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

High-precision prompt-γ-ray spectral data from the reaction Pu 241 (nth, f)

In this paper we present results from the first high-precision prompt-γ-ray spectral measurements from the reaction Pu241(nth, f). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission γ rays with three cerium-doped LaBr3 (two 5.08cm×5.08 cm and one 7.62cm×7.62 cm) and one CeBr3 (5.08cm×5.08 cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average γ-ray multiplicity was determined to be ν̄γ=(8.21±0.09) per fission, the average energy to be εγ=(0.78±0.01) MeV, and the total energy to be Eγ,tot=(6.41±0.06) MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released γ energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-γ heating in nuclear reactors is due to fast-neutron-induced fission on U238 or rather from fission induced by γ rays from neutron capture in the construction material.European Commision NeutAndalus FP7-PEOPLE-2012-CIGPrograma ERINDA 26949

REFLECT – Research flight of EURADOS and CRREAT: Intercomparison of various radiation dosimeters onboard aircraft

Aircraft crew are one of the groups of radiation workers which receive the highest annual exposure to ionizing radiation. Validation of computer codes used routinely for calculation of the exposure due to cosmic radiation and the observation of nonpredictable changes in the level of the exposure due to solar energetic particles, requires continuous measurements onboard aircraft. Appropriate calibration of suitable instruments is crucial, however, for the very complex atmospheric radiation field there is no single reference field covering all particles and energies involved. Further intercomparisons of measurements of different instruments under real flight conditions are therefore indispensable. In November 2017, the REFLECT (REsearch FLight of EURADOS and CRREAT) was carried out. With a payload comprising more than 20 different instruments, REFLECT represents the largest campaign of this type ever performed. The instruments flown included those already proven for routine dosimetry onboard aircraft such as the Liulin Si-diode spectrometer and tissue equivalent proportional counters, as well as newly developed detectors and instruments with the potential to be used for onboard aircraft measurements in the future. This flight enabled acquisition of dosimetric data under well-defined conditions onboard aircraft and comparison of new instruments with those routinely used. As expected, dosimeters routinely used for onboard aircraft dosimetry and for verification of calculated doses such as a tissue equivalent proportional counter or a silicon detector device like Liulin agreed reasonable with each other as well as with model calculations. Conventional neutron rem counters underestimated neutron ambient dose equivalent, while extended-range neutron rem counters provided results comparable to routinely used instruments. Although the responses of some instruments, not primarily intended for the use in a very complex mixed radiation field such as onboard aircraft, were as somehow expected to be different, the verification of their suitability was one of the objectives of the REFLECT. This campaign comprised a single short flight. For further testing of instruments, additional flights as well as comparison at appropriate reference fields are envisaged. The REFLECT provided valuable experience and feedback for validation of calculated aviation doses

Systematics of prompt fission γ-ray spectra characteristics

Systematics from 2001, describing prompt fission γ-ray spectra (PFGS) characteristics as function of mass and atomic number of the fissioning system, has been revisited and parameters have been revised, based on recent experimental results. Although originally expressed for spontaneous and thermal neutron induced fission, validity for fast neutrons was assumed and applied to predict PFGS characteristics for the reaction n + 238U up to incident neutron energies of En = 20 MeV. The results from this work are compared with preliminary experimental results

Prompt γ-ray Spectral Data from 252Cf(SF), 235U(nth, f) and 241Pu(nth, f)

AbstractIn this paper we talk about our work in developing a method to measure and analyze prompt fission γ-rays, as well as our re- sults from the measurement of three different reactions, namely 252Cf(SF), 235U(nth, f) and 241Pu(nth, f). The first two had, at the beginning of our measurements, not been examined since the early 1970s, and the last reaction had never been measured. Our results show a slight improvement over evaluated data-tables in comparison with benchmark experiments, but can still not explain all of the underestimation witnessed. Our results also show that new evaluations is needed, especially for 252Cf(SF) and 241Pu(nth, f)

First experimental prompt γ\gamma-ray spectra in fast-neutron-induced fission of 238U^{238}\mathrm{U}

International audienceThe knowledge of prompt fission γ-ray emission has been of major interest in reactor physics for a few years. Only few experimental spectra were published until now for fast-neutron-induced fission, and measurements would be also valuable in order to improve our understanding of the fission process. A simple experimental method was used to measure the first prompt fission γ-ray spectra up to 10 MeV. In this approach, the γ rays are measured with a bismuth germanate (BGO) detector which offers two significant advantages with respect to other γ-ray detectors: a high peak-to-total ratio and a high efficiency. The prompt fission neutrons are rejected by the time-of-flight technique between the BGO detector and a fission trigger given by a fission chamber. Prompt fission γ-ray spectra were measured for 1.6 ± 0.1, 5.1 ± 0.2 and 15.0 ± 0.6 MeV neutron-induced fission on U238 at the CEA, DAM, DIF Van de Graaff accelerator; average multiplicity and mean photon energy per fission were deduced from the spectra

Fission cross-sections, prompt fission neutron and γ-ray emission in request for nuclear applications

In recent years JRC-IRMM has been investigating fission cross-sections of 240,242Pu in the fast-neutron energy range relevant for innovative reactor systems and requested in the High Priority Request List (HPRL) of the OECD/Nuclear Energy Agency (NEA). In addition to that, prompt neutron multiplicities are being investigated for the major isotopes 235U, 239Pu in the neutron-resonance region using a newly developed scintillation detector array (SCINTIA) and an innovative modification of the Frisch-grid ionisation chamber for fission-fragment detection. These data are highly relevant for improved neutron data evaluation and requested by the OECD/Working Party on Evaluation Cooperation (WPEC). Thirdly, also prompt fission γ-ray emission is investigated using highly efficient lanthanide-halide detectors with superior timing resolution. Again, those data are requested in the HPRL for major actinides to solve open questions on an under-prediction of decay heat in nuclear reactors. The information on prompt fission neutron and γ-ray emission is crucial for benchmarking nuclear models to study the de-excitation process of neutron-rich fission fragments. Information on γ-ray emission probabilities is also useful in decommissioning exercises on damaged nuclear power plants like Fukushima Daiichi to which JRC-IRMM is contributing. The results on the 240,242Pu fission cross section, 235U prompt neutron multiplicity in the resonance region and correlations with fission fragments and prompt γ-ray emission for several isotopes will be presented and put into perspective

Fission cross-sections, prompt fission neutron and γ-ray emission in request for nuclear applications

In recent years JRC-IRMM has been investigating fission cross-sections of 240,242Pu in the fast-neutron energy range relevant for innovative reactor systems and requested in the High Priority Request List (HPRL) of the OECD/Nuclear Energy Agency (NEA). In addition to that, prompt neutron multiplicities are being investigated for the major isotopes 235U, 239Pu in the neutron-resonance region using a newly developed scintillation detector array (SCINTIA) and an innovative modification of the Frisch-grid ionisation chamber for fission-fragment detection. These data are highly relevant for improved neutron data evaluation and requested by the OECD/Working Party on Evaluation Cooperation (WPEC). Thirdly, also prompt fission γ-ray emission is investigated using highly efficient lanthanide-halide detectors with superior timing resolution. Again, those data are requested in the HPRL for major actinides to solve open questions on an under-prediction of decay heat in nuclear reactors. The information on prompt fission neutron and γ-ray emission is crucial for benchmarking nuclear models to study the de-excitation process of neutron-rich fission fragments. Information on γ-ray emission probabilities is also useful in decommissioning exercises on damaged nuclear power plants like Fukushima Daiichi to which JRC-IRMM is contributing. The results on the 240,242Pu fission cross section, 235U prompt neutron multiplicity in the resonance region and correlations with fission fragments and prompt γ-ray emission for several isotopes will be presented and put into perspective