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The ground and first excited states in 15 F were studied in resonant elastic scattering using the thick ͑CH 4 ͒ gas target method in inverse kinematics with a separated 14 O beam. An analysis of the excitation functions of the elastic scattering was carried out with the potential model. The quantum numbers 1 / 2 + (ground state) and 5/2 + (first excited state) were assigned to the lowest two states in 15 F. Also, the widths and the proton decay energies of the unbound levels were obtained. The analysis of the data indicates that a large diffuseness is needed in the Woods-Saxon potential in order to describe single-particle features in drip-line nuclei. Over the past decade it has become clear that drip-line nuclei demonstrate a number of phenomena which are not found in nuclei close to the line of stability. One such feature is the change in magic numbers, which are generated by a conventional Woods-Saxon potential with parameters fitted for stable nuclei [1][2][3]. One example is the intruder singleparticle 2s 1/2 state, which appears to be the ground state in 11 Be [4] and 11 N [5] instead of the 1p 1/2 state. As another example, it has been predicted [1-3] that the diffuseness of nuclear densities for intermediate mass nuclei increases dramatically when approaching the neutron drip line. These phenomena indicate that the parameters of the shell model potential can be unusual for nuclei at the borders of nuclear stability. Figure 1 shows how, for a light nucleus, the energies of the shell model levels in a Woods-Saxon potential depend on the ratio of the diffuseness to radius parameters. It can be seen in Fig. 1 that the 1p 1/2 and 2s 1/2 levels approach each other as the ratio increases. One way to explain the phenomena observed near the drip line is that the singleparticle potential changes its shape giving way to new shell structure. This effect can be tested by an analysis of the nucleon widths of the single-particle states in drip-line nuclei, which are mainly dependent upon the geometrical parameters of the well.15 F is a good system to check the considerations above. The lowest states in 15 F are unstable to proton decay and should have dominantly single-particle structure. The theoretical predictions for the single-particle spectroscopic factors are 0. O on hydrogen with the thick target inverse kinematics method [5,10,11]. An approach similar to Ref.[9] was used in the present experiment. However, there are important differences in the details of the two measurements. In the present work, a gas target, CH 4 , was used instead of a solid CH 2 target. The gas target results in a drastic decrease of the background (see below). Also, only the excitation function at 180°͑c.m.͒ in arbitrary units was measured in Ref. [9], while in the experiment reported here measurements were made at several angles. As a result, we have a better determination of the positions and the widths of the levels which allows us to make conclusions about the parameters of the interaction potential between 14 O and protons. The expe...

Excitation functions for 18 Oϩ␣ elastic scattering were measured by a method using inverse kinematics and a thick gas target. An analysis of the data corresponding to the excitation energy regions of 11.8 -13.7 MeV and 19.0-22.0 MeV in 22 Ne was carried out. A surprising splitting of 1 Ϫ , 3 Ϫ , 7 Ϫ , and 9 Ϫ ␣-cluster levels into doublets was found in 22 Ne.

The thick target inverse kinematic method was applied to the study of isobaric analog states in the neutronrich nucleus 9 Li. For this purpose, an excitation function for 8 Heϩp elastic scattering was measured in the center-of-momentum energy range from 1.6 to 5.8 MeV. Three Tϭ5/2 states in 9 Li ͑isobaric analogs of 9 He) were observed. Restrictions on the spin-parity assignments are provided according to R-matrix calculations, and conclusions regarding the structure of 9 He are given.