479 research outputs found
Gamma-ray Measurements with LaBr3: Ce Detectors -thinking Outside the Box
AbstractRecently developed cerium-doped lanthanum bromide (LaBr3: Ce) scintillation detectors have shown to possess promising properties with respect to the detection of γ-rays compared to previously known materials. In this work however, we demonstrate how these detectors may be used to obtain information not only about γ-rays, but also about neutrons, i.e. thinking”inside” and”outside” the box, respectively. For this purpose γ-rays were detected in coincidence with fission fragments and both their energy and their time-of-flight relative to the instant of a fission event is recorded. By evaluating the time-of-flight distributions of γ-rays, identified as decays of excited states after population by inelastically scattered neutrons inside the scintillation crystal as well as other surrounding materials, we show that it is possible to acquire knowledge from and about the spectrum of incident neutrons. We give three examples for conceivable applications, used to determine geometrical profiles, cross sections and neutron spectra, respectively
Photofission fragment characteristics of 234, 238U and 232Th in the barrier region
The bremstrahlung induced fission of 234, 238U and 232Th has been studied at the superconducting Darmstadt linear accelerator (SDALINAC) in the excitation energy region close to the fission barrier. In this contribution results on the fission fragment mass, total kinetic energy (TKE) and angular distributions will be presented. Fission fragment mass and TKE distributions from 234U were studied for the first time in this energy region. The results have been analyzed in terms of fission modes and a dominant yield of the mass asymmetric standard-2 mode was found in all studied nuclei. No strong dependence of the fission mode weights on the excitation energy of the compound nucleus were found. Correlations between mass, TKE and angular distributions have been investigated in 234U and 232Th. A correlation in form of an increased anisotropy for far-asymmetric masses and low TKE were found in both fissioning systems. A possible interpretation of this correlation in terms of fission modes is discussed
Recent developments for an active UF6 gas target for photon-induced fission experiments
Recent developments for an active uranium-hexafluoride-loaded gas target as well as results on the detector gas properties are presented. The gas of choice is a mixture of argon with small amounts of UF6. This contribution presents the experimental setup and focusses on the electron drift velocity with increasing UF6 content. A time-dependent decrease in electron drift velocity is observed in our setup.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard
Experimental Studies of Prompt Fission Neutron Energy Spectra
AbstractPrompt fission neutron spectra were measured in the reactions 238U(n,f), 235U(n,f) and 237Np(n,f) at different incident neutron energies. The neutrons were detected using a coaxial doped p-terphenyl scintillation detector in coincidence with fission fragments and their time-of-flight was recorded. The properties of the neutron detector were determined and the results are presented in this work. A preliminary neutron detection efficiency was applied to data from the neutron-induced fission of 238U at En = 5.2 MeV, leading to encouraging results
Prompt particle emission in fission – news on systematics and predictions for fission induced by fast neutrons
Neutron-induced Fission Cross Section of240,242Pu
A sensitivity analysis for the new generation of fast reactors [Salvatores (2008)] has shown the importance
of improved cross section data for several actinides. Among them, the240,242Pu(n,f) cross sections require an
accuracy improvement to 1-3% and 3-5%, respectively, from the current level of 6% and 20%. At the Van de Graaff
facility of the Institute for Reference Materials and Measurements (JRC-IRMM) the fission cross section of the two
isotopes was measured relative to two secondary standard reactions,237Np(n,f) and238U(n,f), using a twin Frisch-grid
ionization chamber. The secondary standard reactions were benchmarked through measurements against the primary
standard reaction235U(n,f) in the same geometry. Sample masses were determined by means of low-geometry alpha
counting or/and a 2p Frisch-grid ionization chamber, with an uncertainty lower than 2%. The neutron flux and the
impact of scattering from material between source and target was examined, the largest effect having been found
in cross section ratio measurements between a fissile and a fertile isotope. Our240,242Pu(n,f) cross sections are in
agreement with previous experimental results and slightly lower than present evaluations. In case of the242Pu(n,f)
reaction no evidence for a resonance at En=1.1 MeV was found.Postprint (published version
Sensitivity of measured fission yields on prompt-neutron corrections
The amount of emitted prompt neutrons from the fission fragments increases as
a function of excitation energy. Yet it is not fully understood whether the
increase in \nu(A) as a function of E_{n} is mass dependent. The share of
excitation energies among the fragments is still under debate, but there are
reasons to believe that the excess in neutron emission originates only from the
heavy fragments, leaving \nu_{light}(A) almost unchanged. In this work we
investigated the consequences of a mass-dependent increase in \nu(A) on the
final mass and energy distributions. The assumptions on \nu(A) are essential
when analysing measurements based on the 2E-technique. This choice showed to be
significant on the measured observables. For example, the post-neutron emission
mass yield distribution revealed changes up to 10-30%. The outcome of this work
pinpoint the urgent need to determine \nu(A) experimentally, and in particular,
how \nu(A) changes as a function of incident-neutron energy. Until then, many
fission yields in the data libraries could be largely affected, since they were
analysed based on another assumption on the neutron emission.Comment: 4 pages, 3 figures, Proc. 2013 International Conference on Nuclear
Data for Science & Technology (ND2013), March 4-8, 2013, New York, USA, to be
published in Nuclear Data Sheet
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