The (n, 2n) cross sections of 85Rb, 87Rb and 144Sm

The (n, 2n) cross sections at neutron energies between 14.9 and 17.0 MeV have been measured for ⁸⁵Rb, ⁸⁷Rb and ¹⁴⁴Sm by the mixed-powder method and γ-ray detection by a Ge(Li) spectrometer. Using the ²⁷Al(n, α)²⁴Na reaction for monitoring, the measured cross sections were (in mb): ${}^{85}\text{Rb}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>84(</mtext><mtext>m+g</mtext><mtext>)</mtext>}}\text{Rb}\text{, 1125±141, 1177±148}\text{and}\text{1235±162}\text{at}\text{15.0±0.4}\text{MeV}\text{, 16.2±0.7}\text{MeV and}\text{17.0±0.9}\text{MeV, respectively}\text{;}{}^{85}\text{Rb}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>84</mtext><mtext>m</mtext>}}\text{Rb}\text{, 662±83, 688±87}\text{and}\text{765±99}\text{at}\text{15.0±0.4}\text{MeV}\text{, 16.2±0.7}\text{MeV and}\text{17.0±0.9}\text{MeV}\text{,}\text{respectively}\text{;}{}^{87}\text{Rb}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>86(</mtext><mtext>m+g</mtext><mtext>)</mtext>}}\text{Rb}\text{, 1336±168}\text{and}\text{1301±162}\text{at}\text{15.0±0.4}\text{MeV and}\text{16.2±0.7}\text{MeV respectively}\text{;}{}^{144}\text{Sm}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>143(</mtext><mtext>m+g</mtext><mtext>)</mtext>}}\text{Sm}\text{, 1202±130, 1300±141, 1516±179}\text{and}\text{1514±179}\text{at}\text{14.9±0.3}\text{MeV}\text{, 15.5±0.3}\text{MeV}\text{, 16.4±0.5}\text{MeV and}\text{16.7±0.2}\text{MeV, respectively}$. The measured values are compared with the statistical model calculations of Pearlstein.     

Coulomb excitation of 115Sn

Coulomb excitation of the nucleus ¹¹⁵Sn was studied with beams of ⁴He and ¹⁶O. Level energies, spins, mean-lives and B(E2) and B(M1) transition probabilities were obtained. Spin $\text{3}\text{2}$⁺ states were observed at 497.35 and 1280.08 keV and spin $\text{5}\text{2}$⁺ states were observed at 986.54 and 1416.78 keV. A state of 612.79 keV was observed to be indirectly excited by decay of the Coulomb excited states. Eleven B(E2) values and nine B(M1) values were obtained for the transitions between the low-lying states. In contrast to previous particle transfer results which suggested a clear distinction between shell-model and collective $\text{3}\text{2}$⁺ and $\text{5}\text{2}$⁺ states, our results suggest the collective strength is shared by the two $\text{3}\text{2}$⁺ and two $\text{5}\text{2}$⁺ states.     

Projectile Coulomb excitation of 24Mg

The static quadrupole moment of the first excited J^π = 2⁺ state in ²⁴Mg and the reduced electric quadrupole transition probability between this state and the ground state were measured via projectile Coulomb excitation. The quadrupole moment was deduced from the shapes of γ-ray angular distributions. The result is $\text{Q(}{}^{24}\text{Mg}\text{, 2}{}^{\mathrm{+}}\text{) = ?0.27±0.05}\text{b}$. The transition strength was deduced from yield measurements and by comparison with the yields of target γ-rays, The result is $\text{B(}\text{E}\text{2; 0}{}^{\mathrm{+}}\text{→ 2}{}^{\mathrm{+}}\text{,}{}^{24}\text{Mg}\text{) = 0.044±0.003 e}{}^2\text{·}\text{b}{}^2$. The experimental measurements are compared with theoretical predictions and previous measurements and a detailed discussion is given of corrections to this type of reorientation experiment.     

Investigation of 89Y and 87Rb by (p,p′) reactions

The (p, p′) reaction on ⁸⁹Y at incident energies of 20.51 MeV and 14.33 MeV and on ⁸⁷Rb at 20.89 MeV has been studied. In ⁸⁹Y 28 levels with E_ex between 2 and 4.2 MeV and 79 levels with E_ex between 4.2 and 6 MeV have been identified. In ⁸⁷Rb 45 levels with E_ex up to 4.2 MeV have been found. Transferred orbital angular momenta and deformation parameters have been deduced from a macroscopic DWBA analysis of the differential cross sections. The experimental results are not consistent with the interpretation of states in ⁸⁹Y and ⁸⁷Rb as resulting from the weak-coupling of a proton or proton-hole to excited states of the ⁸⁸Sr core. Simple shell model arguments are able to yield at least a qualitative agreement with the level scheme as found for ⁸⁹Y.     

Coulomb excitation of levels in 143Nd and 145Nd

The low-lying states of ¹⁴³Nd and ¹⁵⁴Nd have been studied by means of Coulomb excitation with ¹⁶O and α-particles. Angular distribution measurements were carried out for some transitions in ¹⁴⁵Nd with 11.2 MeV α-particles. Level energy decay schemes and B(E2)↑ values were measured for two states in ¹⁴³Nd and for six states in ¹⁴⁵Nd. Some spin assignments have been established for the ¹⁴⁵Nd nucleus. ¹⁴³Nd and ¹⁴⁵Nd have been theoretically described by coupling one and three particles, respectively, to quadrupole vibrations, and rather good agreement with experiment was achieved.     

85Rb灯对87Rb原子的光抽运

本文对用⁸⁵Rb灯不经滤光泡直接对⁸⁷Rb吸收泡的光抽运作了观测,得到了比传统的用⁸⁷Rb灯经⁸⁵Rb滤光泡对⁸⁷Rb吸收泡进行光抽运更强的基态0—0跃迁共振讯号。并在一定温度下观察到负的共振讯号。到目前为止,还不能对这种负的共振讯号作出解释。同时还测量了共振线宽和光频移。对在⁸⁷Rb原子频标中应用的可能性作了评述。 关键词：     

Coulomb and nuclear excitation effects on 16O scattering from samarium isotopes

Elastic scattering of ¹⁶O on ^{148, 150, 152}Sm isotopes and inelastic scattering leading to the first 2⁺ state for the three isotopes and the 4⁺ state for ¹⁵²Sm have been measured at several energies in the vicinity of the Coulomb barrier. The whole set of data was reproduced at forward angles with an effective potential taking into account Coulomb excitation and in the full angular range by CCBA calculations including separate nuclear and Coulomb deformations.     

Nuclear and Coulomb deformation parameters of 142Nd

Nuclear and Coulomb deformation parameters have been deduced from DWBA analyses of angular distributions of 67.5 MeV ¹³C ions inelastically scattered from ¹⁴²Nd. Optical model parameters from fits of measured elastic scattering data were used with previously measured B(EL) values to determine initial deformation parameters. Comparison With the experimental data indicates that DWBA calculations can be used to understand the inelastic scattering from the nearly spherical nucleus ¹⁴²Nd.     

Level structure of 82Rb,studied through the 81Br(α, 3n) reaction

Nuclear states of ⁸²Rb were studied through the ⁸¹Br(α, 3n) reaction at various bombarding energies between 30 and 55 MeV. Excitation functions, γ-ray angular distributions, γ-γ coincidences and γ-time distributions with respect to the beam bursts were determined. Levels at 123.2, 187.7, 233.6, 796.3, 1214.1 keV and tentatively at 1835.5 keV were observed. It was not possible to establish whether the lowest state of the proposed level scheme corresponds to the ground state or to the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 6.2}\text{h}$ isomeric state. The 45.9 and 64.5 keV γ-rays do not exhibit any measurable lifetime and a limit $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≦ 5}\text{ns}$ has been determined. The situation is similar for the 123.2 keV γ-ray, although in this case the presence of a long-lived component cannot be ruled out.     

Coupled-channels study of projectile and target excitation in the scattering of 6Li from 12C and 16O

Coupled-channels calculations are presented tor elastic and inelastic ⁶Li + ¹²C scattering at E_c.m. = 16 MeV and 20 MeV, and for ⁶Li + ¹⁶O at 18.7 MeV. Excitation of states within ⁶Li, ¹²C and ¹⁶O are treated with rotational, rotation-vibration and vibrational models only. The 3⁺⁶Li and 2⁺¹²C states are strongly coupled to the elastic scattering and reduce the strengths of both the real and imaginary potentials. The 3^?16O state reduces only the strength of the imaginary potential. All other states are weakly coupled and have little effect on each other or the potential. The data are reasonably well described, with there being some preference for the 3^? state in ¹²C to be K = 0. Excitation of the 0₂⁺ state in ¹²C requires a combination of β-vibration and monopole breathing-mode form factors. The deformation lengths found are in poor agreement with those deduced from electron or proton scattering.     

12C(12C, 8Be)16O angular distributions and excitation functions between 35 and 69 MeV bombarding energy

An array of eight detectors has been developed for identifying the particle unstable ⁸Be nucleus from nuclear reactions with high detection efficiency. Absolute cross sections have been measured for the reaction ¹²C(¹²C, ⁸Be_g.s.)¹⁶O to the ground state and to several excited states in ¹⁶O. Excitation functions at seven angles from 15° to 45° (lab) in 5° steps have been measured for bombarding energies between E¹²_C(lab) = 35 and 69 MeV. Excitation functions were obtained for the following states in the residual nucleus ¹⁶O which were found to be strongly populated: g.s.(0⁺); 6.1 MeV (0⁺, 3^?); 6.9 MeV (2⁺); 10.4 MeV (4⁺); 11.1 MeV (4⁺); 14.7 MeV (6⁺,…) and 16.3 MeV (6⁺,…). The energy range is covered in 250 keV (c.m.) steps; at certain energy ranges in ¹²⁵ keV or 50keV steps. All excitation functions exhibit a strong energy dependence of the cross section; pronounced gross structures with superimposed fine structures, similar to those observed for ¹²C+¹²C elastic and inelastic scattering at these energies, are observed. At 19.3 MeV, where resonant structures were observed in the reactions ¹²C(¹²C, p)²³Na, ¹²C(¹²C, n)²³Mg and ¹²C(¹²C, d)²²Na, no resonance is found for the reaction studied here. At 60, 61 and 63 MeV angular distributions have been measured in 1° and 2.5°(lab) angular steps. The excitation functions have been analyzed in terms of Ericson fluctuations and cross-correlation functions.     

Study of the (3He,d) reactions on 58, 60Ni and 56Fe near the Coulomb barrier

Using spectroscopic information gained by earlier measurements of the proton bound states populated by stripping reactions, (³He, d) reactions on ^{58, 60}Ni and ⁵⁶Fe targets are studied at energies near the Coulomb barrier and evaluation is made of the vertex function . This value is then used to determine spectroscopic factors for low-lying states in ⁵⁷Co.     

Optimum Q-values for the 58Ni(160O,12C) reaction well above the Coulomb barrier

The reaction ⁵⁸Ni(¹⁶O, ¹²C) has been studied at three incident energies, 60, 72 and 81 MeV, for a wide range of scattering angles. The angular and energy dependence of the optimum Q-value has been determined from the data. A simple optimum Q-value model which combines the recoil model of Siemens et al. with a concept of nuclear friction is proposed.     

Levels of 16O near 13 MeV excitation from 15N + P reactions

Angular distributions, a 0° excitation function and Doppler-broadened γ-ray profiles for the reaction ¹⁵N(p, α₁γ), and angular distributions for the ¹⁵N(p, α₀) reaction, have been measured for proton energies from about 900 to 1250 keV. These data, together with analysing powers from the ${}^{15}\text{N}\text{(}\text{p}$, α₀) reaction, have been satisfactorily fitted by means of R-matrix theory in terms of the known levels of ¹⁶O in the 13 MeV region together with background contributions.     

Resonant structures in the excitation functions of elastic and inelastic scattering of 16O on 24Mg

Excitation functions of ²⁴Mg(¹⁶O, ¹⁶O)²⁴Mg were studied between 25 and 64 MeV incident energy. A strongly resonant behaviour was observed for inelastic scattering at backward angles. The data were analysed in terms of coupled channel calculations. While agreement was good at forward angles, at backward angles the calculated cross sections are an order of magnitude too low suggesting that another reaction mechanism or neglected terms in the heavy ion interaction potential are important.     

The 26Mg(14N, 10B)30Si and 26Mg(14N, 11B)29Si reactions

Reactions induced by ¹⁴N on ²⁶Mg at bombarding energies of 60–95 MeV have been studied. Angular distributions for states populated in ²⁹Si by the (¹⁴N, ¹¹B) reaction and in ³⁰Si by the (¹⁴N, ¹⁰B) reaction have been compared with Hauser-Feshbach and DWBA calculations to determine the reaction mechanism and to deduce spectroscopic information. The cross sections for the states populated in ²⁹Si and ³⁰Si are in poor agreement with statistical model calculations, indicating a non-compound nucleus mechanism.     

Reactions of 40Ar with 159Tb, 142Nd and 144Sm; New α-activities from 189Bi, 173Pt and 177Au

Reactions of ⁴⁰Ar ions with targets of ¹⁵⁹Tb, ¹⁴²Nd, and ¹⁴⁴Sm have been studied at energies below 300 MeV with a helium gas-jet system. Excitation functions for (Ar, xn) reactions, where x = 5–10, were obtained for the radioactive products that decay by α-emission. Based on the characteristics of these excitation functions and on the systematics of α-decay, evidence is presented for the existence of the nuclides ¹⁸⁹Bi with α-particle energy E_α = 6.67±0.01 MeV and half-life < 1.5 sec, and ¹⁷³Pt with E_α = 6.19±0.01 MeV; and for the emission from ¹⁷⁷Au of an α-particle with E_α = 6.15±0.01 MeV.     

Study of the 8Be first T = 2 state with 4He + α and 7Li + p initiated excitation functions

In a high resolution study of the ⁴He + α initiated excitation functions in the region of the ⁸Be first T = 2 state, weak resonance excursions have been observed in some reaction channels yielding the total width Γ = 14.7 ± 4.0 keV. No resonance excursion has been observed in the ⁴He + α elastic scattering yielding the branching ratio Γ_α/Γ ≦ 0.003 for the decay of the ⁸Be first T = 2 state into two α-particles. For the decay to the low-lying states of ⁶Li and ⁷Li lower limits of the branching ratio are given. The reinvestigation of the ⁷Li+p initiated excitation functions revealed no resonance anomaly in the region of the ⁸Be first T = 2 state. The upper limit Γ_p/Γ ≦ 0.023 has been derived for the proton decay to the ⁷Li_g.s.. The results are compared with previous measurements and with shell-model calculations.