Elastic and inelastic scattering of neutrons from Fe and Cu : (I). Measurements from 8 to 14 MeV and a spherical optical model analysis

Differential cross sections were measured at 8, 10, 12 and 14 MeV for elastic scattering of neutrons from enriched samples of ⁵⁴Fe, ⁵⁶Fe, ⁶³Cu and ⁶⁵Cu. Inelastic scattering to the first excited state in ^{54, 56}Fe was also observed. For the ^{63, 65}Cu isotopes, the inelastic cross sections for scattering to the combined group of the three (five) states were determined at 8 and 10 MeV (12 and 14 MeV). The elastic scattering data are compared to predictions of earlier global optical models. New spherical optical model representations were obtained. These data were combined with data for nickel, tin and lead to generate a new global parametrization. Comparisons of derived volume integrals for the potentials, total cross sections and potential radii are made to available information.     

20MeV以下快中子与56Fe非弹性散射截面的分歧研究

56Fe的非弹性散射截面在核装置中子输运计算中扮演着重要的角色,但无论从实验数据还是从评价数据,非弹性散射截面都存在很大分歧,它的数据直接影响到核装置的设计、建造与运行维护。本工作从实验数据本身出发,深入分析了不同实验室测得的847 keV的γ产生截面的分歧,经转化后补充非弹性散射截面的实验空白能区,并同时利用满足全截面、去弹截面等截面自洽关系的评价方法推荐了高精度的快中子与56Fe的非弹反应截面结果。积分检验表明,新的非弹截面的改进使得评价数据与积分实验结果一致,较CENDL-3.1的评价数据结果有显著改善。Knowledge about the inelastic scattering cross section of 56Fe is very important in neutron transportation calculation. However there are great discrepancies not only between experimental data but also between evaluated data. More detail analysis was performed for inelastic scattering cross section in the fast range up to 20 MeV where there are significant differences among the main evaluated libraries, mainly caused by the different inelastic scattering cross section measurements. The large discrepancies on 56Fe(n, n₁'γ) cross section which could fill the neutron energy blank of the 56Fe(n,inl) were clarified and were converted to the inelastic scattering cross section of 56Fe. And the high-quality results were evaluated by using the unitarity constrain among total cross section, noelastic reaction and other reactions. The integral experiment result indicates that the new evaluated result of inelastic cross section brings greater improvement than that of CENDL-3.1.     

The (He, t) reaction at intermediate energies : Spin-isospin multipole transitions

Data for the (³He, t) reaction at 900 MeV and 2 GeV on the targets ²⁶Mg, ⁴⁰Ca, ⁴⁸Ca, ⁵⁴Fe, ⁹⁰Zr and ²⁰⁸Pb are presented. A multipole decomposition for the data at 900 MeV has been made and the different distributions have been analysed. From the L = 0 cross section the Gamow-Teller strength distributions are extracted and compared with (p, n) data. The L = 1 and 2 distributions are analysed in a schematic model which describes the general systematics fairly well. The spectra at 2 GeV and Θ = 4° show for all targets a well-developed quasi-elastic peak. The A-dependence of the cross section is analysed in a simple model.     

A study of the level structure in Fe from the (d, p) reaction on Fe

The reaction ⁵⁶Fe(d, p)⁵⁷Fe is investigated at 12 MeV using the Aldermaston multi-channel magnetic spectrograph. The angular distributions of protons leading to various states in ⁵⁷Fe upto an excitation of 6.7 MeV are measured over an angular range 5°–175°. The data are analysed with the distorted wave Born approximation calculations; a satisfactory agreement is found in most cases upto about 100°. Spin, parity and the spectroscopic factors for various states are obtained and the positions of the single-quasiparticle energies determined. The results are compared with those for the isotonic nuclei ⁵⁵Cr and ⁵⁹Ni and with the pairing theory.     

Excitation of giant spin-isospin multipole vibrations in Fe and Ni

Data on (p,n) reactions at 120 and 160MeV have been used to study the excitation of spin-isospin multipole vibrations in ^{54, 56}Fe and ^{58, 60}Ni. In particular, transitions characterized by L = 0 transfer are identified as spin-isospin transitions (excitation of Gamow-Teller states) or as isospin transitions (excitation of isobaric analog states). An effort is made to estimate Gamow-Teller strength, B(GT), at excitation energies between 20–40 MeV. A comparison between GT and M1 strengths is presented for ^{58, 60}Ni. Shell-model calculations for total strengths, Σ B(GT), are compared with the observed results.     

Ranges of 0.2-1.0 GeV/nucleon heavy ions in nuclear photoemulsion

Heavy nuclei transport in matter are studied experimentally and theoretically. Our experimental range and straggling values of 0.2 – 1.0 GeV/nucleon ²⁰Ne, ⁴⁰Ar, ⁵⁶Fe, ¹⁹⁷Au and ²³⁸U nuclei in BR-2 nuclear photoemulsion are presented and compared with model calculations carried out according to our RANGE-program and the PRAL-model (version of 1987) developed by Ziegler et al. The presented data analysis points at the necessity to take into account Z³-correction in Bete-Bloch formula when ionization losses of very heavy multicharge ions (for example ¹⁹⁷Au and ²³⁸U) are calculated. The comparison of experimental and calculated results showed that RANGE program can correctly calculate the ranges and straggling of heavy ions. The difference between experimental and theoretical data do not exceed 5% in all of the cases examined. PRAL model describes the heavy ion ranges quite adequately, but overestimates the particle range straggling.     

Magnetic moments and Fe hyperfine field interactions in Y(Fe1−xRux)2 ternaries

Measurements of magnetization and ⁵⁷Fe Mössbauer spectra have been made for Y(Fe_1−xRu_x)₂. The C15 type cubic structure is stabilized for xx 0.7. The C15 compounds is ferromagnetic with T_c200 K and its saturation moment decreases monotonically with increasing x, while the ⁵⁷Fe hyperfine field decreases only slightly with x. From these results, it is deduced that the Ru atoms have an induced moment of ≈1μ_B in the range x 0.2. In the C14 type phase, no magnetic ordering develops even at 4.2 K.     

Optical pumping of the 2p3sP0 State of Ne (I = 3/2): g factor and metastability exchange cross section

A C.W. multi-mode dye laser is used to obtain by optical pumping an orientation of the 2p⁵ 3s³P₀ (F = 3/2) state of ²¹Ne. A magnetic resonance experiment leads to the measurement of the g factor g (³P₀) = 3.027 (8) × 10⁻⁴ to be compared with the theoretical prediction (3.025(6) × 10⁻⁴). One obtains also the metastability exchange cross section σ(³P₀) = 18.4 ± 4 Ų for collisions between metastable (³P₀) Ne atoms and ground state Ne atoms. This result is compared with other measurements and theoretical evaluation.     

Measurements of fragment mass, charge and kinetic energy distributions in thermal neutron fission of U with a back-to-back ΔE-E detector system

A simultaneous measurement of mass (M), charge (Z) and kinetic energy (E_k) distributions of fragments in thermal-neutron fission of ²³⁵U has been carried out using a back-to-back ΔE-E detector system. A pair of gridded ionization chambers filled with P-5 gas measured the energy losses ΔE₁, ΔE₂ of the complementary fragments in the gas, and the residual fragment energies were measured with a pair of semiconductor detectors. The four-parameter data were analysed to obtain fragment Z-distributions using the mass-momentum conservation relations to obtain M and then using the dependence of ΔE on E/M and Z. The charge resolution for the light-fragment group was determined at the gas pressures of 44, 150, 270 Torr and the best Z-resolution was obtained at 270 Torr. The data at this latter gas pressure were analysed to obtain the variances σ²_z of the fragment charge distributions for different E_k windows and this was compared with the measured variances σ²_A of the fragment mass distribution as a function of E_k as obtained by twoparameter measurements of the correlated fragment energies. The dependence of the measured variances σ²_A, σ²_Z on E_k is considered with a view to learning about the degree of neutron-proton correlations in the nucleon exchanges taking place during the mass division in fission, in analogy with that used in the case of heavy-ion deep inelastic collisions (DIC). The variation of σ²_A/σ²_z with E_k observed in the present work, which is somewhat similar to that seen in heavy-ion DIC, implies that the fragment mass division in fission is governed by nucleon-exchange processes, where the degree of neutron-proton correlations is dependent on the total kinetic energy E_k. While for very large E_k the neutron-proton motion in the exchange processes is found to be uncorrelated, for lower E_k values the motion is seen to be correlated. Implications of these results regarding the applicability of fission models such as statistical model are pointed out.     

Hyperon-Nucleon bound states and electroproduction of strangeness on He

The A(e, e′K⁺)YX reaction has been investigated in Hall C at Jefferson Lab. Data were taken for Q² ≈ 0.35 and 0.5 GeV² at a beam energy of 3.245 GeV for ³He, ⁴He. The missing mass spectra are fitted with Monte Carlo simulations including Λ, Σ⁰, Σ⁻ hyperon production. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Λ-hypernuclear bound states is seen for ^3,4He targets.     

Proton–neutron structure of the N=52 nucleus Zr

Following the successful identification of mixed-symmetric one- and two-phonon states in the N=52 nuclei ⁹⁴Mo and ⁹⁶Ru, we have performed a photon scattering experiment on the N=52 isotone ⁹²Zr. Experimental data and shell model calculations show that both, single particle and collective degrees of freedom are present in the low-lying levels of ⁹²Zr. The second excited quadrupole state shows the signatures of the one-phonon mixed-symmetric 2⁺ state, while calculations and data indicate an almost pure neutron configuration for the 2⁺₁ state, in contradiction with the F-spin symmetric limit. Furthermore, two strong dipole excitations, which are candidates for the two-phonon quadrupole–octupole coupled E1 excitation and for the mixed-symmetric 1⁺ two-phonon state, were observed.     

High spin states in doubly even pf-shell nuclei

High spin states of the yrast band in ⁵⁰Ti, ⁵²Cr, ⁵⁴ and ⁴⁶Ti are investigated in a microscopic approach allowing a coupling of rotations, vibrations and quasiparticle excitations. The lowering of the 6⁺ state in N = 28 nuclei is shown to originate mainly from proton K = 0 two-quasiparticle excitations. Using as a basis the entire pf-shell 8⁺ and 10⁺ states can be predicted for ⁵⁰Ti and ⁵⁴Fe.     

Charge dependence of nuclear forces in ΔJ = 0, ΔT = ±1 beta decays

By assuming the validity of the conserved vector current theory, the Fermi nuclear matrix elements M_F for the beta decays of ²⁰F, ⁴¹Ar, ⁴⁴Sc, ⁵²Mn and ⁵⁶Co which violate the ΔT = 0 selection rule are calculated theoretically in the jj-coupling, shell model. In these calculations, M_F is obtained by considering a short-range, charge-dependent, internucleon potential in addition to the usual Coulomb potential. Experimental values of M_F have been obtained by measuring the asymmetry parameter A appearing in the β-γ circular polarization correlation. Comparison between the theoretical and experimental values yields the result that the deviation of nuclear forces from exact charge independence is about a few per cent, while the deviation from charge symmetry is consistent with a value an order of magnitude smaller. If the conserved vector current theory is not valid, additional contributions to the Fermi nuclear matrix elements can arise from mesonic exchange currents. It is noted that such effects could be as large as those due to charge-dependent forces and would therefore cloud the above interpretation.     

The Fermi matrix elements inferred from β-γ(CP) correlation measurements in Fe decay

Measurements have been made of the β-γ circular-polarization correlation paramter A for the 273 keV β-branch in the decay of ⁵⁹Fe. It has recently been established that each of the principal β-branches of ⁵⁹Fe involves ΔJ=0 and thus has a possible non-zero Fermi matrix element M_F which can be determined from the ƒt value and A. Previous β-γ (_CP) measurements on this nucleide have all employed the usual γ-ray scattering technique. This method is suitable for the 475 keV β-branch but does not produce an accurate measurement of the lower energy branch because of energy discrimination difficulties. A transmission polarimeter with γ-discrimination has been used in the present work to obtain clean data on the 273 keV β-1.29 MeV γ-cascade. Calibration with ⁶⁰Co (1.33 MeV) and ²⁸Al (1.79 MeV) yielded A = −0.154±0.023. This gives for the isospin impurity coefficient and the effective Coulomb matrix element of the 1.29 MeV state (1.1±1.4) × 10⁻³ and 9±11 keV, respectively.     

Elastic and inelastic scattering of neutrons from Fe and Cu : (II). Scattering and nuclear structure effects from coupled channels calculations

The differential cross sections for neutron scattering from ^{54, 56}Fe and ^{63, 65}Cu at energies between 8 and 14 MeV, which were reported in a companion paper, have been analyzed in the framework of the coupled channels formalism. Neutron potential deformations were extracted and compared with corresponding deformations deduced from the reanalysis of proton scattering measurements and Coulomb excitation results. The size of the Coulomb correction term in the absorptive proton potential is discussed. Matter root-mean-square radii are estimated from our potential and compared with results from -particle folding model calculations.     

Fe NMR, magnetization and X-ray study of Cd0.1Cu0.9Fe2O4 ferrite

⁵⁷Fe NMR spin-echo spectra, static magnetization and X-ray diffraction measurements for Cd_0.1Cu_0.9Fe₂O₄ ferrite taken in a wide range of temperatures are presented. The X-ray studies show that above 100 K the structure is cubic. The temperature dependence of the effective magnetic field acting on ⁵⁷Fe nuclei at non-equivalent tetrahedral and octahedral sites has been determined. Different thermal behaviour of the magnetic field at both sublattices and of the specific macroscopic magnetization have been found. Magnetization measurements imply that cadmium substitution does not affect the ferric ion distribution between the sublattices of the ferrite.     

New evidence for a subshell gap at N=32

An 879.9(2) keV γ-ray transition has been identified following the β decay of ⁵⁸V and assigned as the 2⁺₁→0⁺₁ transition in ⁵⁸Cr₃₄. A peak in the energies of the first excited 2⁺ states for the even–even chromium isotopes is now evident at ⁵⁶Cr₃₂, providing empirical evidence for a significant subshell gap at N=32. The appearance of this neutron subshell closure for neutron-rich nuclides may be attributed to the diminished π1f_7/2–ν1f_5/2 monopole proton–neutron interaction as protons are removed from the 1f_7/2 single-particle orbital.     

Magnetic properties of UFe5Sn single crystals

Millimetre-size UFe₅Sn single crystals were grown by the top seed solution growth method and characterized by magnetization, ⁵⁷Fe Mössbauer spectroscopy and specific heat measurements in order to study the magnetic transitions detected in powder samples at 248 and 178 K. The magnetization measurements show different behaviour along the three crystallographic directions but with similar values of spontaneous magnetization along a and c. The transition at 248 K is associated with ferromagnetic ordering of iron moments along the c-axis, while the transition at lower temperature is associated with a reorientation towards b. Mössbauer data show that this reorientation is concomitant to the ordering of the Fe2 sites, which in a large proportion remain paramagnetic between the two transition temperatures. Specific heat measurements are consistent with the establishment of magnetic ordering at 248 K, followed by a spin reorientation at 178 K, yielding γ(0 K)140 mJ/(mol K²) and θ290 K for UFe₅Sn.     

Nuclear Effect on Nucleon Structure Function in the Extended x-Rescaling Model with Parton Recombination Effect

The extended x-rescaling model is tested by taking into account the parton recombination effect to explain the nuclear effects including the EMC effect, nuclear Drell-Yan ratios and the nuclear gluon distributions in the ⁵⁶Fe nucleus. The calculated results satisfactorily agree with the data of the EMC effect, nuclear Drell-Yan ratio and nuclear gluon distributions.     

The dissipative dynamics of the He A-B interface in finite geometries

The ³He A-B interface velocity and the stationary field of temperature and counterflow accompanying the phase transition are calculated employing general boundary conditions and superfluid hydrodynamics. All dissipative mechanisms that may occur are considered, especially including the effects of lateral walls. There are three contributions to the total growth resistance: (i) a microscopically abrupt temperature discontinuity at the interface arising from Andreev scattering of quasiparticles, (ii) two hydrodynamically gentle temperature variations (sq- or diffusive modes) on both sides of the interface that come from collisions among quasiparticles, and (iii) the drag exerted directly on the interface by the wall's roughness.