Shape isomer excitation by mu-minus atomic capture?

The possibility of excitation of the ²³⁸U shape-isomer by the atomic cascade of a negative muon has been investigated by a search for back-decay γ-rays. No candidates for such γ-rays have been found with yields greater than 1% per stopping muon, indicating that the probability of the isomer excitation by muons is less than 3%. The lifetime of a μ^? bound to ²³⁸U has been determined from capture γ-rays to be 79.1 ± 0.5 ns, which also set the upper limit of this probability to 7–15%.     

Spin-parity assignments for the excited states of 91Nb from the 91Zr(p,nγ)91Nb reaction

The energy levels of ⁹¹Nb were studied by means of the (p, nγ) reaction. The de-excitation γ-rays were observed with a Ge(Li) detector in the proton energy range from 3.25 to 5.51 MeV in steps of about 30 keV. Resonances attributed to isobaric analog states in the compound system ⁹¹Nb were observed in the excitation functions of the de-excitation γ-rays. From an analysis of these analog resonances, a Hauser-Feshbach analysis and the γ-decay scheme, the spin-parities of the levels up to 2792.6 keV (22 levels) were assigned.     

中子在大气中产生氮俘获γ的蒙特卡罗模拟研究

为了精确计算早期核辐射,建立了中子及次级γ在大气中输运的蒙特卡罗计算模型,并利用几何分裂算法与时间分裂算法等减方差技巧提高计算效率,计算得到了距源点不同距离球面上中子与中子次级γ的信息,给出了不同位置不同时间的氮俘获γ能量释放率。开展了氮俘获γ能量释放率的规律性研究,并分析了中子能量对氮俘获γ的影响。结果表明,氮俘获γ能量释放率先随源点的距离增加而增大,在距源点约500 m达到峰值,而后随距离增加指数衰减。氮俘获γ能量释放率在时间上服从指数衰减规律,衰减时间在0.1 s左右。引入表征氮俘获γ辐射强度参数a和特征衰减时间参数τ,拟合得到了不同距离不同时间氮俘获γ能量释放率的快速计算公式。研究表明,氮俘获γ辐射强度、衰减时间及其空间分布均与中子能量密切相关。     

Enhancement of the radiative channel in nuclear forward scattering

Two observations of nuclear forward scattering of Mössbauer radiation are presented. In one, a magnetic-resonance device was used to chop the γ-ray beam. After the beam was turned off, the nuclear target became a strong emitter of γ-rays in the forward direction. In the other observation, the energy of the intermediate excited nuclear state was changed suddenly by a hyperfine magnetic field reversal and the de-excitation of the nuclei occurred with the forward emission of γ-rays at the shifted frequency. In both cases, the enhancement of the radiative channel of nuclear scattering was observed.     

High spin states of some nuclei around the N=Z=28 double closed shell

A spectroscopic study is performed for high spin states of⁵⁵Fe,⁵⁵Co and⁵⁷Ni. To populate the investigated residues with a relevant cross section, the fusion evaporation reactions of³⁰Si(²⁸Si, 2pn)⁵⁵Fe,³⁰Si(²⁸Si, 2np)⁵⁵Co and⁴He(⁵⁴Fe,n)⁵⁷Ni were chosen. To identify the newγ transitions and to build the energy level schemes,γ — γ coincidence techniques together with excitation functions were employed. Angular distributions andγ — γ angular correlations allowed us to assign the spin values of the nuclear states. The previous level scheme of⁵⁵Fe is extended into the region between 6.5–11 MeV of excitation energy, up to spin 27/2, while the yrast decay paths of⁵⁷Ni and⁵⁵Co are reported here for the first time. Experimental data are fairly well reproduced by Glaudemans' shell model calculations.     

Measurement of X-ray production cross-sections of Ti,V, Cr,Mn, Fe,Co, Ni and Cu molecules

K shell X-ray production cross-sections in the Ti, V, Cr, Mn, Fe, Co, Ni, and Cu in the molecules were studied at 59.5 keV excitation energy by using a Si(Li) detector ( FWHM = 155 eV at 5.96 keV). The present results are compared with other theoretical values.     

γ-Ray multiplicity in 239Pu fission induced by resonance neutrons: experimental evidence for the (n, γf) reaction

The fission γ-ray multiplicity measurement in the ²³⁹Pu resonances has been carried out, using the Saclay 60 MeV electron linac as a neutron source. Large fluctuations are observed from resonance to resonance, in correlation with the number $\text{}\text{?}$Gn of prompt neutrons, the total energy of these γ-rays and the fission width Γ_f. The results are interpreted in terms of a competition between the fission and the radiative capture during the de-excitation of the compound nucleus. They are the first experimental evidence of the (n, γf) reaction. Some parameters like the width $\text{Г}{}_{\mathrm{\gamma f}}$ are deduced.     

Neutrino Energy Loss by Electron Capture on Nucleus ^56Mn, ^56Fe, ^56Co and ^56Ni in Strong Electron Screening

Based on the p-f shell model, the neutrino energy loss rates for nucleus ^56Mn, ^56Fe, ^56Co and ^56Ni in the electron capture process are canvassed in and not in a strong electron screening. The results show that the neutrino energy loss rates for ^56Mn, ^56Fe, ^56Co and ^56Ni decrease about 15%, 10%, 60% and i order of magnitude correspondingly at the temperature T9 = 15 and even debase 2 orders of magnitude at the temperature T9 = 1.     

The 56Fe(α, γ)60Ni reaction cross section

The yield of 1.332 MeV γ-rays from the reaction ⁵⁶Fe(α, γ)⁶⁰Ni has been measured as a function of α-particle bombarding energy in the range 4.2–7.1 MeV. This energy region includes the (α, n) threshold at E_α = 5.46 MeV. The energy dependence of this γ-ray cross section, as well as the (α, nγ) cross section, is compared with statistical model calculations. Good agreement is achieved between these data and calculations using global optical model parameters to determine the transmission functions. In particular, the pronounced threshold effect in the (α, γ) yield, at the opening of the (α, n) channel, is well represented.     

The absorption of π− at rest on complex nuclei

The energy, width and intensity of prompt nuclear γ-rays following capture of π^? at rest by ⁹Be, ¹⁰B, ¹⁶O, ¹⁹F, ³¹P, Ca and ⁹³Nb were measured with a Ge(Li) detector. In most cases it was possible to identify the final nucleus from the energy of the observed γ-ray. Using the measured Doppler broadening of γ-rays from short-lived states, the vector sum momentum distribution of the emitted nucleons was calculated. From the measured γ-ray intensities, isotopic yields were deduced corresponding to the removal of from 1 to 12 nucleons. The average number of removed nucleons changes from 3.0 to 5.5 as the target varies from ¹⁶O to ⁴⁰Ca. A comparison was made with data from both spallation reactions and multi-nucleon pickup reactions.     

A study of the 59Co(n,n′γ)59Co reaction

The ⁵⁹Co(n, n'γ)⁵⁹Co reaction has been studied for incident neutron energies ranging from 1.3 to 3.9 MeV. The pulsed-beam time-of-flight technique was employed to discriminate between the inelastically scattered neutrons and the de-excitation γ-rays, which were detected by means of a true-coaxial Ge(Li) detector. Thirty-five levels were identified in this way, and their excitation functions have been extensively compared with the predictions of the statistical theory of the compound nucleus. Possible spin assignements to the levels of ⁵⁹Co are discussed and compared with the results available from previous works.     

The effects of ⁶⁰Co γ-ray irradiation on the DC characteristics of enhancement-mode AlGaN/GaN high-electron-mobility transistors

The effects of 60Co γ-ray irradiation on the DC characteristics of AlGaN/GaN enhancement-mode high-electron-mobility transistors (E-mode HEMTs) are investigated. The results show that having been irradiated by 60Co γ-rays at a dose of 3 Mrad (Si), the E-mode HEMT reduces its saturation drain current and maximal transconductance by 6% and 5%, respectively, and significantly increases both forward and reverse gate currents, while its threshold voltage is affected only slightly. The obvious performance degradation of E-mode AlGaN/GaN HEMTs is consistent with the creation of electronegative surface state charges in the source-gate spacer and gate-drain spacer after being irradiated.     

偏振能量色散X射线荧光光谱法在土壤环境监测中的应用

以土壤和水系沉积物标准物质为校准样品,采用粉末样品压片制样.建立了偏振能量色散X射线荧光光谱仪测定土壤中As、Ba、Cu、Co、Cd、Cr、Mo、Mn、Ni、Pb、Sr、Ti、V、Zn、Rb、Sc、Bi、Si、Al、Fe、Ca、Mg、Na、K 24种元素的方法.该方法采用Al、CaF2、Fe、Zn、KBr、Al2O3、...     

Energy levels in 93Mo populated by the 93Nb(p,nγ) reaction

Energy levels of ⁹³Mo have been investigated by means of the ⁹³Nb(p, nγ)⁹³Mo reaction. The excitation functions of the level de-excitation γ-rays were measured with a Ge(Li) detector under proton bombardment in the energy range 3.0 to 5.0 Me V. A detailed γ-ray decay scheme which includes 69 levels and 123 γ-ray lines was constructed from the threshold energies for 64 γ-rays and the γ-ray excitation functions around five isobaric analogue resonances in the ⁹³Nb(p, nγ) reaction. Spin-parity values for 59 levels and favourable values for 8 levels were assigned from the analysis of relative neutron yields via the isobaric analogue resonances of the parent odd-odd nucleus ⁹⁴Nb. The results of the present experiment are compared with shell-model calculations.     

Neutron capture gamma-rays from the low-lying resonances of 54Fe

Neutron capture γ-rays have been observed from the low-lying resonances of ⁵⁴Fe using the Harwell electron linear accelerator HELIOS as a neutron source. Relative values for the partial radiative widths of resolved lines were obtained by area analysis of the γ-rays peaks over neutron resonance regions, and absolute values were obtained by a shape analysis fit to the yield deduced by comparison with a ¹⁰B(n, αγ)⁷Li measurement. For the 7.8 keV s-wave resonance, a comparison of the partial widths with the predictions of the valence model has been made. In both relative and absolute senses, there is good agreement.     

Magnetic ordering in digital alloys of group-IV semiconductors with 3<Emphasis Type="Italic">d</Emphasis>-transition metals

The ab initio investigation of the magnetic ordering in digital alloys consisting of monolayers of 3d-transition metals Ti, V, Cr, Mn, Fe, Co, and Ni introduced into the Si, Ge, and Si_0.5Ge_0.5 semiconductor hosts is reported. The calculations of the parameters of the exchange interactions and total-energy calculations indicate that the ferromagnetic order appears only in the manganese monolayers, whereas the antiferromagnetic order is more probable in V, Cr, and Fe monolayers, and Ti, Co, and Ni monolayers are nonmagnetic. The stability of the ferromagnetic phase in digital alloys containing manganese monolayers has been analyzed using the calculations of magnon spectra.     

The effects of 60Co γ-ray irradiation on the DC characteristics of enhancement-mode AlGaN/GaN high-electron-mobility transistors

The effects of 60Co γ-ray irradiation on the DC characteristics of AlGaN/GaN enhancement-mode high-electron-mobility transistors (E-mode HEMTs) are investigated. The results show that having been irradiated by 60Co γ-rays at a dose of 3 Mrad (Si), the E-mode HEMT reduces its saturation drain current and maximal transconductance by 6% and 5%, respectively, and significantly increases both forward and reverse gate currents, while its threshold voltage is affected only slightly. The obvious performance degradation of E-mode AlGaN/GaN HEMTs is consistent with the creation of electronegative surface state charges in the source-gate spacer and gate-drain spacer after being irradiated.     

Level structure and lifetimes of excited states in 48Ti

The properties of excited states in ₂₂⁴⁸Ti₂₆ populated by means of the ⁴⁵Sc(α, pγ)⁴⁸Ti reaction were investigated. The Doppler-shift attenuation method was employed to determine the mean lives of 16 levels up to an excitation energy of 4073 keV. Proton-γ coincidence techniques were used to record simultaneously the Doppler-shifted de-excitation γ-rays emitted at 26 and 154 degrees to the incident beam direction. A comprehensive level and decay scheme is proposed. Detailed shell-model calculations have been made of M1 and E2 transition matrix elements for depopulation of states whose lifetimes have been measured. Salient nuclear structure aspects of this “self-cross-conjugate” nucleus are examined in light of critical comparisons of measured and calculated Ml and E2 reduced transition probabilities.