Resonance neutron capture in 56Fe

The neutron capture cross section of ⁵⁶Fe has been measured with 0.2–0.3% energy resolution from 2.5 keV up to the inelastic neutron scattering threshold. Results are compared with recent total cross-section data and average parameters are derived for s-, p- and d-wave resonances. The low correlation coefficient observed between the s-wave reduced neutron and radiative widths is consistent with the minor contribution of the valence capture mechanism as calculated in the framework of the optical model. Broad E1 and M1 doorway states for s-, p- and d-wave resonances are postulated to explain the cross-section data and γ-ray spectra up to 1 MeV.     

High-Spin States in the Odd-Odd Nucleus 92Nb

High spin states of the odd-odd nucleus 92Nb are investigated using the S2Se （14N, 4n）92Nb reaction at a beam energy of 54MeV. The level scheme of the 92Nb was extended up to Jπ=（16＋） at about 7.3 MeV and Jπ=（21-） at about 9.7MeV. According to systematic analyses and a comparison with the neighboring nucleus, the higher spin states could be interpreted by the multi-particle excitations in the π（fs/2,P3/2,p1/2,gg/2）@v（p1/x,gg/2,d5/2, g7/2） configuration space.     

Isobaric Analogue State of the 0.211 MeV Level of Mn56 in Fe56

Gamma-ray spectrum from the reaction Mn⁵⁵(p, γ) Fe⁵⁶ at the isobaric analogue resonance at E_p = 1537 ± 4keV has been measured with a 15 cm³ Ge(Li) detector. Double and triple angular correlations at this resonance state have been measured. Proton elastic scattering was studied also at this resonance at the angles 135° and 150°. Analysis of these data yields a spin and parity assignment 2+, proton radiative width 2 ± 0.2 keV and total width 9 keV to this resonance state which is the isobaric analogue of the third excited state of Mn⁵⁶ at excitation energy 0.211 MeV.     

A shared mixed-symmetry state in 56Fe

Analysis of the γ-decay data suggests that the lowest mixed-symmetry 2⁺ state in ⁵⁶Fe is shared almost equally between the two 2⁺ levels at 2.658 MeV and 2.960 MeV.     

Neutron Resonance States in Overdense Crystals

New three-body resonances appeared in the neutron scattering on two nuclei fixed in nodes of overdense crystalline lattice have been calculated for the iron group isotopes. These resonances are strongly dependent on the lattice parameters and characteristics of two-body resonances in neutron–nucleus subsystems. The effective forces created by the neutron resonance rescatterings supplement the Coulomb forces between nuclei of the crystalline lattice. These effective resonance interactions occur only at certain distances between nuclei and are accompanied by gamma radiation.     

Maxwellian Averaged Neutron Capture Cross Sections in 56Fe and 57Fe

Measurements of the keV-neutron capture cross sections and radiative γ-ray spectrum of 56Fe and 57Fe are performed based on a 7 Li（p,n）7 Be reaction neutron source. The incident neutron spectrum on a capture sample is measured by means of a time-of-flight （TOF） method with a 6Li-glass detector. The radiative capture 7-rays emitted from an iron CS Fe or 57 Fe） or standard gold （197Au） sample are detected by a large anti-Compton NaI（TI） spectrometer covered with a heavy shield. The capture yields of samples are obtained by applying a pulse-height weighting technique to the corresponding capture γ-ray pulse-height spectrum. The Maxwellian averaged neutron capture cross sections of 56Fe and 5T Fe are derived according to the present capture cross section results.     

Structure of dipole resonances in iron isotopes 54Fe and 56Fe

The probability distributions of photoexcitations in ⁵⁴Fe and ⁵⁶Fe nuclei were obtained within the particle-core coupling version of the multiparticle shell model by using the spectroscopy of direct pickup reactions.     

Isobaric Analogue State of the 341 KeV Level of Mn56 and Fe56

When Mn⁵⁵ is bombarded by protons, a proton capture resonance is detected at E_p = (1678 ± 4) KeV. The spectral and angular distribution studies of the (p, γ) and (p, p) reactions at this resonance have established J^π = 3⁺, l_p, = 1, Γ_p = (1 = 0.2) KeV and Γ = 17 KeV for the energy level at (11836 ± 4) KeV in the Fe⁵⁶ nucleus. Comparison of the present results with those obtained by (n, γ) and (d, p) reactions on the Mn⁵⁵ nucleus suggests that this resonance state is most probably the isobaric analogue of one member of the doublet at 341 KeV in the Mn⁵⁶ nucleus.     

States of the 12N Nucleus with Increased Radii

The differential cross sections for the ¹²C(³He, t)¹²N reaction leading to formation of the 1⁺ (ground state), 2⁺ (0.96 MeV), 2⁻ (1.19 MeV), and 1⁻ (1.80 MeV) states of ¹²N are measured at E(³He) = 40 MeV. The analysis of the data is carried out within the modified diffraction model and distorted wave Born approximation. Increased rms radii have been obtained for the ground, 2⁻ (1.19 MeV), and 1⁻ (1.80 MeV) states. We revealed that ¹²B, ¹²N, and ¹²C in the isobaric analogue states with T = 1, and spin-parities 2⁻ and 1⁻ have increased radii and exhibit properties of neutron and proton halo states.

     

Kernspektroskopische Untersuchungen zu den Termschemata der Kerne56Fe und56Co

Gamma-gamma directional correlations have been investigated for several cascades in⁵⁶Fe formed in the decay of⁵⁶Mn or⁵⁶Co. A combination of NaI(Tl) and Ge(Li) detectors was used for the experiments. It was established that a level at 3601 keV is populated in the decay of⁵⁶Co. Spins given in the paranthesis were assigned to levels at the following energies: 2658(2), 2960(2), 3123(4), 3370(2), 3445(3), 3601(2), 3856(3), 4049(3), 4100(4), 4120(3), 4298(4), 4395(3) and 4459 keV (3,4). Multipole mixing ratios were determined forγ transitions of the following energies: 978, 1038, 1175, 1360, 1772, 1811, 1964, 2015, 2035, 2113, 2213, 2523, 2599, 3010, 3202, 3254, 3273, 3451 and 3548 keV. Theγ-rays from the decay of⁵⁶Co of energies 674.7 and 2657.4 keV have been observed for the first time, and the presence of several other weakγ-rays in the⁵⁶Fe decay has been confirmed. Nine angular correlations in the decay of⁵⁶Ni have been investigated. The spin sequence 4, 3, 2, 0, 1 was unambiguously determined for the levels at 0, 158.2, 970.1, 1450.7 and 1720.0 keV. The multipolarity of theγ-rays of energies 158.2, 749.9 and 811.9 keV was determined as almost pure M1. The results are discussed within the framework of recent shell model calculations.     

A microscopic classification of high-spin states in 56Fe

A large-scale shell-model calculation on ⁵⁶Fe including positive parity states with spins up to J = 15 shows that several states in the yrast region may be of a particular nature. These states can be locd in groups of which the gamma decay and quadrupole moments show a collective behaviour. The signature of each group is the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ hole structure. This structure is coupled to a definite J_hole and T_hole with the spin J_hole being as large as possible. The level density above the yrast region turns out to be largely independent of J.     

Beta decay of nuclide 56Fe,56Co,56Ni,56Mn,56Cr and 56V due to strong electron screening in stellar interiors

According to a new electron screening theory,we discuss the beta decay rates of nuclide 56Fe,56Co,56Ni,56Mn,56Cr and 56V with and without strong electron screening (SES).The results show that SES has only a slight effect on the beta decay rates for ρ/μe 108 g/cm3.However the beta decay rates would be influenced greatly for ρ/μe 108 g/cm3.Due to SES,the maximum values of the C-factor (in %) on beta decay rates of 56Fe,56Co,56Ni,56Mn,56Cr and 56V is of the order of 95.03%,35.02%,98.05%,80.33%,98.30% and 98.71% at T9 = 4.0 and 98.83%,98.89%,99.65%,10.32%,4.10% and 40.21% at T9 = 7.0,respectively.     

Near-harmonic structure and level similarities in Fe56, Fe58 and Ni60

Near-harmonic structure is known to exist in Fe⁵⁸, and an investigation was undertaken to determine whether this structure is also present in Fe⁵⁶, and Ni⁶⁰. In the case of Fe⁵⁶, no second 2⁺ state with the desired energy or de-excitation characteristics had been reported by previous investigators and a search for a small excitation of such a level from the decay of Mn⁵⁶ is described. The results are inconclusive although some evidence for its existence is presented. Our investigation of the Mn⁵⁶-Fe⁵⁶ decay reveals the presence of an additional beta branch to a 2⁺ level at 3.34 Mev in Fe⁵⁶. The results of the angular correlation measurements on the cascade gamma rays from this and other levels are given. The stopover transitions are found to be mostlyM 1 radiation and hence not of the near-harmonic type. In the case of Ni⁶⁰, the measured angular correlation functions for the 0.85–1.33 and 1.76–1.33 Mev cascades initiated from the decay of Cu⁶⁰ are reported. For the former cascade, the results indicate that the stopover transition is largely E2 radiation, but the experimental difficulties prevent a more quantitative statement. The presence of this type of radiation, together with a stopover to crossover intensity ratio of 15, imply the existence of near-harmonic structure in Ni⁶⁰. The angular correlation function for the latter cascade is found to be nearly identical to that of the corresponding cascade in Fe⁵⁸ which lends weight to the contention that there exist level similarities in these nuclei. Additional evidence for these similarities is also presented.     

135La高自旋态的实验研究

利用在束γ谱实验技术,通过¹²⁸Te(¹⁰B,3n)¹³⁵La反应研究了¹³⁵La的高自旋态.基于γγ符合关系、γ射线的相对强度和各向异性度的测量结果,建立了¹³⁵La的能级纲图.在hω≈0.40MeV附近,观测到基于πh_11/2质子轨道上的负宇称带的带交叉.比较N=78同中子素链能级结构的系统性,认为该带交叉是由一对h_11/2准质子发生转动顺排造成的.在高自旋态处,观测到具有很强M1跃迁、Signature劈裂很小的ΔI=1负宇称带,根据系统性认为该带是建立在πh_11/2(νh_11/2)²组态上的γ≈–60°的扁椭球形变带.     

奇奇核90Nb的高自旋态研究

用能量为80MeV的19F束通过反应76Ge(19F,5n)90Nb布居了90Nb的高自旋态.通过在束γ测量分析90Nb退激γ射线的符合级联关系,发现了19条新的属于90Nb的γ跃迁,建立了90Nb的高自旋态能级纲图.通过经验壳模型计算指定了部分能级的组态,并结合实验DCO比值和与相邻N=49核素的系统比较,确认了新能级的自旋和宇称. The high spin states of~(90)Nb have been populated via reaction~(76)Ge(~(19)F, 5n)~(90)Nb at beam energy of 80 MeV. The de-exciting γ-rays have been measured with in-beam γ-ray spectroscopy method. After γ-γ coincidence analysis, 19 new γ transitions were identified and assigned to~(90)Nb. The new level scheme of~(90)Nb was established. Based on the semi-empirical shell model calculations, the configurations of the levels have been suggested. In addition, the spins and parities of the new levels ...     

过渡区核87Zr的高自旋态研究

通过束流能量为118MeV的⁵⁹Co(³²S,3pn)⁸⁷Zr熔合蒸发反应,用在束r谱学方法研究了⁸⁷Zr的高自旋态.利用7台反康普顿谱仪组成的探测阵列进行r–r符合测量,并确定部分r射线的DCO值,在此基础上建立了自旋直到(37/2⁺)和(43/2^－)的能级纲图.观测到了多条新的能级.与相邻的同中子异荷素的比较表明,中子对核结构性质的影响远大于质子的贡献.随着质子数的增加,第一交叉频率呈减小的趋势.     

12C induced transfer reactions on 56Fe

Transfer reactions ⁵⁶Fe(¹²C, xN) have been investigated. Angular distributions of particles following elastic scattering, one neutron and one proton transfer reaction channels leading to low lying states in respective residual nuclei have been measured. These are analysed using the coupled reaction channel (CRC) formalism. Starting with a double folded real potential, the elastic scattering angular distribution is calculated using the computer code FRESCO. Inclusion of couplings to first excited states in both the target and the projectile already tends to describe the experimental elastic scattering distribution. Additional coupling of one neutron transfer reaction to first five excited states in ⁵⁵Fe and one proton transfer reaction to first three low lying states in ⁵⁷Co improves fit to the elastic scattering angular distribution. Further refinement in fit is brought about by addition of a weak imaginary potential to the complex potential calculated by ERESCO to simulate the absorption effects due to those channels whose coupling is not included explicitly. Such a potential describes the experimental angular distributions for elastic, one neutron and one proton transfer channels correctly in shape and magnitude without any arbitrary normalisation.     

Geometric Phase of Mixed States in the Resonance Fluorescence Spectrum

Berry phase of mixed state is investigated for modified Bloch equation with constant terms, which was used to explain sidebands in the spectrum of fluorescent light. The results show that for the physical phenomenon of sidebands, the Berry phases under the quasicyclic evolution exhibit as a geometric phase transition, where the transition point and region depend fully on the dynamics of population inversion and mixed degree. We find that, furthermore, the transition position is correlated to photon number. Thus the open quantum system preserves indeed a memory of its evolution in terms of the Berry phase, which may provide another clue for looking for devices of quantum memory in terms of geometric sideband approach.     

Mößbauereffekt anFe 57 nach Neutroneneinfang in Fe56

Mößbauer effect measurements with the 14.4 keV gamma rays of Fe⁵⁷ following thermal neutron capture in Fe⁵⁶ are reported. During the transition from the capture level at 7.6 MeV to the first excited state at 14.4 keV recoil energies up to 549 eV are imparted to the Fe⁵⁷ nuclei. Thus the Mößbauer gamma rays are emitted by nuclei displaced from their normal lattice positions. The measurements have been performed in order to get informations about the final position of the recoiled nuclei in metallic iron and in ordered Fe-Al alloys. Mößbauer spectra of recoil atoms in metallic iron did not show any significant deviation from the spectra of atoms on normal lattice positions. In ordered FeAl alloys of CsCl structure changes in the isomer shift due to recoil effects have been found. In a Fe₃Al alloy of DO₃ type order additional changes in the internal magnetic field have been observed. All results are discussed in terms of possible final positions for the primary recoiled iron atoms in the lattice.     

Gamma-ray transitions in56Ni induced by the54Fe(3He,n)56Ni reaction

Ten gamma-ray transitions have been observed in the⁵⁴Fe(³He,n γ)⁵⁶Ni reaction. A new level at 3925±10 keV is established in⁵⁶Ni. Spin-parity assignments of 0⁺, 4⁺ and 2⁺ are proposed for the levels at 3.925, 3.958 and 5.352 MeV, respectively. Branching ratios are given.