Quasi-free Scattering Cross Sections Research Articles

Extended p_{3/2} Neutron Orbital and the N=32 Shell Closure in ^{52}Ca.

The one-neutron knockout from ^{52}Ca in inverse kinematics onto a proton target was performed at ∼230 MeV/nucleon combined with prompt γ spectroscopy. Exclusive quasifree scattering cross sections to bound states in ^{51}Ca and the momentum distributions corresponding to the removal of 1f_{7/2} and 2p_{3/2} neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N=32, found as strong as at N=28 and N=34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f_{7/2} and 2p_{3/2} orbitals of 0.61(23)fm, in agreement with the modified-shell-model prediction of 0.7fm suggesting that the large root-mean-square radius of the 2p_{3/2} orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.

Neutron-neutron quasifree scattering in neutron-deuteron breakup at 10 MeV

New measurements of the neutron-neutron quasifree scattering cross section in neutron-deuteron breakup at an incident neutron energy of 10.0 MeV are reported. The experiment setup was optimized to evaluate the technique for determining the integrated beam-target luminosity in neutron-neutron coincidence cross-section measurements in neutron-deuteron breakup. The measurements were carried out with a systematic uncertainty of $\pm 5.6 \%$. Our data are in agreement with theoretical calculations performed using the CD-Bonn nucleon-nucleon potential in the Faddeev formalism. The measured integrated cross section over the quasifree peak is $20.5 \pm 0.5 \text{(stat)} \pm 1.1 \text{(sys)}$ mb/sr$^2$ in comparison with the theory prediction of 20.1 mb/sr$^{2}$. These results validate our technique for determining the beam-target luminosity in neutron-deuteron breakup measurements.

Proposal for the Simultaneous Measurement of the Neutron–Neutron and Neutron–Proton Quasi-Free Scattering Cross Section via the Neutron–Deuteron Breakup Reaction at E n = 19 MeV

In order to confirm or refute the present discrepancy between data and calculation for the neutron–neutron quasi-free scattering cross section in the neutron–deuteron breakup reaction, we describe a new experimental approach currently being pursued at TUNL.

Level density of 2+states in40Ca from high-energy-resolution (p,p′) experiments

The level density of 2${}^{+}$ states in ${}^{40}$Ca has been extracted in the energy region of the isoscalar giant quadrupole resonance from a fluctuation analysis of high-energy-resolution ($p,{p}^{\ensuremath{'}}$) data taken at incident energies of 200 MeV at the K600 magnetic spectrometer of iThemba LABS, South Africa. Quasifree-scattering cross sections were calculated to estimate their role as a background contribution to the spectra and found to be small. The shape of the background was determined from the discrete wavelet transform of the spectra using a biorthogonal wavelet function normalized at the lowest particle separation threshold. The experimental results are compared to widely used phenomenological and microscopic models.

On the discrepancies in the low-energy neutron–deuteron breakup

In view of recent neutron–deuteron (nd) breakup data for neutron–neutron (nn) and neutron–proton (np) quasi-free-scattering (QFS) arrangements and the large discrepancy found between theoretical predictions and measured nn QFS cross sections, we analyze the sensitivity of the QFS cross sections to different partial wave components of the nucleon–nucleon (NN) interaction. We found that the QFS cross section is strongly dominated by the 1S0 and 3S1–3D1 contributions. Because the standard three-nucleon force (3NF) only weakly influences the QFS region, we conjecture that it must be the nn 1S0 force component which is responsible for the discrepancy in the nn QFS peak. A stronger 1S0 nn force is required to bring theory and data into agreement. Such an increased strength of the nn interaction will, however, not help to explain the nd breakup symmetric-space-star (SST) discrepancy. Further experimental cross-checkings are required.

Systematic measurement ofpdbreakup cross section at quasi-free scattering

Space Star (SS) anomaly in Nd breakup cross section is well known. SS anomaly has large charge asymmetry; experiment is larger than calculation at nd SS and experiment is smaller than calculation at pd SS. There are also reports on anomaly in quasi-free scattering (QFS) cross section in Nd breakup reaction. At nd QFS, experimental cross section was found to be larger than calculation. On the contrary, pd QFS cross section measured by Koln group is smaller than pd calculation. We measured QFS cross section in pd breakup reaction, and compared the data with recent pd calculations to see angular dependence of QFS anomaly.

Light charged particle and neutron production in proton- and α-particle-induced reactions on natSi at energies between 20 and 65 MeV

Inclusive cross sections ( d 2 σ d Ω d E , d σ d E , d σ d Ω and σ T ) for the production of neutron and light charged particles induced by protons of 26.5, 48.5 and 62.9 MeV and alpha-particles of 25.4, 45.5 and 57.8 MeV on natSi targets have been measured. The secondary particles ( p, d, t, 3He, α, 6Li, 7Li and 7Be) were detected at angles from 10° to 165° in steps of ±10° with respect to the beam axis. Neutrons emitted in these reactions were only recorded in coincidence with, at least, one detected light charged particle. A comparison of the proton- and neutron-induced reactions on Si at E = 62 MeV shows evidence of charge independence of the nuclear force. The proton spectra from the two reactions scale as expected from the difference in proton–neutron and proton–proton quasi-free scattering cross sections. The new data are reproduced with moving source fits and are also compared with state-of-the-art nuclear reaction models. The codes used for this purpose, GNASH and TALYS, consider direct nuclear reactions as well as pre-equilibrium and compound nucleus emission, and were found to reproduce the general features of the experimental data, especially for the ( p , p x ) channel. More detailed comparisons with the data indicate that there is still room for improvement in these codes.

Quasi-free scattering in the 3-N continuum

The interaction of a nucleon with the deuteron leading to break-up at the quasi-free scattering (QFS) condition is studied atE lab =12.0, 22.7, 68.0, and 140.0 MeV. Results of rigorous Faddeev calculations and of the impulse approximation (IA) are compared at these energies for bothn-p andp-p QFS in order to study the importance of rescattering terms. For the two-nucleon interaction the Paris potential is used. It is restricted to act in two-body states with total angular momentumj≤2. Also we compare the Faddeev calculations with experimental data for the QFS cross section and analyzing powerA y and find overall agreement. The behaviour of scattering observables turns out to be different forn-p andp-p QFS. Also the energy dependence of rescattering terms is different in the two cases. For all energies studied the IA is not reliable.

Study of the 2H(d, dp)n reaction in the energy range between 50 and 85 MeV

Proton-deuteron coincidence spectra from the 2H(d, dp)n reaction have been measured in the incident energy range from 50 to 85 MeV. Two angle pairs, namely ( θ d, θ p) = (25°, ≈ 44°) and (40°, ≈ 48°), were chosen corresponding to the quasi-free scattering (QFS) and final state interaction (FSI), respectively. The QFS coincidence spectra were projected onto the proton energy axis and compared with the theoretical predictions based on the modified simple impulse approximation (MSIA) using a sharp cut-off radius. Good agreement between experiment and theory was found for all measured spectra, with the cut-off radius decreasing with incident energy. The present results and those from the re-evaluation of the data underlying a previous publication do not support former indications for a “dip” in the QFS cross section at about 60 MeV incident energy. The shapes of the similarly projected FSI coincidence spectra compare well with the theoretical prediction based on the triplet enhancement factor alone.

Attenuation andp−pandp−nquasifree scattering in deuteron breakup

A new energy-dependent-core model for attenuation effects in quasifree scattering is used to explain the difference in quasifree scattering cross sections for the two kinematically equivalent modes of deuteron breakup under proton bombardment.

Quasifree scattering effects in 2H(p,pn)p and 2H(p, pp)nreactions

Recent kinematically complete 2H(p, pn)p and 2H(p, pp)n experiments have yielded the result that the p-n quasifree scattering cross section in the (p, pn) reaction is much larger than the corresponding p-p quasifree scattering cross section in the (p, pp) reaction. We show that as a consequence of the Pauli exclusion principle such a result is expected, but that a dynamical model is required to predict the ratio of the cross sections. Using a spin-dependent separable-potential Faddeev model, we obtain good quantitative agreement with the experimental results.