Absolute measurement of thePu242neutron-capture cross section

Abstract

The absolute neutron-capture cross section of 242 Pu was measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. The first direct measurement of the 242 Pu(n,γ) cross section was made over the incident neutron energy range from thermal to ≈ 6 keV, and the absolute scale of the (n,γ) cross section was set according to the known 239 Pu(n,f) resonance at En,R = 7.83 eV. This was accomplished by adding a small quantity of 239 Pu to the 242 Pu sample. The relative scale of the cross section, with a range of four orders of magnitude, was determined for incident neutron energies from thermal to ≈ 40 keV. Our data, in general, are in agreement with previous measurements and those reported in ENDF/B-VII.1; the 242 Pu(n,γ) cross section at the En,R = 2.68 eV resonance is within 2.4% of the evaluated value. However, discrepancies exist at higher energies; our data are ≈30% lower than the evaluated data at En ≈ 1 keV and are approximately 2σ away from the previous measurement at En ≈ 20 keV.

Measurement of theAm242mneutron-induced reaction cross sections

“…The PPAC's entrance and exit windows are 13 µm thick Kapton foils. A similar PPAC design was used in several previous experiments conducted with DANCE including a 252 Cf spontaneous fission measurement [54] and the recent 242 Pu neutroncapture cross section measurement [51]. The PPAC was operated with ≈4 Torr of isobutane stabilized by a gashandling system, and it was biased up to ≈400 V. The typical pulse height for fission events is several hundred mV.…”

“…The DANCE array consists of 160 equal-volume, equal-solid-angle BaF 2 crystals arranged in a 4π geometry. DANCE has been used to measure neutron-induced reactions on actinides including 237 Np [45] [51]. The detector array is located at the end of a flight path 20.25 m from the neutron source.…”

“…4a in Ref. [51] as an example. Background subtraction was effective for cluster multiplicities M cl = (4,5), and Fig.…”

“…During the first stage of data analysis, γ-ray energies deposited in DANCE were summed over a 200-ns coincident timing window, and then "time alignment" was applied to the 160 BaF 2 scin- tillation crystals. A reference crystal was selected for the alignment, and the timing for each subsequent crystal was corrected for each run, based on the time difference relative to the reference crystal [46,51]. After alignment, γ-ray energies were summed over a narrow, 6-ns coincident time window.…”

Radiative neutron capture on Pu242 in the resonance region at the CERN n_TOF-EAR1 facility

“…A few years later, Wisshak and Käppeler [6,7] measured the cross section in the unresolved resonance region in two energy intervals, 10-90 keV and 50-250 keV. Recently, another time-of-flight measurement was carried out with the DANCE detector at LANSCE by Buckner et al [8], covering the region from thermal to 40 keV but resolving resonances only up to 500 eV due to the limited neutron energy resolution of the DANCE facility. Their results, with a final systematic uncertainty around 6%, show a fairly good agreement with the evaluations in the resonance region and a systematic reduction of 20-30 % above 1 keV compared to ENDF/B-VII [9] (it is to be noted that JEFF-3.2 [10] is in agreement with ENDF/B-VII around 1 keV but 10-20 % larger at ∼10 keV).…”