Level structure of Mg21: Nuclear and astrophysical implications
Resonant elastic scattering of a radioactive $^{20}\mathrm{Na}$ beam incident upon protons in a polyethylene target has been used to probe the level structure of $^{21}\mathrm{Mg}$ above the proton decay threshold. Three states have been observed, and their properties deduced through analysis based on the R-matrix formalism. The results improve and extend previous studies of this nucleus. An estimate of the $^{20}\mathrm{Na}$(p,\ensuremath{\gamma})$^{21}\mathrm{Mg}$ reaction rate, including these new data, suggests this reaction will not play a significant role in explosive hydrogen burning in astrophysical sites such as novae and x-ray bursts.
Spectroscopy of 21F with the (α,2He) reaction
The {sup 19}F({alpha},{sup 2}He){sup 21}F reaction was investigated at 55 MeV incident energy. The transferred angular momenta of prominent transitions excited were determined from a distorted wave Born analysis of the angular distributions. Tentative spin assignments for the observed levels are extracted from shell-model calculations with the {open_quotes}unified{close_quotes} sd-space interaction based on the very good reproduction of the excitation energies and the predicted large two-neutron transfer spectroscopic factors. {copyright} {ital 1997} {ital The American Physical Society}
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.