E.R. Flynn

The (t, p) reaction to the low-lying levels of the zirconium isotopes

Abstract The (t, p) reaction on the isotopes 90,92,94,96 Zr has been carried out at a bombarding energy of 20 MeV. Only weakly excited O + states are observed in 92 Zr and 94 Zr while the first excited O + state in 96 Zr is strongly excited. No O + states are seen in 98 Zr. The results indicate a trend for ground state excitations intermediate between simple shell model and pairing vibration theory. The low-lying levels of 92 Zr and 94 Zr are described by detailed shell model calculations. There is no indication in these nuclei of the rapid onset of deformation previously reported in 100 Zr, nor is there any evidence for an excited rotational band structure in any of the zirconium nuclei studied.

A Q3D spectrometer with a helix detector system

Abstract A spectrometer of the Q3D type with a 50% energy range has recently gone into operation at the Los Alamos Scientific Laboratory. Initial operation of the spectrometer indicated a resolution ( E / ΔE ) of 3200 at 14 msr is obtainable. Kinematic corrections are easily performed for reaction such as 27 Al(t,t) 27 Al. The focal plane detector system is a 50 cm long helix detector with 0.5 mm spatial resolution. This detector also is used to give particle identification information as the anode signal is proportional to the particle energy loss. A scintillator is used behind the helix for a measurement of total energy. A computer program permits the setting of particle gates using a 3-dimensional display of position versus energy loss in the counter as well as an additional restriction on the energy signal.

The 206Pb(t, p)208Pb and 210Pb(p, t)208Pb reactions at 20 MeV

Abstract The 206Pb(t, p)208Pb and 210Pb(p, t)208Pb reactions have been studied at 20 MeV up to an excitation of 6.75 MeV in the (p, t) reaction and up to 8.5 MeV in the (t, p) reaction. Angular distributions of 10°-80° are observed in both reactions. The spin and parity of about thirty states have been tentatively identified from their angular distribution patterns and by comparison of the cross sections measured in the (p, t), (t, p), (p, p′), and (d, p) reactions. Pairing-vibrational states (0+) and 2+) are identified and the presence of a proton pairing vibrational state (0+) at 5.24 MeV is suggested by the data. Two-neutron transfer DWBA cross sections were calculated for about 50 states using one-particle, one-hole wavefunctions calculated by Kuo. These wavefunctions were characterized by having appreciable parentage in the valence neutron particle (hole) configurations of 210Pb(206Pb). Tentative identification with observed states allows a quantitative comparison. The strongly populated pairing-vibrational states are compared with DWBA calculations using the valence neutron wavefunctions of True and Ford, and Redlich for 206 Pb and 210Pb. Discrepancies are discussed in terms of mixing with the analogs of higher lying 2+ states in 210Pb and in terms of the two-particle, two-hole wavefunctions.

A study of the neutron-rich isotopes near A = 100 by means of the (t, p) reaction

Abstract The (t, p) reaction has been used to study the nuclides 102 Mo, 106 Ru and 112 Pd, all of which are two neutrons beyond the stable isotopes. A (t, p) spectrum of the 102 Ru(t, p) 104 Ru process was also obtained. The incident triton energy was 15 MeV in all cases and a magnetic spectrograph was used for momentum analysis of the reaction protons with an energy resolution of ≈ 20 keV FWHM resulting. Differential cross sections were measured for many transitions and spin and parity assignments have been made for a number of states. Examination of the results indicates that only 102 Mo shows characteristics of being a transitional nucleus between regions of different nuclear shape whereas the other nuclei studied appear to be in regions where the coupling scheme changes more slowly. The first 2 + state of 102 Mo is markedly lower in excitation energy than in the lighter isotopes and a low-lying 0 + state is excited with large intensity relative to the ground state. The present results agree with previous results from the Berkeley group on the decay of fission fragments and in a qualitative way support several recent theoretical predictions.

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.

Shape transition between N = 40 and 42 in the Ga and Ge isotopes

Abstract A comparison of (p, t) and (t, p) reactions on Ge isotopes indicates a shape transition around N = 41. A similar transition explains the strong L = 0 population of excited states in the 40 71 Ga(t, p) 42 73 Ga reaction.

Search for (t, p) transitions to excited 0+ states in the actinide region

Abstract The (t,p) reactions from 230,232 Th and 234,236,238 U were studied at 15–20 MeV bombarding energy. The known excited 0 + states in 232 Th, 236,238 U were not observed nor was any excited 0 + strength located in 234 Th or 234 U. The previously reported strong L = 0 (p,t) transitions in this region as well as the weak L = 0 (t,p) strengths reported here constitute a strong indication of the existence of quadrupole pairing correlations in deformed superfluid nuclei.

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.

Energy levels in even actinide isotopes from (t, p) reactions

Abstract Energy levels in 232, 234 Th, 236, 238, 240 U and in 250 Cm have been measured using the (t, p) reaction. Angular distributions were obtained for the 234, 238 U targets and evidence for second order effects in the direct reaction mechanism was found.

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.