C. C. Foster

Gamow-Teller and spin-dipole strength in the 40,48Ca(p,n) reactions at 135 MeV

Abstract Spin-flip probabilities for 48Ca( p n )48Sc reveal that at 0° the apparent continuum under and adjacent to the Gamow-Teller giant resonance is also primarily 1+ strength. A comparison of 40Ca[ p n )40Sc and 48Ca( p n )48Sc shows no discernable signature of Gamow-Teller strength in the region −30 > Q(MeV) >−45. The spin-flip component of the dipole resonance for 40Ca is broader than the non-spin-flip component.

Resonance states in 22Mg for reaction rates in the rp-process

Abstract Motivated by the need of spectroscopic data to better understand the astrophysical rp-process, we developed a new experimental method using the Grand Raiden magnet spectrometer to study protin rich nuclei with α and 3 He induced reactions. First results of the 24 Mg( 4 He, 6 He) 22 Mg reaction at 206 MeV and 0° are presented, showing states relevant for resonant reaction rate calculations of the proton capture 21 Na(p,γ) 22 Mg and the 18 Ne(α,p) 21 Na reaction which controls the break-out of the hot CNO cycles at X-ray burst conditions.

A comparison of methods for determining neutron detector efficiencies at medium energies

Abstract We compare the “Lithium Activation” (LiA) method and the “Isospin Clebsch-Gordan Ratio” (ICGR) method for determining detection efficiencies of neutrons between 100 and 160 MeV. Each method was used to determine the efficiency by relating a measured neutron yield to a cross section measured in another way: γ-ray activation cross sections for LiA; (p, p′) cross sections from experiments at the Indiana University Cyclotron Facility for ICGR. Efficiencies determined by the two methods disagree substantially. Efficiencies calculated with the Monte Carlo code of Cecil et al. agree with the ICGR results. We conclude that the Lithium Activation method is inconsistent at these energies.

Possible observation of the 12+[880] orbital in 96249Cm

Abstract The position of the K 17 2 shell orbital plays a significant role in determining the shell correction energy and hence the stability of the superheavy elements. A deformed component of this orbital, 1 2 + [880] , comes down in energy with increasing prolate deformation, and is expected to have an excitation energy of less than 2 MeV in nuclei with N = 153. We have performed the reaction 248Cm(4He,3He) using 98.5-MeV alpha particles from the IUCF cyclotron to populate high-l states in 249Cm. this reaction preferentially excites high-l states because of the angular momentum mismatch. The emerging 3He ions were momentum analyzed with the K600 magnetic spectrometer. Spectra were measured at θcm = 4.1°, 6.1°, 10.2°, 12.2°, and 16.2° The spectrometer was calibrated with the 208Pb(4He,3He) and 232Th(4He,3He) reactions at the same incident energy. Three strong peaks were identified in the 248Cm(4He,3He) spectrum and these have been given tentative assignments: 593 keV, 15 2 11 2 − [725] ; 1560 keV and 1898 keV, 17 2 1 2 + [880] , 15 2 13 2 − [716] . Our data do not distinguish between the 17 2 + and 15 2 − assignments.

The spin-dipole resonance in (p, n) on 16O and 40Ca☆

Abstract The spin observable D NN ′ ( θ ) was measured for ( p , n ) at 135 MeV on 16 O, 40 Ca, 48 Ca, and 208 Pb. Data for 16 O and 40 Ca are compared with distorted-wave impulse approximation (DWIA) calculations with Tamm-Dancoff (TDA) wave functions; the D NN ′ data generally agree with the J π distribution (O − , 1 − , 2 − ) predicted for the “spin-dipole” resonance.

Level structure of the odd-odd nucleus 22489Ac

Abstract The level structure of the odd-odd nucleus 224Ac has been studied by measuring radiations associated with the α-decay of the 22 h 228Pa isotope. The 228Pa activity was produced by the irradiation of Th metal foils with 45 MeV protons. The Pa fraction was subsequently chemically isolated. Alpha singles as well as αγ-, αe-, αγγ-coincidence measurements were performed with thin sources, and a partial level scheme was deduced for the 224Ac. Although the spins of the observed levels have not been uniquely determined, the data establish positive- and negative-parity bands which exhibit characteristics of parity doublets. In particular, two bands at 354 and 360 keV appear to be members of a parity doublet. The similarity in the hindrance factors of α-decays to the 354 and 360 keV levels, which have opposite parities, indicates that the wavefunctions of the two states are very similar, which is a signature for octupole deformation.

The effects of far-side dominance on the j-dependence of the medium energy 116Sn(d, p)117Sn reaction

We report measurements of the 116Sn(d, p)117Sn reaction to the d32, g72, and h112 low-lying states at 79.0 MeV. Transfer reaction calculations which include an adiabatic deuteron channel wavefunction, finite range including the deuteron S- and D-state, and non-locality corrections are performed for these transitions. A separation of the reaction amplitude into the near- and far-side components shows that the g72 and h112 reaction calculations are far-side dominated. In this context, the proton channel spin-orbit distortions modify the j-dependence of the Ay vector analyzing power and introduce a strong j-dependence in the Ayy tensor analyzing power.

Analyzing powers for 12C(p↘,p′)12C at intermediate energies

Data are presented for the analyzing powers for the 12C(p↘,p′)12C reaction at 120 and 200 MeV to 1+ and 2+ states with T=0 and 1. The isovector transitions do not change much with energy, while the isoscalar transitions are strongly sensitive to it. In particular, A(θ) for the 12.71‐MeV (1+, T=0) transition changes sign. Microscopic DWIA calculations for the 120‐MeV data, which describe the cross sections rather well, exhibit numerous disagreements with the analyzing power data.

Analyzing powers in p→p→pnπ+ and determination of pion S and P wave amplitudes near threshold

Abstract Analyzing powers were measured and used to quantify the observation that s-wave processes dominate near threshold. Values of Ay(θπ,φπ=0°) are presented for η values of 0.22, 0.42 and 0.50. Maximum analyzing powers AN0 are equal to −0.13, −0.24, and −0.28, respectively. A partial wave analysis, made possible by the new analyzing powers and available cross sections, indicates that the s-wave contribution to the cross section constitutes about 91% of the total cross section at η=0.22, or 300 MeV. It decreases to about 75% for η=0.5.

Cross section and analyzing power for the isovector “stretched” 6− state in the 28Si(p, n)28P reaction

Abstract We studied the 28 Si(p, n) reaction with both unpolarized and polarized protons at a nominal energy of 135 MeV, extracted the angular distributions of the differential cross section and the analyzing power for the 6 − , T = 1 state at an excitation energy of 4.95 MeV in 28 P, and compared our results with similar data published for the analog ( p , p ′) reaction to the 6 − , T = 1 state at an excitation energy of 14.35 MeV in 28 Si. These comparisons are consistent with charge independence. The measurements are described well by distorted-wave-impulse-approximation calculations with form factors and spectroscopic amplitudes determined from electron scattering.