Isomeric Yield Ratios Research Articles

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 235U

In the epi-cadmium neutron induced fission of 235U, independent isomeric yield ratios (IR) of fission products 130,132Sb, 131,133Te, 134,136I, 135Xe and 138Cs have been measured by using an off-line gamma-ray spectrometric technique. The average neutron energy of the epi-cadmium reactor neutron spectrum is 1.9 MeV. From the IR values, the root mean square fragment angular momenta (JRMS) were deduced by using spin dependent statistical model analysis. The IR and JRMS values of considered fission products in the epi-cadmium neutron induced fission of 235U were compared with the literature data in the thermal neutron induced fission of 235U to examine the influence of excitation energy on nuclear structure effect.

Independent isomeric yield ratios of fission products in the epi-cadmium neutron-induced fission of 245Cm

Abstract Independent isomeric yield ratios (IR) of 128,130,132Sb, 131,133Te, 132,134I, 135Xe and 138Cs in the epi-cadmium neutron-induced fission of 245Cm have been measured for the first time by using an off-line gamma-ray spectrometric technique. The average energy of the epi-cadmium neutron spectrum (<E n >) is 1.9 MeV. From the IR values, root mean square fragment angular momenta (J RMS) were deduced by using the spin dependent statistical model analysis. The IR and JRMS values of the fission products from the present work were compared with the literature data in the thermal neutron-induced fission of 245Cm to examine the role of excitation energy. Effect of nuclear structure on J RMS value was also examined.

Estimating angular momenta of fission fragments from isomeric yield ratios using TALYS

Angular momenta of fission fragments considerably higher than that of the fissioning nucleus have been observed in many experiments, raising the question of how these high angular momenta are generated. Wilson have proposed a model for the angular momentum as a function of the mass of fission products based on the assumption that the angular momentum is generated from the collective motion of nucleons in the ruptured neck of the fissioning system. This assumption has caused a lot of debate in the community. To estimate the angular momenta of fission fragments based on the observed isomeric yield ratios in 25-MeV proton-induced fission of U238. A surrogate model of the fission code general description of fission observables (GEF) has been developed to generate properties of primary fission fragments. Based on the excitation energy and angular momentum of fission fragments from GEF, an energy-versus-angular-momentum matrix is reconstructed using a set of parameters. With such matrices as input, the reaction code TALYS is used to calculate the deexcitation of the fission fragments, including the population of the isomers, from which the isomeric yield ratios are obtained. By varying one of the parameters, the root-mean-square angular momentum (Jrms), which determines the angular momentum distribution of the matrix, Jrms-dependent isomeric yield ratios are obtained. Considering all primary fission fragments contributing to the isomeric yield ratio for a given fission product, the average angular momentum of those fragments is estimated. Data of 31 isomeric yield ratios in 25-MeV proton-induced fission of U238 were analyzed. From the analysis, the average Jrms, equivalent to average angular momentum Jav, with uncertainties are obtained for 24 fission products, while in seven cases no conclusive result for the angular momentum could be obtained. Furthermore, considering the neutron emissions of the primary fission fragments, the average angular momentum as a function of the average mass number of the primary fission fragment was estimated. A mass dependency of the average angular momentum is observed in the proton-induced fission of U238. Moreover, the average angular momenta for mass numbers larger than 131 could be fairly well described by the parametrization proposed by Wilson However, the average angular momenta of Sn130 and Te131 cannot be described by Wilson's model, which suggests a different lower limit for the validation of the parametrization in the model. In general, higher average angular momenta for A≥132 are observed in the present work compared to those from Wilson This is likely due to the higher excitation energy of the fissioning nuclei in this work. Furthermore, the first systematic observation of the average angular momenta of fission products in the symmetric mass region is presented. In this region, a decreasing trend with mass number is observed, which cannot be explained by the proposal in Wilson's paper. Thus, a different mechanism is needed to explain this observation.Published by the American Physical Society2024

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 239Pu

Measurement of independent isomeric yield ratios (IR) of 128,130,132Sb, 131,133Te, 132.134,136I, 135Xe and 138Cs have been carried out for the first time in the epi-cadmium neutron induced fission of 239Pu by using an off-line gamma-ray spectrometric technique. The average neutron energy (<En>) of the epi-cadmium reactor neutron spectrum is 1.9 MeV. From the IR values, root mean square fragment angular momenta (JRMS) were deduced by using spin dependent statistical model analysis. Effect of nuclear structure on JRMS values was examined. The present data in the epi-cadmium neutron induced fission of 239Pu were compared with the similar data in the thermal neutron induced fission of 239Pu to examine the role of excitation energy on JRMS values.

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 233U

The independent isomeric yield ratios (IR) of 128,130,132Sb, 131,133Te, 132,134,136I, 135Xe and 138Cs have been measured in the epi-cadmium neutron induced fission of 233U by using an off-line gamma-ray spectrometric technique. The average neutron energy of the epi-cadmium reactor neutron spectrum is 1.9 MeV. The root mean square fragment angular momenta (JRMS) were deduced from the IR values by using spin dependent statistical model analysis. The IR and JRMS values of considered fission products in the epi-cadmium neutron induced fission of 233U were compared with the literature data in the thermal neutron induced fission of 233U to examine the influence of excitation energy on nuclear structure effect.

Measurement of isomeric yield ratios of 119m,gTe in the 60 and 70 MeV bremsstrahlung induced reaction of natTe

The isomeric yield ratio i.e. the yield ratio of high to low spin state (IR=Yh/Yl) of 119m,gTe in the natTe(γ,xn) reaction at the bremsstrahlung end-point energies (Ee) of 60-, and 70-MeV were measured for the first time by using an off-line gamma-ray spectrometric technique. The bremsstrahlung energies were generated by impinging pulsed electron energies of 60-, and 70-MeV on a thin W-target at the Pohang Accelerator Laboratory. The present data at 60 and 70-MeV and similar literature data at other energies shows that the IR values of 119m,gTe increases sharply from 10 MeV to 18 MeV, which indicates the role of excitation energy. Thereafter it increases marginally due the opening of other reaction channels, which indicates the partition of excitation energy in different reaction channels.

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 238Pu

In the epi-cadmium neutron induced fission of 238Pu, independent isomeric yield ratios (IR) of 128,130,132Sb, 131,133Te, 134,136I, 135Xe and 138Cs have been measured by using an off-line γ-ray spectrometric technique. The average neutron energy of the epi-cadmium reactor neutron spectrum is 1.9 MeV. From the IR values, root mean square fragment angular momenta (JRMS) were deduced by using spin dependent statistical model analysis. The JRMS values from the present work in the epi-cadmium neutron induced fission of 238Pu were compared with the literature data in the thermal neutron induced fission of 238Pu to examine the role of excitation energy. Effect of nuclear structure on JRMS values was examined.

Global comparison between experimentally measured isomeric yield ratios and nuclear model calculations

The level density steers transition probabilities between different states in the decay and de-excitation of excited nuclei. Reliable level density modelling is, therefore, key in describing, e.g., de-excitation of fission fragments, with implications on neutron and gamma-rays multiplicities, and also manifested in the population of isomeric states. We test six currently used level density models and the spin distribution in the level density by comparing calculations with measured isomeric yield ratios. The model calculations are performed with the TALYS code and experimental data for nuclear reactions populating spin isomers are retrieved from the EXFOR database. On average, calculations are in agreement with measured data. However, we find that the population of the high-spin state in an isomeric pair is clearly favoured in all of the six studied level density models. Further studies are then performed on the three used phenomenological level density models, to investigate the significance of their effect. We find that a significant reduction of the spin width distribution improves the agreement between calculated and experimentally observed isomeric yield ratios. This result is independent of the incident particle in the nuclear reaction. The needed reduction of the spin width distribution to comply with empirical data has, e.g., implications for studies in angular momentum generation in fission using isomeric yield rations, calculations of anti-neutrino spectra from nuclear reactors, as well as neutron and gamma-ray multiplicities in nuclear reactor calculations.

Examination of how properties of a fissioning system impact isomeric yield ratios of the fragments

Examination of how properties of a fissioning system impact isomeric yield ratios of the fragments

Study of the isomeric yield ratio in the photoneutron reaction of natural holmium induced by laser-accelerated electron beams

Introduction: An accurate knowledge of the isomeric yield ratio (IR) induced by the photonuclear reaction is crucial to study the nuclear structure and reaction mechanisms. 165Ho is a good candidate for the investigation of the IR since the Ho target has a natural abundance of 100% and the residual nuclide has a good decay property.Methods: In this study, the photoneutron production of 164m, gHo induced by laser-accelerated electron beams is investigated experimentally. The γ-ray spectra of activated Ho foils are off-line detected. Since the direct transitions from the 164mHo are not successfully observed, we propose to extract the IRs of the 164m, gHo using only the photopeak counts from the ground-state decay.Results: The production yields of 164m, gHo are extracted to be (0.45 ± 0.10) × 106 and (1.48 ± 0.14) × 106 per laser shot, respectively. The resulting IR is obtained to be 0.30 ± 0.08 at the effective γ-ray energy of 12.65 MeV.Discussion: The present data, available experimental data, and TALYS calculations are then compared to examine the role of the excitation energy. It is found that besides the giant dipole resonance, the excitation energy effect also plays a key role in the determination of the IRs.

Investigation of (γ, xpxn)-reactions on titanium, lutetium, nickel and chromium nuclei at Ebr=37 MeV

For the first time, both the flux-weighted average yields of the 50Cr(γ,pn+2n)48V, natTi(γ,pxn)46Sc, 48Ti(γ,p)47Sc reactions and the isomeric yield ratios of the 175Lu(γ,n)174Lum,g reaction were measured at a bremsstrahlung end-point energy of 37 MeV. The flux-weighted average yields of the 52Сr(γ,n)51Cr, 58Ni(γ,n)57Ni and 58Ni(γ,p)57Co reactions were also measured and their values coincided with the results of the works of the other authors. According to the results of modeling within the framework of the TALYS-1.96 code, a significant contribution of non-statistical processes is ascertained to the mechanisms of the 48Ti(γ,p)47Sc and 50Cr(γ,pn+2n)48V reactions.

Independent isomeric yield ratios of fission products in the epi-cadmium neutron induced fission of 241Pu

Abstract Independent isomeric yield ratios (IR) of 130,132Sb, 131,133Te, 134,136I, 135Xe and 138Cs have been measured in the epi-cadmium neutron induced fission of 241Pu by using an off-line gamma-ray spectrometric technique. The average neutron energy (&lt;E n&gt;) of the epi-cadmium reactor neutron spectrum is 1.9 MeV. From the IR values, root mean square fragment angular momenta (J RMS) were deduced by using spin dependent statistical model analysis. Effect of nuclear structure on J RMS values was examined. The present data in the epi-cadmium neutron induced fission of 241Pu were compared with the similar data in the thermal neutron induced fission of 241Pu to examine the role of excitation energy on fragment angular momentum.

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

The 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 at the bremsstrahlung end-point energy 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 and the IR for the isomeric pair from the reaction were calculated using the partial cross-sections from the TALYS1.95 code for six different level density models. For the investigated range of , 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.

Applying machine learning methods for the analysis of two-dimensional mass spectra

In a measurement of isomeric yield-ratios in fission, the Phase-Imaging Ion-Cyclotron-Resonance technique, which projects the radial motions of ions in the Penning trap (JYFLTRAP) onto a position-sensitive micro-channel plate detector, has been applied. To obtain the yield ratio, that is the relative population of two states of an isomer pair, a novel analysis procedure has been developed to determine the number of detected ions in each state, as well as corrections for the detector efficiency and decay losses. In order to determine the population of the states in cases where their mass difference is too small to reach full separation, a Bayesian Gaussian Mixture model was implemented. The position-dependent efficiency of the micro-channel plate detector was calibrated by mapping it with ^{133}Cs^+ ions, and a Gaussian Process was trained with the position data to construct an efficiency function that could be used to correct the recorded distributions. The obtained numbers of counts of excited and ground-state ions were used to derive the isomeric yield ratio, taking into account decay losses as well as feeding from precursors.

Measurement of the isomeric yield ratios of 196m,gAu and 195m,gHg in the 197Au(p,x) reaction

Abstract In this study, the isomeric yield ratio (IR) values of 196m,gAu and 195m,gHg in the 197Au(p,x) reaction within the proton energy range of 49.8–65.5 MeV were measured at the high-intensity proton linac facility (KOMAC) in Korea using an offline γ-ray spectrometric technique. Furthermore, the IR values of the above-mentioned products at different proton energies were calculated from the cross-sections based on the data in the TENDL-2019 library and are found to be higher than the experimental values. The IR values of 196m,gAu and 195m,gHg in the 197Au(p,x) reaction from the present and other works are compared with the similar literature data in the 197Au(γ,n), 196Hg(γ,n), 197Au(n,2n), 196Hg(n,2n), natPt(α,x) and natPt(3He,x) reactions to examine the role of compound nucleus spin, excitation energy, and input angular momentum.

Measurement of isomeric yield ratios for 104m,gAg and 106m,gAg isotopes using bremsstrahlung end-point energies of 45–75 MeV

In this study, the isomeric yield ratio (IR) values of 104m,gAg and 106m,gAg in an natAg(γ,xn) reaction at the bremsstrahlung end-point energies (Ee) of 45, 50, 55, 60, 70, and 75 MeV were measured using an off-line gamma-ray spectrometric technique. The IR values at different bremsstrahlung end-point energies were also calculated from the cross-section data available in the TENDL-2019 library, and they were found to exhibit a similar trend with some differences in the magnitude. Herein, the IR values of 104m,gAg and 106m,gAg with the bremsstrahlung end-point energies of 70 and 75 MeV were measured for the first time. The present data were compared with those from the literature for 107,109,natAg(γ,xn), natAg(n,xn), natPd(p,xn), and 103Rh(α,xn) reactions to examine the role of the excitation energy and input angular momentum.

Yield Ratios of Isomeric Pairs \(^{196m,g}\)Au, \(^{186m,g}\)Ir, and \(^{183m,g}\)Os in the \(^{197}\)Au\((\gamma,xnyp)\) Reactions with 2.5 GeV Bremsstrahlung

The yield ratios of high to low spin states of the 196m,gAu, 186m,gIr, and 183m,gOs isomeric pairs produced by 197Au(γ,xnyp) reactions with a bremsstrahlung end-point energy of 2.5 GeV have been measured. Measurements were performed by the activation method in combination with off-line γ-ray spectrometry. The induced activity of the studied radionuclides was derived from the photo-peak area of the selected γ-ray after making the necessary corrections. The isomeric yield ratios obtained in this work are the first measurement. The relationships between the yield ratios of studied isomeric pairs with the value of high spin states, the spin difference between the high spin states and the target nucleus, and the number of nucleons emitted from the target nucleus are discussed.

Isomeric yield ratio of 115m,gCd in the 116Cd(γ,n) and 116Cd(n,2n) reactions

The isomeric yield ratio (IR) of 115m,gCd in the 116Cd(γ,n) reaction at the bremsstrahlung endpoint energies of 70 and 75 MeV and in the 116Cd(n,2n) reaction at the average neutron energies (<En > ) of 21.4 and 30.1 MeV were measured via an offline γ -ray spectrometric technique. The bremsstrahlung energies were produced by impinging the electron beam energies of 70 and 75 MeV on a thin W-target at the Pohang Accelerator Laboratory, Korea. The neutron beams were obtained from the 9Be(p,n) reaction with the proton energies of 35 and 45 MeV using the MC-50 cyclotron at the Korean Institute of Radiological and Medical Sciences. The IR values at different bremsstrahlung and neutron energies were also calculated from the cross-section values of the TENDL-2019 library based on the TALYS-1.9 code. The theoretical values agreed with the experimental data for the bremsstrahlung endpoint energies but were slightly higher for all neutron energies. The current and literature data showed that in both the 116Cd(γ,n) and 116Cd(n,2n) reactions, the IR value of 115m,gCd increases with the projectile energy, indicating the role of excitation energy. However, the experimental and theoretical IR values at the same excitation energy were significantly higher for the 116Cd(n,2n) reaction than that for the 116Cd(γ,n) reaction, highlighting the role of compound nucleus spin.

Measurements of natCd(γ, x) reaction cross sections and isomer ratio of 115m,gCd with the bremsstrahlung end-point energies of 50 and 60 MeV * *Supported by the National Research Foundation of Korea (NRF) through a grant provided by the Ministry of Science and ICT (NRF-2017R1D1A1B03030484, NRF-2013M7A1A1075764, NRF-2018R1A6A1A06024970)

The flux-weighted average cross sections of natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions were measured at the bremsstrahlung end-point energies of 50 and 60 MeV. The activation and off-line γ-ray spectrometric technique was carried out using the 100 MeV electron linear accelerator at the Pohang Accelerator Laboratory, Korea. The natCd(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 natCd(γ, xn)115g,m,111m,109,107,105,104Cd and natCd(γ, x)113g,112,111g,110mAg reactions. The isomeric yield ratio (IR) of 115g,mCd in the natCd(γ, xn) reaction was determined for the two bremsstrahlung end-point energies. The measured isomeric yield ratios of 115g,mCd in the natCd(γ, xn) reaction were also compared with the theoretical values of the nuclear model codes and previously published literature data of the 116Cd(γ, n) and 116Cd(n, 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,mCd in the 116Cd(n, 2n) reaction compared to that in the 116Cd(γ, n) reaction indicates the role of compound nuclear spin alongside excitation energy.

Compilation and Evaluation of Isomeric Fission Yield Ratios

Fission yields are essential data for reactor physics, forensics, and astrophysics. In some cases, the fission yield of a fragment is divided between the ground state and a long-lived excited state, and the relative population of the two states is referred to as the isomeric ratio. In this work, we present a comprehensive compilation of experimental isomeric fission yield ratios for all target and projectile combinations. When possible, these data are combined to provide recommended isomeric fission yield ratios for low energy neutron-induced fission and spontaneous fission. The recommended ratios are compared to the traditional Madland-England model, which attempts to describe the isomeric ratios with a single parameter relating to the angular momentum of the fragment. It is found that the model does not reliably reproduce isomeric ratios outside the few nuclei it was fitted to, and its simplified treatment of the statistical process following population in fission results in average spin values, which are neither constant nor follow a recently observed saw-tooth pattern.