Quasi-monoenergetic Neutron Beams Research Articles

Measurement of fast neutron induced (n,γ) reaction cross-section of 68Zn, 96Zr, 121Sb and 123Sb in the energy range of 1 to 2 MeV

The (n,γ) reaction cross-section for the elements 68Zn, 96Zr, 121Sb and 123Sb, present in the reactor structural/shielding materials, was measured by neutron activation technique in the neutron energy region of 1–2 MeV as very limited data is available in this energy range. Further, the neutron spectrum peaks in this energy region for the fast breeder reactors and proposed accelerator driven sub-critical systems. The natural strontium (natSr) element was used as a neutron flux monitor by considering effective combined reaction cross-section for 86Sr(n,γ)87Srm and 87Sr(n,n′)87Srm reactions. The pellets of mixture of sample and monitor were irradiated by a quasi-mono energetic fast neutron beam, generated by 7Li(p,n)7Be reaction at FOTIA, Bhabha Atomic Research Centre, Mumbai, India. The activity of activation products was measured by off-line gamma-ray spectrometry using High Purity Germanium Detector (HPGe). The present data with improved uncertainty and covariance analysis enhance the cross-section data base for better constraining the evaluated data and theoretical models. The theoretical (n,γ) reaction cross-sections were calculated using TALYS 1.96, which could reasonably explain the present data with the Fermi gas level density prescription.

Energy-Dependent Fission-Product Yields in the Region of Second-Chance Fission

The energy dependence of high-yield fission products has been measured using quasi-monoenergetic neutron beams at energies between 5.5 and 11.0 MeV. The absolute number of fissions during the irradiation period was determined via dual-fission ionization chambers, while the fission products were measured via direct g-ray spectroscopy. This paper presents absolute fission product yields from neutron-induced fission of 235U, 238U, and 239Pu isotopes for five incident energies in the second chance fission region.

On the accuracy of cross-section measurements of neutron-induced reactions using the activation technique with natural targets: The case of Ge at E[formula omitted] MeV

Several cross-section measurements of neutron-induced reactions on Ge found in literature, are performed utilizing natGe targets. The production of the same residual nucleus as the measured one might occur as a result of the unavoidable presence of neighboring isotopes in the same target, acting as a contamination. Corrections must be made based on theoretical calculations and models in order to resolve this problem. The accuracy and limits of a methodology for these “theoretical corrections” are investigated in this work using isotopically enriched targets, which can produce very accurate results without the need for such corrections. Experimental cross-section measurements have been made for the 76Ge(n,2n)75Ge, 72Ge(n,α)69mZn and 72Ge(n,p)72Ga reactions, via the activation technique, with the 27Al(n,α)24Na reaction used as reference, employing both a natGe and isotopically enriched Ge targets. The 3H(d,n)4He (D–T) reaction was used for producing the quasi-monoenergetic neutron beam in the 5.5 MV Tandem Accelerator Laboratory of the National Centre for Scientific Research “Demokritos” in Athens, Greece, at an incident deuteron beam energy of 2.9 MeV. Using HPGe detectors, γ-ray spectroscopy was applied to determine the induced γ-ray activity of the residual nuclei.

Neutron activation analysis: Gamma-ray spectra analysis of thin foils irradiated with high-energy neutrons

iThemba LABS is participating in a joint research project to measure neutron-induced cross-sections for the (n, xn) reactions for various target materials. For neutron energies above 20 MeV, the (n, xn) set of reactions is becoming increasingly important for neutron fluence monitoring and spectra unfolding for future generation IV nuclear reactors. Test experiments commenced at the iThemba LABS facility with irradiations of target materials using quasi-monoenergetic neutron beams at high energies (above 40 MeV). These experiments are meant to evaluate the sensitivity of generating a clear γ-ray spectrum above the background level of the counting system. For this contribution, we report on the neutron activation analysis of the following target materials, 197Au and 169Tm using a quasi-monoenergetic neutron beam of about 90 MeV. The discussion focuses on calibrating the gamma-ray detector, and counting, and analyzing the gamma-ray spectra of the neutron-activated foils. The following reaction products were identified 194Au, 196Au, 198Au, 167Tm, and 168Tm. Using the background-corrected gamma-ray spectra, the activities of the reaction products were calculated with uncertainties ranging between 5 % and 30 %.

Measurement of Cumulative fission product yields on 235U induced by 2.8 MeV neutrons

Off-line gamma-ray spectrometry was used to accurately measure the Cumulative fission product yields (CFPYs) of fission products in the 235U (n, f) reaction induced by 2.8 MeV neutrons. The 2.8 MeV quasi-monoenergetic neutron beam was produced by the CPNG-600 Cockcroft Walton accelerator at the China Institute of Atomic Energy （CIAE）and the gamma spectra were measured by the HPGe γ-ray Spectrometer. After fully considering and revising the sources of uncertainty, high-precision CFPYs of 4 fission products were obtained. This study has important applications in reactor design and operation and is conducive to the establishment of an evaluated nuclear database.

Semiconductor Detector Study for Detecting Fusion Neutrons using Geant4 Simulations

Accurate neutron flux measurements in fusion reactors are essential, in order to determine the feasibility and progress of the reaction as well as for safety issues. Semiconductor neutron detectors exhibit promising characteristics for operation in the extreme environmental conditions of fusion reactors. Silicon, Diamond and Silicon Carbide are the most studied and anticipated materials for constructing detectors with high efficiency and irradiation resistance. The ITER fusion reactor is expected to run D-D plasma measurements in the near future, so the detection of 2.45 MeV neutrons with appropriate detectors is of great and immediate importance. In the present work the study of 2.45 MeV neutrons interactions with a silicon, diamond and silicon carbide detector was made, using GEANT4 [1] simulations, in order to compare their response. An experimental study will follow at the neutron production facility of the TANDEM accelerator of the I.N.P.P. of the NCSR “Demokritos”, with detectors provided by CIVIDEC Instrumentation GmbH, so the geometry of the simulations was built accordingly. A quasi-monoenergetic neutron beam of 2.45 MeV was produced through 3H(p,n) reactions in a TiT target. Due to the low cross section of the reaction, biasing techniques were implemented in the simulation to increase the counting rate and thus producing realistic results. These biasing techniques were studied, with various tests and the parameters affecting the choice of the biasing factor are shown and discussed.

Cross Section Measurements of (n,x) Reactions In the Energy Range Between 16.4 and 18.9 MeV Using Highly Enriched Ge Isotopes

In this work, the cross sections of the neutron induced reactions 70Ge(n,2n)69Ge, 76Ge(n,2n)75Ge, 73Ge(n,p)73Ga, 72Ge(n,p)72Ga, 73Ge(n,d/np)72Ga, 74Ge(n,d/np)73Ga, 74Ge(n,α)71mZn, 72Ge(n,α)69mZn, 73Ge(n,nα)69mZn have been measured in the energy range between 16.4 and 18.9 MeV via the activation technique with respect to the 27Al(n,α)24Na reference reaction. Most of the existing experimental datasets found in literature for these reactions, were obtained with the use of a natGe target. In this case however, the residual nucleus produced from some reaction channels, could also be produced from neutron induced reactions in neighboring isotopes that exist in the natGe in their natural abundance, acting as a contamination to the measured yield of the reaction of interest. This parasitic contribution should then be subtracted, based on theoretical calculations that bear their own uncertainties. Isotopically enriched targets on the other hand, do not suffer from such contaminations, leading to more accurate experimental cross section results. In this work, five highly enriched targets have been used that helped in the determination of accurate cross section data, especially in the case of the73Ge(n,d/np)72Ga, 74Ge(n,d/np)73Ga and 73Ge(n,nα)69mZn challenging reactions, that will be presented in detail in this manuscript. The experiments were carried out at the 5.5 MV Tandem Van de Graaff accelerator of N.C.S.R. “Demokritos”, implementing the 3H(d,n)4He reaction for the production of the quasi-monoenergetic neutron beams.

Cross Section Measurements of (n,x) Reactions at 17.9 and 18.9 MeV Using Highly Enriched Ge Isotopes

Nine neutron induced reactions on Ge isotopes (70Ge(n,2n)69Ge, 76Ge(n,2n)75Ge, 73Ge(n,p)73Ga, 72Ge(n,p)72Ga, 73Ge(n,d/np)72Ga, 74Ge(n,d/np)73Ga, 74Ge(n,α)71mZn, 72Ge(n,α)69mZn, 73Ge(n,nα)69mZn) have been measured in this work at energies 16.4-18.9 MeV. For these reactions, most of the experimental datasets in literature were obtained with a natGe target. However, the residual nucleus produced by some reaction channels can also be produced from neighboring isotopes, acting as a contamination for the measured reactions. This contribution must be subtracted, based on theoretical calculations, bearing their own uncertainties. The use of enriched targets however, does not suffer from such contaminations, leading to accurate experimental results. In this scope, five highly isotopically enriched Ge samples have been used in this work. The quasi-monoenergetic neutron beams were produced via the 3H(d,n)4He reaction at the 5.5 MV Tandem Van de Graaff accelerator of N.C.S.R. ‘Demokritos’. The cross section of these nine reactions were measured using the activation method, with respect to the 27Al(n,α)24Na reference reaction.

Neutron Filtering System for Neutron Capture Cross Section Measurement at the ANNRI beamline of MLF/J-PARC

A neutron filtering system has been designed and implemented in the Accurate Neutron-Nucleus Reaction Measurement Instrument (ANNRI) beamline in the Materials and Life Science (MLF) facility of the Japan Proton Accelerator Research Complex (J-PARC) to bypass the effect of the double-bunch mode of JPARC by molding the incident neutron flux into quasi-monoenergetic neutron beams. Filter assemblies using Fe, Si and Cr as filter materials were analyzed by means of experimental analysis, together with Monte Carlo simulations. The characteristics of the filtered neutron beam are presented and discussed alongside its viability in future applications for neutron cross-section measurements in the keV neutron region.

Cumulative fission yield measurements with 14.7 MeV neutrons on 238U* *Supported by the National Natural Science Foundation of China (11975113)

The fission yield data in the 14 MeV energy neutron induced fission of 238U play an important role in decay heat calculations and generation-IV reactor designs. In order to accurately measure fission product yields (FPYs) of 238U induced by 14 MeV neutrons, the cumulative yields of fission products ranging from 92Sr to 147Nd in the 238U(n, f) reaction with a 14.7 MeV neutron were determined using an off-line γ-ray spectrometric technique. The 14.7 MeV quasi-monoenergetic neutron beam was provided by the K-400 D-T neutron generator at China Academy of Engineering Physics (CAEP). Fission products were measured by a low background high purity germanium gamma spectrometer. The neutron flux was obtained from the 93Nb (n, 2n)92mNb reaction, and the mean neutron energy was calculated using the cross-section ratios for the 90Zr(n, 2n)89Zr and 93Nb(n, 2n)92mNb reactions. With a series of corrections, high precision cumulative yields of 20 fission products were obtained. Our FPYs for the 238U(n, f) reaction at 14.7 MeV were compared with the existing experimental nuclear reaction data and evaluated nuclear data, respectively. The results will be helpful in the design of a generation-IV reactor and the construction of evaluated fission yield databases.

Cross Section Measurements of (n,x) Reactions at 17.9 MeV Using Highly Enriched Ge Isotopes

Τhe 70Ge(n,2n)69Ge, 72Ge(n,a)69mZn, 72Ge(n,p)72Ga and 73Ge(n,p)73Ga reactions have been measured by means of the activation technique at neutron energy 17.9 MeV. The quasimonoenergetic neutron beam was produced via the 2H(d,n)3He reaction at the 5.5 MV Tandem Van de Graaff accelerator of NCSR “Demokritos.” Isotopically highly enriched targets of 70Ge, 72Ge and 73Ge, provided by the nTOF collaboration at CERN, have been used, thus allowing accurate cross section measurements since no corrections are needed to compensate for the parasitic reactions from neighboring isotopes that exist in the case of using natural Ge target. The cross section has been deduced with respect to the 27Al(n,α)24Na reference reaction.

Cross-sections for production of [formula omitted] by quasi-monoenergetic neutrons within 7-20 MeV

The measurement of cross-sections producing In115m has been carried out within the energy range of 7–20 MeV. The neutron activation analysis (NAA) followed by off-line γ-ray spectrometry have been used for the purpose. The quasi-monoenergetic neutron beam was produced using the Li(p,n)7 reaction at the 14UD BARC-TIFR Pelletron accelerator facility at Mumbai, India. The ratio technique of covariance analysis has been used to estimate the uncertainty and correlation between the current experimental data which considers the collective uncertainty from all the attributes in the measurement. The measured cross-sections were compared with the experimental data from the previous literatures, different evaluated data libraries such as ENDF/B-VIII.0, JEFF-3.3, JENDL-4.0, CENDL-3.2 and the theoretically predicted results using the TALYS 1.95 and EMPIRE 3.2.3. The experimental results presented in this work are crucial for the measurement of neutron flux in the NAA technique.

Measurement of the [formula omitted] reaction cross section induced by 14.8 MeV neutrons

The measurement of the 59Co(n,2n)58Co reaction cross section with the neutron energy of 14.8 MeV has been performed by the activation method and relative measurement principle. The 300 kV Cockcroft Walton Accelerator of China Institute of Atomic Energy was used to produce quasi monoenergetic neutron beams by the T(D, n)4He reaction. Two thin 27Al and 93Nb foils were attached to the 59Co target and performed as monitors. After the irradiation, the HPGe detector and the GammaVision software were used to measure the activity of the irradiated samples and record the counts of γ-rays, respectively. Finally, some relevant physical quantities were corrected after comparing the results with experimental data in the EXFOR database and evaluated data in the ENDF database.

Cross-section measurements of the Dy156(n,2n)Dy155 reaction at neutron energies higher than 17 MeV

In the present work the cross section of the $^{156}\mathrm{Dy}(n,2n)^{155}\mathrm{Dy}$ reaction (${E}_{\mathrm{th}}=9.51$ MeV) was measured at neutron beam energies above 17 MeV: 17.1, 18.1, and 19.0 MeV. The irradiations were performed at the 5.5-MV tandem accelerator of the Institute of Nuclear and Particle Physics at N.C.S.R. ``Demokritos'', where quasi-monoenergetic neutron beams were produced via the $^{3}\mathrm{H}(d,n)^{4}\mathrm{He}$ reaction. The cross-section measurements were performed by means of the activation technique relative to the $^{27}\mathrm{Al}(n,\ensuremath{\alpha})^{24}\mathrm{Na}$ reference reaction. Within the present work the experimental study is framed by theoretical calculations performed via the talys code (version 1.95).

Erratum to: Measurement of the $$^{232}$$Th(n,f) cross section with quasi-monoenergetic neutron beams in the energy range 2–18 MeV

Erratum to: Measurement of the $$^{232}$$Th(n,f) cross section with quasi-monoenergetic neutron beams in the energy range 2–18 MeV

Measurement of the 124Xe (n,2n) reaction cross section induced by 14.8 MeV neutron

The measurement of the 124Xe(n, 2n)123Xe reaction cross section at 14.8 MeV neutron has been performed by the activation method. Quasi monoenergetic neutron beams were produced at the Cockcroft Walton Accelerator of China Institute of Atomic Energy, by the T(d, n)4He reaction. A cell made of polymethyl methacrylate (PMMA) was used as the container of 124Xe (99.95% abundance) gas, and the mass of 124Xe in cell was determined by weighing method. Two high-purity thin 93Nb foils were attached to the cell and performed as monitors of the neutron flux determination by 93Nb(n, 2n)92mNb reaction. After the irradiation, the activities of 123Xe and 92mNb were measured by off-line gamma-ray spectrometric technique using a pre-calibrated HPGe detector. As a result, the cross section has been deduced at 14.8 MeV, and the result was compared with the literature data and evaluations.

Measurement of the ^{232}Th(n,f) cross section with quasi-monoenergetic neutron beams in the energy range 2\u201318 MeV

The fission cross section of ^{232}Th has been measured at fast neutron energies, using a setup based on Micromegas detectors. The experiment was performed at the 5.5 MV Van de Graaff Tandem accelerator in the neutron beam facility of the National Centre for Scientific Research “Demokritos”. The quasi-monoenergetic neutron beams were produced via the ^{3}H(p,n), ^{2}H(d,n) and ^{3}H(d,n) reactions, while the ^{238}U(n,f) and ^{235}U(n,f) reactions were used as references, in order to acquire cross-section data points in the energy range 2–18 MeV. The characterization of the actinide samples was performed via alpha -spectroscopy with a Silicon Surface Barrier (SSB) detector, while Monte Carlo simulations with the FLUKA code were used to achieve the deconvolution of the ^{232}Th alpha peak from the alpha background of its daughter nuclei present in the spectrum. Special attention was given to the study of the parasitic neutrons present in the experimental area, produced via charged particle reactions induced by the particle beam and from neutron scattering. Details on the data analysis and results are presented.

Neutron beam filter system for fast neutron cross-section measurement at the ANNRI beamline of MLF/J-PARC

A neutron filtering system has been introduced in the Accurate Neutron–Nucleus Reaction Measurement Instrument (ANNRI) beamline in the Materials and Life Science (MLF) facility of the Japan Proton Accelerator Research Complex (J-PARC) in order to produce quasi-monoenergetic neutron beams. The filtered neutron spectrum by the filter assemblies was analyzed by means of capture and transmission measurements and also by Monte Carlo simulations using PHITS. The characteristics of the filtered neutron beam are discussed alongside its viability in future applications for neutron cross-section measurements in the fast neutron region.

Subtraction Method for an Effective Quasi-monoenergetic Neutron Beam by Using Continuous Energy Spectra

The cross sections of 89Y(n, 3n)87m,87gY and 209Bi(n, 4n)206Bi reactions at a neutron energy of 30 MeV are measured by making use of neutron beams of continuous energy spectra and a subtraction method. By impinging proton beams of 30 and 35 MeV to a thick beryllium target, neutron beams of continuous and broad energy spectra are produced and are guided to Y and Bi sample targets. The difference between the two neutron spectra generated by two neighboring proton energies is found to be peaked in a narrow energy range and thus can be regarded as quasi-monoenergetic, which can be used to extract (n, xn) cross sections. The uncertainty in the neutron fluence is reduced by analyzing the activities of aluminum and niobium reference samples placed on top of the Y and Bi samples. The use of a subtraction method by employing neutron beams of continuous energy spectra gives us the 89Y(n, 3n)87m,87gY and 209Bi(n, 4n)206Bi cross sections in fair agreement with the existing experimental data and nuclear data libraries.

Fast neutrons at LNL Legnaro

In this contribution we describe NEPIR, the fast-neutron irradiation facility under construction at the 70 MeV cyclotron SPES facility of the INFN laboratory of Legnaro (LNL). NEPIR will be constructed in stages, according to the available funds. The initial configuration, based on a thick Be neutron production target, will be operational in 2022; it will be used for shielding studies against fast neutrons for space applications and to investigate neutron-induced Single Event Effects (SEE) in microelectronic devices and systems. In its final configuration NEPIR will have two target systems: one will deliver a Quasi Mono-energetic Neutron (QMN) beam, of general interest, with an adjustable energy peak in the 20–70 MeV range; the second target will deliver a specialized continuous energy neutron beam for studying the effects of fast neutrons produced in cosmic ray air-showers in electronic devices and systems. We review the use of NEPIR to characterize the sensitivity of electronics, describe the neutron production targets and the facility layout. In closing we describe ways, presently under investigation, to use the 15 MV XTU Tandem of LNL to produce nearly monochromatic fast neutrons that would complement the QMN system by allowing one to probe for SEE below 20 MeV.