J. R. Leslie

A Heavy Water Detector to Resolve the Solar Neutrino Problem

Abstract The observation of the following three reactions: νed→ppe; νxe→νxe; and νxd→νxpn (where νx is any left- handed neutrino) in a heavy water Cerenkov detector which is being designed, allows the solar 8B ve flux, spectrum and direction to be measured. In addition, the total solar 8 Bν c neutrino flux, direction and integral spectrum, independent of neutrino flavor, may be determined to provide several independent methods to resolve the solar neutrino problem.

Analogue states in 61Cu

Abstract Resonances in the reaction 60Ni(p, γ)61Cu have been studied in the energy region Ep ≈ 1550–1950 keV. Decay schemes and branching ratios are presented for 12 resonances and the resonance strength has been determined for most of these. Gamma-ray angular distribution measurements on two resonances yield the following spin assignments (E p ( keV ; J): (1668; 5 2 ), (1850; 3 2 , 5 2 ) . Several of the resonances studied are identified as fragments of the analogue states of the ground and first two excited states in 61Ni. M1 transitions strengths to the corresponding antianalogue candidates have been measured.

The γ-ray decay properties of analogue states of 55Fe excited in the reaction 54Fe(p, γ)55Co

Gamma-ray angular distribution, polarization and resonance strength measurements have been carried out on resonances observed in the reaction 54Fe(p, γ)55Co at proton energies of 1803 and 1887 keV. These resonances at excitation energies of 6833 and 6916 keV in 55Co have Jπ = (32−) and 52− and resonance strengths of (2J + 1) ΓγΓpΓ = 0.98 and 0.45 eV respectively. These resonance states have been identified as analogues of the 2050 keV (Jπ = 32−) and 2144 keV (52−) states in 55Fe. A state at 4722 keV (32−) has been identified as the analogue of the ground state of 55Fe. Transition probabilities for γ-rays de-exciting these analogue states are examined. Although no strong analogue-antianalogue transitions from the resonance levels are observed there are strong transitions between the analogue states and also from the analogue of the 55Fe ground state to a T = 12 state in 55Co.

A study of the 58Ni(p, γ)59Cu reaction

Abstract Eleven resonances in the reaction 58Ni(p, γ)59Cu have been investigated in the proton energy region 0.9 ≦ Ep (E p ( keV ); J): (1376; 3 2 ), (1424; 3 2 ), (1833; 5 2 , 9 2 ), (1883; 3 2 ), (2238; 7 2 ), (2275; 5 2 ) . In addition spins of several low-lying levels were determined (or limited). They are E x ( keV ); J): (1398; 7 2 ), (1865; 7 2 ), (1987; 5 2 ), (2265; 3 2 ), (2318; ( 1 2 )), (2324; 3 2 ), (2663; 5 2 , 9 2 ), (2707; 5 2 ), (2714; 7 2 ), (2927; 5 2 ), (3022; 5 2 , 7 2 ), (3025; ( 3 2 )), (3114; ( 5 2 )), (3130; ( 3 2 )), (3434; ( 5 2 )), (3438; ( 1 2 )), (3615; 3 2 ), (3663; 1 2 , 3 2 ), and (4181; 5 2 , 9 2 ) . Previously unreported states have been observed at Ex = 2663, 2707, 3022, 3025, 3114, 3438, 3742 and 4181 keV. Branching ratios and multipole mixing ratios have been measured for the decay of several bound levels and these results are compared with recent theoretical calculations. Four of the resonance studied have been identified as isobaric analogues of low-lying 59Ni levels. As well, the γ-decay of the (presumed) 59Ni g.s analogue at 3905 keV has been observed. The log ƒ:t values for the β+ decay of 59Cu to various 59Ni states are calculated from measured γ-widths in analogue state decay and are compared to values measured in β+ decay.

Hole states of 20F and 20Ne

Abstract The structure of the low-lying states of 20F has been investigated with the reaction 21Ne(d, 3He)20F induced by 26 MeV deuterons. Spins, parity assignments and spectroscopic factors for the populated states are compared with the predictions of the Nilsson model and recent shell-model and projected Hartree-Fock calculations. The reaction 21Ne(d, t)20Ne, studied simultaneously, excites strongly the T = 1 states in 20Ne which are analogues of the low-lying states of 20F. The spectroscopic factors of parent and analogue are consistent to within 20% for states excited by a single l-transfer.

Lifetime of 19 Ne * (4.03 MeV)

The Doppler-shift attenuation method was applied to measure the lifetime of the 4.03 MeV state in {sup 19}Ne. By utilizing a {sup 3}He-implanted Au foil as a target, the state was populated using the {sup 20}Ne({sup 3}He, {alpha}){sup 19}Ne reaction in inverse kinematics at a {sup 20}Ne beam energy of 34 MeV. De-excitation {gamma} rays were detected in coincidence with {alpha} particles. At the 1{sigma} level, the lifetime was determined to be 11{sub -3}{sup +4} fs and at the 95.45% confidence level the lifetime is 11{sub -7}{sup +8} fs.

Confirmation of the l-forbidden Gamow-Teller decay branch of 39Ca

Abstract A search for Gamow-Teller decay branches of 39Ca to excited states in 39K was conducted with a large HPGe detector which observed the decays of 39Ca samples delivered by a helium-jet transport system. A pair of plastic scintillators in front of the HPGe detector were used to reject events due to bremsstrahlung from the 39Ca positrons. With this setup, weak γ-rays could be observed with a degree of sensitivity not previously achieved. The l- forbidden 1 d 3 2 → 2 s 1 2 transition to the first excited state in 39K, was observed with a branching ratio of (2.50 ± 0.27) × 10−5. This result agrees with but is more accurate than the only previous measurement. Thus, the ratio of the l-forbidden Gamow-Teller and isovector M1 matrix elements in mass-39 nuclei continues to disagree with theoretical values obtained by Towner and Khanna from calculations involving core-polarization and meson-exchange currents. This leaves very few possibilities to explain the discrepancy between theory and experiment.

Lifetimes of states in 19Ne above the 15O+α breakup threshold

The 15 O(α, γ) 19 Ne reaction plays a role in the ignition of type I x-ray bursts on accreting neutron stars. The lifetimes of states in 19 Ne above the 15 O+α threshold of 3.53 MeV are important inputs to calculations of the astrophysical reaction rate. These levels in 19 Ne were populated in the 3 He( 20 Ne , α) 19 Ne reaction at a 20 Ne beam energy of 34 MeV. The lifetimes of six states above the threshold were measured with the Doppler-shift attenuation method. The present measurements agree with previous determinations of the lifetimes of these states and in some cases are considerably more precise.

The gamma decay of analogue states in61Cu

Resonances in the reaction60Ni(p, γ)61Cu have been studied in the proton energy rangesEp=1840–1880 keV and 2220–2300 keV. Decay schemes and branching ratios have been determined for a number of resonances, three of which are identified as analogue fragments of the 283 keV (1/2−) and 656 keV (3/2−) states in61Ni. The split analogue components of the 283 keV state atEx≈6.6 MeV are seen to decay significantly to a group of states in the region of excitation 3–4 MeV. Gamma ray angular distributions yield the following resonance spins:Ep=2248 keV,J=3/2;Ep=2263 keV,J=5/2. Also, the61Cu ground stateβ+ decay to parent levels in61Ni has been compared to the respective analogue stateM1 gamma decay to the61Cu ground state.

The l-forbidden m1 decay of the 2522 keV level in 39K

Abstract The mean lifetime of the first excited 1 2 + level in 39 K has been measured to be τ = 93 ± 13 fs by high recoil velocity DSAM. The level was excited by bombarding a 4 He-implanted Ta target with a 100 MeV 39 K beam. The lifetime was determined by fitting the Doppler-broadened lineshape of the 2522 keV gamma-ray transition to the 3 2 + ground state. Together with the measured B (E2), the B (M 1; d 3 2 → S 1 2 ) for this l -forbidden M1 transition was determined to be 0.0100 ±0.0027 μ 2 N . A theoretical calculation, taking into account core polarization, delta excitation and mesonexchange current contributions, underestimates the B ( M )1) by more than a factor of six. The experiment also measured the lifetimes of the 3019 keV and 3883 keV levels to be 20 ±4 fs and 11 ± 6 fs, respectively.