Search

A polarization direction correlation measurement of γ rays from the 7.044 MeV level in 30Si results in Jπ = 5− for this level and implies a Jπ = 4− assignment for the level at 6.503 MeV. A particle gamma ray coincidence measurement establishes a new decay branch (15 ± 4%) for the 6.503 MeV level to the 5.485 MeV Jπ = 3− level. The Doppler shift attenuation method was used to measure the mean lifetime of the 7.044 MeV level as [Formula: see text]. A simple shell model structure for the low lying negative parity states is presented and shown to be consistent with experimental measurements.

States in 32S have been populated using the 31P(p,γ) reaction at the Ep = 895, 1438, and 1583 keV resonances. Angular distributions, a linear polarization measurement, and the results from the 32S(α,α′) reaction at 180° yielded the following spin and/or parity assignments for bound levels Jπ(6.62) = 4−, Jπ(6.76) = 3−, 4+, 5−, Jπ(6.85) = 3−, 4+, and Jπ(7.95) = 3, 4, 5−, and for resonance states J(10.26) = 4 and J(10.40) = 4. The γ decay of selected excited states has been studied and mixing ratios were obtained for the strongest branches. Doppler shift measurements yielded lifetimes of 810 (−250, +350) fs, > 300 fs and 110 (−40, +60) fs for the states at 6.62, 6.76, and 7.95 MeV respectively. The results are discussed and compared with shell model predictions.

States in34Ar up to 5.5 MeV excitation energy, populated by the32S(3He,nγ) reaction at 8–12 MeV bombarding energy, have been investigated with the Doppler shift attenuation method,nγ angular correlation andnγγ triple coincidence measurements. For the states at 2.09, 3.29 and 4.52 MeV the lifetimes 200±60 fs, 130±60 fs and 260±80 fs have been found, respectively. Thenγ correlations yielded the spin assignmentsJμ=(2+) for the level at 4.13 MeV andJμ=3− for the 4.52 MeV state, and the mixing ratiosδ(3.29→2.09)=−0.12±0.05 andδ(4.13→3.29)=−0.52±0.15. The results are compared with shell model calculations and predictions from the weak coupling unified model.

States in34S up to 6 MeV excitation energy, populated by the reaction31P(α, pγ), have been investigated by Doppler shift and line shape analysis andpγ andγγ angular correlation measurements. The strengths of electromagnetic transitions between even parity levels are compared with theoretical predictions of the weak coupling unified model and the many-particle shell model. The experimental evidence for a weak coupling of the single particle motion to vibrational modes is discussed.

The lifetimes of excited states up to E x = 3.65 MeV in 42 Ca were measured by the DSAM. The stopping material was Au. In a pγ angular correlation measurement, the spin of the 3.65 MeV state was found to be J π = 2 + , the mixing ratio of its decay to the 1.52 MeV state is δ (E2/M1) = −0.06 ± 0.17.

The lifetimes of the excited states at 0.61, 1.59 and 1.89 MeV in 42Sc were measured by the DSAM in the reaction 40Ca(3He, pγ)42Sc and found to be 140±40, 90±45 and 60±30 fs, respectively. By n-γ coincidence and n-γ-γ triple coincidence measurements in the reaction 40Ca(3He, nγ)42Ti the γ-decay of 42Ti levels up to Ex = 3.75 MeV has been investigated. For the states at 1.55, 2.39 and 2.67 MeV the lifetimes 560±160, 310±180 and ≧ 1600 fs have been found, respectively.

The first J π = 2 + states of some doubly even nuclei in the sd shell have been excited in α-particle-induced reactions. From the Doppler broadened and shifted line shape of the subsequent γ-ray transitions, the following lifetimes have been found: E x ( MeV ) τ (ps) 20 Ne 1.634 0.84±0.20 28 Si 1.774 0.87±0.22 32 S 2.232 0.30±0.08 34 S 2.216 0.35±0.06 3.300 0.12±0.03 36 Ar 1.972 0.46±0.11 38 Ar 2.163 0.45±0.11

The E x = 6477 keV level in 27 Al was populated at the E p = 2293 keV, J π = 7 2 − , T = 3 2 resonance in the 26 Mg(p, γ) reaction. The angular distribution and polarization of the R → 6477 keV γ-ray transition yields a unique spin-parity assignment J π (6477) = case 72 − . The lifetime of the E x = 6477 keV level was measured, using the Doppler-shift attenuation method, as τ = 21 ± 6 fs.

From Doppler shift attenuation and delayed coincidence measurements in the reaction 35 Cl( α , p0 γ ), lifetimes have been determined for the 38 Ar states at 3.81 MeV ( τ = 0.15 ± 0.05 ps), 4.48 MeV ( τ > 1.0 ps ), 4.59 MeV ( τ ≦ 350 ps) and 4.89 MeV ( τ = 0.24 ± 0.08 ps). Analogies to levels in 40 Ca are discussed.

Calculates analytically the energy gained by an electron during one transit of an idealized one dimensional magnetic mirror field B in the presence of a given microwave electric field. The heating rate is defined as this energy gain over the transit time. It depends on the initial energy and the position of the turning point of the electron. The heating rate for relativistic electrons not crossing the resonance surfaces can be comparable to that of 'resonant electrons'. A comparison of the heating rate and energy loss rates from multiple collisions and radiation suggests an equilibrium at energies of 102-103 keV, depending on the mirror ratio, microwave field strength and frequency, and the density of the cold electron group responsible for the collisional energy losses. The fraction of electrons heated to this equilibrium energy is calculated.

The Doppler shift attenuation method was used to measure the lifetimes of the J π = 2 + 2.23 MeV and 3.50 MeV states in 30 Si. The states were produced in the reaction 27 Al(p,αγ). Their mean lifetimes were found to be τ (2.23) = 0.26±0.06 ps and τ (3.50) = 0.086±0.020 ps, respectively. Fairly good agreement with the predictions of the weak-coupling uniform model was obtained.

A high-pressure gas cell for DSA lifetime measurements is described. Lifetimes in 17O and 43Ca were measured and the results are found to depend systematically on the beam intensity.

A formalism is presented for the determination of unstable electrostatic oscillations in a model mirror‐confined plasma with a Gaussian density variation of arbitrary scale length along the magnetic field. A formal solution to the collisionless Boltzman equation is obtained for a plasma confined in a parabolic well. Using this solution, one may numerically solve Poisson's equation to obtain the eigenfunctions (perturbed potentials) and eigenvalues (densities) of the system for a given frequency and growth rate. As no mathematical limits on plasma length exist for obtaining these solutions, the infinite‐plasma results may be recovered in the limit of very long plasmas.