A study of T=1, T=3/2, and T=2 states in some light nuclei using (He^3,n) reactions

The (He³, n) reactions on B¹¹, N¹⁵, O¹⁶, and O¹⁸ targets have been studied using a pulsed-beam time-of-flight spectrometer. Special emphasis was placed upon the determination of the excitation energies and properties of states with T = 1 (in Ne¹⁸), T = 3/2 (in N¹³ and F¹⁷) and T = 2 (in Ne²⁰). The identification of the T = 3/2 and T = 2 levels is based on the structure of these states as revealed by intensities and shapes of angular distributions. The reactions are interpreted in terms of double stripping theory. Angular distributions have been compared with plane and distorted wave stripping theories. Results for the four reactions are summarized below:

1) O¹⁶ (He³, n). The reaction has been studied at incident energies up to 13.5 MeV and two previously unreported levels in Ne¹⁸ were observed at E_x = 4.55 ± .015 MeV (Γ = 70 ± 30 keV) and E_x = 5.14 ± .018 MeV (Γ = 100 ± 40 keV).

2) B¹¹ (He³, n). The reaction has been studied at incident energies up to 13.5 MeV. Three T = 3/2 levels in N¹³ have been identified at E_x = 15.068 ± .008 MeV (Γ ˂ 15 keV), E_x = 18.44 ± .04, and E_x 18.98 ± .02 MeV (Γ = 40 ± 20 keV).

3) N¹⁵ (He³, n). The reaction has been studied at incident energies up to 11.88 MeV. T = 3/2 levels in F¹⁷ have been identified at E_x = 11.195 ± .007 MeV (Γ ˂ 20 keV), E_x = 12.540 ± .010 MeV (Γ ˂ 25 keV), and E_x = 13.095 ± .009 MeV (Γ ˂ 25 keV).

4) O¹⁸ (He³, n). The reaction has been studied at incident energies up to 9.0 MeV. The excitation energy of the lowest T = 2 level in Ne²⁰ has been found to be 16.730 ± .006 MeV (Γ ˂ 20 keV).

Angular distributions of the transitions leading to the above higher isospin states are well described by double stripping theory. Analog correspondences are established by comparing the present results with recent studies (t, p) and (He³, p) reactions on the same targets.

High energy heavy ion induced enhanced adhesion

The work described in this thesis represents an attempt to summarize to date the information collected on the process of high energy heavy ion induced enhanced adhesion. Briefly, the process involves the irradiation of materials covered by thin (≾3μm) films with high energy (E > 200 keV I nucleon) heavy ion beams (such as Fluorine or Chlorine). Enhanced adhesion has been observed on all material combinations tested, including metal on metal, metal on semiconductor, metal on dielectric and dielectric on dielectric systems. In some cases, the enhancement can be quite large, so that a film that could be wiped off a substrate quite easily before irradiation can withstand determined scrubbing afterwards.

Very little is understood yet about this adhesion mechanism, so what is presented are primarily observations about systems studied, and descriptions of the actual preparation and irradiation of samples used. Some discussion is presented about mechanisms that have been considered but rejected.

Beta and gamma vibrational bands in deformed nuclei

Energies and relative intensities of gamma transitions in ¹⁵²Sm, ¹⁵²Gd, ¹⁵⁴Gd, ¹⁶⁶Er, and ²³²U following radioactive decay have been measured with a Ge(Li) spectrometer. A peak fitting program has been developed to determine gamma ray energies and relative intensities with precision sufficient to give a meaningful test of nuclear models. Several previously unobserved gamma rays were placed in the nuclear level schemes. Particular attention has been paid to transitions from the beta and gamma vibrational bands, since the gamma ray branching ratios are sensitive tests of configuration mixing in the nuclear levels. As the reduced branching ratios depend on the multipolarity of the gamma transitions, experiments were performed to measure multipole mixing ratios for transitions from the gamma vibrational band. In ¹⁵⁴Gd, angular correlation experiments showed that transitions from the gamma band to the ground state band were predominantly electric quadrupole, in agreement with the rotational model. In ²³²U, the internal conversion spectrum has been studied with a Si(Li) spectrometer constructed for electron spectroscopy. The strength of electric monopole transitions and the multipolarity of some gamma transitions have been determined from the measured relative electron intensities.

The results of the experiments have been compared with the rotational model and several microscopic models. Relative B(E2) strengths for transitions from the gamma band in ²³²U and ¹⁶⁶Er are in good agreement with a single parameter band mixing model, with values of z₂= 0.025(10) and 0.046(2), respectively. Neither the beta nor the gamma band transition strengths in ¹⁵²Sm and ¹⁵⁴Gd can be accounted for by a single parameter theory, nor can agreement be found by considering the large mixing found between the beta and gamma bands. The relative B(E2) strength for transitions from the gamma band to the beta band in ²³²U is found to be five times greater than the strength to the ground state band, indicating collective transitions with strength approximately 15 single particle units.