Electro- and photoinduced spallation reactions on27Al and51V at intermediate energies

Cross sections for some electro- and photoinduced spallation reactions on²⁷Al and⁵¹V have been measured in the energy region 130–580 MeV with the activation method. The cross sections per photon are compared to Monte-Carlo calculations based on a cascade-evaporation model. The electrodisintegration cross sections are compared to calculations based on the Dalitz formalism for virtual photon spectra.     

Isomeric ratios in photon-induced spallation reactions at intermediate energies

Available experimental isomeric cross-section ratios in photon-induced spallation reactions at intermediate energies are compiled. The experimental data are compared to calculations based on the statistical model formalism.     

27Al+27Al重离子耗散碰撞中能量自关联函数的分析

测量了²⁷Al+²⁷Al耗散反应产物的激发函数,束流²⁷Al⁸⁺的入射能量从114MeV到127MeV变化,能量步长为200keV.探测角度覆盖了实验室系10°—57°的连续区域.用不同的理论模型分析了耗散产物的能量自关联函数.结果表明,反应所形成的中间双核系统的阻尼相干转动造成了激发函数中不可平滑的涨落结构,相干转动的阻尼来自量子混沌运动.     

A study of the (α, t) reaction on 19F, 27Al, 51V and 59Co

The angular distributions of tritons from the (α, t) reaction on ¹⁹F, ²⁷Al, ⁵¹V and ⁵⁹Co nuclei corresponding to the (0⁺) ground states and (2⁺) excited states in the final nuclei have been measured in the angular range between 15° and 170° at α-particle energies of 25 MeV. For reactions on ²⁷Al and ⁵¹V nuclei, the differential excitation functions have also been obtained at different angles of outgoing tritons at E_α from 20 to 25 MeV. The experimental angular distributions are analysed by the DWBA approximation on the assumption of a nucleon stripping mechanism. The analyses of the present results and the data obtained earlier for the (α, t) reaction on the 1 p shell nuclei, A ? 30, reveal that the distinguishing feature of the reaction under study is the presence of backward angle peaks in the reaction cross section, which appear to be associated with exchange processes. For the (α, t) reaction on the heavier nuclei (A > 30), the dominant mechanism is nucleon stripping.     

Photospallation of51V at intermediate energies

The yields of⁵¹V(, xpyn) reactions have been measured at maximum bremsstrahlung energies from 75 to 800 MeV. Mean cross sections have been deduced, compared to Monte-Carlo calculations and analysed with a semiempirical Rudstam formula. Total isobaric mean cross sections and anN/Z dispersion curve in the mass regionA = 42–48 have been obtained. The results are in agreement with cascade-evaporation theory and with earlier data obtained with photons and protons.     

Photonuclear reactions in medium weight nuclei 51V, 55Mn and Cu

New results on the photospallation of the medium weight nuclei ⁵¹V, ⁵⁵Mn and Cu at maximum bremsstrahlung energy between 2 and 5 GeV are presented. The yields of residual nuclei were measured by the activation method using a Ge(Li) detector. The results are analyzed with the empirical Rudstam formula and compared with data obtained in lower energy photon and proton induced reactions.     

The excited states of 27Al

The γ-decay of 60 and the strengths of 51 ²⁶Mg(p, γ)²⁷Al resonances were studied for E_p < 2.20 MeV. The energies of 32 and the γ-decay of 54 bound levels were determined. Spin and parity assignments $\text{J}{}^{\mathrm{\pi }}\text{=}\text{5}\text{2}{}^{\mathrm{+}}\text{,}\text{5}\text{2}{}^{\mathrm{?}}\text{,}\text{3}\text{2}{}^{\mathrm{?}}\text{,}\text{3}\text{2}{}^{\mathrm{+}}\text{,}\text{3}\text{2}{}^{\mathrm{+}}\text{and}\text{3}\text{2}{}^{\mathrm{+}}$ were made to the bound states at E_x = 4.81, 5.44, 6.61, 6.78, 7.68 and 7.86 MeV, respectively. Spin assignments $\text{J =}\text{5}\text{2}$and $\text{3}\text{2}$ were made to the bound levels at Einx = 5.55 and 6.08 MeV, respectively. For other levels spin and parity limitations were set. Lifetimes or lifetime upper limits of 19 bound levels were measured by means of the DSA technique. The spins and/or parities of 15 resonances were unambiguously determined from γ-ray angular distributions and strengths.     

The transfer reactions induced by 38 MeV 19F ions on 27Al

The reactions induced by 38 MeV ¹⁹F on ²⁷Al have been studied using the Tandem Van de Graaff accelerator at Harwell together with a mass identification system based on a combination of a Buechner magnetic spectrograph and position sensitive silicon detectors in the focal plane of the magnet. Comparison of the elastic scattering measurements with Coulomb cross sections provided an absolute normalisation to the measured reaction yields. Transfer reactions were measured as a function of emitted particle energy and angle for single nucleon pick-up and stripping and for 2, 3 and 4 particle stripping. Essential features of the experimental technique are outlined and the experimental results are presented. The significance of the energy spectra and angular distributions are discussed. The results of DWBA analyses of one-nucleon transfer reactions yield spectroscopic factors for levels in ²⁸Si, ²⁸Al and ²⁶Al which are in fair agreement with those obtained in other studies.     

The 51V(p,n)51Cr reaction at Ep = 160 MeV

The ⁵¹V(p, n)⁵¹Cr reaction has been studied at E_p = 160 MeV using the Indiana University beam-swinger facility. Data have been obtained at several angles up to θ_L = 20°. The 0° spectrum is used to obtain a ΔL = 0 response function from which Gamow-Teller strength is derived. A shell-model calculation of the GT strength distribution is presented and compared with the experimental results. The M1 strength is also calculated and compared with available results from (e, e') and (p, p') experiments. A comparison is made with other N = 28 nuclei. Effects of a truncated shell-model space are presented.     

Proton-4He elastic scattering at intermediate energies

Differential elastic cross sections and polarizations are calculated in a multiple-scattering formalism for proton-⁴He scattering for energies in the range 0.6–24.0 GeV and for momentum transfers up to 4.0 fm^?1. The calculations include Coulomb and spin effects. Corrections due to target-nucleon overlap and charge exchange are estimated. The results are compared with experimental data.     

The 27Al(t,p)29Al reaction at Et = 15 MeV

The ²⁷Al(t, p)²⁹Al reaction was studied at an incident energy of E_t = 15 MeV. Proton angular distributions were measured for the first 23 low-lying states. Comparisons of the data to DWBA calculations based on cluster-model and pure-configuration form factors were made which provided decompositions of the angular distributions into contributing L-values. Comparisons were also made to DWBA predictions based on microscopic amplitudes from a complete, sd-basis shell-model calculation.     

The photoproton decay of 27Al

Photoproton spectra from ²⁷Al were measured from 14.8 to 27.6 MeV excitation energy in 400 keV steps. From these, high resolution photoproton cross sections to low-lying states of the residual ²⁶Mg nucleus were deduced. The large integrated cross sections to these states justify the interpretation of the de-excitation γ-ray measurements which consistently indicate strong population of low-lying residual states following photodisintegration. Further, the results are discussed with reference to the particle-hole model. By examination of the microscopic configurations of the possible GDR states an explanation is proposed for the differences in the cross sections to various residual states. Finally, the results are compared with spectroscopic factors determined from pickup reactions on ²⁷Al.     

The 51V(n, γ)52V reaction studied with polarized neutrons and polarized vanadium nuclei

Circular polarization of γ- radiation following capture of polarized thermal neutrons by unoriented nuclei and the angular distribution of such radiation, using polarized neutrons and polarized nuclei, made it possible to assign spins to 13 levels of ⁵²V. In addition the admixtures of spin-3 and spin-4 reaction channels could be derived for 20 primary γ-ray transitions. With this information interference phenomena in the ⁵¹V(n, γ) reaction were studied. The low-lying levels of ⁵²V are compared with shell-model calculations. The capture mechanism is discussed in terms of a doorway-state model.     

A study of 50V using the direct reactions 49Ti (3He,d) and 51V(d,t)

Energy levels in ⁵⁰V up to 4.3 MeV have been studied using the ⁴⁹Ti(³He, d)⁵⁰V and ⁵¹V(d,t)⁵⁰V reactions with ³He particles of 22 MeV and deuterons of 19.5 MeV incident energy. More than eighty levels are seen, with angular distributions taken for forty-one levels in the (³He, d) reaction and for the ten lowest levels in the (d, t) reaction. The angular distributions are compared with the distorted-wave Born approximation (DWBA) to extract the l-values of the transferred nucleons and obtain the spectroscopic strengths. In the stripping reaction, a small amount of l = 0 and l = 2 strength is seen, indicating the presence of s and d proton holes in the g.s. of ⁴⁹Ti. The results are compared with a recent shell-model calculation based on an $\text{(}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^{\mathrm{n}}$ configuration, and show qualitative agreement.     

高转速下采用S-RESIDOR方法测量1H-27Al偶极偶合常数

提出利用S-RESIDOR(Symmetry-based Resonance Echo Saturation Irradiation DOuble Resonance)方法测量¹H-²⁷Al偶极偶合常数. 通过理论模拟,讨论了四极作用常数、饱和照射脉冲功率、照射时间对¹H/²7Al S-RESIDOR实验的影响. 发现四极作用常数对¹H/²⁷Al S-RESIDOR偶极去相曲线影响较小,中等强度的饱和照射功率即能满足实验要求. 高转速下,在氢型丝光沸石上进行了¹H/²⁷Al S-RESIDOR实验,测量得到Br-nsted酸位上的 ¹H与骨架上²⁷Al的偶极偶合常数为874 Hz.     

Elastic and inelastic4He-scattering on208Pb,232Th and234, 236, 238U

The angular distributions of the elastic⁴He-scattering on²⁰⁸Pb and the elastic and inelastic⁴He-scattering on²³²Th and^234,236,238U at E_4He = 50 MeVE_{4_{He} } = 50 MeV were measured between 20° and 60°. The⁴He-particles were detected with a position sensitive detector in the focal plane of a split-pole spectrograph. The aim was to get data to determine the deformation parameters of the equilibrium states by coupled channels calculations.     

Compound nucleus fission and quasi-fission in reactions of 238U with 16O and 27Al

The thermodynamics of pion-condensed nuclear matter is investigated in a relativistic field theory in the mean field approximation. The conditions of the thermodynamical equilibrium of the system lead to a set of self-consistent equations for the meson field amplitudes and for the wave vector of the pion condensate. It is proved, that in the thermodynamical equilibrium the pressure tensor of isolated, infinite nuclear matter is isotropic at any values of the temperature and chemical potential.