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

Gamma-ray measurements with LaBr3: Ce detectors - thinking outside the box

Recently 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 gamma-rays, but also about neutrons, i.e. thinking "inside” and "outside” the box, respectively. For this purpose gamma-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 gamma-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.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

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.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Neutron measurements with lanthanum-bromide scintillation detectors - A first approach

In this paper we report on the measurement of gamma-rays with a 2in. x 2in. LaBr3:Ce scintillation detector. The gamma-rays were emited in the spontaneous fission of Cf-252 and the reaction U-235 (nth,f), respectively, and detected in coincidence with fission fragments. After presenting some of the properties of the detector, we show how well gamma-rays produced in different reactions may easily be distinguished by their characteristic time-of-flight. Then we focus on the analysis of gamma-rays from inelastically scattered neutrons in the scintillation crystal and demonstrate how this information may be used for neutron spectroscopy. We determine the neutron detection efficiency and compare it to the result of calculations based on existing reaction cross sections. We also give a first example for an application, where the spectrum of fission neutrons is assessed. Finally, we discuss the detection performance in relation to other detector systems, commonly used for neutron monitoring.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Predictions of characteristics of prompt-fission γ -ray spectra from the n + 238U reaction up to En = 20 MeV

Systematics from 2001, describing prompt-fission γ -ray spectra (PFGS) characteristics as a function of mass and atomic number of the fissioning system, was revisited and parameters were 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 in good agreement with corresponding results from both model calculations and experiments.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Neutron measurements with lanthanum-bromide scintillation detectors-A first approach

In this paper we report on the measurement of gamma-rays using a 2 in. x 2 in. LaBr3:Ce scintillation detector. The gamma-rays were emitted in the spontaneous fission of Cf-252 and detected in coincidence with fission fragments. After presenting some of the properties of the detector, we show how well gamma-rays produced in different reactions may easily be distinguished by their characteristic time-of-flight. Then we focus on the analysis of gamma-rays from inelastically scattered neutrons in the scintillation crystal and demonstrate how this information may be used for neutron spectroscopy. We determine the neutron detection efficiency and compare it to the result of calculations based on existing reaction cross-sections. Finally, we discuss the detection performance in relation to other detector systems commonly used for neutron monitoring

New prompt spectral gamma-ray data from the reaction Cf-252(sf) and its implication on present evaluated nuclear data files

We present results from new spectral prompt gamma-ray measurements from the spontaneous fission of Cf-252. Apart from one recent experiment, about four decades have passed since the last dedicated experiments were reported in the literature. Hence, there was a need for a revision. We have measured prompt fission. rays with both cerium-doped LaBr3 and CeBr3 scintillation detectors, both of which exhibit excellent timing and good energy resolution. The emission yield was determined to be nu(gamma) = (8.30 +/- 0.08)/fission and nu(gamma) = (8.31 +/- 0.10)/fission, with the average energy of is an element of(gamma) = (0.80 +/- 0.01) MeV and is an element of(gamma) = (0.80 +/- 0.01) MeV and total energy of E-gamma,E-tot = (6.64 +/- 0.08) MeV and E-gamma,E-tot = (6.65 +/- 0.12) MeV, with the LaBr3 and CeBr3 detectors, respectively. Since the results from the two detectors are in excellent agreement and confirm the historical data, but not those in the present evaluated nuclear data files, we strongly recommend an update

Impact of low-energy photons on the characteristics of prompt fission gamma-ray spectra

In this paper we report on a new study of prompt gamma-rays from the spontaneous fission of Cf-252. Photons were measured in coincidence with fission fragments by employing four different lanthanide halide scintillation detectors. Together with results from a previous work of ours, we determined characteristic parameters with high precision, such as the average gamma-ray multiplicity (nu) over bar (gamma) = (8.29 +/- 0.13), the average energy per photon is an element of(gamma) = (0.80 +/- 0.02) MeV, and the total gamma-ray energy release per fission E-gamma,(tot) = (6.65 +/- 0.10) MeV. The excellent agreement between the individual results obtained in all six measurements proves the good repeatability of the applied experimental technique. The impact of low-energy photons, i.e., below 500 keV, on prompt fission gamma-ray spectra characteristics has been investigated as well by comparing our results with those taken with the DANCE detector system, which appears to suffer from absorption effects in the low-energy region. Correction factors for this effect were estimated, giving results comparable to ours as well as to historical ones. From this we demonstrate that the different techniques of determining the average gamma-ray multiplicity, either from a properly measured and normalized spectrum or a measured multiplicity distribution, give equivalent and consistent results

New prompt spectral gamma-ray data from the reaction 252Cf(sf) and its implication on present evaluated nuclear data files

We present results from new spectral prompt gamma-ray measurements from the spontaneous fission of 252Cf. Apart from one recent experiment, about four decades have passed since the last dedicated experiments were reported in the literature. Hence, there was a need for a revision. We have measured prompt fission gamma rays with both cerium-doped LaBr3 and CeBr3 scintillation detectors, both of which exhibit excellent timing and good energy resolution. The emission yield was determined to be nu_gamma=(8.30±0.08)/fission and nu_gamma=(8.31±0.10)/fission, with the average energy of epsilon_gamma=(0.80±0.01) MeV and epsilon_gamma=(0.80±0.01) MeV and total energy of E_gamma,tot=(6.64±0.08) MeV and E_gamma,tot=(6.65±0.12) MeV, with the LaBr3 and CeBr3 detectors, respectively. Since the results from the two detectors are in excellent agreement and confirm the historical data, but not those in the present evaluated nuclear data files, we strongly recommend an update.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

New prompt spectral gamma-ray data from the reaction Cf-252(sf) and its implication on present evaluated nuclear data files

We present results from new spectral prompt gamma-ray measurements from the spontaneous fission of Cf-252. Apart from one recent experiment, about four decades have passed since the last dedicated experiments were reported in the literature. Hence, there was a need for a revision. We have measured prompt fission. rays with both cerium-doped LaBr3 and CeBr3 scintillation detectors, both of which exhibit excellent timing and good energy resolution. The emission yield was determined to be nu(gamma) = (8.30 +/- 0.08)/fission and nu(gamma) = (8.31 +/- 0.10)/fission, with the average energy of is an element of(gamma) = (0.80 +/- 0.01) MeV and is an element of(gamma) = (0.80 +/- 0.01) MeV and total energy of E-gamma,E-tot = (6.64 +/- 0.08) MeV and E-gamma,E-tot = (6.65 +/- 0.12) MeV, with the LaBr3 and CeBr3 detectors, respectively. Since the results from the two detectors are in excellent agreement and confirm the historical data, but not those in the present evaluated nuclear data files, we strongly recommend an update