Isomeric Yield Ratios Research Articles

Isomer yields in nuclear fission

The generation of angular momentum in the fission process is still an open question. To shed light on this topic, we started a series of measurements at the IGISOL-JYFLTRAP facility in Finland. Highprecision measurements of isomeric yield ratios (IYR) are performed with a Penning trap, partly with the aim to extract average root-mean-square (rms) quantities of fragment spin distributions. The newly installed Phase-Imaging Ion-Cyclotron Resonance (PI-ICR) technique allows the separation of masses down to tens of keV, which is suffcient to disentangle many isomers. In this paper, we first summarize the previous measurements on the neutron and proton-induced fission of uranium and thorium, e.g. the odd cadmium and indium isotopes (119 ≤ A ≤ 127). The measurements revealed systematic trends as function of mass number, which stimulated further exploration. A recent measurement was performed at IGISIOL and several new IYR data will soon be published, for the first time. Secondly, we employ the TALYS nuclear-reaction code to model one of the newly measured isomer yields. Detailed GEF and TALYS calculations are discussed for the fragment angular momentum distribution in 134I.

Measurement and analysis of the isomeric cross section ratios for the Tc94 nucleus

We report on an isomer yield ratio study of biologically important $^{94}\mathrm{Tc}$ following the fusion of the $^{9}\mathrm{Be}+^{89}\mathrm{Y}$ system, carried out using the offline $\ensuremath{\gamma}$-ray spectroscopy in continuation to the online activation method. The incident beam energies considered are above the Coulomb barrier for the present paper. The platypus model in conjunction with a potential model calculation was employed to analyze the data. An agreement in the order of magnitude between the experimental data and the theoretical predictions has been achieved by applying a phenomenological approach. The approach was further tested with isomer yield ratios of $^{94}\mathrm{Tc}$ formed through $^{3}\mathrm{He}+^{93}\mathrm{Nb}$ reactions. Possible factors that relate to the isomer yield ratios are also presented.

Employing TALYS to deduce angular momentum rootmean-square values, Jrms, in fission fragments

Fission fragments exhibit large angular momenta J, which constitutes a challenge for fission models to fully explain. Systematic measurements of isomeric yield ratios (IYR) are needed for basic nuclear reaction physics and nuclear applications, especially as a function of mass number and excitation energy. One goal is to improve the current understanding of the angular momentum generation and sharing in the fission process. To do so, one needs to improve the modeling of nuclear de-excitation. In this work, we have used the TALYS nuclear-reaction code to relax excited fission fragments and to extract root-mean-square (rms) values of initial spin distributions, after comparison with experimentally determined IYRs. The method was assessed by a comparative study on 252Cf(sf) and 235U(nth,f). The results show a consistent performance of TALYS, both in comparison to reported literature values and to other fission codes. A few discrepant Jrms values were also found. The discrepant literature values could need a second consideration as they could possibly be caused by outdated models. Our TALYS method will be refined to better comply with contemporary sophisticated models and to reexamine older deduced values in literature.

Determining spontaneous fission properties by direct mass measurements with the FRS Ion Catcher

We present a direct method to measure fission product yield distributions (FPY) and isomeric yield ratios (IYR) for spontaneous fission (SF) fragments. These physical properties are of utmost importance to the understanding of basic nuclear physics, the astrophysical rapid neutron capture process ('r process') of nucleosynthesis, neutron star composition, and nuclear reactor safety. With this method, fission fragments are produced by spontaneous fission from a source that is mounted in a cryogenic stopping cell (CSC), thermalized and stopped within it, and then extracted and transported to a multiple-reflection time-of-flight mass-spectrometer (MR-TOF-MS). We will implement the method at the FRS Ion Catcher (FRS-IC) at GSI (Germany), whose MR-TOF-MS relative mass accuracy (~ 10-7) and resolving power (~ 600,000 FWHM) are sufficient to separate all isobars and numerous isomers in the fission fragment realm. The system's essential element independence and its fast simultaneous mass measurement provide a new direct way to measure isotopic FPY distributions, which is complementary to existing methods. It will enable nuclide FPY measurements in the high fission peak, which is hardly accessible by current techniques. The extraction time of the CSC, tens of milliseconds, enables a direct measurement of independent fission yields, and a first study of the temporal dependence of FPY distributions in this duration range. The ability to resolve isomers will further enable direct extraction of numerous IYRs while performing the FPY measurements. The method has been recently demonstrated at the FRS-ICr for SF with a 37 kBq 252Cf fission source, where about 70 different fission fragments have been identified and counted. In the near future, it will be used for systematic studies of SF with a higher-activity 252Cf source and a 248Cm source. The method can be implemented also for neutron induced fission at appropriate facilities.

Isomeric yield ratio of 196m, gAu in the 197Au(n, 2n) reaction with fast neutron based on the 9Be(p, n) reaction

The isomeric yield ratios (IR) of 196m, gAu in the 197Au(n, 2n) reaction at the average neutron energies ($ \langle E_{n}\rangle$) of 14.4, 21.8 and 29.5 MeV have been measured by using the off-line gamma-ray spectrometric technique. The neutron beams were obtained by using the 9Be(p, n) reaction with the proton energies of 25, 35 and 45 MeV from the MC-50 cyclotron at KIRAMS. The IR values at different neutron energies were also calculated from the cross sections values based on TENDL-2017 library and are found to be in agreement around 10–18 MeV but not at higher energy. The IR values of 196m, gAu at the neutron energies of 21.8 and 29.5 MeV have been measured for the first time. The present data along with the literature data at other energies in the 197Au(n, 2n) reaction are compared with the similar data in the 197Au($ \gamma$, n) reaction to examine the role of entrance channel parameters and occurrence of non-compound or pre-equilibrium process at higher projectile energy.

Isomeric yield ratios of 195m,gHg and 197m,gHg in the 196Hg(γ, n) and 198Hg(γ, n) reactions induced by bremsstrahlung energy within giant dipole resonance region

We have measured the isomeric ratios of isomeric pairs 195m,gHg and 197m,gHg produced in 196Hg(γ, n)195m,gHg and 198Hg(γ, n)197m,gHg reactions within the giant dipole resonance (GDR) region by the activation method. In order to improve the accuracy of the experimental results, the necessary corrections were made in the gamma activity measurements and data analysis. The results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy, nucleon configuration and the reaction channel effects in the isomeric ratios. The isomeric ratios from 18 to 24 MeV for 197m,gHg and from 14 to 24 MeV for 195m,gHg are the first time measurements.

Isomer yield ratios in Re184 from the Be9+Ta181 reaction

The isomer yield ratios of 184R in the incomplete fusion of the 9Be + 181Ta system were measured at energies around the Coulomb barrier, using online activation followed by offline γ-ray spectroscopy method. The PLATYPUS code that is based on a classical dynamical model is employed to analyze the measurements. By applying a phenomenological approach, model calculation managed to fairly reproduce the order of magnitude of the yield ratios at above barrier energies. Through the study, it is shown that the PLATYPUS code in conjunction with a phenomenological analysis can provide a reasonable explanation of isomer yield ratios resulted from incomplete fusion of weakly bound projectiles.

Extraction of angular momenta from isomeric yield ratios

.The generation of angular momentum in fission is difficult to model, in particular at higher excitation energies where data are scarce. Isomeric yield ratios (IYR) play an important role in deducing angular momentum properties of fission fragments (FF), albeit this requires some assumptions and simplifications. To estimate FF angular momentum, fission codes can be used to calculate IYRs and compare them to experimental data. Such measurements have systematically been performed at the IGISOL facility using novel experimental techniques. In conjunction, a new method has been developed to infer the angular momentum of the primary FF using the nuclear reaction code TALYS. In this work, we evaluate this new method by comparing our TALYS calculations with values found in the literature and with results from the GEF fission code, for a few well-studied reactions. The overall results show a consistent performance of TALYS and GEF, as well as of many reported literature values. However, some deviations were found, possibly pinpointing the need to re-examine some of the reported literature values. A sensitivity analysis was also performed, in which the role of excitation energy, neutron emission, discrete level structure and level density models were studied. Finally, the role of multiple chance fission, of relevance for the reactions studied at IGISOL, is discussed. Some literature data for this reaction were also re-analyzed using TALYS, revealing significant differences.

Isomeric fission yield ratios for odd-mass Cd and In isotopes using the phase-imaging ion-cyclotron-resonance technique

Isomeric yield ratios for the odd-$A$ isotopes of $^{119-127}$Cd and $^{119-127}$In from 25-MeV proton-induced fission on natural uranium have been measured at the JYFLTRAP double Penning trap, by employing the Phase-Imaging Ion-Cyclotron-Resonance technique. With the significantly improved mass resolution of this novel method isomeric states separated by 140 keV from the ground state, and with half-lives of the order of 500 ms, could be resolved. This opens the door for obtaining new information on low-lying isomers, of importance for nuclear structure, fission and astrophysics. In the present work the experimental isomeric yield ratios are used for the estimation of the root-mean-square angular momentum ($J_\mathrm{rms}$) of the primary fragments. The results show a dependency on the number of unpaired protons and neutrons, where the odd-$Z$ In isotopes carry larger angular momenta. The deduced values of $J_\mathrm{rms}$ display a linear relationship when compared with the electric quadrupole moments of the fission products.

β -decay half-lives of Sb134,134m and their isomeric yield ratio produced by the spontaneous fission of Cf252

A number of fission products possess isomeric states which have a nuclear spin significantly different from that of the ground state. The yield ratio of these states following fission is influenced by the angular momentum present in the fissioning system. The $^{134m,134}\mathrm{Sb}$ yield ratio had not been previously measured in the spontaneous fission of $^{252}\mathrm{Cf}$; however, it had previously been observed to favor the (${7}^{\ensuremath{-}}$) isomer over the (${0}^{\ensuremath{-}}$) ground state in $^{235}\mathrm{U}({n}_{th},f$) and $^{232}\mathrm{Th}$(25 MeV $p,f$). Using a mass-separated beam of low-energy $^{134,134m}\mathrm{Sb}$ ions produced by $^{252}\mathrm{Cf}$ spontaneous fission at the CARIBU facility, $\ensuremath{\beta}$ particles and $\ensuremath{\gamma}$ rays were detected using the SATURN/X-Array decay station to determine the fission-yield ratio and $\ensuremath{\beta}$-decay half-lives. The $^{134m}\mathrm{Sb}$ to $^{134}\mathrm{Sb}$ fission yield was determined to be $2.03\ifmmode\pm\else\textpm\fi{}0.05$ and the half-lives of $^{134m}\mathrm{Sb}$ and $^{134}\mathrm{Sb}$ were found to be $9.87\ifmmode\pm\else\textpm\fi{}0.08$ s and $0.674\ifmmode\pm\else\textpm\fi{}0.004$ s, respectively. These results represent the first isomeric yield ratio measurement for this nucleus, and improved measurements of the $^{134}\mathrm{Sb}$ ground state and the $^{134m}\mathrm{Sb}$ isomer half-lives.

First isomeric yield ratio measurements by direct ion counting and implications for the angular momentum of the primary fission fragments

We report the first experimental determination of independent isomeric yield ratios using direct ion counting with a Penning trap, which offered such a high resolution in mass that isomeric states ...

Isomeric yield ratio of 152m1Eu(8−)–152m2Eu(0−) produced in (γ, n) photonuclear reaction in the giant dipole resonance region

In this work, the isomeric ratio of 152m1Eu(8−)–152m2Eu(0−) produced from the 153Eu(γ, n)152Eu reaction have been measured in the whole giant dipole resonance region by the activation method. In order to improve the accuracy of the experimental results, the necessary corrections were made in the gamma activity measurements and data analysis. The results were discussed and compared with the similar data from literature to examine the excitation energy, the spin difference and the nuclear reaction channel effects and can be used for the interpretation on the structure of the nucleus and the mechanisms of nuclear reactions. The data for bremsstrahlung end-point energies of 19–23 MeV are first-time measurements.

Measurement of cross sections and isomeric yield ratios for 110m, gIn, 111m, gIn and 112m, gIn from natIn( $\gamma$ γ , xn) reactions in the bremsstrahlung end-point energies of 65-75 MeV

The flux weighted average cross sections and the isomeric yield ratios of 110m, gIn, 111m, gIn and 112m, gIn in the natIn( $\gamma$ ,xn) 112-110In reactions with the bremsstrahlung end-point energies of 65, 70 and 75 MeV have been determined by activation and off-line $\gamma$ -ray spectrometric technique using the 100 MeV electron linac at Pohang accelerator laboratory, Korea. It was found that the natIn( $\gamma$ ,xn) 112-110In reaction cross sections increase very fast from the threshold energy to a certain value of the bremsstrahlung energy, where the other reaction channel opens. After a certain energy, it remains constant because the cross section of the other reaction channel starts to increase. This indicates the partition of the excitation energy in different reaction channles. The isomeric yield ratios of 110m, gIn, 111m, gIn and 112m, gIn in the natIn( $\gamma$ ,xn) reactions decrease very fast with the bemsstrahlung end-point energy from the threshold value to 15-30 MeV due to the giant dipole resonance (GDR) effect. Above that, the isomeric yield ratios increase slowly with the bremsstrahlung energy due to the increase of excitation energy.

Measurement of isomeric yield ratios of 86m,gY and 87m,gY in the quasi-monoenergetic neutron induced reactions of 89Y

The isomeric yield ratios (IR) of 86m,gY and 87m,gY were measured in the 23 to 37 MeV quasi-monoenergetic neutron induced reaction of 89Y by using an off-line γ-ray spectrometric technique. The IR values in the 89Y(n,xn) reactions were also calculated using the TALYS 1.8 code and found to be in good agreement for 87m,gY but slightly less for 86m,gY. The IR values of 86m,gY and 87m,gY from the present work in the 89Y(n,xn) reactions were compared with the literature data in the 89Y(γ,xn), 89Y(p,x) and 89Y(α,x) reactions. It was found that the IR values of 86m,gY and 87m,gY in all these reactions increase with excitation energy. At the same excitation energy, the IR values are higher in the alpha induced reaction than in the proton, neutron and photon induced reactions due to higher input angular momentum in the former than in the later. These two observations indicate the role of entrance parameters. However, it is surprising to see that at the same excitation energy, the IR values of 86m,gY and 87m,gY in the 89Y(n,xn) reaction are nearly constant and significantly higher than in the 89Y(γ,xn) reaction.

Measurement of fission yields and isomeric yield ratios at IGISOL

Data on fission yields and isomeric yield ratios (IYR) are tools to study the fission process, in particular the generation of angular momentum. We use the IGISOL facility with the Penning trap JYFLTRAP in Jyväskylä, Finland, for such measurements on 232Th and natU targets. Previously published fission yield data from IGISOL concern the 232Th(p,f) and 238U(p,f) reactions at 25 and 50 MeV. Recently, a neutron source, using the Be(p,n) reaction, has been developed, installed and tested. We summarize the results for (p,f) focusing on the first measurement of IYR by direct ion counting. We also present first results for IYR and relative yields for Sn and Sb isotopes in the 128-133 mass range from natU(n,f) based on γ-spectrometry. We find a staggering behaviour in the cumulative yields for Sn and a shift in the independent fission yields for Sb as compared to current evaluations. Plans for the future experimental program on fission yields and IYR measurements are discussed.

Measurement of isomeric yield ratios for the heavy cerium isotopes in the (γ,n) reactions

Measurement of isomeric yield ratios for the heavy cerium isotopes in the (γ,n) reactions

Measurement of isomeric yield ratios of 99m,g;101m,g;102m,gRh in the natPd(γ,pxn) reactions with the bremsstrahlung end-point energies of 50–70 MeV

The isomeric yield ratios of 99m,gRh, 101m,ggRh, and 102m,gRh isomeric pairs produced from the natPd(γ,pxn) reactions were measured with the bremsstrahlung end-point energies of 50-, 55-, 60-, 65-, and 70-MeV at the 100MeV electron linac of the Pohang Accelerator Laboratory, Korea. The measurements were carried out with the activation method in combination with off-line γ-ray spectrometry. In order to improve the accuracy of the activity measurements, the separation of the overlapping γ-rays and the necessary corrections for the counting losses were made. The new experimental results are compared with the theoretical values of the TALYS-1.6 code.

Izomerni vidnoshennya ta seredni kutovi momenty pervynnykh frahmentiv 97Nb pry fotopodili 235U ta 238U

The isomeric yield ratios are measured for 97Nb fragments obtained at the bremsstrahlung photofission of 235U and 238U nuclei with gamma-quantum end-point energies of 10.5, 12.0, and 18.0 MeV. The mean angular momenta of primary fission fragments are determined, by using the generalized Huizenga–Vandenbosh statistical model and with the help of TALYS 1.6 and EMPIRE 3.2 codes.

Measurement of photo-neutron cross sections and isomeric yield ratios in the 89Y(γ,xn)89−x Y reactions at the bremsstrahlung end-point energies of 65, 70 and 75 MeV

Abstract The flux-weighted average cross sections of the 89Y(γ,xn; x=1–4)89−x Y reactions and the isomeric yield ratios of the 87m,gY, 86m,gY, and 85m,gY radionuclides produced in these reactions with the bremsstrahlung end-point energies of 65, 70 and 75 MeV have been determined by an activation and off-line γ-ray spectrometric technique using the 100 MeV electron linac in Pohang Accelerator Laboratory, Korea. The theoretical 89Y(γ,xn; x=1–4)89−x Y reactioncross sections for mono-energetic photonshave been calculated using the computer code TALYS 1.6. Then the flux-weighted theoretical values were obtaind to compare with the present data. The flux-weighted experimental and theoretical 89Y(γ,xn; x=1–4)89−x Y reaction cross sections increase very fast from the threshold values to a certain bremsstrahlung energy, wherethe other reaction channels open up. Thereafter it remains constant a while and then slowly decreases with the increase of cross sections for other reactions. Similarly, the isomeric yield ratios of 87m,gY,86m,gY and 85m,gY in the 89Y(γ,xn; x=2–4)89−x Y reactions from the present work and literature data show an increasing trend from their respective threshold values to a certain bremsstrahlung energy. After a certain point ofenergy, the isomeric yield ratios increase slowly with the bremsstrahlung energy. These observations indicate the role of excitation energy and its partitioning in different reaction channels.

Application of isochronous mass spectrometry for the study of angular momentum population in projectile fragmentation reactions

Isochronous mass spectrometry was applied to measure isomeric yield ratios of fragmentation reaction products. This approach is complementary to conventional gamma-ray spectroscopy in particular for measuring yield ratios for long-lived isomeric states. Isomeric yield ratios for the high-spin I = 19/2 states in the mirror nuclei 53Fe and 53Co are measured to study angular momentum population following the projectile fragmentation of 78Kr at energies of 480A MeV on a beryllium target. The 19/2 state isomeric ratios of 53Fe produced from different projectiles in the literature have also been extracted as a function of mass number difference between projectile and fragment (mass loss). The results are compared to ABRABLA07 model calculations. The isomeric ratios of 53Fe produced using different projectiles suggest that the theory underestimates not only the previously reported dependence on the spin but also the dependence on the mass loss.