Angular distributions of the 2h(d, γ)4he reaction

Angular distributions of γ-rays from the ²H(d, γ)⁴He reaction have been measured at the deuteron energies E_d = 6.05, 8.96 and 11.67 MeV with a 12.7 cm × 15.2 cm NaI(Tl) crystal enclosed in a Cerenkov anticoincidence shield. A least-square fit of the angular distributions indicates that the differential cross section is proportional to sin²θ cos²θ and that the process proceeds through an E2 transition of the type ${}^1\text{D}{}_2\text{→}{}^1\text{S}{}_0$.     

Fusion near the threshold: A comparative study of the systems 40Ar + 112, 116, 122sn and 40Ar + 144, 148, 154Sm

Fusion excitation functions for the systems ⁴⁰Ar + ^{112, 116, 122}Sn and ⁴⁰Ar + ^{144, 148, 154}Sm have been determined, covering cross sections ranging from several hundred mb down to the μb level. The data show a pronounced correlation of the subbarrier behaviour with low-energy collective properties of the nuclei involved and are well reproduced by simplified coupled-channel calculations coupling fusion to inelastic channels. The possibilities of parameterizing the data in terms of a simple dynamic barrier-fluctuation phenomenon are discussed and result in the prediction of remarkably diffuse partial-wave distributions above the barrier. This is shown to be important for the analysis of deexcitation phenomena following fusion reactions.     

Nuclear reaction studies of 168Tm

The intrinsic structure of ¹⁶⁸Tm has been studied using the (³He, d) and (α, t) proton stripping reactions as well as the (d, t) and (³He, α) neutron pick-up reactions. The beams of 24 MeV ³He particles, 25 MeV α-particles and 12 MeV deuterons were obtained from the McMaster tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge-type magnetic spectrograph and detected with photographic emulsions. The spectra have been interpreted in terms of the coupling of an odd proton and an odd neutron, each moving independently in a spheroidal potential, which gives rise to intrinsic two-quasiparticle states with $\text{K = ¦Ω}{}_1\text{±Ω}{}_2\text{¦}$. The identification of the intrinsic states was made by comparing the experimental cross-section patterns with those predicted with the aid of Coriolis coupling and distorted-wave Born approximation (DWBA) calculations. Rotational bands superimposed on the K^π = 3⁺ and $\text{K}{}^{\mathrm{\pi }}\text{= 4}{}^{\mathrm{+}}\text{, {}\text{7}\text{2}{}^{\mathrm{+}}\text{[633]}{}_{\mathrm{n}}\text{±}\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{p}}\text{}}$ configurations, the first of which is the ground state, ha been observed in the spectra of all four reactions. New assignments have been made for configurations resulting from coupling the $\text{1}\text{2}$^? [541], $\text{7}\text{2}$⁺ [404], $\text{5}\text{4}$⁺ [402] and $\text{1}\text{2}$^? [530] p to the $\text{7}\text{2}$⁺ [633] neutron state. The neutron pick-up measurements confirmed the earlier assignments based on (d, t) reaction studies and suggested tentative assignments for the {$\text{1}\text{2}$⁺ [400]_n±$\text{1}\text{2}$⁺ [411]_p} and {$\text{3}\text{2}$⁺ [402]_n±$\text{1}\text{2}$⁺ [411]_p}     

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 ?.     

Energy dependence of the 24Mg(16O, 12C)28Si reaction

Excitation functions for the reaction ²⁴Mg(¹⁶O, ¹²C)²⁸Si(g.s., 2⁺₁) were measured at 5°(lab) in the energy range 32 < E_c.m. < 49 MeV. Although the resonant structure, previously observed at lower energies, becomes progressively weaker, three new correlated maxima have been observed near E_c.m. = 37.5, 40.2 and 43.5 MeV. Angular distribution measurements at these energies yield spin assignments, from P²_j(cos θ) comparisons, of 27, 29 and 31, respectively. Attempts to find a consistent optical-model fit to the elastic scattering in the entrance channel and an exact finite-range DWBA fit to the four-nucleon transfer reaction in this energy range were unsuccessful. Such a failure is to be expected if strong couplings between the elastic channel and inelastic channels of either the initial or final system are important. The features of the resonance phenomena in the transfer reaction are discussed within a band crossing model framework.     

High-spin structure in 169W and 170W

High-spin states in ^{169, 170}W have been populated in ${}^{154}\text{Gd}\text{(}{}^{20}\text{Ne}\text{, x}\text{n}\text{)}$ reactions. In-beam γ-ray spectroscopic techniques with multi-detector set-ups, multiplicity filters and an anti-Compton shield have been used. Levels up to about spin 30 (tentatively up to 36) in ¹⁷⁰W and up to $\text{57}\text{2}$ (tentatively up to $\text{61}\text{2}$) in ¹⁶⁹W have been identified. The data are interpreted within the framework of a pairing-selfconsistent cranking model. The nuclear shape evolution with increasing spin is studied theoretically within a configuration-controlled shell correction approach and also pairing effects are studied. The behaviour of the yrast states around 28⁺ in ¹⁷⁰W can be related in a model-dependent way to a reduction of the neutron-pairing correlations.     

Coupled-channel fusion and inelastic scattering calculations for 18O + 44Ca and 12C + 48Ti

Fusion and inelastic scattering coupled-channel calculations are carried out for the systems ¹⁸O + ⁴⁴Ca and ¹²C + ⁴⁸Ti. Comparison between ¹²C + ⁴⁸Ti and ³²S + ²⁴Mg sub-barrier fusion cross-section enhancement is made using simple analytical expressions. The distribution of the angular momentum absorbed by the compound nucleus is discussed in a quantum-mechanical coupled-channel model.     

Neutron-induced charged-particle reactions in 6Li and 9Be

Angular distributions of tritons from the ⁶Li(n, t)⁴He reaction were measured at E_n = 7.25, 6.77, 6.57, 5.24 and 4.71 MeV. Angular distributions of douterons from respectively, the ⁶Li(n, d)⁵He two-body breakup reaction were measured at E_n = 6.77 and 6.57 MeV, and of protons from the ⁶Li(n, p)⁶He reaction at E_n = 6.77, 5.24 and 4.71 MeV. All these reactions in ⁶Li were analyzed as direct interaction in the formalism of the distorted wave Born approximation. The optical model for the nuclear interaction was found to apply reasonably well to nuclei as light as ⁴He, ⁵He, ⁶He and ⁶Li. In addition, ⁶Li as an alpha-deuteron cluster gives the best bound-state wave function to describe the experimental angular distribution of tritons. The excitation functions at forward angles of the ⁶Li(n, t)⁴He, ⁶Li(n, d)⁵He and ⁶Li(n, p)⁶He reactions were measured for incident neutron energies between 4.4 and 7.3 MeV. It is found that the ⁶Li(n, d)⁵He two-body breakup reaction has a threshold at about E_n = 5.3 MeV. Angular distributions at E_n = 18.3 MeV for tritons and protons from the ⁹Be(n, t)⁷Li and ⁹Be(n, p)⁹Li, respectively, were also measured.     

Odd-even features in 3He + 3H scattering

The single-channel resonating-group method is used to study effects of the Pauli principle on ³He + ³H scattering. Comparison is made with previous similar calculations for d + ³He scattering, and it is found that the Pauli principle affects the s = 0 state of the ³He + ³H system rather similarly to the way it affects the s = 1 state, whereas the Pauli principle affects the $\text{s =}\text{3}\text{2}$ state of the d + ³He system quite differently from the way it affects the $\text{s =}\text{1}\text{2}$ state. Mention is made of the possibility of observing similar effects of the Pauli principle in other nuclear systems.     

The reaction 14C(3He,n)16O and the coexistence model of 16O

The reaction ¹⁴C(³He, n)¹⁶O has been measured at a ³He bombarding energy of 25.4 MeV. The zero-degree differential cross section for the excitation of the three low lying 0⁺T = 0 states, at energies 0.0, 6.05 and 12.05 MeV are, respectively, 1.33 ± 0.10, 0.49 ± 0.10, and 0.50 ± 0.10 mb/sr These measured cross sections are in rough agreement with single-step zero-range DWBA calculations using an empirically determined ¹⁴C ground state wave function and in which the Brown and Green coexistence-model wave functions are used to describe the ¹⁶O 0⁺ states. The angular distribution of the transition to the ground state is measured between 0° and 32°.     

Two-step processes in the 40Ca(α, 3He)41Ca reaction

The ⁴⁰Ca(α, ³He) reaction has been studied at 36 MeV incident energy. About fifty levels have been observed up to 7.1 MeV excitation energy and angular distributions were measured from 6–60° using a split-pole spectrometer. A local zero-range DWBA analysis has been carried out, and the deduced l-assignments and spectroscopic factors are compared with those obtained from previous neutron stripping experiments. Core-excited states in ⁴¹Ca with a [3^? ? f_7,2], [2⁺ ? f_7,2] and [5^? ? f_7,2] component previously observed in inelastic scattering experiments, are selectively excited by the (α, ³He) reaction. Their angular distributions are compared with coupled-reaction-channel calculations, assuming a pure two-step reaction mechanism. The agreement between theory and experiment may be considered as rather satisfactory for a number of levels. In particular the $\text{1}\text{2}{}^{\mathrm{+}}\text{and}\text{3}\text{2}{}^{\mathrm{+}}$ levels and the high-spin states with $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{?}}\text{,}\text{11}\text{2}{}^{\mathrm{+}}\text{,}\text{15}\text{2}{}^{\mathrm{+}}\text{and}\text{17}\text{2}{}^{\mathrm{+}}$ are successfully described within the framework of the weak-coupling model.     

A study of the 14C(6Li, 6He)14N reaction at 93 MeV

The reaction ¹⁴C(⁶Li, ⁶He)¹⁴N was investigated with 93 MeV ⁶Li ions in an angular interval of 7–26°. Angular distributions were analysed for the four most intense groups of ⁶He nuclei, corresponding to transitions to the ground (1₁⁺) and the excited (1₂⁺, 2₁^?, 4₁^?) states of ¹⁴N. In the theoretical analysis a mechanism of the spin-isospin excitation was suggested in the DWBA frame with the finite range of interaction and recoil in the light system (⁶Li⁶He) taken into account. In the calculations both shell-model wave functions and transition densities obtained in the theory of finite Fermi systems (FFS) were used. From the comparison between theory and experiment the Landau-Migdal force constant g′ is estimated in order to obtain some information on the degree of nuclear proximity to the threshold of pion condensation.     

Cross-section measurements and thermonuclear reaction rates for 46Ti(p, γ)47V, 47Ti(p, γ)48V, 47Ti(p,n)47V and 48Ti(p, γ)49V

The yield of γ-rays from the reaction ⁴⁶Ti(p, γ)⁴⁷V has been measured as a function of bombarding energy over the range 0.72–3.00 MeV, from ⁴⁷Ti(p, γ)⁴⁸V over the range 0.74–3.50 MeV, and from ⁴⁸Ti(p, γ)⁴⁹V over the range 0.72–4.40 MeV. The yields of γ-rays following (p, p') reactions on all three targets were also measured and (p, p') cross sections were deduced for the first excited state proton groups for ⁴⁶Ti and ⁴⁸Ti and for the first ten proton groups for ⁴⁷Ti. The yield of neutrons from the reaction ⁴⁷Ti(p, n)⁴⁷V has been measured over the range from threshold to 4.40 MeV. All these data are compared with statistical-model calculations, and good agreement is achieved. Thermonuclear reaction rates for the (p, γ) and (p, n) reactions are calculated for the temperature range 5 × 10⁸–10¹⁰ K which includes the range of temperatures of interest in nucleosysnthesis calculations.     

Proton-hole states in 115In observed in the 116Sn(d, 3He) reaction

The ¹¹⁶Sn(d, ³He)¹¹⁵In reaction has been investigated at E_d = 50 MeV. Thirteen transitions to states up to 3 MeV excitation energy were studied. The measured angular distributions were compared with DWBA calculations and transferred angular momenta and spectroscopic factors were deduced. Levels at 1.04, 2.23 and 2.52 MeV were found to be excited most likely by l = 3 angular momentum transfer in contrast to previous investigations at lower incident energies in which no l = 3 transitions have been observed.     

Investigation of states in 30P via the 30Si(3He,t)30P reaction at 30 MeV

The ³⁰Si(³⁰He, t)³⁰P reaction has been measured for about 100 levels in ³⁰P with E_x < 8.8 MeV. Little selectivity in the population of states has been observed. For 75 levels angular distributions have been analysed using a “fingerprint method” by determining the L-value from a comparison in shape with transitions to states with known J^π. For possible mixed L-transitions a dominance of the higher L-value is observed for almost all cases. Coulomb displacement energy calculations utilizing shell-model wave functions have been used to identify T = 1 states.     

The (3He,n) reaction on 16O and 18O

The (³He, n) reaction on ¹⁶O and ¹⁸O has been used to study low-spin states in ¹⁸Ne and ²⁰Ne up to E_x ≈ 8 and 20 MeV, respectively. The measured neutron angular distributions have been analysed using DWBA. By a comparison with shell-model calculations in the (s, d) shell it is found that most of the two-proton transfer strength can be explained within that shell. Important contributions, however, from the (f, p) shell in low-lying negative parity states are also present.     

194Pt(12C, 12C′) reaction and the triaxial-rotor model

Elastic and inelastic scattering differential cross sections for the ¹⁹⁴Pt(¹²C, ¹²C′) reaction at a bombarding energy of 78 MeV have been measured. Data have been obtained for 0⁺, 2⁺, 4⁺, and 2^+′, states in ¹⁹⁴Pt. The data have been analyzed using a rigid asymmetric-rotor model in coupled-channels reaction calculations. It is found that satisfactory fits to all data can be obtained but only if the hexadecapole deformation is included in the asymmetric-rotor model.     

Energy levels in 23Na from the 19F(α, n)22Na reaction

The 0° differential cross sections for the production of four neutron groups, populating the ground state and the four lowest excited states of the residual ²²Na nucleus were measured. For incident α-energies of up to 4.7 MeV more than sixty resonances, corresponding to levels in ²³Na were seen; most of them had not been reported previously. Angular distributions were measured at eight α-energies. The excitation curve for the ¹⁹F(α, P₁γ)²²Ne reaction was also obtained and eighteen additional levels were identified in ²³Na.     

Decay of the compound nucleus 74Kr formed in the reaction 16O + 58Ni

Gamma-ray and charged-particle emission has been studied after bombardment of ⁵⁸Ni with ¹⁶O at energies from 44.5–76.5 MeV. The excitation functions for various reaction channels have been measured. The locus in energy and spin of maximum cross section (the entry line) of the γ-emitting region in the 2pγ and 3pγ channels have been studied through measurement of γ-ray multiplicity, average particle energy and average γ-ray energy. The standard deviations in both energy and spin of the distributions of cross section are presented. Statistical model calculations including shell corrections in the level density show very satisfactory agreement with the experimental results. The moment of inertia at high spin and excitation energy is deduced from the measured entry line.     

States in 53Mn from the 52Cr(p, γ)53Mn reaction

Eight resonances have been observed in the ⁵²Cr(p, γ)⁵³Mn reaction between E_p = 0.90 and 1.03 MeV. Gamma-ray spectra have been accumulated at four of the resonances. Spin assignments have been made to the resonant states on the basis of the measured angular distributions of primary γ-rays. Excitation energies and γ-ray branching ratios have been determined for 36 levels between 2.0 and 5.6 MeV. Mean lives for nine of the states have been extracted by the Doppler shift attenuation method.