Assaying of targets for nuclear measurements with a gridded ionization chamber

Absolute and relative cross section measurements of237Np(n,f) and238U(n,f) at the National Physical Laboratory

“…The signals were treated with a baseline correction and a RC 4 filter to obtain their pulse height (PH). The analysis of both the grid and the anode signals allowed the quality of the samples being used to be verified as well as to trace back signals with a PH which was not well understood [6]. A typical 2D grid versus anode PH plot is presented in Fig.…”

Neutron inelastic cross-section measurements forMg24

“…We should also note that our neutron energy resolution deteriorates with energy. We conclude therefore that the resonant structures we observe correspond to individual levels in 25 Mg only for very low energies. Already above E n = 2.5-3 MeV these structures represent Ericson fluctuations [41] arising from the overlap of many states from the compound nucleus.…”

“…In order to calculate the total number of fissions, the plateau is extrapolated to zero pulse height. The total number of the neutron-induced fission fragments is then calculated from the yield of the fission events above the threshold corrected for the polarity effect of the chamber [17], the number of the fission fragments that stop in the deposits [25], and the inhomogeneity of the UF 4 foils [26]. For the threshold used in this measurement the efficiency of the fission chamber was 84(2)%.…”

“…7(b)]. Although a detailed R-matrix fit of the data is beyond the scope of the present article, we performed some simple estimates in order to understand if the resonances represent individual states from the compound nucleus 25 Mg or overlap of such states causing fluctuations and resonant structures. We employed the TALYS 1.6 code to determine which total angular momenta are populated in the compound nucleus during the neutron inelastic scattering on 24 Mg. Then we estimated the level densities at the corresponding total angular momenta and excitation energies using the backshifted Fermi gas model (BSFG) following the simple prescription from Refs.…”

Accurate measurement of a fission chamber efficiency using the prompt fission neutron method

“…This device allows one to estimate the emission angle of the FF. If the fissionfragment angular distribution is known, the missing FF at high angle can be inferred [13]. The uncertainty of this method can be as low as 1% [14].…”