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Elastic scattering data are presented for 6Li at 36 MeV from 12O and 26Mg and for 7Li at 28.8 MeV from 15N and at 27 MeV from 25Mg over the range 15-95 degrees in the centre-of-mass frame. Microscopic optical potentials are generated for these scattering systems using the double-folding model. The sensitivity of the potentials to the prescriptions used for the nuclear density calculations is studied. The elastic scattering data are analysed within the framework of the optical model using both Woods-Saxon potentials and double-folding model real potentials with Woods-Saxon imaginary wells. Equally good fits to the data are obtained with the phenomenological and microscopic potentials. The double-folding potentials must be normalised by factors of 0.5 or 0.6 to fit the data in all cases except for 6Li scattering from 16O, for which a normalisation of 0.8 is favoured. These results are supplemented by those from an inelastic scattering analysis using DWBA and the collective rotational model for the first 2+ states in 12C and 26Mg. The shapes of the phenomenological and microscopic potentials around the strong absorption radius are compared and the gradients are found to differ significantly for 7Li+15N and 6Li+ 12C systems.

The transitions 1s2s3S-1s2p3P of Si12+ have been excited using the beam-foil method, and the wavelengths measured for the first time, for beam energies in the range 21-57 MeV. The measurements may be used to test calculations of the 3P fine-structure splitting to +or-1%, and when better calculations become available, the Lamb shift contributions to the transitions energy may be evaluated to +or-11%.

A new high resolution magnetic spectrometer — the Oxford MDM-2 spectrometer — has been designed, installed and tested. The layout of the magnetic elements is in the order: entrance sextupole and multipole, gradient-field dipole and exit multipole. The device has a “normal” focal plane, and the 1.6 m radius dipole magnet has a maximum mass-energy product of 315 MeV amu. At the maximum solid angle of 8 msr, the ratio of energies that can be accepted by the spectrometer (Emax/Emin) is 1.31. Precide measurements have been performed on the magnetic elements. The dipole magnet has very low hysteresis and field integral errors that amount to less than 1 part in 104. After some in situ modifications the field distributions of the magnets closely approximated the original design specifications. On-line tests with various ion-beams have revealed the optimum setting for each element. These are close to theoretical predictions from the program RAYTRACE, incorporating the parameterised results of the magnetic measurements. An aberration limited resolution (E/ΔE) of greater than 3000 has been observed at 8 msr solid angle.

We report the first observation of a laser-induced $M1$ transition in a fast beam. This new method has been applied to a measurement of the $F=\frac{1}{2}\ensuremath{-}\frac{3}{2}$ and $F=\frac{3}{2}\ensuremath{-}\frac{5}{2}$ hyperfine components of the $1s2p^{3}P_{1}\ensuremath{-}^{3}P_{2}$ fine-structure interval in heliumlike fluorine. The results are 953.60(3) and 961.77(3) ${\mathrm{cm}}^{\ensuremath{-}1}$, respectively. From these we extract the fine-structure splitting ${\ensuremath{\Delta}}_{12}=957.88(3)$ ${\mathrm{cm}}^{\ensuremath{-}\phantom{\rule{0ex}{0ex}}1}$.

A /sup 8/Be identifier of high detection efficiency was utilized to investigate the (..cap alpha.., /sup 8/Be) reaction on /sup 16/O, /sup 15/N, /sup 14/N, /sup 13/C, /sup 12/C, /sup 11/B, /sup 10/B, and /sup 9/Be targets at bombarding energies between 65 and 72.5 MeV. Differential cross sections were measured from theta/sub c.m./ = 20degree--70degree for solid targets and over a more restricted range for the nitrogen gas targets. Excitation functions were obtained over a larger energy range for the /sup 12/C and /sup 16/O targets. At these energies, the (..cap alpha.., /sup 8/Be) reaction was found to proceed predominantly via a direct ..cap alpha..-cluster pickup mechanism and to populate strongly only those levels consistent with this mechanism. The data were analyzed in the framework of the exact finite-range disorted-wave Born approximation. Absolute and relative ..cap alpha..-particle spectroscopic factors were extracted for 22 states using finite-range distorted-wave Born approximation. Good agreement was found between these experimental values and the theoretical predictions of Kurath and of Rotter for the extent of ..cap alpha.. clustering in these light nuclei. (AIP)

A laser resonance technique using Doppler tuning has been applied to measure transitions between highly excited states of highly ionized fluorine. Resonance transitions between n=9 and n=10 levels of 19F8+ with a mean wavelength of 4796.06±0.24 A were observed. This wavelength is close to the calculated value of 4796.16 A for the wavelength of the 92L17/2–102M19/2 transition.

Author(s): Cerny, Joseph; Jelley, N.A.; Hendrie, D.L.; Maguire, C.F.; Mahoney, J.; Scott, D.K.; Weisenmiller, R.B.

A resonance at E α = 4647 keV in the 16 O(α, γ) 20 Ne reaction has been located and assigned to a 5 − state in 20 Ne at 8447 ± 3 KeV. The radiative width of the 5 − to 3 − transition has been measured and found to be 13 ± 3 meV corresponding to a transition strength of 26 ± 6 Weisskopf units. Comparisons are made with rotational and shell model predictions.

The γ -ray decay of the lowest T =2 state (0 + ) in 28 Si at has been investigated with a Ge(Li) detector using the reaction 24 Mg (α,γ) 28 Si . Transitions to 1 + , T =1 levels in 28 Si at 11445 ± 3 (40%), 10901 ± 3 (43%), 10724 ± 3 (9%, T =(1)) and 10598 ± 3 (8%, T =(1)) keV excitation were observed and a comparison is made with a simple shell-model description of the T =2 and T =1 levels. Limits have been placed on Γ γ 1 and Γ p o and values are given for Γ , Γ α 1 , Γ p 1 and Γ p 2 .

A 1.53±0.04 MeV proton activity with a 245±20 ms half-life has been observed in the reaction of 16O on 40Ca. The most plausible origin of this activity is the proton radioactivity of 53Com, although the decay of this isomer by beta-delayed proton emission remains a possibility.

The usefulness of a Tandem Van de Graaff accelerator in beam foil spectroscopy for studying properties of excited electronic states in highly ionised systems was discussed in some depth by Jordan (1), but comparatively little work has so far been reported in this field. The most fundamental aspect of such work would appear to be the possibility of making accurate atomic structure measurements in systems containing 1, 2 or 3 electrons, where such measurements can constitute a severe test of atomic structure theory. Another field of interest in this context is the study of spectra and lifetimes in ions of astrophysical and plasma-physics importance.

Radiation emitted from silicon beams at 35, 38 and 45 MeV excited by passage through thin carbon foils has been studied in the range 3-9 AA using a curved-crystal X-ray spectrometer. More than 100 lines have been observed, of which only one quarter had been observed or predicted from solar or laboratory plasma spectra. Most of the previously unobserved lines may be attributed to satellites of H- and He-like transitions arising in three- and four-electron Si ions. The lifetime of the Si XIII 23P1 state has been measured, and a preliminary experimental value of 6.5+or-1.3 ps obtained.

Angular distributions have been measured for the (9Be, 10B0, 1) reactions on 63Cu, 54Fe, 26,24Mg and 16O at 43 MeV and on 40Ca at 45 and 30 MeV. Several of these experiments were performed with the Oxford MDM-2 spectrometer and the design and testing of its 30 cm focal plane detector, which is of the "hybrid" type, is described. Despite the size of the counter, in particular the large cathode to Frisch-grid separation, the resolution of the ionization signals is comparable with that of smaller counters. The position resolution is < 0.6 mm. Optical potentials have been obtained from the measured elastic scattering of 9Be from 16O, 26Mg and 40Ca, and 10B from 25Mg and 39K. The exact finite-range DWBA calculations have generally well reproduced the shape of the experimental reaction cross-sections. However, inconsistencies of up to 50% between the extracted spectroscopic factors for 10B0 and 10B1 have been found. This anomaly was found insensitive to changes in either optical potential or bound state parameters. A new method of form factor calculation is described that uses a shell model potential in conjunction with a surface-peaked potential, the depth of which is adjusted to give the correct asymptotic form to the wavef unctions. Whilst this form factor showed some success, it did not account for the 10B0/10B1 anomaly. Collective model DWBA analyses of the inelastic excitation of the first 2+ state in 26Mg and 3- state in 40Ca have given values for deformation parameters in reasonable agreement with light-ion work. A CCBA analysis of the 26Mg 2+ state was carried out to estimate the effect of the coupling. Calculations performed for a two-step reaction process through inelastic excitation of a strongly coupled 5/2- state in the projectile showed that this indirect route is important, but it could not solve the 10B0/10B1 problem alone. The conclusion is that other routes (projectile or target excitation) must be included.

A simple and practical arrangement of coupling lenses for viewing a fast beam light source with a grating spectrometer is shown to provide very efficient light collection with good spectral and spatial resolution together with a simple procedure for calibrating spectra.