Measurement of the neutron-induced total cross sections of ^(nat)Pb from 0.3 eV to 20 MeV on the Back-n at CSNS

The neutron-induced total cross sections of natural lead have been measured in a wide energy range(0.3 eV-20 MeV)on the back-streaming white neutron beamline(Back-n)at the China Spallation Neutron Source.Neutron energy was determined by the neutron total cross-section spectrometer using the time-of-flight technique.A fast multi-cell fission chamber was used as the neutron detector,and a 10-mm-thick high-purity natural lead sample was employed for the neutron transmission measurements.The on-beam background was determined using Co,In,Ag,and Cd filters.The excitation function of ^(nat)Pb(n,tot)reaction below 20 MeV was calculated using the TALYS-1.96 nuclear-reaction modeling program.The present results were compared with previous results,the evaluated data available in the five major evaluated nuclear data libraries(i.e.,ENDF/B-VIII.0,JEFF-3.3,JENDL-5,CENDL-3.2,and BROND-3.1),and the theoretical calculation curve.Good agreement was found between the new results and those of previous experiments and with the theoretical curves in the corresponding region.This measurement obtained the neutron total cross section of natural lead with good accuracy over a wide energy range and added experimental data in the resonance energy range.This provides more reliable experimental data for nuclear engineering design and nuclear data evaluation of lead.

Source-less density measurement using an adaptive neutron-induced gamma correction method

The use of radioactive isotopes,such as Cs-137,to measure formation density is a common practice;however,it poses high risks such as environmental contamination from lost sources.To address these challenges,the use of pulsed neutron sources for density measurements,also known as“source-less density”,has emerged as a promising alternative.By collecting gamma counts at different time gates according to the duty cycle of the pulsed sequence,the inelastic gamma component can be isolated to obtain more accurate density measurements.However,the collection of gamma rays during the neutron burst-on period often contains a proportion of capture gamma rays,which can reduce the accuracy of density measurements.This proportion can vary depending on the formation environment and neutron duty cycle.To address these challenges,an adaptive capture gamma correction method was developed for density measurements.This method distinguishes between“burst-on”and“burst-off”periods based on the gamma time spectra,and derives the capture ratio in the burst-on period by iteratively fitting the capture gamma time spectra,resulting in a more accurate net inelastic gamma.This method identifies the end of the pulse by automatically calculating the differential,and fits the capture gamma time spectra using Gaussian process regression,which considers the differences in formation attenuation caused by different environments.The method was verified through simulations with errors of below 0.025 g/cm3,demonstrating its adaptability and feasibility for use in formation density measurements.Overall,the proposed method has the potential to minimize the risks associated with radioactive isotopes and improve the accuracy of density measurements in various duty cycles and formation environments.

A method for neutron-induced gamma spectra decomposition analysis based on Geant4 simulation

In various monitoring and detection tools that use pulsed neutron generators as radiation sources,the gamma rays induced by the interaction with various nuclei at different stages of neutron transport can reflect information about the medium.These gamma rays are generated in two major interactions:inelastic scattering of fast neutrons and radiative capture of thermal neutrons,corresponding to the inelastic and capture gamma rays,respectively.However,the two types of gamma rays that reflect different properties of the medium are difficult to collect by normal detectors independently.The proportion of the two gamma rays needs to be solved for the separation of inelastic and capture gamma.Therefore,this study proposes an optimized spectra decomposition method to calculate the inelastic-to-capture ratio in the measured total gamma spectra based on the net inelastic and capture spectra obtained using the Geant4 simulation.Because the simulated data cannot reflect the energy resolution of the measured spectra,we introduce the Gaussian broadening function of the gamma detector while calculating the proportion of the spectra components,and achieve optimization of the proportion values and resolution parameters simultaneously.Based on the results,the total simulated spectra obtained by superimposing the broadened net inelastic and capture gamma spectra according to the calculated inelastic-to-capture ratio are in good agreement with their measured counterpart.

Long-lived neutron-induced radioisotopes in OKTAVIAN facility concrete wall after 38 year-operation

An intense 14 MeV neutron source facility named OKTAVIAN was installed in the A15 building,Osaka University in 1981.Along the operation period,new radioisotopes with various half-life have been produced as neutron activation products in its concrete wall shield.In this work,we investigated the concrete wall in the heavy irradiation room of OKTAVIAN using gamma spectrometry method to discover the presence of radioisotope having large half-life value(long-lived radioisotope)as neutron activation products.Computational simulations were performed prior to measurement to predict the presence of long-lived radioisotopes by employing MCNP5 and FISPACT codes.A pre-calibrated Germanium detector with high energy resolution was employed to measure the concrete.Several long-lived activation products have been observed such as 152 Eu,54 Mn,65 Zn,22 Na and 60 Co.The activity of each radioisotope was derived after estimating the detector efficiency using MCNP5.As a result of the measurement and analysis,the followings are concluded:(1)Though presence of activation products represents radiological risk to everyone who performs an experimental activity in the irradiation room of the OKTAVIAN facility,the present result shows that past experiments were carried out safely without any significant additional exposure dose coming from the wall for the last 38 years.(2)The approximated total fluence of D-T neutrons to the wall was successfully estimated from the produced radioisotope,152 Eu,because it has the longest half-life of 13.5 years among the observed radioisotopes.(3)From the results of(1)and(2),it could be possible to estimate the total activity of the concrete wall in the OKTAVIAN facility,which is very essential and important information,because this would be very valuable for decommissioning or disposal of the facility in the future.

Measurement and analysis of the neutron-induced total cross-sections of 209Bi from 0.3 eV to 20 MeV on the Back-n at CSNS

The neutron-induced total cross-section of ^(209)Bi is crucial for the physical design and safety assessment of lead-based fast reactors, and the quality of experimental data should be improved for evaluation and application.A recent experiment was conducted on the back-streaming white neutron beamline(Back-n) at the China Spallation Neutron Source(CSNS) using the neutron total cross-section spectrometer(NTOX). The neutron energy was determined using a fast multi-cell fission chamber and the time-of-flight technique. Two high-purity bismuth samples,6 mm and 20 mm in thickness, were chosen for neutron transmission measurements and comparisons. The neutron total cross-sections of ^(209)Bi, ranging from 0.3 e V to 20 Me V, were derived considering neutron flight time determination, flight path calibration, and background subtraction. A comparison of the experimental results with the data in the ENDF/B-VⅢ.0 library showed fair agreement, and the point-wise cross-sections were found to be consistent with existing experimental data. Special attention was given to the determination of resonance parameters, which were analyzed using the R-matrix code SAMMY and Bayesian method in the 0.5 ke V to 20 ke V energy range. The extracted resonance parameters were compared to previously reported results and evaluated data. This study is recognized as the first one where the neutron total cross-section of bismuth across such a broad energy spectrum is measured in a single measurement or experiment, and it provides valuable data for the assessment of related reaction information for evaluated libraries and the advancement of lead-bismuth-based nuclear systems.

Monte Carlo simulation of fast neutron-induced fission of 237Np

The potential-driving model is used to describe the driving potential distribution and to calculate the preneutron emission mass distributions for different incident energies in the 237 Np(n, f)reaction. The potential-driving model is implemented in Geant4 and used to calculate the fission-fragment yield distributions, kinetic energy distributions, fission neutron spectrum and the total nubar for the 237 Np(n, f)reaction. Compared with the built-in G4 ParaFissionModel, the calculated results from the potential-driving model are in better agreement with the experimental data and evaluated data. Given the good agreement with the experimental data, the potential-driving model in Geant4 can describe well the neutron-induced fission of actinide nuclei, which is very important for the study of neutron transmutation physics and the design of a transmutation system.

Kinetic energy distribution for neutron-induced fission of neptunium isotopes

The mean total kinetic energy as a function of fission fragments,the<TKE>distribution,is presented for neutron-induced fission of ^(235-239)Np using the scission point model.The calculated results of<TKE>for neutron-induced fission of ^(237,238) Np are compared with the available experimental data to obtain the deformation parameters in the scission point model.The deformation parameters of fission fragments are discussed at the scission point.The calculated results are also compared with the results from other methods and with experimental data.The behavior of the<TKE>distribution is then studied for the neutron-induced fission of actinides.This indicates that the<TKE>values for neutron-induced fission of actinides with odd mass numbers are greater than for those with even mass numbers.

Neutronic investigation and activation calculation for CFETR HCCB blankets

The neutronic calculations and activation behavior of the proposed helium cooled ceramic breeder（HCCB） blanket were predicted for the Chinese Fusion Engineering Testing Reactor（CFETR） design model using the MCNP multi-particle transport code and its associated data library. The tritium self-sufficiency behavior of the HCCB blanket was assessed, addressing several important breeding-related arrangements inside the blankets. Two candidate first wall armor materials were considered to obtain a proper tritium breeding ratio（TBR）. Presentations of other neutronic characteristics, including neutron flux, neutron-induced damages in terms of the accumulated dpa and helium production were also conducted. Activation, decay heat levels and contact dose rates of the components were calculated to estimate the neutron-induced radioactivity and personnel safety. The results indicate that neutron radiation is efficiently attenuated and slowed down by components placed between the plasma and toroidal field coil.The dominant nuclides and corresponding isotopes in the structural steel were discussed. A radioactivity comparison between pure beryllium and beryllium with specific impurities was also performed. After a millennium cooling time, the decay heat of all the concerned components and materials is less than 1？×？10-4 k W, and most associated in-vessel components qualify for recycling by remote handling. The results demonstrate that acceptable hands-on recycling and operation still require a further long waiting period to allow the activated products to decay.

A formula used to subtract the effect of gamma-ray of the others to that of measured reaction in measurement of cross section of nuclear reaction and its application

According to the regulation of growing and decay of artificial radioactive nuclide, a formula used to subtract the effect of characteristic γ-ray of the others to that of measured reaction was deduced. And then the cross sections of ^120Te （n, 2n）^119mTe reaction induced by neutrons around 14 MeV were measured by activation relative to the ^93Nb （n, 2n）^92mNb. In the process of the cross sections measured to be calculated, it was subtracted that the effect of characteristic γ-ray of ^126Te （n, p）^126Sb to that of measured ^120Te （n, 2n）^119mTe reaction using the formula deduced. The experimental results were （689±37） and （750±41） mb at the neutron energies of （13.5±0.3） and （14.6±0.3） MeV, respectively. Measurements were carried out by T-detection using a coaxial HPGe detector. As samples, spectroscopically pure tellurium powder has been used. The fast neutrons were produced by the T（d, n）4He reaction. The neutron energies in these measurements were determined by the method of cross-section ratios between ^90Zr （n, 2n） ^89m＋gZr and ^93Nb （n, 2n） ^92mNb reactions.

Prompt fission neutron spectra of n+^(235)U above the(n,nf) fission threshold

Calculations of prompt fission neutron spectra （PFNS） from the ^235U（n, f） reaction were performed with a semi-empirical method for En = 7.0 and 14.7 MeV neutron energies. The total PFNS were obtained as a superposition of （n,xnf） pre-fission neutron spectra and post-fission spectra of neutrons which were evaporated from fission fragments, and these two kinds of spectra were taken as an expression of the evaporation spectrum. The contributions of （n,xnf） fission neutron spectra on the calculated PFNS were discussed. The results show that emission of one or two neutrons in the （n,nf） or （n,2nf） reactions influences the PFNS shape, and the neutron spectra of the （n,xnf） fission-channel are soft compared with the neutron spectra of the （n,f） fission channel. In addition, analysis of the multiple-chance fission component showed that second-chance fission dominates the PFNS with an incident neutron energy of 14.7 MeV whereas first-chance fission dominates the 7 MeV case.

Cross-sections for(n,2n),(n,α),(n,p),(n,d),and(n,t)reactions on molybdenum isotopes in the neutron energy range of 13 to 15 MeV

Given the insufficient cross-sectional data regarding the 14-MeV-neutron experiment of molybdenum,the vital fusion reactor structural material,and the significant heterogeneities among the reported values,this study examined the(n,2n),(n,α),(n,p),(n,d),and(n,t)reaction cross sections in molybdenum isotopes based on the neutrons produced via a T(d,n)4He reaction carried out in the Pd-300 Neutron Generator at the China Academy of Engineering Physics(CAEP).A high-resolution gamma-ray spectrometer,which was equipped with a coaxial high-purity germanium detector,was used to measure the product nuclear gamma activities.In addition,27Al(n,α)24Na and 93Nb(n,2n)92mNb reactions were utilized as the neutron fluence standards.The experimental 92Mo(n,2n)91Mo,94Mo(n,2n)93mMo,100Mo(n,2n)99Mo,98Mo(n,α)95Zr,100Mo(n,α)97Zr,92Mo(n,p)92mNb,96Mo(n,p)96Nb,97Mo(n,p)97Nb,98Mo(n,p)98mNb,92Mo(n,d)91mNb,and 92Mo(n,t)90Nb reaction cross sections were acquired within the 13-15 MeV neutron energy range.Thereafter,we compared and analyzed these obtained cross sections based on the existing IAEA-EXFOR database-derived experimental data,together with evaluation results corresponding to ENDF/B-Ⅷ.0,JEFF-3.3,BROND-3.1,and CENDL-3.1 and the theoretical outcomes acquired through TALYS-1.95 and EMPIRE-3.2.3(nuclear-reaction modeling tools).

Neutron and Alpha Structure in Neutron Deficient Nuclei in Astrophysics

The paper includes discussions on the important role of neutron and alpha configurations in proton-rich nuclei in nuclear astrophysics in terms of nucleosynthesis under extremely high-temperature hydrogenburning conditions. The νp-process, which is supposed to take place at the very early epoch of type II supernovae, has considerable neutrons and alphas together with protons. The alpha-induced reactions on proton-rich unstable nuclei in the light mass regions is expected to play a crucial role, but very few of them were investigated well yet because of the experimental difficulties. Specifically, I report our recent experimental effort for the breakout process from the pp-chain region,~7Be(α, γ)^(11)C(α,p)^(14)N under the νp-process. The neutron-induced reactions on proton-rich nuclei, which is even more a challenging subject, were investigated previously for very few nuclei. One possible experimental method is the Trojan Horse Method(THM). We successfully have applied THM to the ^(18)F(n,α)^(14)N reaction study with an unstable beam of ^(18)F.