Special features of the isospin splitting of the giant dipole resonance in the <Superscript>90</Superscript>Zr nucleus

Data on the proton and neutron channels of the ⁹⁰Zr photodisintegration were analyzed in detail, basic parameters of the isospin splitting of the giant dipole resonance in ⁹⁰Zr being determined by the properties of these channels. New data concerning the cross sections for the partial photoneutron reactions ⁹⁰Zr(γ, n)⁸⁹Zr and ⁹⁰Zr(γ, 2n)⁸⁸Zr and resulting from a simultaneous correction of data from experiments performed in Livermore (USA) and Saclay (France) by using beams of quasimonoenergetic annihilation photons were invoked. Use was made of information about the positions on the energy scale of states characterized by different isospin values in the ⁹⁰Zr nucleus and nuclei neighboring it, which are members of the respective isospin multiplet. New data on the parameters of the isospin splitting of the giant dipole resonance in the ⁹⁰Zr nucleus were obtained on the basis of a global analysis of data on the giant-dipole-resonance states of the ⁹⁰Zr nucleus, which are manifested in the respective photoneutron and photoproton cross sections and in their decay channels involving states of different isospin in neighboring nuclei.     

Gamow-teller strength distribution in the vicinity of A = 90: (I). Schematic calculation of GT strength in 90, 92, 94Nb

The distributions of Gamow-Teller strength in ^{90, 92, 94}Nb have been calculated utilizing the so-called GT force in the random phase approximation. For ⁹⁰Nb the calculated distribution is in striking agreement with that part of the ⁹⁰Zr(p, n) excitation function leading to 1⁺ excitations in ⁹⁰Nb and qualitative agreement is demonstrated for data from the reactions ^{92, 94}Zr(p, n). Some 25 % of the GT strength is found to lie well below the structureless giant resonance proposed by Ikeda et al. The implications of this result to the β-decay properties of neutron rich nuclei near A = 90 are discussed.     

Structure of 3P size resonance in neutron strength functions

Neutron capture cross sections of 21 nuclei have been determined using the activation technique and an antimony-beryllium photoneutron source. The nuclei have been selected in the mass range 60 < A < 140 so as to cover the 3P size resonance region of neutron strength functions. Using the latest available data on the low energy resonance parameters, the P-wave neutron strength functions of the 21 isotopes are extracted, and found to be in general agreement with similar isotopic values reported in literature. The values of experimental P-wave neutron strength functions in the 3P resonance region (60 < A < 140) are compared on the one hand with the theoretical predictions of Fiedeldey and Frahn and on the other with those of Buck and Perey. The shape and structure of the 3P size resonance, as revealed experimentally, are found to agree better with the predictions of Fiedeldey and Frahn, who assumed twice the normal spin-orbit force in their calculations.     

A study of the photoneutron contribution to the giant dipole resonance in doubly even Mo isotopes

By using a variable monochromatic photon beam, the partial photoneutron cross sections σ(γ, n) + σ(γ, pn), σ(γ, 2n) and σ(γ, 3n) are determined in the region of the giant dipole resonance for the doubly even Mo isotopes ⁹²Mo, ⁹⁴Mo, ⁹⁶Mo, ⁹⁸Mo and ¹⁰⁰Mo. Measured integrated photoneutron cross sections are compared with available integrated photoproton cross sections as a function of A. Broadening of the giant dipole resonance as A increases is observed in good agreement with the predictions of the dynamic collective model. A tentative study of some isospin splitting effects is also carried out.     

Cross section measurements on zirconium isotopes for ~14 MeV neutrons and their theoretical calculations of excitation functions

The cross sections for the ⁹⁴Zr(n,d*)^93m+gY, ⁹⁶Zr(n,γ)⁹⁷Z, ⁹⁶Zr(n,2n)⁹⁵Zr, ⁹⁰Zr(n,α)^87mSr, ⁹⁴Zr(n,α)⁹¹Sr,⁹⁰Zr(n,p)^90mY, ⁹²Zr(n,p)⁹²Y, and ⁹⁴Zr(n,p)⁹⁴Y reactions have been measured in the neutron energy range of 13.5-14.8 MeV by means of the activation technique. The neutrons were produced via the D-T reaction. A high-purity germanium detector with high energy resolution was used to measure the induced γ activities. In combination with the nuclear reaction theoretical models, the excitation curves of the above-mentioned eight nuclear reactions within the incident neutron energy range from the threshold to 20 MeV were obtained by adopting the nuclear theoretical model program system Talys-1.9. The resulting experimental cross sections were analyzed and compared with the experimental data from published studies. Calculations were performed using Talys-1.9 and are in agreement with our experimental results, previous experimental values, as well as results of the theoretical excitation curves at the corresponding energies. The theoretical excitation curves generally match the experimental data well.     

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.     

Isobaric spin mixing in the analog states of 90Zr

A 90° photoproton energy spectrum has been obtained from the reaction ⁹⁰Zr(γ, p)⁸⁹Y using an isotopically enriched target foil. Previously unreported proton groups are observed at E_p = 6.95, 9.55, 10.68 and 11.03 MeV. A total photoneutron cross section and a low-energy neutron energy spectrum are also presented, and isospin mixing is demonstrated by comparison with the photoproton data. The possibility of T_> strength in the region 23–24 MeV excitation is noted.     

Reliable cross sections of partial photoneutron reactions on 188,189Os isotopes free of neutron multiplicity sorting problems

Experimental data on the cross sections of partial photoneutron reactions, obtained for ^188,189Os isotopes using quasimonoenergetic annihilation photon beams and neutron multiplicity sorting method, are analyzed. Using special criteria (transition multiplicity functions F _i = σ(γ, in)/σ(γ, xn), the ratios of the cross section of the corresponding partial reaction to the total neutron yield reaction’s cross section σ(γ, xn) = σ(γ, 1n)+ 2σ(γ, 2n) + 3σ(γ, 3n) free of the problems associated with experimental neutron multiplicity sorting), it is demonstrated that the data contain significant systematic errors. New data are evaluated for cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n), (γ, 3n) and total photoneutron reaction (γ, sn) for ^188,189Os isotopes within an experimental-theoretical approach proposed earlier. It is shown that the significant systematic errors in the experimental cross sections of partial reactions can be attributed to the ambiguity of the relation between the photoneutrons’ multiplicity and their kinetic energy.     

New Data on Photoneutron Reaction Cross Sections for 76,78,80,82Se Nuclei

The problem of reliability of the cross section data obtained for partial photoneutron reactions on ^76,78,80,82Se nuclei in beams of quasimonoenergetic annihilation photons by means of neutron multiplicity sorting is discussed by employing objective physical criteria. It is shown that, because of substantial systematic uncertainties, experimental data on the (γ, 1n) and (γ, 2n) cross sections are unreliable. New data satisfying the reliability criteria are obtained for the partial photoneutron reaction cross sections for ^76,78,82Se nuclei by an experimental—theoretical method for evaluating such cross sections and are compared with experimental data and with data evaluated earlier for the isotope ⁸⁰Se. The evaluated integrated cross sections for the total photoneutron reactions on ^76,78,80,82Se nuclei are compared with the predictions of the Thomas-Reiche-Kuhn classical dipole sum rule.

     

The photoneutron cross section of 45Sc

The photoneutron cross section of ⁴⁵Sc has been measured from threshold to 25 MeV using bremsstrahlung and direct neutron detection. The cross section is found to exhibit a large width of approximately 8 MeV and this is interpreted in terms of the Danos hydrodynamic model for the giant resonance of deformed nuclei. The integrated cross section to 25 MeV is 158 ± 24 MeV mb.     

14MeV中子引起的Pb(n,x)203Hg, W(n,x)182Ta和W(n,x)183Ta的核反应截面测量

利用活化方法测量了14MeV中子引起的Pb(n,x)²⁰³Hg,W(n,x)¹⁸²Ta和W(n,x)¹⁸³Ta的反应截面.中子注量由监督反应⁹³Nb(n,2n)^92mNb给出,中子能量利用⁹⁰Zr(n,2n)^89m+gZr和⁹³Nb(n,2n)^92mNb反应的截面比来确定.     

The neutron total and capture cross sections of 92, 94Zr

The neutron total and capture cross sections of^92,94Zr have been measured at the 80 and 40 m flight stations, respectively, on the Oak Ridge Electron Linear Accelerator (ORELA). Resonance analysis of the total cross sections gave values of s, $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ strength functions. Strong intermediate structure was observed in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ cross section of ⁹²Zr. Significant single particle transitions identified in the p-wave capture cross section indicate the importance of the valence process for both nuclei. It is noted that the intermediate structure in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ total cross section leads to enhanced valence effects in the capture cross section. The effects of non statistical E1 transitions following particle-hole annihilation in the compound states were not observed in either the ⁹²Zr or ⁹⁴Zr capture cross sections as they had been in that for ⁹⁰Zr.     

A study of the 91Zr(d,p)92Zr reaction using vector-polarized deuterons

Differential cross sections and vector analyzing powers were measured for the ⁹¹Zr($\text{d}$, d)⁹¹Zr and ⁹¹Zr($\text{d}$, p)⁹²Zr reactions at an incident deuteron energy of 12 MeV. Deuteron optical-model parameters were determined from an analysis of the elastic data. Comparison of the proton data to DWBA predictions showed that the DWBA does not quantitatively reproduce the measured analyzing powers, hence empirical analyzing power calibration curves were required to analyze the data. New spectroscopic information about the configurations of the excited states in ⁹²Zr has been determined and is compared to the results of previous experiments as well as a shell-model calculation. The results of this experiment are in quantitative agreement with the predictions of the shell-model calculation for most of the transitions although some discrepancies do exist.     

Cross Section Measurements for (n,d*)(n,t) and (n,n'α) Reactions

Cross sections for some (n,d*),(n,t) and (n,n'α)reactions have been measured by using the activation method relative to cross sections of ²⁷Al(n,α)²⁴Na or ⁹³Nb(n,2n)^92mNb reactions in neutron energies around 14MeV.In this paper some of the published cross section data have also been listed and compared with our results.The neutron energies were determined by the method of cross section ratios for the reactions of ⁹⁰Zr(n,2n) ^89m+gZr and ⁹³Nb(n,2n)^92mNb.     

Statistical model calculations for medium and strong absorption in theA=90 region

Calculations of elastic, inelastic and total neutron cross sections as well as of (p, n) reaction cross sections in theA=90 mass region have been performed, using the statistical model of Hofmann, Richert, Tepel and Weidenmüller. The optical model parameters were obtained by Finckh et al. from the neutron decay of IAR in the⁹¹Zr(p, n)⁹¹ Nb reaction. The calculations are in very good agreement with the published experimental data. The optical model parameters proved to be satisfactory up to aboutE _n=8.0 MeV. The present work might be relevant to the evaluation of neutron data for reactor technology.     

Strength functions of primary transitions following thermal neutron capture in strontium

The primaryE1,M1 andE2γ-radiation in^87,88,89Sr observed after thermal neutron capture was compared with the predictions of single particle and giant resonance models. The nuclei feature a wide range of neutron binding energies between 6.3 and 11.1 MeV, which makes a 5.5 MeV spectrum of primary transition energies available for investigation. The (n, γ) reaction was used to estimate the parameters of the spin-flip M1 giant resonance in strontium. The total energy weightedM1 strength of this resonance exceeds the results of shell model and random phase approximation calculations for⁹⁰Zr by a factor of 3–4. TheE1 strengths were found to agree with the established giant dipole resonance model. The few data on primaryE2 transitions do not allow to differentiate between the giant quadrupole resonance and the single particle models.     

Experimental photoneutron cross sections of natural zirconium from 8 MeV to 134 MeV

The inclusive partial photoneutron cross sections and the total photoneutron cross section \(\sigma ^{(1)} (E_\gamma ) = \sum\limits_{i = 1}^{i_{\max } } {\sigma (\gamma ,in...)} \) for natural Zr have been measured from 8 MeV to 134 MeV, with monochromatic photons obtained by in flight annihilation of monoenergetic positrons. The integrated total photoneutron cross section up tillE _γ=140 MeV is (1.59±0.11)σ ₀, whereσ ₀ is the Thomas-Reiche-Kuhn sum-rule. The integrated total photonuclear absorption cross section is evaluated to be (1.73±0.15)σ ₀. The behaviour of the total photoneutron cross section as a function of Eγ, in the 40 MeV <E _γ<140 MeV energy range, is well described by a modified version of the quasideuteron model.     

High-spin states in the isotones 89Zr, 91Mo and 93Ru populated in α-particle-induced reactions

The reactions (α, 3nγ) and (α, α′nγ) on ⁸⁸Sr, ⁹⁰Zr and ⁹²Mo were used to populate excited states in ⁸⁹Zr, ⁹¹Mo and ⁹³Ru. The de-excitation of these states was studied by in-beam γ-ray spectroscopy. The short-lived radioactivity of the ⁹²Mo target was measured in order to study the decay of ⁹³Ru. Many new levels were observed, particularly in ⁹¹Mo. They are interpreted as due to the coupling of a $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ neutron hole with known excited states in ⁹⁰Zr, ⁹²Mo and ⁹⁴Ru.     

Measurement of Cross Sections for Pb(n,x)203Hg,W(n,x)182Ta and W(n,x)183Ta Reactions Induced by 14 MeV Neutrons

The cross sections for Pb(n,x)²⁰³Hg,W(n,x)^l82Ta and W(n,x)¹⁸³Ta reactions have been measured by the activation method. The neutron fluences were determined by the cross sections of ⁹³Nb (n,2n)^92mNb reaction. The neutron energies in the measurements were determined by the cross section ratios of Zr(n,2n)^89m+gZr and Nb(n,2n)^92mNb reactions.     

Theoretical study of fusion reactions 32S + 94,96Zr and 40Ca + 94,96Zr and quadrupole deformation of 94Zr

The dynamic coupling effects on fusion cross sections for reactions~(32)S + ~(94,96)Zr and ~(40)Ca + ~(94,96)Zr are studied with the universal fusion function formalism and an empirical coupled channel(ECC) model. An examination of the reduced fusion functions shows that the total effect of couplings to inelastic excitations and neutron transfer channels on fusion in ~(32)S +~(94)Zr(~(40)Ca +~(94)Zr) is almost the same as that in ~(32)S +~(96)Zr(~(40)Ca +~(96)Zr). The enhancements of the fusion cross section at sub-barrier energies due to inelastic channel coupling and neutron transfer channel coupling are evaluated separately by using the ECC model. The results show that effect of couplings to inelastic excitations channels in the reactions with94 Zr as target should be similar as that in the reactions with ~(96) Zr as target. This implies that the quadrupole deformation parameters β_2of ~(94)Zr and~(96) Zr should be similar to each other.However, β_2 's predicted from the finite-range droplet model, which are used in the ECC model, are quite different. Experiments on~(48) Ca +~(94)Zr or~(36) S +~(94)Zr are suggested to solve the puzzling issue concerning β_2for~(94)Zr.