J. W. Sunier

A fast timing light pulser for scintillation detectors

Abstract We report on the development of a compact, inexpensive and fast light pulser system designed to set up the timing of scintillators in a medium energy physics spectrometer.

Spectroscopy of proton hole states in the thallium nuclei with the (t, α) reaction☆

Abstract Proton hole states are observed in 203,205,207Tl isotopes using the ( t , α) reaction. The study was made with a beam of tritons with 75 % polarization and with the reaction α-particles being detected in a Q3D spectrometer by a helix detector system. The 206 Pb ( t , α) 207 Tl results serve as a template for the analyzing powers of the various transferred proton spins. Distorted wave calculations agree well with these results and are used to make Q and mass corrections. A number of spin assignments are made in 205Tl although the emphasis is on 203Tl where few spin assignments were previously available. The systematic trend of the proton hole energy centroids as a function of mass in the region Z = 82 is also presented.

12C(7Li, t)16O and stellar helium fusion

The reaction 12C(7Li, t)16O has been studied at E(7Li) = 34 MeV with the LASL tandem accelerator and QDDD magnetic spectrometer. Angular distributions to levels with Ex < 11 MeV have been obtained from 0° to 90°, including 0°. The results have been analyzed with finite-range distorted-wave Born approximation theory. The α-particle spectroscopic factors and reduced widths obtained are compared with those calculated with group theory (SU(3)) and other models. The analysis of data for the 7.1 and 9.6 MeV Jπ = 1− levels, which are of great importance in stellar helium buring, yields a ratio, R, of dimensionless reduced α-widths θ2a(7.1 MeV)θ2a(9.6 MeV) = 0.35b ± 0.13. The observed line width of the 9.6 MeV level (Γc.m. = 390 ± 60 keV) is less than the accepted value (Γc.m. = 510 ± 60 keV) and implies θ2a(9.6 MeV) ≈ 0.6. These results as well as data for the 6.92 MeV Jπ = 2+ and 10.35 MeV Jπ = 4+ “α-cluster” states indicate 0.09 < θ2a(7.1 MeV) < 0.33 with a mean value θ2a(7.1 MeV) = 0.14 ± 0.04. The implication for stellar helium burning is discussed.

Single-proton states in 151Pm

Abstract The 152 Sm ( t , α) 151 Pm reaction was studied using 17 MeV polarized tritons from the tandem Van de Graaff accelerator at the Los Alamos Scientific Laboratory. The α-particles were analyzed using a Q3D magnetic spectrometer and detected with a helical-cathode position-sensitive counter. The overall resolution was ∼ 18 keV FWHM. Measurements of the 150 Nd( 3 He, d) 151 Pm reaction were made using 24 MeV 3 He beams from the McMaster University tandem accelerator. The deuteron spectra were analyzed with a magnetic spectrograph using photographic emulsions for detectors, yielding a resolution of ∼ 13 keV FWHM. By comparing the measured angular distributions of ( t , α ) and ( 3 He, d) cross sections and ( t , α ) analyzing powers with DWBA predictions it was possible to assign spins and parities to many levels. The present results confirm earlier assignments of rotational bands based on the low-lying 5 2 + [413], 5 2 − [532], 3 2 + [411] and 1 2 + [420] orbitals. In addition, states at higher excitation have now been assigned to the 1 2 + [411] and 7 2 + [404] orbitals, and members of the 3 2 + [422], 5 2 + [402], 3 2 − [541] and 7 2 − [523] bands are tentatively proposed. The spectroscopic strengths can be explained reasonably well by the Nilsson model when pairing and Coriolis mixing effects are included.

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.

Two-particle transfer in O (6) nuclei

Abstract We present the first comparison between empirical two-neutron transfer strengths in Pt and Os nuclei and the predictions of the O (6) limiting symmetry of the interacting boson approximation model.

Two-quasiproton states in 168Er studied by the 169Tm(t, α)168Er reaction

Abstract The 169 Tm ( t , α) 168 Er reaction has been studied using 17 MeV polarized tritons from the Los Alamos National Laboratory tandem Van de Graaff accelerator. The α-spectra were analyzed with a Q3D magnetic spectrometer. The overall energy resolution was typically ~ 15 keV (FHWM) and angular distributions of cross sections and analyzing powers were obtained for levels up to ~ 2.7 MeV. The fact that spins and parities for all levels up to ⩾ 2 MeV were previously known from an extensive series of (n, γ) studies made it possible to determine specific two-quasiproton structures for many bands from the present results. The Kπ = 2+ γ-vibrational band was found to have a large 3 2 + [411] p + 1 2 + [411] p admixture, consistent with the predicted microscopic composition of this phonon, but no 5 2 [413] p − 1 2 + [411] p component was observed. The Kπ = 04+ band at 1833 keV has ∼ 25% of the 1 2 + [411] p − 1 2 + [411] p two-quasiproton strength. This is in excellent agreement with the Soloviev model but is inconsistent with the interacting boson model, in which the Kπ = 04+ band is composed almost completely of multiphonon configurations that should not be populated in a single-nucleon transfer reaction. The K π = 4 − , 7 2 − [523] p + 1 2 + [411] p two-quasiproton and the K π = 4 − , 7 2 + [633] n + 1 2 − [521] n two-quasineutron states are mixed strongly with each other, but the two Kπ = 3− bands composed of antiparallel couplings of the same particles are not. A good qualitative explanation of this mixing pattern is provided in terms of the effective neutron-proton interaction.

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.

Levels in 165Ho populated in the 166Er(t, α) reaction

Abstract The 166 Er ( t , α) 165 Ho reaction has been studied using 17 MeV tritons with a polarization of ≈ 0.81 from the Los Alamos tandem Van de Graaff accelerator facility. The reaction products were momentum analyzed with a Q3D magnetic spectrometer and detected with a helicalcathode positionsensitive proportional counter. The analyzing powers were large, and the ( t , α ) reaction was found to be a very powerful technique for spin determinations in this mass region. The data also made it possible to give Nilsson model assignments for some levels for which previous information was conflicting or incomplete.

136,138Ba(t, p) and the systematics of neutron pairing vibrations at N = 82

Abstract The 136,138 Ba(t, p) reaction has been studied at E t = 17 MeV. The neutron monopole and quadrupole pairing vibration states were located in 138 Ba at 3.612 MeV and 4.043 MeV, respectively. These results, when combined with previous observations in the Ce and Nd isotopes at the N = 82 closed shell, lead to a linear relationship between the two-neutron binding energies and the proton number. Predictions of locations of other pairing vibration states at the N = 82 shell are possible from these relations.