A study of the photoneutron contribution to the giant dipole resonance in doubly even Mo isotopes

By using a variable monochromatic photon beam, the partial photoneutron cross sections σ(γ, n) + σ(γ, pn), σ(γ, 2n) and σ(γ, 3n) are determined in the region of the giant dipole resonance for the doubly even Mo isotopes ⁹²Mo, ⁹⁴Mo, ⁹⁶Mo, ⁹⁸Mo and ¹⁰⁰Mo. Measured integrated photoneutron cross sections are compared with available integrated photoproton cross sections as a function of A. Broadening of the giant dipole resonance as A increases is observed in good agreement with the predictions of the dynamic collective model. A tentative study of some isospin splitting effects is also carried out.     

Elastic and inelastic scattering of 79.5 MeV 11B and 87.5 MeV 10B ions

The elastic scattering of 79.5 MeV ¹¹B ions has been studied for seven targets ranging in mass from ²⁴Mg to ¹⁹⁷Au and of 87.5 MeV ¹⁰B ions for three of these targets (^{24, 25}Mg, ⁶⁰Ni). Angular distributions were measured from ~10° c.m. in steps of 0.5°, to angles beyond 40° c.m. where the elastic cross sections are ? 10^?3 of the Rutherford values (except for ¹⁹⁷Au). Inelastic data for exciting the lowest 2⁺ states of ^24,26Mg and ⁶⁰Ni were also obtained. Important odd-A-even-A differences are observed in the ¹¹B elastic angular distributions for the Mg and Al targets; for ¹⁰B scattering these are obscured by projectile quadrupole moment effects on the elastic scattering. The elastic data were analyzed using the optical model with potentials of both Woods-Saxon and double-folding form. The data for both ¹⁰B and ¹¹B are consistent with the potential obtained in the folding model with the M3Y interaction without renormalization. The inelastic data were analyzed by the distorted-waves method.     

Sub-coulomb energy 12C + 10, 11B and 14N + 10B fusion cross sections

Total fusion cross sections have been measured for the following reactions and energy intervals: ¹²C + ¹⁰B, E_c.m. = 2.10–5.38 MeV; ¹²C + ¹¹B, E_c.m. = 2.10–5.99 MeV; ¹⁴N + ¹⁰B, E_c.m. = 2.64–5.97 MeV. Absolute cross sections were extracted from the prompt γ-rays emitted by the various residual nuclei and measured by two large NaI detectors. No resonance structure was observed in the three reactions. The elastic scattering excitation function was also measured at θ_c.m. = 90.4° for ¹²C + ¹⁰B over the energy range E_c.m. = 3.18–6.82 MeV. Optical model potentials were found which could consistently describe both the fusion and elastic scattering data.     

The photoneutron production cross section in Be

The photoneutron production cross section in ⁹Be was measured with a synchrotron using energy sweeping. Neutrons were detected with a multi-BF₃-counter flat-response detection system. Under high resolution the cross section shows 23 maxima between 6 and 27 MeV which are caused predominantly by E1 transitions.     

A study of the photoneutron contribution to the giant dipole resonance of nuclei in the 64 ≦ A ≦ 86 mass region

The partial photoneutron cross sections [σ(γ, n) + σ(γ, pn)] and σ(γ, 2n) of ⁶⁴Zn, Ga, ^70,72,74,76Ge, ⁷⁵As and ^76,78,80,82Se were measured with a monochromatic photon beam and a high efficiency neutron detecting system in the photon-energy range 8 ≦ E ≦ 30 Me V. Integrated cross sections are discussed. The evolution of the GDR as observed through the neutron exit channel only, is tentatively interpreted either in terms of isospin splitting or in terms of the dynamic collective model.     

The 42Ca photoneutron cross section

The reaction ⁴²Ca(γ, n_t)⁴¹Ca has been measured from 10.5 MeV to 28 MeV using an enriched metal target and the yield curve technique. The resultant cross section shows gross structure which is shown to be consistent with predictions of isospin splitting of the giant dipole resonance.     

Cross sections for 6Li production in the reactions 10B + 16O and 12C + 14N at low energies

Absolute cross sections have been measured for the reactions ¹⁰B(¹⁶O, ⁶Li)²⁰Ne and ¹²C(¹⁴N, ⁶Li)²⁰Ne at several energies in the range E_c.m. = 7.5–16.2 MeV, and 13.8–16.6 MeV, respectively. The predictions of Hauser-Feshbach calculations show generally good agreement with the experimental data without parameter variation. The consequences of an angular momentum cutoff in the entrance channel and in the compound nucleus are discussed.     

Transfer reactions of B with Ta

Excitation functions and mean recoil ranges are reported for the formation of ¹⁸²Os, ¹⁸³Re, ¹⁸²Re, ¹⁸¹Re and ¹⁸²Ta in ^{10, 11}B interactions with ¹⁸¹Ta. The stacked foil technique was used. The results are indicative of formation through a transfer reaction. We have considered a nucleon group transfer mechanism in a surface interaction followed by de-excitation via nucleon emission from the excited intermediate. Thus the energy dependence of recoils and cross sections of single nucleon and multinucleon transfer products have been calculated and found in good agreement with experimental results.     

Folding model analysis of 10, 11B, 12C + 27Al, 39K and 40Ca

Elastic scattering angular distributions for ^{10, 11}B + ⁴⁰Ca at E_lab = 46.6 and 51.5 MeV and¹²C+³⁹K at E_lab = 54 and 63 MeV have been measured and compared with Woods-Saxon and double-folding optical models. The oscillatory structure observed previously for ¹²C + ⁴⁰Ca disappears when the projectile is changed to ^10,11B or the target is changed to ³⁹K. The angular distributions are adequately reproduced by a double-folding analysis, which employs the nucleon-nucleon potential of Bertsch et al., with a range of real normalizations N_R = 1.0–1.38. This same range of real normalizations was also able to describe previously measured ^10,11B, ¹²C + ²⁷A1 data. The double-folding analysis of ¹²C + ⁴⁰Ca scattering indicates that this system behaves differently from neighboring systems.     

Total reaction and transfer cross sections for 11B + 9Be and 13C + 9Be reactions at low energies

The total reaction cross sections for ¹¹B + ⁹Be and ¹³C + ⁹Be have been measured by the total γ-ray yield method over the energy intervals E_c.m. = 1.4–4.4 MeV and E_c.m. = 2.0–5.2 MeV, respectively. The cross sections for the neutron transfer reactions ¹¹B(⁹Be, ⁸Be)¹²B, leading to the ¹²B 0.953 and 1.674 MeV states, and ¹³C(⁹Be, ⁸Be)¹⁴C, leading to the ¹⁴C 6.094, 6.728 and 6.902 MeV states, have been obtained from the yields of the characteristic γ-rays. The α-transfer reaction ¹¹B(⁹Be, ⁵He)¹⁵N, leading to many unresolved ¹⁵N states, has been observed with large cross section. There is, however, no evidence for the ¹³C(⁹Be, ⁵He)¹⁷O transfer process in the ¹⁷O + nα channels. This different behaviour of the ¹¹B + ⁹Be and ¹³C + ⁹Be systems seems to indicate that the α-transfer reaction at sub-barrier energies is not a direct transfer process, and that it probably occurs via molecular state formation.     

The photoneutron cross section of 45Sc

The photoneutron cross section of ⁴⁵Sc has been measured from threshold to 25 MeV using bremsstrahlung and direct neutron detection. The cross section is found to exhibit a large width of approximately 8 MeV and this is interpreted in terms of the Danos hydrodynamic model for the giant resonance of deformed nuclei. The integrated cross section to 25 MeV is 158 ± 24 MeV mb.     

The photoneutron cross section of 6Li

The photoneutron cross section of ⁶Li has been measured from threshold to 17 MeV using bremsstrahlung from an electron synchrotron. Neutrons were detected by a high-efficiency multi-BF3-counter detection system. The cross section shows broad peaks at 12 MeV and 16 MeV with no other structure apparent.     

A study of N by means of the B(α, α)B reaction

The ¹¹B(α, α)¹¹B cross section has been measured as a function of energy and angle for bombarding energies from 4 to 8 MeV. Many resonances are observed. The data from 4 to 5 MeV were fitted using an R-matrix formalism with background phase shifts evolved from an optical-model potential. The three levels in ¹⁵N resulting from this analysis fit into the APCETS scheme for ¹⁵N.     

A study of three-nucleon transfer reactions on 18O

The reactions ¹⁸O¹¹B, ⁸Li)²¹Ne, ¹⁸O(¹²C, ⁹Be)²¹Ne and ¹⁸O(¹³C, ¹⁰B)²¹F have been studied, using beams of 115 MeV ¹¹B and ¹²C and 105 MeV ¹³C incident on a gas target. Shell-model calculations have been performed for ²¹Ne and ²¹F, for comparison with the experimental data. It is found that the data can be interpreted using the shell-model spectroscopic factors and a semiclassical reaction theory. Assignments are suggested for several previously unidentified high-spin states in ²¹Ne and ²¹F.     

A study of the C(p, p′) reactions at 135 MeV

A relativistic mean field approach is used to determine and compare the single-particle Dirac potentials for nuclei and hypernuclei (Λ, Σ, Ξ). A simple model is used and the Dirac-Hartree-Fock equations are reduced to a Schrödinger-like equation. The subsequent central and spin-orbit shell-model potentials are compared to those of phenomenological approach and other recent microscopic approaches. In the case of hypernuclei the Hartree approximation works already quite well without any need of taking into account the strangeness exchange part coming from strange mesons. The influence of the anomalous magnetic moment of the baryon on the spin-orbit term is found to be rather important for both Λ- and Σ-hyperons.     

The reactions 6, 7Li, 9Be, 10B(e,e′p) at 700 MeV and DWIA analysis

The proton spectral functions of ⁶Li, ⁷Li, ⁹Be and ¹⁰B obtained from the (e, e′p) reactions at 700 MeV are presented. The results were analyzed in the distorted-wave impulse approximation, using the shell-model single-particle wave functions consistent with the elastic electron scattering results. The observed Ip proton momentum distributions for the nuclei ⁶Li, ⁷Li and ⁹Be show significant disagreement with the shell-model momentum distributions. The occupation probabilities of the proton single-particle states are around 0.7, with a few exceptions.     

Recoil study of multinucleon transfer reactions: Capture of six charges by Nd targets in Ar induced reactions

Multinucleon transfer reactions induced with Ar ions and involving the capture of six charges by the target have been studied. The targets were all the separated isotopes of Nd, and the observed nuclei were ^149gTb, ¹⁵⁰Dy, ¹⁵¹Dy. The experimental technique involved the measurement of the cross sections, angular distributions, and recoil range at each recoil angle, of the heavy residual nuclei. After transformation of the data into the c.m. system, the angular distributions appear to be peaked backwards, close to 180°. This observation suggests that the present reactions are of the same type as the multinucleon transfer reactions studied by other authors for which the angular distribution of the light fragment was peaked forward in the c.m. system. The energy distributions in the c.m. system were used to check the feasibility of various mechanisms which could lead to the production of the observed isotopes. Each mechanism was supposed to be a two-step process: the first step was the exchange, from the projectile to the target, of a number n of nucléons, leading to an excited intermediate nucleus, and the second step the deexcitation of the intermediate nucleus by nuclear evaporation. This analysis indicates that the most probable mechanisms correspond to n close to 12 (6 protons and 6 neutrons), and to an excitation energy of about 60 MeV for the intermediate nucleus. The distribution of cross sections versus the number of nucléons gained by the target is also in accord with this reaction model.