Nelson Stein

Application of the helical cathode proportional chamber to magnetic spectrographs for nuclear reaction studies

Abstract A proportional chamber with a single wire helical cathode has been employed in the focal plane of a magnetic spectrograph for nuclear reaction studies. The spatial resolution attributable to the detector is less than 0.33 mm fwhm over its 25 cm length with particles incident at an angle of 37° to the plane of the detector. The resolution achieved with a collimated 55Fe X-ray source at normal incidence was 0.25 mm. Rates of 105 counts/s are possible before degradation of the peak shapes is observed. The d E d x resolution is 27% for protons, deuterons and tritons in the energy range of 10–16 MeV. The counter has been used with an on-line computer program to measure the 27Al(d,p)28Al and 59Co(t,d)60Co differential cross sections.

A study of 64Cu, 66Cu, 68Cu and 70Cu by (t, 3He) reactions

Abstract Levels in 64,66,68,70 Cu that are populated in the 64,66,68,70 Zn (t, 3 He) reactions at 24 MeV triton energy have been studied. Mass excesses for the lowest states observed in 68 Cu and 70 Cu are found to be −65576±20 keV and −62982±20 keV, respectively. A multiplet of states, populated with large intensities, is observed to move systematically towards decreasing excitation energy as the neutron number approaches 40. It is concluded that this multiplet has a π p 3 2 ν g 9 2 configuration.

High resolution study of the reactions 54, 56, 58Fe(16O, 12C)58, 60, 62Ni and a comparison with (6Li, d) α-transfer spectroscopy

Abstract Spectra and angular distributions for the reactions 54, 56, 58 Fe( 16 O, 12 C) 58, 60, 62 Ni ( E x = 0.0–4.5 MeV) have been measured at 50 MeV with an energy resolution of 45–80 keV using a Q3D spectrograph. The selectivity of the ( 16 O, 12 C) reaction is found to be very similar to the ( 6 Li, d) reaction. The close correspondence recently noted between the ( 6 Li, d) spectra and levels strongly excited in (t, p) and ( 3 He, n) two-nucleon transfer reactions is also observed to be present for the ( 16 O, 12 C) reaction. Relative α spectroscopic factors for ( 16 O, 12 C) and ( 6 Li, d) obtained in a DWBA analysis assuming direct one-step α-cluster transfer are in very good quantitative agreement. Unnatural parity states, whose excitation is forbidden in the DWBA α-cluster approximation, are observed to be very weakly populated. These results, together with previous work on s-d shell and Ni targets, strongly suggest that the spectroscopic information provided by the ( 16 O, 12 C) and ( 6 Li, d) reactions is essentially the same and that this information may be reliably extracted by DWBA analysis.

The 209Pb single-neutron states and the l = 4 levels of 205Pb studied by the (d, p) reaction

Abstract Differential cross sections and vector and tensor analyzing powers have been measured for the ( d ,p) reaction to the single-particle states of 209Pb with spins ranging from 1 2 to 15 2 . Distorted-wave calculations are compared to all of these results and reasonable agreement is obtained with the cross sections and vector analyzing powers but not the tensor analyzing powers. The d and g vector analyzing powers for the spin-orbit partners are found to have opposite signs and this fact is used to assign g 9 2 spin to three l = 4 states seen near 2.6 MeV in 2205Pb.

Multipole pairing states and the correspondence between two- and four-particle transfer reactions

Abstract Data for the 58,60 Ni( 6 Li, d) 62,64 Zn reactions, together with an analysis in terms of a simple multipole pairing model, indic that two-phonon states are extremely weakly excited. This result arises from the dominance of monopole pairing correlations in four-particle transfer reactions and explains the observed correspondence between two- and four-particle transfer reactions populating the same final nucleus.

12Be levels studied with the 14C(14C, 12Be)16O reaction

Abstract The 14 C( 14 C, 12 Be) 16 O reaction has been measured at 60 MeV incident energy to study the 12 Be nucleus. The previously reported 0 + ground state and 2 + , 2.09 MeV first excited state are confirmed, and a third state at 2.68 MeV is unambiguously assigned to 12 Be. Angular distributions for the three states are presented, and the ground state excitation function is reported between 50 and 63 MeV.

Resonances in 36Ar via the 24Mg(12C, α)32S reaction☆

Abstract Measurements of the 24Mg(12C, α)32S reaction at θlab = 5° between Elab = 27.5 and 35.5 MeV show resonance structure in the excitation functions for the ground and first excited states. Ground state angular distributions at five incident energies can be fit by P2J (cos θ) functions with J-values ranging from 10 to 14, which are consistent with the entrance channel grazing angular momenta. The data are discussed within the contexts of (1) Ericson fluctuations and (2) a rotational-like band of resonances.

The 88Sr(t, p)90Sr reaction at 20 MeV and the systematics of pairing excitations near N = 50

Abstract The 88 Sr(t, p) 90 Sr reaction has been studied at 20 MeV incident energy. Forty-seven levels were observed up to 5.6 MeV excitation with angular distributions measured between 12° and 55° lab angle. A DWBA analysis is used to extract L -values, and a number of new spin-parity assignments are made. The low-lying levels are discussed in terms of pairing multipole excitations. The data are compared with previous (t, p) work on other targets involving N = 50 → 52 neutron transfer. Similarities with 89 Y(t, p) and differences from 90 Zr(t, p) are noted. A discussion of the systematics of pairing vibrations in the region of N = 50 is presented.

Elastic scattering of 28Si on 24Mg and 26Mg

Abstract Backward-angle excitation functions and angular distributions measured in 28 Si + 24 Mg elastic scattering show structure of intermediate width. The nature of this structure is investigated. Complementary data for 28 Si + 26 Mg display a smooth backward-angle excitation function.

The 58Fe(16O, 14C)60Ni reaction at 50 MeV

Abstract The two-proton transfer reaction 58 Fe( 16 O, 14 C) 60 Ni has been investigated at 50 MeV bombarding energy with a resolution of ≈ 65 keV. The 60 Ni states at 0 MeV (0 + ), 1.33 MeV (2 + ), 2.50 MeV (2 + ), 3.33 MeV (0 + ), 3.57 MeV, 3.66 MeV (4 + ) and 4.04 MeV (3 − ) were excited and two-proton strengths have been derived by a DWBA analysis of the measured cross sections. Good agreement with ( 3 He, n) data from the literature is obtained.