Study of the excitation of high-spin isomers in <Superscript>190</Superscript>Ir and <Superscript>196,198</Superscript>Au in the near-threshold region

The isomeric ratios of the yields for ^190m,g Ir and ^196m,g Au have been measured in the (γ,n) reaction in the near-threshold region at γ-ray energies of 12 and 12.5 MeV. The isomeric ratios for ^198m,g Au have been measured in the (d,p) and (n,γ) reactions. The statistical nature of the (γ,n) and (n,γ) reactions is shown.     

Low-lying excited states of106Ag studied with the103Rh (α,nγ)106Ag and104Pd (α,pnγ)106Ag Reactions

The level scheme of¹⁰⁶Ag has been studied using the¹⁰³Rh(α,nγ)¹⁰⁶Ag and¹⁰⁴Pd(α,pnγ)¹⁰⁶Ag Reactions. The experimental information is taken fromγ-ray coincidence data using Ge(Li)-Ge(Li) and HPGe-planar Ge(Li) configurations andγ-ray angular distributions. With these measurements 126 γ rays have been assigned to¹⁰⁶Ag with 116 deexciting 78 states below 2.26 MeV in excitation. The location of the 8.4-day 6⁺ isomer is established at 89.63±0.09 keV. Many of the low-lying states are interpreted in terms of a slightly deformed rotor model.     

Level density parameters from excitation cross sections of isomeric states

Cross section ratios were measured for the production of the isomeric pairs^99m,gRh,^101m,gRh,^102m,gRh,^104m,gRh and^108m,gIn in the (p,n)-reaction,^107m,gIn and^109m,gIn in the (p, γ)-reaction over the energy range up to 9 MeV, and^116m,gSb and^118m,gSb in the (α,n)-reaction up to 24 MeV. The experimental results for these nuclei as well as for other isometric pairs excited in the (p, n)-reaction were analysed in the frame of the statistical model for extracting the level density parameter values in the vicinity of closed nucleon shells. The level density parameter behaviour is discussed in the range of nuclear mass numbers under study.     

Bestimmung der Halbwertszeit von108m Ag über (n, 2n)-Querschnitte des Silbers

The half-life of^108m Ag was determined as (310±132) years by measuring the absolute activity of a sample containing a known number of^108m Ag nuclei. This could be done by evaluating the cross section for the production of the isomerσ ¹⁰⁹Ag(n, 2n)^108mAg=(670±266) mb. From the measured half-life a logft-value of 8.9 for the electron capture decay of the isomer to the 1770 keV state of¹⁰⁸Pd and a transition probability of (1.0±0.4) · 10^?2 Weisskopf units for the M4 transition to the 2^?state of¹⁰⁸Ag were derived. The cross section for thermal neutrons¹⁰⁷Ag(n, γ)^108mAg could be calculated to be (7.5±3.2) b by using a related measurement from the literature.     

Spin-dependent level density in interacting boson-fermion-fermion model

Yield curves for the production of^117g In,^117m In,^116m1In,^115m In,^113m In,¹¹¹In,^110h In,^110l In,¹⁰⁹In,^108hIn and^108lIn from enriches¹¹⁸Sn have been measured by the activation method in the energy region 75–800 MeV. The cross sections have been deduced and for¹¹⁷In,¹¹⁰In and¹⁰⁸In isomeric cross section ratios have been determined. The experimental cross sections are compared to calculations with a cascade-evaporation model and to cross sections calculated with a semi-empirical formula. The isomeric ratios are compared to calculations based on the statistical formalism by Huizenga and Vandenbosch together with cascade-evaporation theory. The (γ, p) cross section and isomeric ratio are also compared to calculations based on a direct knock-out formalism.     

Critical consideration of the statistical model analysis of photonuclear isomeric cross-section ratios

We have measured isomeric cross-section ratios for the photonuclear reactions ¹⁸¹Ta(γ, 3n) ^178m,gTa, ¹⁴²Nd(γ, n)^141m,gNd, ¹¹⁰Pd(γ, n)^{109m₁,m₂,g}Pd, ¹⁰⁸Pd(γ, n)^107m₁,m₂Pd, ¹⁰⁰Mo(γ, n) ^99m,gMo, ⁹²Mo(γ, n)^91m,gMo and ⁸⁹Y(γ, n)^88m₁,m₂Y. The experimental results were compared with statistical model calculations according to the method of Huizenga and Vandenbosch. The applicability and limits of this method, especially the simple decision model for the population of the isomeric state and the ground state of the residual nucleus, were tested and discussed. Additionally, it is shown that for photonuclear reactions on magic nuclei, contributions of a direct reaction mechanism are not negligible.     

High spin states in107Ag

¹⁰⁷Ag hasbeen investigated by the reactions¹⁰⁴Ru(⁶Li, 3nγ) and¹⁰⁴Ru(⁷Li, 4ny). γ-singles spectra,γ-γ-Δt-coincidences,γ-angular distributions and polarization measurements were taken. A level scheme has been established, spins and parities have been assigned.     

Cross section of metastable state population in the photoneutron decay of the E1 giant resonance for 110Pd, 112Cd, and 113In nuclei

The cross sections of isomeric state excitation in the ¹¹⁰Pd(γ, n)^109m Pd, ¹¹²Cd(γ, n)^111m Cd, and ¹¹³In(γ, n)^112m In reactions have been investigated. The measurements were performed in the γ-ray energy range 9–18 MeV with a step ΔE = 0.5 MeV. The dependences of the isomeric ratios on the γ-ray energy are obtained. The experimental data are compared with the results of calculations within the cascade-evaporation model.     

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.     

The spin of the 1029 keV level in200Hg

The spin of the 1,029 keV level in²⁰⁰Hg has been determined to be 0 through measurements of theγ-γ-angular correlation of the 661 keV and 368 keVγ-rays following slow neutron capture in¹⁹⁹Hg. The upper limit for theγ-intensity ratioIγ(1,029 keV)/Iγ(661 keV) obtained from the curved crystal spectrometer (n, γ)-data is much lower than the ratio found during the²⁰⁰Tl→²⁰⁰Hg decay studies. This implies that the 1,029 keVγ-line seen in the decay work does not lead from the 1,029 keV level to the ground state in²⁰⁰Hg, but that it depopulates a level which is only weakly fed through the (n, γ)-process.     

Levels in154Eu populated by thermal neutron capture

The level scheme of¹⁵⁴Eu has been investigated by means of thermal neutron captureγ-rays and conversion electrons. The high energyγ-ray spectrum from thermal neutron capture in enriched¹⁵³Eu has been studied in the energy range of 5700 to 6500 keV. Low energyγ radiation has been observed with Ge(Li) and Si(Li) detectors from 5 to 300 keV and conversion electrons have been measured from 15 to 300 keV. Low energy (n, γγ) coincidences and half lives of transitions have been measured. The data, combined with three very recent studies of the 8^? isomer decay in¹⁵⁴Eu has led to the construction of a level scheme with 12 excited levels. Nuclear Reaction¹⁵³Eu(n, γ),E _n =thermal, measuredE _γ ,I _γ ,E _ce ,I _ce ,γγ-coincidence, halflives,¹⁵⁴Eu deduced levels.     

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

The flux-weighted average cross sections of ^natCd(γ, xn)^{115g,m,111m,109,107,105,104}Cd and ^natCd(γ, x)^{113g,112,111g,110m}Ag 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,109,107,105,104}Cd and ^natCd(γ, x)^{113g,112,111g,110m}Ag 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.     

Isomeric ratios of the products of (γ, xnp) reactions on 90,91Zr nuclei for a maximum bremsstrahlung energy of 84 MeV

We present the results from measuring and calculatoffing the isomeric ratios for the ^87m,g Y nucleus produced in the ⁹⁰Zr(γ, 2np)^87g,m Y and ⁹¹Zr(γ, 3np)^87g,m Y reactions, and for the ^86m,g Y nucleus produced in the ⁹⁰Zr(γ, 3np)^86g,m Y and ⁹¹Zr(γ, 4np)^86g,m Y reactions. The method of measuring the induced activity of irradiated samples with a semiconductor spectrometer based on an HPGe detector with a relative efficiency of 20% and an energy resolution of 1.9 keV for the 1332 keV ⁶⁰Co line was used to determine the isomeric ratios. The obtained results are compared to calculations using the TALYS code, employing statistical and preequilibrium model approaches.     

Magnetic rotation of levels of 53Mn and 54Mn following the 53, 54Cr(p,n) and 51V(α, n) reactions

The low-lying levels of ⁵³Mn and ⁵⁴Mn have been studied using the ^{53, 54}Cr(p, nγ) and ⁵¹V(α, nγ) reactions. Angular distributions of γ-rays have been measured and their integral rotations in iron alloy targets studied. The g-factor of the 377 keV, $\text{5}\text{2}{}^{\mathrm{?}}$ level of ⁵³Mn is g = + 1.15±0.17. Products gτ have been found for the 55, 156, 368, 408 and 1072 keV levels of ⁵⁴Mn to be 124±42, 360±60, 75±25, > 10 and 150±80 ps respectively. Using shell model estimates for the g-factors, the lifetimes of the levels have been deduced. An interpretation of the results in terms of shell model wave functions is given.     

Energy levels,decay scheme, γ-ray branching ratios and lifetimes in 55Fe from the 55Mn(p,nγ)55Fe reaction

The reaction ⁵⁵Mn(p, nγ)⁵⁵Fe has been studied at E_p = 4.0 and 6.0 MeV using a pulsed beam. From the experiments at 6.0 MeV, the energy levels of ⁵⁵Fe up to an excitation of 3810 keV, their decay scheme and the γ-ray branching ratios have been determined. Levels have been identified for the first time in the (p, nγ) reaction. The results have been compared with those available from the literature. From the 4.0 MeV experiment, the mean lifetime of the 1408 keV level has been determined to be 142.7 ± 6.6 ps by direct timing techniques.     

Measurement of the 50Cr(γ, n)49Cr cross section with monochromatic γ-rays

The ⁵⁰Cr(γ, n)⁴⁹Cr cross section has been measured over the energy range E_γ = 20.43 to E_γ = 22.22 MeV using monochromatic γ-rays from the ³H(p, γ)⁴He reaction and detecting the resulting ⁴⁹Cr positon activity. The γ-rays were monitored by a 12.7 cm × 15.2 cm NaI(Tl) crystal. The positon activity was determined by a coincidence detector consisting of two 7.62 cm × 7.62 cm NaI(Tl) crystals set on the annihilation radiation photopeaks. The γ-ray energy resolution was less than 110 keV over the whole energy range. Structure in the cross section was not observed.     

Low-lying states in112In

Low-lying states below 500 keV excitation in¹¹²In have been investigated via the¹¹²Cd(p, nγ) reaction. New levels have been established atE ^x=206.5keV and 456.1 keV from the measuredγ-ray excitation functions,γ?γ coincidences and the precision measurements of the (p, n) threshold energy of the ground state and of the 206.5 keV state of¹¹²In. Spins and parities of the 206.5 keV state (2⁺) and the 456.1 keV state (3⁺) and multipolarities and mixing ratios of the deexcitationγ-rays have been determined from the angular distributions and linear polarizations of the deexcitation γ-rays as well as the excitation functions of the residual levels. Possible configurations of the newly-found levels are discussed. Half-lives of two states have been remeasured:T _1/2=15.2±0.1 min for the ground state andT _1/2=20.9±0.1 min for the 156.4 keV (4⁺) state. The ground stateQ-value for the¹¹²Cd(p, n)¹¹² In reaction has been measured to be ?3.376±0.006 MeV.     

The excitation functions and Isomer ratios for neutron-induced reactions on Mo and Zr

Absolute cross sections of the reactions ⁹²Mo(n, 2n)^91m,91gMo, ⁹²Mo(n, p)⁹²Nb and ⁹²Mo(n, α)^{89m, 89g}Zr, relative cross sections of the reaction ⁹⁰Zr(n, 2n) ^89mZr and isomer ratios of the ⁹⁰Zr(n, 2n) reaction have been measured in the neutron energy range 13–15 MeV. The results for the (n, 2n) reactions are in good agreement with those of the previous studies. The present results for the (n, p) and (n, α) reactions are in disagreement with the previous works. The experimental data are analysed by the statistical model to determine the level-density parameter a, the moment of inertia ? and the strength of the γ-ray transition S_l in order to simultaneously reproduce the experimental data on the excitation function and the isomer ratio in the (n, 2n) reaction. The γ-ray competition, the yrast level and the experimental information on the excited levels of the residual nucleus in the (n, 2n) reaction are taken into account. The obtained values of a, ? and S_l are consistent with those deduced from other types of nuclear data.     

The reaction 35Cl(n,γ)36Cl studied with non-polarized and polarized thermal neutrons

The γ-radiation following capture of non-polarized and polarized thermal neutrons in ³⁵Cl has been investigated. Of the 420 γ-rays ascribed to the ³⁵Cl(n,γ)³⁶Cl reaction, 236 have been placed in a ³⁶Cl decay scheme. The branching ratios and the excitation energies (with 0.04–0.9 keV errors) of 72 bound states have been determined. Unambiguous spin assignments are given for 11 levels. The multipole mixing ratios for some primary γ-ray transitions have been determined. There exists a significant correlation between (d, p) stripping strengths and (n, γ) reduced primary transition probabilities for transitions to l_n(d, p) = 0 levels.