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

Retrospective radon dosimetry

Knowledge of the precise life-time radon history in houses is essential for epidemiologists, mitigation professionals and house-owners. For radon dosimetry and to make a reasonable health-risk study similar information about the indoor aerosol environment is necessary. For this purpose a combined data analysis from measurements of the 210Po activity implanted in glass-surfaces as well as trapped in spongy materials is proposed. This analysis technique provides a characterization of the average indoor aerosol-particle environment. As a consequence, a radon dose estimation improves by a factor of about 3 compared to the commonly applied single surface-activity analysis

First use of single-crystal diamonds as fission-fragment detector

Single crystal chemical vapor deposited diamond (sCVD) was investigated for its ability to act as Fission fragment detector. In particular we investigated timing and energy resolution for application in a simultaneous time and energy measurement to determine the mass of the detected fission fragment. Previous tests have shown that poly crystalline chemical vapor deposited (pCVD) diamonds provide sufficient timing resolution, but their poor energy resolution did not allow complete separation between very low energy fission fragments, alpha-particles and noise. Our present investigations prove artificial sCVD diamonds to show similar timing resolution as pCVD diamonds close to 100 ps. Improved pulse height resolution allows the unequivocal separation of fission fragments, and the detection efficiency reaches 100%, but remains with about a few percent behind requirements for fragment mass identification. With high-speed digital electronics a timing resolution well below 100 ps is possible. However, the strongly varying quality of the presently available diamond material does not allow application on a sufficiently large scale within reasonable investments

Prompt particle emission in fission – news on systematics and predictions for fission induced by fast neutrons

As a consequence of recent experimental results, previously established systematics for prompt fission γ-ray spectra (PFGS) characteristics as function of both atomic and mass number of the compound system have been revised. Although based on purely empirical dependences, it allows estimating average gamma-ray multiplicity, mean and total photon energy in cases, where the target nuclei are either not available or not accessible experimentally. Based on this systematics, we show in this paper that PFGS characteristics may also be predicted for fission induced by fast neutrons. Our calculations were performed for the target nuclei 238U, 235U and 239Pu in the neutron energy range from 0 to 20 MeV, and the results are compared to existing experimental and theoretical values

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