Gamma-rays from a 241AmO2 Source in an Al2O3 Matrix

Americium is a minor actinide making an important component of high level nuclear waste. A considerable number of studies have been performed or are ongoing to determine cross sections for neutron-induced reactions on 241Am. Recently, two measurements of the neutron-induced capture reaction on 241Am were performed at the n_TOF facility of CERN. One of these measurements used the C6D6 detectors, the other used the BaF2 calorimeter. In both cases, a sample from IRMM was used that had been prepared at ITU [1]. This sample consisted of 241AmO2 which was dispersed in a matrix of Al2O3. The material was pressed into a disk, calcined and enclosed in an aluminium container. It contained about 40 mg of 241Am. The samples had been prepared for measurements of the 241Am(n,2n)240Am reaction cross section [2]. Further details about the sample and these measurements may be found in [1,2]. During the measurements at CERN it was noted that several high energy gamma-rays were emitted by the sample. This presented the question as to the exact energies and origin of these gamma-rays. For this purpose the sample was returned to IRMM and gamma-ray spectroscopy with a high purity germanium (HPGe) detector was performed. The energy and origin of most gamma-rays was determined in this way. Here we report about these measurements paying attention only to gamma-rays that are not known from the decay of 241Am [3] and to the gamma-ray energy range from 844 keV to 13 MeV. There are two mechanisms leading to gamma-ray emission. First there is the natural activity of 241Am and the three known actinide impurities: 237Np (0.021), 233-236,238U (0.000094) and 239,240Pu (0.0017; fractions by weight). Of these 241Am dominates the spectrum, even after applying absorbers to completely stop the 59 keV transition. From the main impurity, 237Np, no gammas are found but there are those of its daughter, 233Pa. For the other actinide impurities and their descendants no gamma-rays were found in the measurement. The second source of gamma-rays are alpha-induced reactions. For energies below the maximum alpha energy of 5.485 MeV, Q-values, thresholds and main characteristic gamma-rays are given in table 1 for the likely candidate reactions. Reactions conclusively identified are 27Al(alpha,alpha’gamma)27Al, and 27Al(alpha,p)30Si and these explain nearly everything besides the 241Am and 233Pa gammas already discussed. There is a clear indication for the 27Al(alpha,n)30P reaction, but for the 27Al(alpha,gamma)31P reaction the evidence is not conclusive due to an overlap with gammas from 30Si. No evidence was found for alpha-induced reactions on the isotopes of oxygen. The measurements are described in the section Experiment. A table with gamma-ray energies and figures with the gamma-ray spectra are given in the section Results. The origin of these gammas is indicated there as well. Only three gamma-rays remain unattributed. A spectrum taken at CERN with a germanium detector showing many additional lines cannot be confirmed. Most likely this was taken under very poor background conditions.JRC.DG.D.5-Nuclear physic

Nuclear data from AMS & nuclear data for AMS - some examples

We summarize some recent cross-section measurements using accelerator mass spectrometry (AMS). AMS represents an ultra-sensitive technique for measuring a limited, but steadily increasing number of longer-lived radionuclides. This method implies a two-step procedure with sample activation and subsequent AMS measurement. Applications include nuclear astrophysics, nuclear technology (nuclear fusion, nuclear fission and advanced reactor concepts and radiation dose estimations). A series of additional applications involves cosmogenic radionuclides in environmental, geological and extraterrestrial studies. Lack of information exists for a list of nuclides as pointed out by nuclear data requests. An overview of some recent measurements is given and the method is exemplified for some specific neutron-induced reactions.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Monte Carlo simulation of the experimental pulse height spectra produced in diamond detectors by quasi-mono-energetic neutrons

This work was carried out in view of the possible use of diamond detectors as high resolution neutron spectrometers for the ITER project. An MCNP5(X) based computational tool has been developed to simulate the fast neutron response of diamond detectors. The source neutrons are generated by a source routine, developed earlier, that includes deuteron beam energy loss, angular straggling, and two-body relativistic kinematics. The diamond detector routine calculates a pulse height spectrum that is built up by elastic and inelastic scattering, (n,a), (n,p), and (n,d) reaction channels. A combination of nuclear data from ENDF/B-VII.0, TENDL-2010, and ENSDF is used. The simulated spectra are compared with measured spectra. It is shown that the simulation tool allows an interpretation of most of the characteristic features in the spectrum. This is an important step towards the use of diamond detectors for spectral analysis and fluence measurements.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Measurement of Neutron Reaction Cross Sections in Carbon using a Single Crystal Diamond Detector

A single crystal diamond detector was exposed to the quasi mono-energetic neutron fields in the energy range from 7 MeV to 20.5 MeV produced by the Van de Graaff neutron generator of the EC-JRC-IRMM. Pulse Height Spectra (PHS) of the neutron interaction with the diamond (carbon) were recorded in order to derive the experimental response function of this detector to neutrons in view of its use as a compact fast neutron spectrometer. Several peaks produced by outgoing charged particles produced when neutrons interact with carbon were identified using the reaction Q-values. The corresponding nuclear reactions, such as (n,alpha), (n,p), (n,d) for different excitation states were identified in the PHS. The analysis of the peaks allows the derivation of some neutron reaction cross sections in carbon. The results are presented in this paper together with the associated uncertainties.JRC.D.4-Nuclear physic

Tritium Production in Neutron Induced Reactions

We present an overview of the present knowledge of (n,t) reaction excitation functions in the 14-21 MeV energy range for Cd, Cr, Fe, Mg, Mo, Ni, Pb, Pd, Ru, Sn, Ti, Zr. Experimental data are compared with evaluated data libraries, cross-section systematics, and TALYS calculations. The new values for the 50Cr(n,t)48V cross-section measured using g-spectrometry at 15, 16, 17.3 MeV are presented.JRC.D.5-Nuclear physic

The response of single crystal diamond detectors to 17–34 MeV neutrons

The first measurements of the response of diamond detectors to neutrons in the energy range 17–34MeV are presented. The diamond detectors were irradiated with quasi-monoenergetic neutrons generatedthrough the 7Li(p,n)7Be reaction. The measured pulse-height spectra show specific peaks associated to neutroninduced reactions in carbon. The peak of the 12C(n,0)9Be was clearly separated from the rest of thespectra. The 12C(n,d0)11B and 12C(n,p0)12B peaks were clearly identified on a continuum originating fromthe breakup 12C(n,3) reaction, which dominates the low-energy part of the pulse-height spectra. The 12C(n,0)9Be, 12C(n,d0)11B and 12C(n,p0)12B cross sections that have never been measured in this high-energy rangebefore were determined. The measured data are compared with the European Activation File EAF-2010 libraryevaluated values.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Effects of an Energy Broadened Proton Beam on the Neutron Distribution for the 7Li(p,n)7Be Reaction near Threshold

A common method for simulating the thermal neutron conditions in the stellar interior is based on the 7Li(p,n)7Be reaction near threshold energy. This method was pioneered at FZK, Karlsruhe, by Ratynski and Kaeppeler [1]. Maxwellian-averaged neutron capture cross-sections of mean energy 25 keV, relevant to the s-process nucleosynthesis, are measured at existing Van-de-Graaff (VdG) proton accelerators. Soreq NRC Applied Research superconducting linear Accelerator Facility (SARAF) phase 1 [2] is in its final stage of commissioning. Maxwellian averaged neutron capture cross-section measurements are planned to be conducted using a forced-flow closed-loop liquid-lithium target (LiLiT) [3]. The proton beam energy spread of RF linear accelerators, such as SARAF, is typically larger than the spread of proton beams of VdG accelerators. The energy spread of SARAF proton beam at 1912 keV is calculated to be of the order of 20-40 keV FWHM as compared to about 3 keV FWHM for VdG accelerators. For simulating the SARAF proton beam we performed an experiment at the IRMM-Geel VdG using a gold foil degrader positioned before the LiF target. This degrader shifts the mean proton energy to 1912 keV and it broadens the proton beam energy to values simulating the spread of the proton beam at SARAF. For calibrating the cross-sections we also performed a 7Li(p,n)7Be experiment without the gold foil degrader at a proton energy of 1912 keV. The VdG was operated in a pulse mode and the neutron energies were determined by time-of-flight measurements using 6Li glass detectors. Detector efficiencies were obtained by Monte Carlo calculations. We present our study and compare the results for both narrow and broad energy proton beams. Comparison to calculations is also shown.JRC.D.5-Nuclear physic

Simulation of the neutron spectrum from the 7Li(p,n) reaction with a liquid-lithium target at Soreq Applied Research Accelerator Facility

The 7Li(p,n)7Be reaction has been used for the last 25 years to produce quasi-Maxwellian neutrons in order to measure Maxwellian-Averaged Cross-Sections in the relevant temperatures for stellar nucleosynthesis. A liquid-lithium target at the Soreq Applied Research Accelerator Facility is expected to allow us to perform such measurements at higher neutron intensities. Here we describe a Monte Carlo tool, SimLiT, developed to evaluate neutron spectra, intensities and angular distributions resulting from this reaction. We also demonstrate the feasibility to couple SimLiT with an advanced transport code, resulting in a powerful tool for planning and analysis of experiments using the 7Li(p,n) reaction as a neutron source.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Energy-broadened proton beam for production of quasi-stellar neutrons from the 7Li(p,n)7Be reaction

Production of quasi-stellar neutrons by the 7Li(p,n)7Be reaction has been used for measuring s-process cross sections and efforts to upgrade the proton beam intensity with RF linear accelerators are presently ongoing. We investigated the effect of an energy-broadened proton beam, as is expected for a RF linear accelerator, on the produced 25-keV semi-Maxwellian neutron spectrum and compared it to that of a Van de Graaff accelerator with well-defined proton energy. Neutron spectrum measurements from 0○ to 80○ were carried out with a pulsed proton beam at the IRMM Van de Graaff accelerator using time-of-flight techniques, both with a narrow energy spread (sigma≈1.5 keV) proton beam and with an energy-broadened beam (sigma≈20 keV) obtained by straggling through a Au-foil degrader. In the latter case, the neutron spectrum is closer to the Maxwellian flux distribution in the high neutron energy region.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Quasi-stellar neutrons from the 7Li( p,n)7Be reaction with an energy-broadened proton beam

Neutrons produced by the 7Li(p,n)7Be reaction close to the reaction threshold are widely used to measure the cross section of s-process nucleosynthesis reactions. While experiments have been performed so far with Van de Graaff accelerators, future use of rf accelerators with higher intensities is planned to enable investigations on radioactive targets. Such accelerators have, however, poorer energy definition. We investigate in this work the effects of an energy-broadened proton beam on the spectrum of neutrons emitted in the thick-target 7Li(p,n) reaction at Ep = 1912 keV and on the experimental cross section of the 197Au(n,γ )198Au reaction in these conditions. Measurements were made with the bunched and chopped proton beam at the Van de Graaff facility of the Institute for Reference Materials and Measurements using the time-of-flight technique, both with a narrow-energy proton beam (standard deviation of the distribution σ ≈ 1.5 keV) and with a broad-energy proton beam (σ ≈ 20 keV) obtained with a gold foil degrader. Neutron spectra measured with the narrow-energy proton beam are consistent with those previously reported. The angle-integrated spectrum obtainedwith the broad-energy proton beam more closely resembles a Maxwellian-flux distribution. The measured neutron spectra agree well with Monte Carlo simulations that include experimentally measured cross sections, two-body kinematics and proton energy loss in the target. Gold activation studies were performed for both narrow-energy and broad-energy proton beams to check the impact of the ensuing spectra on this important reference standard for activation measurements.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard