Neutron-induced Reaction Cross Sections Research Articles

Measurement of 232Th(n,σ)233Th, 98Mo(n,σ)99Mo, 186W(n,σ)187W, 115In(n,σ 116m1In, and 92Mo(n,p 92mNb Cross Sections in the Energy Range of 1.6 to 3.7 MeV

Neutron-induced reaction cross sections for the reaction 232Th(n, σ)233Th have been measured at neutron energies of 1.6 ± 0.03 MeV, 2.2 ± 0.03 MeV, 3.0 ± 0.03 MeV, and 3.7 ± 0.03 MeV. We have also measured cross sections for the reactions 98Mo(n, σ)99Mo, 186W(n, σ)187W, 115In(n, σ)116m1In, and 92Mo(n, p)92mNb at a neutron energy of 3.2 ± 0.03 MeV. The 7Li(p, n)7Be reaction was used as the neutron source with the proton beam from the 14-MV Pelletron accelerator, Mumbai, and the standard off-line gamma counting method was followed for activation measurement. The present measurements supplement the existing data and provide new data in the neutron energy range where no results are available. While the cross-section values for the 98Mo(n, σ)99Mo and 186W(n, σ)187W reactions are reported for the first time, the data for 92Mo(n, p)92mNb exists with a large discrepancy between the two available data sets. For the 115In(n, σ)116m1In reaction, our measurement at 3.2 MeV is an additional data point where there exists significant disagreement among the data measured by different groups. The measurements are performed relative to the 115In(n, n′)115mIn and 197 Au(n, σ)198 Au cross sections of International Reactor Dosimetry File 2002. Detailed theoretical calculations using the statistical model code EMPIRE-II (latest version EMPIRE-2.19) have been performed. Good agreement with the present data along with the existing data set has been obtained by suitable adjustment of the level density parameter for all the systems. The experimental and theoretical results have been compared with the recent evaluations of ENDF/B-VII.0, JENDL-4.0, and JEFF-3.1.

Bayesian Based Uncertainties of Neutron-Induced Reaction Cross Sections of Mn-55

le for neutron-induced cross sections of Mn-55 between 1 and 150 MeV. The evaluated le takes into account experimental data of the EXFOR data base and is generated by Bayesian statistics via the code GENEUS. Due to the scarcity of experimental data beyond 20 MeV, the prior, based on the nuclear model set of TALYS-1.0, plays an essential role for the reliability of the le in this energy regime. Therefore much eort was devoted to an optimized choice of the model parameters for the range 20 Z 28. Employing the recent formalisms a prior including parameter uncertainties and model defects was evaluated by GENEUS and used as a starting point of the evaluation process. In addition a careful analysis of experimental data was performed to estimate the covariance matrices of the experiments, which are used by GENEUS in the Bayesian procedure. The quality and the specic features of the evaluated data le and associated uncertainties are discussed.

Cross sections for neutron-induced reactions up to 1.6 GeV for target elements relevant for cosmochemical, geochemical, and technological applications

We determined neutron excitation functions from the respective reaction thresholds up to 1.6 GeV for almost 100 target-product combinations relevant for cosmochemical, geochemical, and technological applications. We started with thick target production rates that have been obtained by irradiating iron and stone spheres with protons having energies between 600 MeV and 1.6 GeV. From the particle spectra of primary protons, secondary protons, and secondary neutrons, and the usually well known cross sections for the proton-induced reactions we calculated the production rates only due to protons. By subtracting these data from the measured total production rates we obtained production rates only due to secondary neutrons. With the modelled neutron spectra, guess functions calculated using nuclear model codes, and sophisticated energy-dependent deconvolution procedures we were able to determine almost 100 neutron excitation functions with their uncertainties. With the thus obtained neutron cross sections we are able to describe the experimental production rates in the thick target experiments, meteorites, the lunar surface, and terrestrial surface samples usually within the uncertainties, i.e., to within 10–15%. The adjusted neutron cross sections ( a posteriori) are compared to results from the theoretical nuclear model codes INCL4.5/ABLA07 and TALYS. The TALYS code usually describes the a posteriori data reasonably well, i.e., mostly within a factor of a few. The quality of the INCL4.5 + ABLA07 predictions depends on the reaction type and increases with increasing number of ejectiles, i.e., increasing target-product mass difference. The neutron cross section database, though successful in quantifying production rates in terrestrial and extraterrestrial matter, presents by no means a final step and experiments with quasi-monoenergetic neutrons are needed.

Erratum: Cross sections of neutron-induced reactions [Phys. Rev. C82, 044613 (2010)

Comments by Dr. I. Angeli and Dr. J. Csikai raise concerns and questions regarding omission of references, proper name of the model, energy dependence of the radius and average chord length as 4R/3 which are briefly replied.

Cross sections of neutron-induced reactions

We study the properties of the neutron-nucleus total and reaction cross sections for several nuclei. We have applied an analytical model, the nuclear Ramsauer model, justified it from the nuclear reaction theory approach, and extracted the values of 12 parameters used in the model. The given parametrization has an advantage as phenomenological optical model potentials are limited up to $150\ensuremath{-}200$ MeV. The present model provides good estimates of the total cross sections for several nuclei particularly at high energies.

The systematics of (n, α) reaction cross-sections at 14.5 MeV neutron energy

A comprehensive review of the experimental data for 14.5 MeV neutron induced reaction crosssections for (n, α) reaction has been made for the isotopes having Z up to 82. Two different parameter groups have been considered by the classification of nuclei into odd-mass and even-even nuclei. The empirical formulae with two parameters for the evaluation of (n, α) reaction cross-sections are discussed in the present study. The odd-even effects have been observed as the cross-sections of odd-mass nuclei are higher as compared to their neighboring even-even nuclei. The shell effects have also been established at magic nucleon numbers for these reaction cross-sections.

STARS/LiBerACE: Segmented silicon and high-purity germanium detector arrays for low-energy nuclear reaction and structure studies

The Silicon Telescope Array for Reaction Studies (STARS) consists of large-area annular double-sided silicon detectors for charged-particle identification. The Livermore Berkeley Array for Collaborative Experiments (LiBerACE) is an array of six Compton-suppressed high-purity germanium Clover detectors for efficient detection of γ-rays. These detector arrays are versatile tools for studies of neutron-induced reaction cross-sections, fission, light neutron-rich nuclei, and other low-energy nuclear physics topics through transfer, fusion, incomplete-fusion, and inelastic-scattering reactions. The STARS and LiBerACE arrays and typical experimental configurations are described in detail.

Measurement ofγ-emission branching ratios forGd154,156,158compound nuclei: Tests of surrogate nuclear reaction approximations for(n,γ) cross sections

The surrogate nuclear reaction method can be used to determine neutron-induced reaction cross sections from measured decay properties of a compound nucleus created using a different reaction and calculated formation cross sections. The reliability of $(n,\ensuremath{\gamma})$ cross sections determined using the Weisskopf-Ewing and ratio approximations are explored for the $^{155,157}\mathrm{Gd}$$(n,\ensuremath{\gamma})$ reactions. Enriched gadolinium targets were bombarded with 22-MeV protons and $\ensuremath{\gamma}$ rays were detected in coincidence with scattered protons using the Silicon Telescope Array for Reaction Studies/Livermore-Berkeley Array for Collaborative Experiments (STARS/LiBerACE) silicon and germanium detector arrays. The $\ensuremath{\gamma}$-emission probabilities for the $^{154,156,158}\mathrm{Gd}$ compound nuclei were measured at excitation energies up to 12 MeV. It is found that the approximations yield results that deviate from directly measured $^{155,157}\mathrm{Gd}$$(n,\ensuremath{\gamma})$ cross sections at low energies. To extract reliable cross sections, a more sophisticated analysis should be developed that takes into account angular-momentum differences between the neutron-induced and surrogate reactions.

A detector system for neutron resonance capture imaging

Neutron resonance capture analysis (NRCA) is used in the Ancient Charm project to determine element concentrations in cultural heritage objects. NRCA employs gamma-ray detectors to determine time-of-flight spectra that reveal the resonance structure in neutron induced reaction cross sections. One of the objectives is to produce a high-detection efficient NRCA system capable of mapping element distributions. The detection system is described together with the results of neutron beam tests at the time-of-flight facility GELINA and at the pulsed neutron spallation source ISIS (UK).

Study on Some Structural Fusion Materials for (n,p) Reactions up to 30 MeV Energy

The neutron incident energy around 14–15 MeV is enough to excite the nucleus for the reactions such as (n,p), (n,d), (n,2n), (n,t) and (n,α). In fusion reactor structures, a serious damage mechanism has been gas production in the metallic resulting from diverse nuclear reactions, mainly through (n,p) and (n,α) and to some extent through (n,d) and (n,t) reactions above a certain threshold energy. So, working out the systematic of the neutron induced reaction cross sections is of great importance for the definition of the excitation function character for the given reaction taking place on various nuclei at different energies. In this study, (n,p) reactions for some structural fusion materials such as 27Al, 51V, 52Cr, 55Mn and 56Fe have been investigated. The new calculations on the excitation functions of 27Al(n,p)27Mg, 51V(n,p)51Ti, 52Cr(n,p)52V, 55Mn(n,p)55Cr and 56Fe(n,p)56Mn reactions have been carried out up to 30 MeV incident neutron energy. In these calculations, the pre-equilibrium and equilibrium effects have been investigated. Also in the present work, the (n,p) reaction cross-sections have calculated by using evaluated empirical formulas developed by Tel et al. at 14–15 MeV energy. The calculated results are discussed and compared with the experimental data taken from EXFOR database.

Radiochemical determination of nuclear data for theory and applications

A vast knowledge of nuclear data is available and is grouped under three headings, namely, nuclear structure, nuclear decay and nuclear reaction data. Still newer aspects are under continuous investigation. Data measurements are done using a large number of techniques, including the radiochemical method, which has been extensively worked out at Julich. This method entails preparation of high-quality sample for irradiation, isolation of the desired radioactive product from the strong matrix activity, and preparation of thin source suitable for accurate measurement of the radioactivity. It is especially useful for fundamental studies on light complex particle emission reactions and formation of low-lying isomeric states, both of which are rather difficult to describe by nuclear model calculations. The neutron induced reaction cross section data are of practical application in fusion reactor technology, particularly for calculations on tritium breeding, gas production in structural materials and activation of reactor components. The charged particle induced reaction cross section data, on the other hand, are of significance in medicine, especially for developing new production routes of novel positron emitters and therapeutic radionuclides at a cyclotron. Both neutron and charged particle data also find application in radiation therapy. A brief overview of advances made in all those areas is given, with major emphasis on nuclear reaction cross section data.

Double-Differential Cross Sections of the Particle Emission in Neutron-Induced Reactions on 209Bi

All cross sections of neutron-induced reactions, including energy spectra and double-differential cross sections for neutron, proton, deuteron, triton, helium, and alpha-particle emissions, are consistently calculated for the 209Bi nucleus at incident neutron energies below 200 MeV. The results are compared with existing experimental data.

Advanced nuclear energy systems and the need of accurate nuclear data: the n_TOF project at CERN

To satisfy the world's constantly increasing demand for energy, a suitable mix of different energy sources has to be devised. In this scenario, an important role could be played by nuclear energy, provided that major safety, waste and proliferation issues affecting current nuclear reactors are satisfactorily addressed. To this purpose, a large effort has been under way for a few years towards the development of advanced nuclear systems with the aim of closing the fuel cycle. Generation IV reactors, with full or partial waste recycling capability, accelerator driven systems, as well as new fuel cycles are the main options being investigated. The design of advanced systems requires improvements in basic nuclear data, such as cross-sections for neutron-induced reactions on actinides. In this paper, the main concepts of advanced reactor systems are described, together with the related needs of new and accurate nuclear data. The present activity in this field at the neutron facility n_TOF at CERN is discussed.

( n,2 n) and ( n,3 n) cross-sections of neutron-induced reactions on 150Sm for [formula omitted] MeV

Cross-section measurements were made of prompt discrete γ -ray production as a function of incident neutron energy ( E n = 1 – 135 MeV ) on a 150Sm sample of 1550 mg / cm 2 of Sm 2 O 3 enriched to 95.6% in 150Sm. Results are compared with enhanced Hauser–Feshbach model calculations including the pre-equilibrium reactions. Energetic neutrons were delivered by the Los Alamos Neutron Science Center facility. The prompt-reaction γ -rays were detected with the compton-suppressed germanium array for neutron-induced excitations (GEANIE). Incident neutron energies were determined by the time-of-flight technique. Excitation functions for thirteen individual γ -rays up to E x = 0.8 MeV in 149Sm and one γ -ray transition between the first excited and ground state in 148Sm were measured. Partial γ -ray cross-sections were calculated using GNASH, an enhanced Hauser–Feshbach statistical nuclear reaction model code, and compared with the experimental results. The particle transmission coefficients were calculated with new systematic “global” optical model potential parameters. A coupled-channels optical model based on a soft rotor model was employed to calculate the particle transmission coefficients. The pre-equilibrium part of the spin-distribution in 150Sm was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK) and incorporated into the GNASH reaction model code. The partial cross-sections for discrete γ -ray cascade paths leading to the ground state in 149Sm and 148Sm have been summed (without double counting) to estimate lower limits for reaction cross-sections. These lower limits are combined with Hauser–Feshbach model calculations to deduce the reaction channel cross-sections. These reaction channel cross-sections agree with previously measured experimental and ENDF/B-VII evaluations.

Numerical simulations of production rates for 10Be, 26Al and 14C in extraterrestrial matter using the MCNPX code

Abstract Numerical simulations of production rates for cosmogenic 10Be, 26Al and 14C in well-documented samples from the meteorite Knyahinya and the Apollo 15 deep core were performed using the MCNPX (Monte Carlo N Particle eXtended) code for cosmic-ray interactions. Comparisons of experimental measurements and our numerical simulations were done to test our calculations and show that the numerical simulations reproduce well experimental measurements. The effective fluxes of GCR proton determined from our comparisons are important parameters for future calculations. Additional measurements of some radionuclide activities and of cross sections for neutron-induced reactions are needed.

Generation IV nuclear energy systems and the need of accurate nuclear data

To satisfy the world's demand of energy, constantly increasing over the years, a suitable mix of different energy sources has to be envisaged. In this scenario, an important role may be played by nuclear energy, provided that major safety, waste and proliferation issues affecting current nuclear reactors are satisfactorily addressed. In this respect, a large effort is under way since a few years towards the development of advanced nuclear systems that would use more efficiently the uranium resources, and produce a minimal amount of long-lived nuclear waste. The main activity concerns Generation IV reactors, with full or partial waste recycling capability. Their design requires R&D in numerous fields. Among the different needs, it is of fundamental importance to improve the knowledge of basic nuclear data, such as cross-sections for neutron-induced reactions on actinides. The main characteristics and principle of operation of the new generation nuclear systems are here described, together with the related needs of new and accurate nuclear data. Finally, an example of activity currently undergoing in the field is shown, with the recent experimental results obtained at the neutron facility n_TOF at CERN.

Theoretical Calculations and Analysis for the n + 59Co Reaction up to 20 MeV

All cross sections of neutron-induced reactions, angular distributions, double-differential cross sections, and energy spectra for neutron, proton, deuteron, triton, helium, and alpha-particle emissions are consistently calculated and analyzed for 59Co with incident neutron energies below 20 MeV by using nuclear theoretical models, which are the optical model, preequilibrium and equilibrium reaction theories, and the distorted wave Born approximation theory. Theoretical calculated results are compared with existing experimental data and with evaluated data from ENDF/B-VII and JENDL-3.3.

Calculation and Evaluations for n + 54,56,57,58,natFe Reactions

All cross sections of neutron-induced reactions, angular distributions, energy spectra and double-differential cross sections are consistently calculated and analyzed for 54,56,57,58,natFe at incident neutron energies below 200 MeV based on the nuclear theoretical models, which are the optical model, preequilibrium and equilibrium reaction theories, and the distorted wave Born approximation theory. Theoretical calculated results are compared with existing experimental data and the evaluated results in ENDF/B-VII and JENDL-3. The optical model potential parameters are obtained according to the experimental data of total and nonelastic-scattering cross sections, and elastic-scattering angular distributions.

Neutron induced reaction cross sections for the radioactive target nucleus 99Tc

We present the first measured and interpreted excitation functions for three nuclear reactions on the radioactive target nucleus 99Tc over the energy range from threshold to 20.6 MeV. Excitation functions for the 99Tc( n , n ′ γ ) 99mTc, 99Tc( n , p ) 99Mo, and 99Tc( n , α ) 96Nb reactions were measured using the activation method. High-resolution γ-ray spectroscopy was used requiring special attention to suppress Bremsstrahlung. The irradiated samples consisted of pressed pellets of metallic 99Tc in Al-capsules. Quasi mono-energetic neutrons were produced via the 3H( p , n ) 3He, 2H( d , n ) 3He, and 3H( d , n ) 4He reactions. The neutron fluence was monitored via the well-known 115In( n , n ′ ) 115mIn, 27Al( n , α ) 24Na, 27Al( n , p ) 27Mg, 56Fe( n , p ) 56Mn, and 93Nb( n , 2 n ) 92mNb standard reactions. Statistical model calculations incorporating precompound effects were performed for all the measured reaction channels using two different codes, namely TALYS and STAPRE. Good agreement was obtained for the reactions in which a charged particle was emitted and for the excitation of the isomer in inelastic scattering, above 5 MeV.

Lithium Production on a Low-Mass Secondary in a Black Hole Soft X-Ray Transient

We examine production of Li on the surface of a low-mass secondary in a black hole soft X-ray transient (BHSXT) through the spallation of CNO nuclei by neutrons which are ejected from a hot (>10 MeV) advection-dominated accretion flow (ADAF) around the black hole. Using updated binary parameters, cross sections of neutron-induced spallation reactions, and mass accretion rates in ADAFs derived from the spectrum fitting of multiwavelength observations of quiescent BHSXTs, we obtain the equilibrium abundances of Li by equating the production rate of Li and the mass transfer rate through accretion to the black hole. The resulting abundances are found to be in good agreement with the observed values in seven BHSXTs. We note that the abundances vary on a timescale longer than a few months in our model. Moreover, the isotopic ratio 6Li /7Li is calculated to be about 0.7-0.8 on the secondaries, which is much higher than the ratio measured in meteorites. Detection of such a high value is favorable to the production of Li via spallation and the existence of a hot accretion flow, rather than an accretion disk corona system in quiescent BHSXTs.