A. Celler

Exclusive pion production from few nucleon systems in the region of the [Delta][sub 1232] resonance

Angular distributions of the differential cross sections and analyzing powers have been measured for the [sup 3]He([ital [rvec p]],[pi][sup +]) [sup 4]He and [sup 4]He([ital [rvec p]],[pi][sup +])[sup 5]He reactions at proton bombarding energies between 240 and 507 MeV. These new results provide a comprehensive set of data spanning the region of the [Delta][sub 1232] resonance and are compared with a phenomenological model that incorporates the amplitudes for the [ital pp][r arrow][ital d][pi][sup +] reaction, and with calculations from a microscopic ([ital p],[pi][sup +]) model. A [sup 5]He final state interaction calculation based upon the low energy [ital n]+[alpha] elastic phase shifts indicates that the [sup 4]He([ital p],[pi][sup +])[sup 5]He spectra are nearly independent of pion angle and proton energy. Comparisons made with the time reversed charge symmetric reaction [sup 3]H([ital n],[pi][sup [minus]])[sup 4]He reaction indicate substantial Coulomb effects are still present at 300 MeV.

Distribution of spin dipole transition strength in the sup 15 N( n , p ) sup 15 C reaction

The reaction {sup 15}N({ital n},{ital p}){sup 15}C was studied at a neutron energy of 288 MeV using the TRIUMF ({ital n},{ital p}) charge-exchange facility and a high-pressure gas target. The angular distributions for spin dipole ({Delta}{ital L}=1) transitions to the states in {sup 15}C at energies 0 and 0.740 MeV, as well as for higher excitation energies, were measured and the results were compared with distorted-wave impulse approximation calculations. The measured distribution of the spin dipole strength agrees well with shell-model predictions, indicating that a rather simple model provides a satisfactory description of the {sup 15}N ground state, and of positive-parity states in {sup 15}C up to about 18 MeV excitation. The magnitude of the peak cross sections (at {congruent}7{degree}) is described well by the calculations when the theoretical cross section is renormalized by a factor of 0.7. The calculated cross sections near 0{degree} are generally smaller than experimental data. If this is a general feature of {Delta}{ital L}=1 transitions, it suggests that estimates of Gamow-Teller strength based on a multipole decomposition of measured cross sections may be too high.