Beta-delayed proton emission from 97Cd and 99Cd

Two new β-delayed proton precursors, ^97,99Cd, have been identified at the ISOLDE on-line isotope separator. The proton branching ratio for ⁹⁹Cd is (1.7^+1.1_?0.5) × 10^?3. The ⁹⁹Cd proton spectrum is discussed in terms of the statistical model with Porter-Thomas fluctuations. The half-life of ⁹⁹Cd was determined to be 16±3 sec. A search for ⁹⁸Cd was also performed and it was found to be a pure β-emitter with a probable half-life of ≈ 8 sec.     

Recherche de l'isotope 19N par la réaction 10Be(11B, 2p)19N

The ¹⁰Be(¹¹B, 2p)¹⁹N reaction has been used to search for the ¹⁹N isotope. No evidence was found for delayed γ-rays from ¹⁹N(β^?)¹⁹O. Delayed neutrons were observed with a half-life of 0.42 ± 0.04 s, which are tentatively assigned to the neutron emitting states in ¹⁹O fed by the β-decay of ¹⁹N. Analysis of the data implies allowed β-transitions to neutron emitting ¹⁹O states, and makes probable an assignment of even parity for the 3.945 MeV ¹⁹O state.     

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.     

Neutron resonances in 185Re and 187Re

In a search for intermediate structure, neutron time-of-flight spectra corresponding to 1 and 4 MeV capture γ-ray thresholds were measured for the target isotopes ^{185, 187}Re. The data were analyzed from the point of view of level spacings as well as intermediate structure. A method was developed for estimating the neutron widths of the resonances even in those cases where the neutron widths are comparable to the γ-widths. On the basis of this analysis it was decided which resonances were most likely to be due to p-wave capture. While some unusual behavior was observed, there is no conclusive evidence for intermediate structure. The statistics of level spacings agree with the long range ordering described in the theory of Dyson and Mehta, and are inconsistent with an uncorrelated Wigner distribution. Energies, estimated neutron widths and p-wave probabilities (if over 10 %) for 488 resonances in ¹⁸⁵Re and 335 resonances in ¹⁸⁷Re are tabulated for the energy range 24 eV to 2 keV.     

Search for a narrow resonance in 6Be with the 4He(3He,n) reaction

The ⁴He(³He, n)⁶Be reaction has been investigated at 36.20 MeV bombarding energy in search for a narrow resonance near the ³He-³He threshold which has been proposed as a possible explanation for the missing solar neutrinos in Davis' experiment. Neutrons have been detected at θ_b = 0° with an effective resolution < 25 keV in the c.m. system, in coincidence with protons emitted at θ_p = 50°. No indication for the existence of such a resonance has been found and an upper limit (dσ/dω)_res ≦ 7.5 μb/sr has been established.     

The 12C(18O, α)26Mg and 12C(18O, 8Be)22Ne reaction

Excitation functions for α-emission leading to the ground and first excited states of ²⁶Mg and ⁸Be emission leading to the ground and first and second excited states of ²²Ne have been measured at several forward angles for E_c.m. = 15 to 22.4 MeV. There is little evidence for correlated structure. The angular distribution at 16.5 MeV for the α + ²⁶Mg(g.s.) channel is rather structureless while that for the ⁸Be+²²Ne(g.s.) channel appears to be dominated by a J = 13 contribution. Statistical model calculations indicate that much of the yield for both the α and ⁸Be exit channel is compound nuclear in origin, with some indication of a larger direct contribution for the ⁸Be channel at the lower end of the bombarding energy range.     

Electron scattemng studies of 184W and 186W

Anomalous results obtained in recent electron-nucleus scattering experiments suggest that a dispersion correction may contribute significantly to elastic cross sections in the region of the first diffraction minimum. Such a dispersion correction describes the effect of possible virtual nuclear excitations neglected in the conventional phase-shift analyses of electron scattering data. To investigate these effects, the Yale University electron accelerator has been used to study the scattering from ¹⁸⁴W and ¹⁸⁶W at incident energies between 40 and 65 MeV and scattering angles between 70° and 150°. No evidence of a dispersion effect is seen in the nucleus ¹⁸⁶W. In the case of ¹⁸⁴W, a comparison of the measured cross sections with those expected on the basis of the results of muonic X-ray experiments indicates that any dispersive effect is limited to less than 10% in the region of the first diffraction minimum. A summary of the results of this laboratory's search for dispersion effects in Nd, Sm, and W is appended.     

Atomic antiproton states in 16O, 18O, 32S, 40Ca, 44Ca and 122Sn

Atomic levels for the systems p? plus ¹⁶O, ¹⁸O, ³²S, ⁴⁰Ca, ⁴⁴Ca and ¹²²Sn are calculated in optical potentials based on the N?N interaction of Dover and Richard.     

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.     

15N excitation contribution to 48Ca(16O, 15N)49Sc reaction

The effect of ¹⁵N excitation process is studied in the reaction ⁴⁸Ca(¹⁶O, ¹⁵N)⁴⁹Sc. The excitation process is included into a generalized non-local optical potential for a scattersing ¹⁵N-⁴⁹Sc and is found to be responsible for a shift of a grazing peak in the exact finite-range DWBA calculation.     

12C1 and 8Be production in 12C + 208Pb collisions

The mechanisms involved in the production of fast α-particles in ¹²C-induced reactions have been studied for the ¹²C + ²⁰⁸Pb system at the bombarding energies of E_12c = 132, 187 and 230 MeV. Absolute cross sections for the reactions ²⁰⁸Pb(¹²C. ¹²C¹→α + ⁸Be), ²⁰⁸Pb(¹²C, ⁸Be(g.s.)) and ²⁰⁸Pb(¹²C, ⁸Be(2.94 MeV)) have been determined by coincidence measurement of two or three correlated α-particles. Inclusive α-particle production cross sections were also measured at E_12c = 187 MeV. It is found that the inelastic process (¹²C, ¹²C¹→α + ⁸Be) does not contribute significantly to fast α-particle production but that the production of ⁸Be by projectile fragmentation is an important source of α-particles. At the highest bombarding energy (230 MeV) it appears that the ¹²C → 3α fragmentation reaction becomes more prominent at the expense of the ¹²C→α + ⁸Be fragmentation channel.     

Spin assignments from the 142Nd(7Li, 6He)143Pm and 144Sm(7Li, 6He)145Eu reactions at 52 MeV

Angular distributions have been measured for transitions to low-lying states in ¹⁴³Pm and ¹⁴⁵Eu populated by the ¹⁴²Nd(⁷Li, ⁶He)¹⁴³ and the ¹⁴⁴Sm(⁷Li, ⁶He)¹⁴⁵Eu reactions at $\text{E(}{}^7\text{Li}\text{) = 52}$ MeV. Elastic scattering of ⁷Li at 52 MeV on ¹⁴²Nd and ¹⁴⁴Sm, and ⁶Li at 46 MeV on ¹⁴²Nd and at 45 MeV on ¹⁴⁴Sm, were measured. Optical-model parameters extracted from fits to the scattering data were used in a finite-range DWBA analysis of the angular distributions for levels below 1.40 MeV excitation energy in ¹⁴³Pm and 1.84 MeV in ¹⁴⁵Eu. The reaction cross sections forward of 6° c.m. allow unambiguous distinction to be made between 2d_{$\text{5}\text{2}$} and 2d_{$\text{3}\text{2}$} final states. Final-state spins have been assigned to d-states in ¹⁴³Pm at 1.40 MeV($\text{3}\text{2}$⁺)and in ¹⁴⁵Eu at 1.042 MeV ($\text{3}\text{2}$⁺). Existing assignments to other levels in both residual nuclei have been confirmed.     

Investigation of pairing vibration states in 88Sr and 90Zr via the (d, 6Li) reaction and search for α-vibration states

With a 45 MeV deuteron beam the ⁹⁴Mo(d, ⁶Li)⁹⁰Zr and ⁹²Zr(d, ⁶Li)⁸⁸Sr reactions have been studied to search for α-vibration states in ⁹⁰Zr and in ⁸⁸Sr. No evidence is found for such a state in both nuclei with a strength > 5 % than that of the ground state. Strongly excited 0⁺ states in ⁸⁸Sr and ⁹⁰Zr are those also seen in two-nucleon stripping and pickup reactions.     

The α-transfer reactions 27Al(6Li,d)31P, 29Si(6Li,d)33S and 31P(6Li,d)35Cl at 36 MeV

The α-transfer reactions ²⁷Al(⁶Li, d)³¹P, ²⁹Si(⁶Li, d)³³S and ³¹P(⁶Li, d)³⁵Cl have been studied at a ⁶Li energy of 36 MeV. Absolute cross sections and angular distributions have been measured and an exact finite-range distorted-wave Born approximation analysis assuming a direct cluster transfer has been used to extract from the data α-particle spectroscopic strengths for levels populated in ³¹P, ³³S and ³⁵Cl in the three reactions respectively. The results show that in the case of most of the low-lying excited states of ³¹P, a single value of L of the transferred α-particle contributes, though a multiplicity of L-values are allowed by angular momentum selection rules. It is also found that the α-particle spectroscopic strength of the ground state of ³¹P is a factor of 2 more than the strengths of the ground states of ³³S and ³⁵Cl. The α-spectroscopic strengths of ground states of these, as well as other odd-A s-d shell nuclei, are compared with the presently available shell model calculations.     

Energy levels of 94Ru observed with the 96Ru(p,t) reaction

The level structure of the neutron-magic nucleus ⁹⁴Ru, up to an excitation energy of 4 MeV, has been studied by means of the (p, t) reaction. Particular emphasis was placed on a search for excited 0⁺ levels, none of which have been reported previously. Among new levels observed in this study are 0⁺ levels at 2.995, 3.615 and 3.770 MeV, and the 3^? octupole vibration at 2.965 MeV.     

12C(7Li,t)16O和20Ne(d,6Li)16O反应的研究

本文把用于处理重离子引起的单粒子转移反应的Goldfarb-Buttle方法推广到多粒子转移反应。计算了¹²C(⁷Li,t)¹⁶O和²⁰Ne(d,⁶Li)¹⁶O反应,用了¹⁶O的全相干波函数,考虑了某些反冲因素,并将结果与实验作了比较。     

Scattering and reactions of 14C + 14C and 14C + 14C

We have studied elastic scattering, inelastic scattering and several transfer channels of the systems ¹⁴C + ¹⁴C and ¹⁴C + ¹²C over a wide range of energies up to E_c.m. = 35 eMeV and 32 MeV, respectively. The reaction channels were identified by means of kinematic coincidences between solid-state detectors, γγ coincidences were measured to determine cross sections for mutual inelastic scattering of ¹⁴C + ¹⁴C.Pronounced regular gross structures, similar to those found for ¹⁶O + ¹⁶O, are observed in the elastic excitation function of ¹⁴C + ¹⁴C at θ_c.m. = 90°, The angular distributions measured at the energies of the maxima and an optical-model analysis suggest that one or a few surface partial waves dominate the scattering behaviour. Correlated structure of narrower width is found in the inelastic channels and, to a lesser degree, in the transfer channels which appear with rather small cross sections.In ¹⁴C + ¹²C elastic scattering the gross structures are strongly fragmented, in contrast to ¹⁴C + ¹⁴C but similar to ¹²C + ¹²C. While the ¹²C(2⁺) excitation is very weak, the observed strengths of the ¹⁴C(3^?) excitation and of neutron transfer point to a substantial role of these channels as coupling partners to the elastic configuration and to their influence on the elastic scattering behaviour. A correlated intermediate structure is observed near 23.5 MeV, where a dominance of l = 18 is suggested by the elastic scattering angular distribution. This unexpectedly high l-value exceeds l_graz at this energy by at least two units of ?.     

Analyzing powers of the continuum spectra: 65 MeV polarized protons on 12C, 28Si, 45Sc, 58Ni, 93Nb, 165Ho, 166Er and 209Bi

Analyzing powers of the continuum spectra were measured for 65 MeV protons from ¹²C, ²⁸Si, ⁴⁵Sc, ⁵⁸Ni, ⁹³Nb, ¹⁶⁵Ho, ¹⁶⁶Er, ${}^{209}\text{Bi}\text{(}\text{p}\text{,}\text{p\#}\text{prime;}\text{X}\text{)}$ and ($\text{p}$, dX) reactions and from ⁹³Nb, ²⁰⁹Bi($\text{p}$, αX) reactions. The analyzing powers of the continuum spectra were found to be small at forward angles where the pre-equilibrium process is important. However they do not show a systematic tendency. This feature indicates the importance of the spin-dependent interaction as well as nuclear structure effects. On the other hand, the analyzing powers were very large and positive at backward angles where the shape of the energy spectra resembles that of an evaporation spectrum. The maximum values of the analyzing power in the backward hemisphere depend on the target mass for the A < 45 mass region and they are as large as 15%, 20% and 35% for ${}^{93}\text{Nb}\text{(}\text{p}\text{,}\text{p}\text{′}\text{X}\text{)}$, ($\text{p}$, dX), ($\text{p}$, αX) reactions at E_X = 20 MeV, respectively. These large values are mainly due to the entrance channel effect. There is no appreciable even-odd mass effect on the analyzing power for medium-mass nuclei. These features were unexpected from the conventional pre-equilibrium reaction models.     

Beta decays of 25Na, 25Al and 29Al

The radioactivities ²⁵Na, ²⁵Al, and ²⁹Al were produced in the ²³Na(t, p)²⁵Na, ²⁴Mg(d, n)²⁵Al, and ²⁷Al(t, p)²⁹Al reactions using a 3.5 MV Van de Graaff. γ-radiations were measured by means of a target-transfer system and a Ge(Li) detector with or without Compton suppression. Decay schemes derived for ²⁵Na and ²⁹Al are in general agreement with earlier results, but with improved accuracy of branching ratios and much sharper limits on the intensities of certain unobserved β- and γ-ray transitions. Precision measurements of the energies of principal γ-rays gave results in keV for the listed decaying bodies as follows: ²⁵Na ? 1611.716(11); ²⁵Al ? 1611.708(11); and ²⁹Al ? 1273.361(9). The energy determinations of the ²⁵Mg 1612 keV γ-transition measured in the decays of ²⁵Na and ²⁵Al differ by 8 ± 9 eV.     

A study of the 26Mg(12C, 12B)26Al charge-exchange reaction

The reaction ²⁶Mg(¹²C, ¹²B)²⁶A1(5⁺, 3⁺) has been studied using a beam of 102 MeV of ¹²C. Shell-model, microscopic direct model and finite-range coupled reaction channel (CRC) calculations including recoil effects, have been performed, for comparison with the experimental data. DWBA calculations were performed for the intermediate states of interest in the ¹¹B + ²⁷Al and in the ¹³C + ²⁵Mg channels and these results were also compared with the experimental ones. The dominant reaction mechanism for ²⁶Mg(¹²C, ¹²B)²⁶Al(5⁺, 3⁺) appears to be the sequential mode.