Transfer reactions induced by 17, 18O on 12, 13C at c.m. energies between 12.6 TO 14.0 MeV

Angular distributions for one-neutron and many-nucleon transfer reactions were measured in the systems ^{17, 18}O and ^{12, 13}C at c.m. energies between 12.6 to 14.0 MeV. All the cross sections were analyzed in terms of the full-recoil finite-range DWBA model. For multi-nucleon transfer processes an inert cluster transfer was assumed. The sensitivity of DWBA calculations to various parameter sets is discussed, and the effect of the no-recoil approximation on the phase and magnitude of the transfer amplitude is studied. For one-neutron transfer reactions the forward part of the angular distributions was reproduced reasonably well by the DWBA model, yielding satisfactory spectroscopic information. The rise of the cross section at the backward angles was not reproduced by the DWBA model. Possible contributions of cluster-exchange and compound-nucleus reactions are discussed. For multi-nucleon transfer reactions poorer fits were obtained, particularly in the ¹⁸O+¹²C system.     

Elastic and inelastic scattering of nucleons from 16O

Measurements of differential elastic and inelastic cross sections for neutron scattering from ¹⁶O at incident energies 18 to 26 MeV are presented. In addition to cross sections for neutron scattering differential cross sections for proton scattering up to 66 MeV are described in terms of phenomenological optical model potentials. At 24.5 MeV incident energy inelastic scattering up to 11.5 MeV excitation was measured. The elastic and inelastic compound nucleus contributions were examined. Direct inelastic scattering from the normal parity states was calculated using the DWBA and coupled-channel formalisms. The inelastic scattering cross section from non-normal parity state 2⁻ was calculated using the coupled-channel formalism via multi-step processes. Cross sections due to inelastic scattering from some of the states, which are thought to be members of an excited state rotational band were calculated using both vibrational and rotational approaches and were compared.     

High-resolution study of the 118Sn(d,p)119Sn reaction at 17 MeV

Energy levels in ¹¹⁹Sn up to 4.75 MeV excitation have been studied with the ¹¹⁸Sn(d, p)¹¹⁹Sn reaction at an incident deuteron energy of 17 MeV. The scattered particles were analysed by a magnetic spectrograph and detected in nuclear emulsions with a resolution of ≈ 9 keV. Seventyseven energy levels were identified. Angular distributions were compared to DWBA predictions allowing the identification of transferred angular momenta and the determination of spectroscopic factors for 49 states. The results obtained are compared with pairing theory and the weakcoupling model.     

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.     

A proton stripping study of92Nb

Levels up to energies of 4 MeV have been studied with the⁹¹Zr(³He,d)⁹²Nb reaction with an incident particle energy of 25.5 MeV. The product deuterons were analyzed by a split-pole spectrometer. Angular distributions were obtained for many of the transitions and compared with DWBA calculations. The assigned transferl values and spectroscopic factors were used to assign shell model structures to these levels.     

Study of the (d, α) reaction applied to 50Cr and 52Cr

The reactions ⁵⁰Cr(d, α)⁴⁸V and ⁵²Cr(d, α)⁵⁰V have been carried out at an incident deuteron energy of 15 MeV to investigate the structure of the low-lying levels of ⁴⁸V and ⁵⁰V in the light of shell model expectations. Excitation energies and angular distributions have been measured for states up to about 1.5 MeV. For all resolved and strongly excited levels angular momentum transfers could be assigned by comparison with DWBA calculations. For ⁵⁰V spectroscopic factors have been extracted in relative units assuming pure configurations for the transferred pair of nucleons. The results indicate the existence of seniority and configuration mixing in the level structure of the ⁴⁸V and ⁵⁰V isotopes. In both reactions some transitions show characteristic deviations from the direct reaction mechanism. These deviations cannot be reproduced by the DWBA 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.     

A study of the 11B(3He,p)13C reaction at 12, 10, 8, 6 and 4 MeV

Angular distributions for eight proton groups corresponding to states in ¹³C have been measured at incident ³He energies of 4, 6, 8, 10 and 12 MeV. These states are p₀(ground state), P₁(3.09), p₁(3.68), p₃(3.85), p₄(6.86), p₇(7.68), pio(9.50) and p₁₁ (9.90). The angular distributions have been fitted with DWBA analyses using a zero-range approximation. No radial cut-offs were used. In general the data are reasonably well fit at incident energies of 10 and 12 MeV.     

A study of the 91Zr(d,p)92Zr reaction using vector-polarized deuterons

Differential cross sections and vector analyzing powers were measured for the ⁹¹Zr($\text{d}$, d)⁹¹Zr and ⁹¹Zr($\text{d}$, p)⁹²Zr reactions at an incident deuteron energy of 12 MeV. Deuteron optical-model parameters were determined from an analysis of the elastic data. Comparison of the proton data to DWBA predictions showed that the DWBA does not quantitatively reproduce the measured analyzing powers, hence empirical analyzing power calibration curves were required to analyze the data. New spectroscopic information about the configurations of the excited states in ⁹²Zr has been determined and is compared to the results of previous experiments as well as a shell-model calculation. The results of this experiment are in quantitative agreement with the predictions of the shell-model calculation for most of the transitions although some discrepancies do exist.     

Exact finite-range DWBA description of the60Ni(160,12C)64Zn reaction at 60 MeV incident energy

Cross section angular distributions of⁶⁰Ni(¹⁶O,¹²C)⁶⁴Zn reactions leading to three strongly excited states at 60 MeV incident energy and the¹⁶O+⁶⁰Ni and¹²C+⁶⁴Zn elastic scattering at 60 MeV respectively 45 MeV and 54 MeV have been measured using aQ3D magnetic spectrograph. EFR-DWBA calculations assuming the transfer of anα-cluster in its 0s ground state are able to describe the general features of the strongly oscillating experimental angular distributions using a surface transparent optical model potential. The optical model parameters used in the DWBA calculations are obtained from fits of the elastic scattering data of incident and exit channels. The importance of “correct” optical model parameters in the exit channels for relative spectroscopic factors will be discussed and the extracted relative spectroscopic factors will be compared to previous (⁶Li,d) results.     

Study of the 90Zr(p,α)87Y reaction at 22 MeV

The (p,α) reaction on ⁹⁰Zr has been studied in a high resolution experiment at an incident proton energy of 22 MeV. The cross section and asymmetry angular distributions for transitions to 36 levels of ⁸⁷Y with an excitation energy up to 3 MeV have been measured. DWBA analyses of experimental angular distributions, using either Woods-Saxon or Double Folded potentials for the exit channel, have been done, allowing either the confirmation of previous spin and parity values or the assignment of new spin and parity to a large number of states. The structure of low lying states of ⁸⁷Y has been studied in the framework of the shell model, using the OXBASH code. With the interaction PMM90 reasonable agreement is obtained for part of the negative parity spectrum. Received: 17 November 1997     

A study of the 138Ba(d,p)139Ba reaction at 19 MeV

The ¹³⁸Ba(d,p) reaction has been studied at an incident deuteron energy of 19 MeV, using the injector-tandem accelerator and the multichannel magnetic spectrograph of the University of Oxford. Deuteron and proton optical model parameters have been obtained from the analysis of elastic scattering experiments on a ¹³⁸Ba target. The parameters have been used to calculate theoretical (d, p) angular distributions on the basis of the DWBA. From the comparison of experimental and theoretical distributions, orbital angular momentum transfers have been deduced and spectroscopic factors determined for all the levels observed up to an excitation energy of 2.5 MeV in ¹³⁹Ba. The spectroscopic information thus obtained is more complete than that from previous studies, and is in satisfactory agreement with expected sum rule limits. A notable item of new information is the assignment of an l_n = 6 transition to the level at 1.54 MeV in ¹³⁹Ba.     

The (p,d) reaction at 65 MeV

The (p, d) reaction on ¹²C, ¹⁴N, ¹⁶O, ⁴⁰Ca and ⁹⁰Zr has been studied with 65 MeV incident protons. DWBA calculations have been carried out to investigate the importance of finite range and non-locality effects. The experimental angular distributions for the strong transitions have been compared to DWBA calculations to study the effect of the deuteron optical potential. This comparison supports the use of the adiabatic deuteron potential which includes the effect of deuteron breakup.     

Study of 31P with the 29Si(3He,p)31P reaction

The ²⁹Si(³He, p)³¹P reaction has been investigated at a bombarding energy of 15.0 MeV. Excitation energies and angular distributions were measured for 28 levels below 7.2 MeV in excitation. L-values were extracted from DWBA fits to the data. Angular distributions for the low-lying states were compared with DWBA curves calculated from Nilsson-model wave functions.     

Alpha-cluster break-up and reaction mechanism in (p, α) reactions on light nuclei

The differential cross sections for the ¹¹B(p, α)⁸Be and ²³Na(p, α)²⁰Ne reactions were measured at bombarding energies between 6 and 24 MeV. The observed angular distributions can be divided into two domains: at low energies the shapes vary rapidly with incident energy indicating a compound nucleus reaction ; at higher energies rather stable diffraction patterns are seen exhibiting a direct reaction mechanism and DWBA calculations are able to describe the shapes. The change from one region to the other is rather abrupt and this behaviour seems typical for reactions having an α-like compound nucleus. The energy at which this change occurs corresponds to an excitation energy in the compound nucleus of about 20 MeV above the α-threshold.     

Elastic and inelastic scattering of 12C ions at intermediate energies

Elastic and inelastic scattering of ¹²C ions on ¹²C and ²⁰⁸Pb targets have been measured at the incident energies per nucleon E / A = 120 MeV/u and E / A = 200 MeV/u. Optical-model analysis is reported and nuclear surface transparency effects are discussed, together with the nuclear potential-energy dependence. The transparency region extends down to a radial internuclear distance of about 3 fm for the ¹²C-¹²C system and 8 fm for the ¹²C-²⁰⁸Pb system. A decrease of the imaginary potential with increasing incident energy is deduced for the two systems. Anomalous collapse of the real potential in the surface region is observed for ¹²C-²⁰⁸Pb system at 200 MeV/u. DWBA analysis of data on the 2⁺, 4.4 MeV state of ¹²C is reported and trends for the energy dependance of mean-field excitations are deduced.     

Spin-dependence and coherent summations in two-nucleon transfer reactions

The differential cross sections of the ¹⁹F(p, ³He)¹⁷O and ¹⁹F(p, t)¹⁷F reactions leading to the ground and first three excited states have been measured at an incident energy of 42.4 MeV. The polarization analysing powers of two of the (p, ³He) reactions have been measured at a higher energy of 49.5 MeV with a polarized incident beam. The experimental results have been analysed in terms of conventional DWBA theory, and the importance of interference terms arising from the proper coherent summations contained in the definition of the differential cross section and analysing power, have been investigated. It is found that the interference term arising from the coherent summation over the transferred spin S is significant and should not normally be neglected.     

Energy dependence of the 28Si(32S, 36Ar)24Mg reaction between 90 and 103 MeV incident energy

Angular distributions for the ²⁸Si(³²S, ³⁶Ar)²⁴Mg reaction have been measured from 90 to 103 MeV of incident lab energy, in steps of 0.5 MeV. The ground state, the 2₁⁺ level in each nucleus and the mutual excitation of both 2₁⁺ states have been resolved. The data have been analysed in the frame of finite range DWBA calculations. The deduced relative spectroscopic factors show good agreement with those predicted by the model of Chung and Wildenthal but are smaller than those deduced in other experiments.     

Heavy-ion inelastic scattering

The ²⁴Mg(¹⁶O, ¹⁶O'γ)²⁴Mg(2⁺) reaction has been investigated at 42 MeV incident energy. In-plane (¹⁶O, γ) angular correlations were measured for outgoing ¹⁶O ions between 6° and 40°. The results are compared with DWBA and coupled channels calculations.