W.P. Alford

Gamow-Teller strength observed in the 48Ti(n, p)48Sc reaction: Implications for the double beta decay of 48Ca

Abstract Cross sections for the 48 Ti(n, p) reaction have been measured at angles of 0°, 6°, and 12° at an energy of 200 MeV. The measurements are compared with results of DWIA calculations to obtain estimates of transition strengths for L = 0, 1, and ⩾2 up to an excitation energy of 25 MeV. Gamow-Teller strength ( L = 0) is peaked between 3 and 4 MeV excitation energy, with a significant distribution extending to about 12 MeV. The L = 1 strength is found mainly between 6 and 20 MeV while the cross section for transitions with L ⩾2 increases from 10 MeV to the upper limit of the measurements. The distribution of Gamow-Teller strength is in poor agreement with theoretical distributions used to calculate the lifetime for double beta decay of 48 Ca.

Ratio of the isovector effective interaction strengths ‖Jστ/Jτ‖2 between 200 and 450 MeV from the 14C(p, n) 14N reaction

Abstract The cross section at 0° for the reaction 14 C(p, n) 14 N has been measured at energies of 200, 300, 400 and 450 MeV using a nucleon charge-exchange facility recently commissioned at TRIUMF. Energy resolution of 1 MeV or better was obtained at each energy, permitting a reliable measurement of the cross section ratio for the Gamow-Teller transition to the 1 + state at 3.95 MeV and the Fermi transition to the 0 + state at 2.31 MeV. The deried values of ‖ J στ / J τ ‖ 2 are in clear disagreement with impulse approximation calculations using a free NN t -matrix.

The (n, p) reaction as a probe of Gamow-Teller strength

Abstract The ground state differential cross sections for the (n, p) reaction at 0° on 6 Li, 12 C and 13 C have been measured for 198 MeV neutrons with a precision of about 4% relative to the corresponding value for the H(n, p) reaction. These data, together with the accurately known ft values for the β- decay of 6 He, 12 B and 13 B provide three calibrations of the (n, p) reaction as a probe of Gamow-Teller strength for isospin raising transitions.

The (3He, n) reaction on N = 82 targets and even isotopes of neodymium

Abstract Angular distributions of neutrons from the ( 3 He, n) reaction were measured at 25.4 MeV over the angular range 0°–22° for the N = 82 targets 136 Xe, 138 Ba, 139 La, 142 Nd and 144 Sm. In addition, measurements were carried out for the targets 144, 146, 148, 150 Nd spanning the transition from spherical to permanently deformed ground states. For each even A , N = 82 target, transitions to excited states were observed with considerable L = 0 and L = 2 strength. Weak transitions to excited states were observed for the 144 Nd and 139 La targets. Only the ground state transition was observed for the other targets. A careful search was made for the 0 + vibrational states excited in the (t, p) reaction at 0.747 MeV in 150 Sm and 0.686 MeV in 152 Sm, but these were not populated with measurable strength in the ( 3 He, n) reaction. The Q -value for the 144 Sm( 3 He, n) 146 Gd(g.s.) reaction was measured to be 0.977±0.030 MeV, yielding a ground state mass of 145.91832±0.00003 amu for 146 Gd.

Gamow-Teller strength and giant resonances in 90Zr(n,p) at 198 MeV☆

Abstract The 90 Zr(n,p) 90 Y reaction has been studied at a bombarding energy of 198 MeV in a search of GT + strength. Up to 10 MeV excitation in 90 Y, we obtain a firm upper limit of S β + ⩽ 3.6. The majority of the strength at low excitations is identified as spin dipole.

Two-neutron excitations in 26Mg and 30Si

Abstract The reactions 24 Mg(t, p) 26 Mg and 28 Si(t, p) 30 Si have been studied at an incident energy of 18 MeV. Angular distributions have been measured for strongly excited states up to an excitation energy of about 10.5 MeV. A comparison with DWBA calculations using transition amplitudes resulting from a full (sd) shell model calculation generally shows good agreement up to an excitation energy of about 6 MeV, although a few states show significant discrepancies. At higher excitation energies the natural-parity states of the (f 7 2 d 5 2 ) multiplet, and the 2 + and 4 + states of the (f 7 2 ) 2 configuration can be identified in both 30 Si and 26 Mg. The 6 + state is identified in 30 Si, but not in 26 Mg. The expected 0 + states are not clearly identified in either case, although relatively strong transitions with “uncharacteristic” angular distributions are observed near the expected location of these states. DWBA calculations with a (f 7 2 ) 2 form factor suggest that these may in fact be the 0 + states of the (f 7 2 ) 2 configuration.

Structure of 22Mg, 26Si, 34Ar and 38Ca via the (3He, n) reaction

Abstract The (3He, n) reaction has been studied on targets of 20Ne, 24Mg, 32S and 36Ar at 25.4 MeV using a time-of-flight spectrometer. Angular distributions were measured for neutron groups up to excitation energies ranging from 8.55 MeV in 22Mg to 7.47 MeV in 38Ca. New levels were found at 6.98 ± 0.08, 7.84 ± 0.09, 8.29 ± 0.04 and 8.55 ± 0.09 MeV in 22 Mg ; 5.62 ± 0.03 and 6.99 ± 0.05 MeV in 34 Ar ; and 7.47 ± 0.05 MeV in 38 Ca . DWBA analysis along with comparisons with results of (t, p) studies on the same targets permits a number of new spin-parity assignments. Comparison with results of (sd) shell model calculations shows generally good agreement for 22Mg and 26Si up to excitation energies of about 5 MeV. At higher excitation, transition strengths show the increasing importance of (fp) shell contributions. Results for 34Ar show significant deviations from model predictions for most excited states. For 38Ca, only the ground state transition shows appreciable strength for (sd) transfer. In all nuclides strong transitions to negative parity states are observed, and (fp) contributions to measured cross sections become important for even parity states at high excitation.

A study of spin isovector giant resonances with the208Pb(n, p)208Tl reaction

Abstract The 208 Pb(n, p) 208 Tl reaction was studied at 198 and 458 MeV in a search for isovector spin giant resonances. Peaks at 5.1 MeV and 13.6 MeV excitation in 208 Tl are observed and discussed as candidates for the T > spin giant dipole resonance (SGDR), the spin isovector monopole resonance (SIVM), and the spin isovector quadrupole resonance (SIVQ).

Nuclear spectroscopy of the (fcase72)2, f72p32xand f72p12 multiplets from the 41Ca(d, p)42Ca reaction

Angular distributions of the cross section and the vector analyzing power have been measured for the 41Ca(d, p)42Ca reaction using 11 MeV deuterons. The vector analyzing power data have been used to determine the total angular momentum j of the captured neutron for 42 positive parity levels. Spectroscopic strengths were extracted separately for each of the allowed j-values which contributed to the cross section and identification of the major components of the f72, p32and p12 strength distributions have been obtained. An almost total absence of mixing of the p32and p12 strength was observed. Of 32 states populated by pure l = 1 transfer, only two consist of a mixture of p32and p12. The effective (f72)2, (f72p32) and (f72p12) two-particle matrix elements are compared with the modified Kuo-Brown matrix elements of McGrory. They agree to within a few hundred keV. The monopole energy centroid of the (f72p32) and (f72p32) multiplets are measured to be slightly repulsive, whereas Kuo-Brown predict a small attractive monopole contribution.

The effective T = 1 two-particle matrix elements in the fp shell

Abstract The 41 Ca( d , p) 42 Ca reaction has been used to locate the strength distributions for p 3 2 and p 1 2 transfer in 42 Ca. Effective ( f 7 2 ) 2 , f 7 2 p 3 2 and 7 2 1 2 two-body matrix elements are derived from the data and compared to theoretical predictions.