Giant Dipole Resonance Region Research Articles

Gamma Strength Functions and Level Densities from High-Resolution Proton Scattering under 0°

Inelastic proton scattering at energies of a few 100 MeV and forward angles including 0° provides a novel method to measure gamma strength functions (GSF) in nuclei in an energy range of about 5 – 20 MeV. The experiments provide not only the E1 but also the M1 part of the GSF. The latter is poorly known in heavy nuclei. Comparison with gamma decay data (e.g. from the Oslo method) allows to test the generalised Brink-Axel (BA) hypothesis in the energy region of the pygmy dipole resonance (PDR) crucial for the modelling of (n,γ) and (γ,n) reactions in astrophysical reaction networks. From the two test cases studied, 208Pb remains inconclusive in the energy region of the PDR because of large Porter-Thomas fluctuations due to the small level density (LD), while the BA hypothesis seems to hold in case of 96Mo. A fluctuation analysis of the high-resolution data also provides a direct measure of the LD in the energy region of the isovector giant dipole resonance (IVGDR) well above the neutron threshold, where hardly any experimental information is available. This permits an independent test of the decomposition of GSF and LD in Oslo-type experiments.

Yield Ratios of the Isomeric Pair \(^{179m,g}\)W Produced in the \(^{nat}\)W(g,xn)\(^{179m,g}\)W Reactions with 50-65 MeV Bremsstrahlung

In this work we present the yield ratios of the \(^{179m,g}\)W isomeric pair produced in the photonuclear reactions \(^{nat}\)W(g,xn)\(^{179m,g}\)W with bremsstrahlung end-point energies of 50-, 55-, 60-, and 65-MeV. The measurements were carried out by the induced activity method in combination with direct gamma-ray spectrometry. The measured activities were corrected for overlapping gamma-ray peaks, self-absorption of low energy gamma-rays and true coincidence summing effects. The present results are measured for the first time with bremsstrahlung end-point energies beyond the giant dipole resonance region. The obtained results are discussed with respect to the incident bremsstrahlung energies and reaction channel effect.

Measurement of [formula omitted] reaction cross-section within the proton energy range of 3.38 to 19.63 MeV

The Fe58(p,n)Co58 reaction cross-section within Giant Dipole Resonance (GDR) region i.e. from 3.38 to 19.63 MeV was measured by stacked-foil activation and off-line γ-ray spectrometric technique using the BARC-TIFR Pelletron facility at Mumbai. The present data were compared with the existing literature data and found to be in good agreement. The Fe58(p,n)Co58 reaction cross-section as a function of proton energy was also theoretically calculated by using the computer code TALYS-1.8 and found to be in good agreement, which shows the validity of the TALYS-1.8 program.

Isomeric ratios in photonuclear reactions of molybdenum isotopes induced by bremsstrahlung in the giant dipole resonance region

We have determined the isomeric ratios of isomeric pairs 97m,gNb, 95m,gNb and 91m,gMo produced in 98Mo(γ, p)97m,gNb, 96Mo(γ, p)95m,gNb and 92Mo(γ, n)91m,gMo photonuclear reactions in the giant dipole resonance (GDR) region by the activation method. The results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy, neutron configuration, channel effect and direct and pre-equilibrium processes in (γ, p) photonuclear reactions. In this work the isomeric ratios for 97m,gNb from 14 to 19 MeV, for 195m,gNb from14 to 24 MeV except 20 and 23.5 MeV and for 91m,gMo at 14 and 15 MeV are the first time measurements.

γ strength function and level density of Pb208 from forward-angle proton scattering at 295 MeV

Gamma strength functions (GSFs) and level densities (LDs) are essential ingredients of statistical nuclear reaction theory with many applications in astrophysics, reactor design, and waste transmutation. The aim of the present work is a test of systematic parametrizations of the GSF recommended by the RIPL-3 data base for the case of $^{208}$Pb. The upward GSF and LD in $^{208}$Pb are compared to gamma decay data from an Oslo-type experiment to examine the validity of the Brink-Axel (BA) hypothesis. The E1 and M1 parts of the total GSF are determined from high-resolution forward angle inelastic proton scattering data taken at 295 MeV at RCNP, Osaka, Japan. The total LD in $^{208}$Pb is derived from the $1^-$ LD extracted with a fluctuation analysis in the energy region of the isovector giant dipole resonance. The E1 GSF is compared to parametrizations recommended by the RIPL-3 data base showing systematic deficiencies of all models in the energy region around neutron threshold. The new data for the poorly known spinflip M1 resonance call for a substantial revision of the model suggested in RIPL-3. The total GSF derived from the present data is larger in the PDR energy region than the Oslo data but the strong fluctuations due to the low LD resulting from the double shell closure of $^{208}$Pb prevent a conclusion on a possible violation of the BA hypothesis. Using the parameters suggested by RIPL-3 for a description of the LD in $^{208}$Pb with the back-shifted Fermi gas model, remarkable agreement between the two experiments spanning a wide excitation energy range is obtained. Systematic parametrizations of the E1 and M1 GSF parts need to be reconsidered at low excitation energies. The good agreement of LD provides an independent confirmation of the approach underlying the decomposition of GSF and LDs in Oslo-type experiments.

Energy dependence of exotic nuclei production cross sections by photofission reaction in GDR range

Photofission of actinides is studied in the region of nuclear excitation energies that covers the entire giant dipole resonance (GDR) region. The mass distributions of 238U photofission fragments have been explored theoretically for eight different endpoint bremsstrahlung energies from 11.5 to 67.7 MeV, which correspond to average photon energies of 9.09 to 15.90 MeV. Among these energies, 29.1 MeV corresponds to the average photon energy of 13.7 ± 0.3 MeV, which coincides with the GDR peak for 238U photofission. The integrated yield of 238U photofission, as well as charge distribution of photofission products, is calculated and its role in producing nuclei and their neutron-richness is investigated.

Yields of neutron-rich nuclei by actinide photofission in the giant dipole resonance region

Photofission of actinides is studied in the region of nuclear excitation energies that covers the entire giant dipole resonance (GDR) region. A comparative analysis of the behavior of the symmetric and asymmetric modes of photon induced fission as a function of the average excitation energy of the fissioning nucleus is performed. The mass distributions of $^{238}$U photofission fragments are obtained at the endpoint bremsstrahlung energy of 29.1 MeV which corresponds to mean photon energy of 13.7$\pm$0.3 MeV that coincides with GDR peak for $^{238}$U photofission. The integrated yield of $^{238}$U photofission as well as charge distribution of photofission products are calculated and its role in the production of neutron-rich nuclei and their exoticity is explored.

The Study of Isomeric Ratios in Photonuclear Reactions Forming High Spin Isomers in the Giant Dipole Resonance Region

We studied the isomeric ratios in odd-odd nuclei \(^{196}\)Au,\(^{182}\)Ta and \(^{194}\)Ir with high spin isomeric states produced in \(^{197}\)Au\((\gamma, n)\) \(^{196m,g}\)Au, \(^{183}\)W\((\gamma, p)\) \(^{182m,g}\)Ta and \(^{185}\)Pt\((\gamma, p)\)\(^{194m,g}\)Ir reactions by using the activation technique and \(\gamma\)-ray spectroscopic method in the giant dipole resonance (GDR) region. The high-purity natural Au, W and Pt foils in disc shape were irradiated with bremsstrahlungs generated from an electron accelerator Microtron. The irradiated foils were measured by the high resolution \(\gamma\)-ray spectroscopic system which consists of a Ge(HP) detector and a multichannel analyzer. In order to improve the accuracy of the experimental results, necessary corrections were made in the \(\gamma\)-ray activity measurements and data analysis. The results were analyzed, discussed and compared with those of other authors as well as with theoretical model calculations. The study shows that the isomeric ratios in nuclei with high spin isomeric states are much lower than that in low spin isomeric state isomers.

Study of the isomeric ratios in photonuclear reactions of natural platinum induced by end-point bremsstrahlung energies in the giant dipole resonance region

We have determined the isomeric ratios of isomeric pairs 194m,gIr and 197m,gPt produced in 195Pt(γ, p)194Ir and 198Pt(γ, n)197Pt photonuclear reactions in the giant dipole resonance (GDR) region by the activation method. The results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy and difference in the isomeric and ground state spins. The isomeric ratios of 194m,gIr and 197m,gPt from the present work, namely from 19 to 23 MeV for 194m,gIr and from 18 to 24 MeV for 197m,gPt are the first time measurements.

Study of the \(^{nat}\)Sm\((\gamma ,xn)^{143m,g}\)Sm Reactions Induced by Bremsstrahlung with End-point Energies Just above GDR Region

We investigate the energy dependence of the isomeric yield ratios for the \(^{nat}\)Sm\((\gamma ,xn)^{143m,g}\)Sm reactions with bremsstrahlung energies of 40-, 45-, and 50-MeV, just above the giant dipole resonance (GDR) region by the off-line $\gamma $-ray spectrometric method. The bremsstrahlung photons were produced from the 100 MeV electron linear accelerator (linac) at the Pohang accelerator laboratory (PAL), Pohang, Korea. In order to improve the accuracy of the experimental results the necessary corrections were made. The present results are compared with similar literature data of the $^{nat}$Sm($\gamma $,xn)$^{143m,g}$Sm reactions measured at various photon energies and of the $^{nat}$Sm(n,2n)$^{143m,g}$Sm reaction induced by 14 MeV neutrons in order to examine the effects of an excitation energy and an input angular momentum.

Neutron angular distribution in (γ, n) reactions with linearly polarized γ-ray beam generated by laser Compton scattering

In 1957, Agodi predicted that the neutron angular distribution in (γ, n) reactions with a 100% linearly polarized γ-ray beam for dipole excitation should be anisotropic and universally described by the simple function of a+b⋅cos⁡(2ϕ) at the polar angle θ=90°, where ϕ is the azimuthal angle. However, this prediction has not been experimentally confirmed in over half a century. We have verified experimentally this angular distribution in the (γ, n) reaction for 197Au, 127I, and natural Cu targets using linearly polarized laser Compton scattering γ-rays. The result suggests that the (γ→, n) reaction is a novel tool to study nuclear physics in the giant dipole resonance region.

Study of the isomeric ratios in 107Ag(γ, n)106m,gAg reaction of natural silver induced by bremsstrahlungs with endpoint energies in the giant dipole resonance region

We measured for the first time the isomeric ratios in 107Ag(γ, n)106m,gAg reaction by using the activation method and γ-ray spectroscopic method for the whole giant dipole resonance region. The high-purity natural Ag foils in disc shape were irradiated with bremsstrahlungs generated from an electron accelerator Microtron. The induced gamma spectra in the irradiated foils were measured by the high resolution γ-ray spectroscopic system which consists of a high-purity germanium detector and a multichannel analyzer. In order to improve the accuracy of the experimental results, necessary corrections were made in the γ-ray activity measurements and data analysis. The results were analyzed, discussed and compared with those of other authors. For the above mentioned reaction, the isomeric ratios in the energy range from 14 to 24 MeV bremsstrahlungs in this work (except the values at 14, 18 and 20) are new measurements.

Measurement of isomeric yield ratios for the natHo(γ,xn)164m,g;162m,gHo reactions in the bremsstrahlung energy region from 45 to 65 MeV

We have measured the isomeric yield ratios for the 164m,gHo and the 162m,gHo isomeric pairs formed via photonuclear reactions 165Ho(γ,n)164m,gHo and 165Ho(γ,3n)162m,gHo in the bremsstrahlung energy region from 45 to 65 MeV in steps of ∆E = 5 MeV by the activation method. The induced γ-activities of the irradiated holmium foils were measured by a coaxial high-purity germanium detector coupled to a PC-based multichannel analyzer. In order to improve the accuracy of the experimental results the necessary corrections were made. The experimental results at bremsstrahlung energies of 45, 50, 55, 60, and 65 MeV are 0.408 ± 0.027, 0.413 ± 0.027, 0.427 ± 0.029, 0.452 ± 0.032, and 0.448 ± 0.031 for the 164m,gHo isomeric pair, and 0.587 ± 0.041, 0.624 ± 0.044, 0.652 ± 0.045, 0.637 ± 0.045, and 0.668 ± 0.046 for the 162m,gHo isomeric pair, respectively. The present results are the first measurements at bremsstrahlung energies just above the giant dipole resonance region. The obtained results confirm the dependence of isomeric ratios on the incident photon energy as observed in some earlier experiments.

Study of the isomeric ratios in photonuclear reactions of natural indium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region

We have determined the isomeric ratios in 113In(γ, n)112m,g In and 113In(γ, 2n)111m,g In photonuclear reactions of natural indium induced by bremsstrahlungs with end-point energies in the giant dipole resonance (GDR) region. The investigated samples were irradiated at the electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna. The gamma spectra of the samples irradiated were measured with a spectroscopic system consisting of an 8192-channel analyzer and a high-energy resolution (180 keV at gamma ray 1332 keV of 60Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors. For both the mentioned reactions, the isomeric ratios in the bremsstrahlung energy range from 19 to 24 MeV in this work are new measurements.

Determination of the total bremsstrahlung photon flux from electron accelerators by simultaneous activation of two monitors

We have determined the total bremsstrahlung photon fluxes with end-point energies in the giant dipole resonance (GDR) region produced by electron accelerator Microtron MT—25 (the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia) and that of 65 MeV bremsstrahlung produced by the linear electron accelerator (the Pohang Neutron Facility, Pohang, South Korea). The method that we used was the photon activation technique. To ensure the accuracy of the results, we carried out simultaneous photon activation of two monitors made of Cu and Au foils in the same irradiation conditions. The results are discussed in the paper.

Isomeric yield ratios for the natSb(γ,xn)120m,g,122m,gSb reactions measured at 40-, 45-, 50-, 55-, and 60-MeV bremsstrahlung energies

We measured the isomeric yield ratios for the 120m,gSb and 122m,gSb isomeric pairs produced by natSb(γ,xn)120m,g,122m,gSb photonuclear reactions in the bremsstrahlung energy region from 40 to 60MeV with a step size of ΔE=5MeV by the activation method. The induced γ-activities of the irradiated samples were measured by a coaxial high purity germanium detector coupled to a PC-based multichannel analyzer. The necessary corrections were made to improve the accuracy of the experimental results. The experimental results at bremsstrahlung energies of 40, 45, 50, 55, and 60MeV were 0.045±0.003, 0.046±0.003, 0.048±0.003, 0.050±0.003, and 0.049±0.003 for the 120m,gSb isomeric pair, and 0.341±0.022, 0.362±0.020, 0.374±0.021, 0.371±0.021, and 0.358±0.022 for the 122m,gSb isomeric pair, respectively. The present results are the first measurements at bremsstrahlung energies just above the giant dipole resonance region. The obtained results confirm the dependence of the isomeric yield ratios on the incident energy and the reaction channel effect observed in some earlier experiments.

Study of the isomeric ratios in photonuclear reactions of natural Selenium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region

Study of the isomeric ratios in photonuclear reactions of natural Selenium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region

The isomeric ratios in photonuclear reactions of natural barium induced by bremsstrahlungs with endpoint energies in the giant dipole resonance region

We have determined the isomeric ratios in 113In(γ, n)112m,g In and 113In(γ, 2n)111m,g In photonuclear reactions of natural indium induced by bremsstrahlungs with end-point energies in the giant dipole resonance (GDR) region. The investigated samples were irradiated at the electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna. The gamma spectra of the samples irradiated were measured with a spectroscopic system consisting of an 8192-channel analyzer and a high-energy resolution (180 keV at gamma ray 1332 keV of 60Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors. For both the mentioned reactions, the isomeric ratios in the bremsstrahlung energy range from 19 to 24 MeV in this work are new measurements.

Study of the isomeric ratios in photonuclear reactions of natural holmium and lutetium induced by bremsstrahlungs with endpoint energies in the giant dipole resonance region

We have determined the isomeric ratios in 165Ho(γ, n)164m,gHo and 175Lu(γ, n)174m,gLu photonuclear reactions of natural holmium and lutetium induced by bremsstrahlungs with end-point energies in the giant dipole resonance (GDR) region. The investigated samples were irradiated at electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The gamma spectra of the samples irradiated were measured with spectroscopic system consisting of 8192 channel analyzer and high-energy resolution (180 keV at gamma ray 1332 keV of 60Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors.

The isomeric ratios in photonuclear reactions of natural tellurium induced by bremsstrahlungs with endpoint energies in the giant dipole resonance region

We have determined the isomeric ratios in 120Te(γ, n)119m,gTe, 122Te(γ, n)121m,gTe, 128Te(γ, n)127m,gTe and 130Te(γ, n)129m,gTe photonuclear reactions of natural tellurium induced by bremsstrahlungs with end-point energies in the giant dipole resonance (GDR) region. The investigated samples were irradiated at electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The gamma spectra of the samples irradiated were measured with spectroscopic system consisting of 8192 channel analyzer and high-energy resolution (180 keV at gamma ray 1,332 keV of 60Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors.