn, 53Cr, and 27A. The 55Mn and 53Cr are elements within the Nitronic-40
holder. The 27A is from the Al normalizer discussed in the previous section.
States seen in the plutonium target data, but not in the blank Nitronic-40
background data, are associated with plutonium.
Pu >> data
- 1G dtia
200 , rPP
2000 2080 2160 2240 2320 2400 2480 260
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Johnson, M S; McNabb, D P & Norman, E B. Final Task Report on NRF Measurements of Photon Scattering Resonances in Plutonium at the High Voltage Research Laboratory of MIT, report, February 23, 2007; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc891132/m1/4/: accessed January 21, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.