Photonuclear production of nuclear isomers using bremsstrahlung induced by laser-wakefield electrons

In this study,we theoretically investigate the feasibility of using laser-wakefield accelerated(LWFA)electrons for the photonuclear measurement of nuclear isomers according to the characteristics of the electrons obtained from LWFA experiments conducted at the Compact Laser-Plasma Accelerator(CLAPA)laboratory.The experiments at the CLAPA show that a stable electron beam with an energy of 78-135 MeV and a charge of 300-600 pC can be obtained.The bremsstrahlung spectra were simulated using Geant4,which suggests that a bremsstrahlung source with a peak intensity of 10^(19) photons/s can be generated.Theoretical calculations of isomer production cross sections from the photonuclear reactions on six target nuclei,^(197)Au,^(180)Hf,^(159)Tb,^(115)In,^(103)Rh,and ^(90)Zr,were performed and compared with the available experimental data in EXFOR,which suggest that further experiments are required for a series of photonuclear reaction channels.Flux-averaged cross sections and isomer ratios(IR)resulting from such bremsstrahlung sources are theoretically deduced.The results suggest that IR measurements can be used to constrain nuclear components,such asγstrength function and optical model potential.In addition,the detection of the decay characteristics was evaluated with Geant4 simulations.The use of the LWFA electron beam and its bremsstrahlung for photonuclear studies involving nuclear isomers is anticipated.

Measurement of^(134)Xe(n,2n)^(133m),gXe reaction cross sections in 14‑MeV region with detailed uncertainty quantification

A lead-shielded HPGe detector and offlineγ-ray spectra of the residual product were used to measure the cross section(CS)and ratios of isomeric CS(σm/σg)in^(134)Xe(n,2n)^(133m),gXe reactions at different energies(13.5 MeV,13.8 MeV,14.1 MeV,14.4 MeV,14.8 MeV)relative to the^(93)Nb(n,2n)^(92)mNb reaction CS.The target was high-purity natural Xe gas under high pressure.The T(d,n)4He reaction produces neutrons.TALYS code(version 1.95)for nuclear reactions was used for calculations,with default parameters and nuclear level density models.The uncertainties in the measured CS data were thoroughly analyzed using the covariance analysis method.The results were compared with theoretical values,evaluation data,and previous experimental findings.CS data of the 134Xe(n,2n)133mXe and 134Xe(n,2n)133gXe reactions and the corresponding isomeric CS ratios at 13.5 MeV,13.8 MeV,and 14.1 MeV neutron energies are reported for the first time.This research advances our knowledge of pre-equilibrium emission in the(n,2n)reaction channel by resolving inconsistencies in the Xe data.

Direct neutron decay of analogue resonances in ^105Rh

A new method, while takes into account the contribution of direct neutron decay of analogue resonances to the isomeric ratio resulting from （p,n） reaction, is used to analyse the published experimental data for the reaction ^104Ru（p,n） ^104Rh and also estimate a minimum probability of direct decay.

Interaction of photons with silver and indium nuclei at energies up to 20 MeV

The yields of photonuclear reactions in the 107Ag,113In,and 115In nuclei were measured.Monte Carlo simulations were performed using the Geant4 code,and the results were compared with the experimental values.The isomeric ratios of the yields in the reactions 107Ag(γ,n)106m,gAg and 113In(γ,m)112m,gIn were determined,and the cross sections for the reactions 107Ag(γ,n)106gAg and 107Ag(γ,2n)105Ag at an energy of 20 MeV were calculated based on the experimental data.

Isomeric ratio of the ^(181)Ta(γ,3n)^(178m,g)Ta reaction products at energy Eγmax up to 95 MeV

The photoneutron reaction^(18)Ta(y,3m)(178m,g)Ta was investigated with the beam from the NSC KIPT electron linear accelerator LUE-40.The measurements were performed using the residual y-activity method.The bremsstrahlung flux-averaged cross sections((E_(γmax))>.(r(E_(γmax))>m.<r(E_(γmax))g and the isomerie ratio of the re-action products d(E_(γmax))were measured.The theoretical values of the averaged cross-sections and isomeric ratio were calculated using the partial cross-sections from the TALYS1.95 code for different level density models LD 1-6..The obtained experimental d(E_(γmax))agree with the data in the lterature,but differ from the theoretical values in ab-solute magnitude and the behavior of the energy dependence.A comparison of the determined averaged cross-sec-tions with the calculated cross sections showed the best agreement for the case of the LD 5 model.

Determination of the half-life of^(184g)Re and the isomeric ratio of^(184m,g)Re induced by D-T neutrons

The isomeric ratio of^(184m,g)Re and the half-life of^(184g)Re were measured in the ^(185)Re(n,2n)^(184)Re reaction at 14.8 MeV,and the uncertainty was discussed in detail.The measurements were performed using the activation method implemented for a rhenium sample using the K-400 neutron generator at the Chinese Academy of Engineering Physics(CAEP).Isomeric state and ground state nuclei of ^(184)Re were identified by their γ-ray spectra.To eliminate the effect of the γ-ray emitted from the isomer on the counting of the ground state characteristic peaks,the isomeric ratio of^(184m,g)Re was calculated to be 0.29±0.11 according to the neutron activation cross-section formula.This result is consistent with previous data within the uncertainty and can be used to determine parameters that characterize the dependence of the level density on the excitation energy and angular momentum.Through exponential function fitting and a detailed discussion of the uncertainty evaluation,the half-life of^(184g)Re was determined as 35.43±0.16 d,which is consistent with the currently recommended value;however,the uncertainty assessment of the latter was barely documented.In addition,this study indicates that the half-life of the ground state can be obtained by eliminating the contamination of γ-rays emitted from the isomer,which provides the possibility of determining the half-lives of nuclides containing isomers.

Measurements of ^(nat) Cd(γ,x)reaction cross sections and isomer ratio of ^(1,5m.g)Cd with the bremsstrahlung end-point energies of 50 and 60 MeV

The flux-weighted average cross sections ^(nat) Cd(γ,xn)^(115g,m,111m,109,107,105,104)Cd and ^(nat) Cd(γ,x)^113g,112,111g,110m)Ag reactions were measured at the bremsstrahlung end-point energies of 50 and 60 MeV.The activa tion and off-line y-ray spectrometric technique was carried out using the 100 MeV electron linear accelerator at the Pohang Accelerator Laboratory,Korea.The ^(nat)lCd(γ,xn) reaction cross sections as a function of photon energy were theoretically calculated using the TALYS-1.95 and the EMPIRE-3.2 Malta codes.Then,the flux-weighted average cross sections were obtained from the theoretical values of mono-energetic photons.These values were compared with the flux-weighted values from the present study and were found to be in general agreement.The measured experimental reaction cross-sections and integral yields were described for cadmium and silver isotopes in the ^(nat)Cd(γ,xn)^(115g,m,111m,109,107,105,104) and ^(nat)Cd(γ,x)^(113g,112.111g,110m)Ag reactions.The isomeric yield ratio(IR) of ^(115g.m)Cd in the ^(nat)Cd(γ,xn) reaction was determined for the two bremsstrahlung end-point energies.The measured isomeric yield ratios of ^(115g,m)Cd in the ^(nat)Cd(γ,xn) reaction were also compared with the theoretical values of the nuclear model codes and previously published literature data of the ^(116)Cd(γ,x) and ^116(γ,2n) reactions.It was found that the IR value increases with increasing projectile energy,which demonstrates the characteristic of excitation energy.However,the higher IR value of ^(115g.m)Cd in the ^(116)Cd(n,2n)reaction compared to that in the ^(116)Cd(γ,x)reaction indicates the role of compound nuclear spin alongside excitation energy.

Isomeric pair 95m,g Nb in the photonuclear reactions on natMo at the bremsstrahlung end-point energy of 38–93 MeV

The ^(nat)Mo(γ,xnp)^(95m,g)Nb photonuclear reaction was studied using the electron beam from the NSC KIPT linear accelerator LUE-40.The experiment was performed using the activation and off-line γ-ray spectrometric technique.The experimental isomeric yield ratio(IR) was determined for the reaction products ^(95m,g)Nb at the bremsstrahlung end-point energy E_(γmax) range of 38-93 MeV.The obtained values of IR are in satisfactory agreement with the results of other studies and extend the range of previously known data.The theoretical values of the yields Y_(m,g)(E_(γmax)) and the IR for the isomeric pair ^(95m,g)Nb from the ^(nat)Mo(γ,xnp) reaction were calculated using the partial cross-sections σ(E) from the TALYS1.95 code for six different level density models.For the investigated range of E_(γmax),the theoretical dependence of IR on energy was confirmed-the IR smoothly increases with increasing energy.The comparison showed a noticeable difference(more than 3.85 times) in the experimental IR relative to all theoretical estimates.

Distribution and origin of polycyclic aromatic hydrocarbons in surface sediments from an urban river basin at the Metropolitan Region of Curitiba,Brazil

The concentrations of 16 polycyclic aromatic hydrocarbons（PAHs） were determined in surface sediment samples from nine sites located at the Iguau River Basin in the Metropolitan Region of Curitiba,Brazil to evaluate their distribution and sources.The total concentration of the PAHs was greater for sediments from highly urbanized areas,while the sediments from the Iraí Environmental Protection Area（Iraí EPA） showed significantly low concentrations.The sediments from the Iguau and Barigui rivers were classified as highly contaminated,while those from the Cercado and Curralinho rivers were classified as moderately contaminated.The predominance of PAHs containing two to four aromatic rings in most of the samples suggested the direct input of raw sewage into the water resources evaluated.Benzo[g,h,i]perylene,dibenzo[a,h]anthracene and indeno[1,2,3-cd]pyrene were predominant in sediments from the areas under the greatest urban and industrial development.The correlation between thermodynamic stability and the kinetics of evolution presented by the isomeric pairs indicated that combustion is the predominant source of PAHs in the sediments because the combustion of fossil fuels affected most of the points evaluated,followed by combustion of biomass and eventually combustion of oil product inputs.In general,the results showed that areas under strong urban influence,as well as the Iraí EPA,receive contributions of PAHs from similar sources.