H. Fuchs

One-proton and two-proton stripping between 26Mg, 27Al and 28Si

Abstract The reactions 26 Mg(τ, n) 28 Si and 27 Al(d, n) 28 Si have been investigated with the time-of-flight method at 5.7 and 6 MeV bombarding energy, respectively. Deuterons and α-particles from the 26 Mg(τ, d) 27 Al and 26 Mg(τ, α) 25 Mg reactions at E τ = 11 MeV have been detected in a solid-state counter telescope. Angular distributions are extracted, and for the one-nucleon transfer reactions, analysed with DWBA to yield l -values and spectroscopic factors. These are compared to the results of previous measurements. Together with data from a previous 28 Si(n, d) 27 Al study, the transition strengths of the one-proton transfer reactions are compared to the predictions of the unified model both in strong and weak coupling. The 26 Mg(τ, d) 27 Al results are compatible with a strong coupling description for a deformation η = 2 of both nuclei. The (n, d) as well the (d, n) reaction between 27 Al and 28 Si contradict both versions of the unified model. Predictions from a TDA treatment of p-h states in 28 Si are also compared to the 27 Al(d, n) strengths. The 26 Mg(τ, n) 28 Si data indicate an appreciable amount of core excitation in the 28 Si ground state.

States in 12C and 16O investigated by the 11B(d, n) and 15N(d, n) reactions

Abstract Neutrons from the 6 MeV deuteron bombardment of 11 B and 15 N have been investigated by the time-of-flight method. Angular distributions of (d, n) transitions to nine states in 12 C up to 16.11 MeV and to five states in 16 O up to 8.88 MeV excitation energy are obtained and analysed with DWBA theory to yield l -values and spectroscopic factors. The results are reasonably well interpreted in the framework of the shell model by ascribing a predominant one-particle-one-hole component to most of the observed excited states. Prominent exceptions are the 0 + (7.66 MeV) state in 12 C and the 2 + (6.92 MeV) state in 16 O for which a more complicated structure is required.

Nuclear spectroscopy and study of pairing modes near N = 28 with the (τ, n) reaction

Abstract Energy spectra and angular distributions of neutrons from the (τ, n) reaction on 48,50 Ti, 50,52 Cr, and 54 Fe at 13 MeV bombarding energy have been measured with the time-of-flight technique. Altogether 65 new levels in the final nuclei have been observed. The DWBA analysis of the angular distributions yielded 56 new J π assignments, among them 26 levels with J π = 0 + and 27 levels with J π = 2 + The transitions to 0 + states have been compared with predictions of the shell model and the pairing model. The purely harmonic pairing vibration model gives correct predictions near 56 Ni, but the agreement becomes worse with increasing distance from A = 56. The inclusion of anharmonicity effects, however, leads to a good overall description of all data (energies of ground and excited states, transitions strengths).

Investigation of states in 40Ca by the 39K(d, n) reaction

Abstract Neutrons from the 6 MeV deuteron bombardment of 39 K have been investigated by the time-of-flight method; 30 angular distributions of (d, n) transitions to states in 40 Ca up to an excitation energy of 10 MeV are obtained. They have been analysed with DWBA to yield l -values and spectroscopic factors. The l = 1 character of 14 transitions to states above 7.9 MeV determines their parity to be negative. From comparison with 39 K(d, p) data, four levels above 9.4 MeV are proposed as possible analogues of 40 K states with dominant d 3 2 −1 p 3 2 configuration. The experimental transition strengths are compared to previous (τ, d) results and to predictions of the simple shell model. The main component of two shell-model particle-hole states is found in two other 40 Ca states than in previous investigations. At least 45% of the d 3 2 −1 p strength is moved away from the zero-order particle-hole states of the shell model. Theoretical spectroscopic factors were derived from the wave functions of Gerace and Green obtained by mixing spherical 1p-1h states with deformed 3p-3h states. Near to quantitative agreement with experiment is observed.

Study of the off-energy-shell n-15N total cross section by means of 15N(d, p) stripping into the continuum of 16N

Abstract The 15 N(d, p) reaction leading to unbound states of 16 N has been studied at E d = 12 MeV. The proton spectra display patterns very similar to the energy dependence of the corresponding n- 15 N total cross section, including interference phenomena between resonances and continuum. The variation of resonance intensity with momentum transfer in the (d, p) reaction probes the off-energy-shell behaviour of the neutron scattering amplitude. A simple approximation is discussed, in which the off-shell effect is attributed mainly to a momentum dependence expressed by penetration factors. This model is found to give a semiquantitative description of the differential cross sections of 15 N(d, p), and presents a new and sensitive method for the determination of resonance angular momenta l . Spectroscopic results for 16 N resonances are given.

Transfer reactions leading to states of 11C

Abstract The stripping reactions 10B(d, n)11C and 10B(τ, d)11C were studied at 5.8 and 11.0 MeV, respectively. The reaction 12C(τ, α.)11C was investigated at 9.5, 10.5, 11.5 MeV. The results are described by DWBA and spectroscopic factors are extracted, where possible. Comparison of the different reactions yields estimates of the inherent uncertainty of the procedure. While the (d, n) and (τ, d) reactions are largely direct and yield spectroscopic information, the 12C(τ, α) reaction exhibits interference of more complicated reaction mechanisms. The spins of 11C levels at 8.65 MeV and 8.69 MeV are determined to be 5 2 or 7 2 .

The (d, n) reactions on even argon isotopes

Abstract Neutrons from the 5.6 MeV deuteron bombardment of 36, 38, 40Ar have been investigated by the time-of-flight method. Altogether 23 angular distributions of (d, n) transitions to states in 37, 39, 41K were obtained and have been analysed with DWBA to yield l-values and spectroscopic factors. By comparison with 40Ar(d, p) data, levels at 8.38 and 8.87 MeV in 41K are proposed as the two lowest analogue states. Similarly, a level at 7.72 MeV in 39K is shown to contain the major fraction of the lowest 3 2 − analogue state. The experimental transition strengths are compared to predictions of the simple shell model, and deviations are discussed. The extended shell-model calculations of Glaudemans et al. and Wildenthal et al. yield qualitatively correct predictions for transitions to the lowest even-parity states in 37K and 39K.

The 60Ni(d,n) reaction above and below the Coulomb barrier and the deuteron optical-model potential

Abstract Neutrons from the deuteron bombardment of 60 Ni have been investigated with the time-of-flight method. Angular distributions have been obtained at 6 and 3.8 MeV bombarding energies. The differential cross sections at E d = 6 MeV are analysed with DWBA to yield l -values and spectroscopic factors. These are compared to previous measurements and to weak-coupling predictions. From the differential cross sections of the ground state transition, deuteron optical-model potentials have been evaluated for 6 and 3.8 MeV bombarding energies by means of a DWBA search procedure. It is shown that the (d,n) reaction allows a determination of the deuteron potential at subcoulombic energies, where the elastic scattering may not be used for this purpose.

Study of states in 25Al and 26Al by the 24Mg(d, n) and 25Mg(d, n) reactions

Abstract Neutrons from the 5.5 or 6 MeV deuteron bombardment of 24 Mg and 25 Mg, respectively, have been investigated by the time-of-flight method. Angular distributions of (d, n) transitions to eight states in 25 Al up to 3.08 MeV and to 38 states in 26 Al up to 6.1 MeV excitation energy are obtained. The stronger transitions, altogether 33, have been analysed with DWBA theory to yield l -values and spectroscopic factors. The observed l -values of the 25 Mg(d, n) transitions determine the spin of the 26 Al states at 2.66, 5.13 and 5.49 MeV to 2 or 3, their parity as positive and the parity of the levels at 4.699, 4.766 and 5.24 MeV also as positive. Negative-parity states appear at 5.39, 5.45 MeV, around 5.7 MeV and at 5.91 MeV. From comparison with 25 Mg(d, p) 26 Mg, isospin T = 1 is proposed for the levels at 5.13 and 5.24 MeV, and spins I = 2 and I = (2, 3), respectively. The experimental spectroscopic factors are compared to predictions of the Nilsson model for 25 Al and 26 Al. No substantial agreement is obtained for 26 Al, whereas the 25 Al results are compatible with the theory. A comparison of spectroscopic factors from the 25 Mg(d, n) 26 Al and the 25 Mg( 3 He, d) 26 Al reactions is included and discussed.

Study of 43Sc states with proton transfer reactions on 42Ca

Abstract The proton transfer reactions (d, n) and (τ, d) on 42Ca have been studied. The reaction 42Ca(d, n)43Sc has been studied by the time-of-flight method at deuteron energies between 5.0 and 6.05 MeV. The reaction 42Ca(τ, d)43Sc has been studied at 18.0 MeV with a magnetic spectrograph. Altogether 54 levels in 43Sc up to an excitation energy of 6.92 MeV have been identified including states at 4.234 and 6.145 MeV which are T = 3 2 analogues of the f 7 2 ground state and the 2.048 MeV p 3 2 state respectively in 43Ca. The l-values and spectroscopic strengths have been determined for 31 transitions. Within the errors of the experiments and the DWBA analyses, the spectroscopic strengths derived from the (d, n) and the (τ, d) experiments are in agreement for both T = 1 2 and T = 3 2 states, i.e. there are no T-dependent discrepancies. Similar agreement is found in the strengths of the s- and d-hole transitions which reflect the degree of particle-hole impurity in the 42Cag,s. wave function. A second 1 2 + state is indicated at 2.657 MeV. It appears a likely candidate for the head of a second K π = 1 2 + band of 6p-3h character as proposed by Johnstone.