B. Larson

A segmented high pressure gas target for (n, p) studies at TRIUMF

Abstract We have developed an (n,p) target chamber consisting of four target layers sandwich between five detector layers. The two] central targets are gas cells separated from the detector gas volume by thin windows. The two outer targets are solids. The chamber has been used with isotopic targets of 20 Ne, 3 He and 15 N at the TRIUMF (n, p) facility. With the gas cells and gas box operated at 20 atm (20.3 bar) substantial target thickness can be achieved, while the contamination of (n, p) spectra from extraneous materials is minimized. The simultaneous accumulation of data from the two gas cells and two solid targets has the advantages of: 1) normalization by including targets of known cross section in the target stack and/or 2) obtaining the spectral shape of the incident neutron flux by choosing C and CH 2 for the solid targets.

Gamow-Teller strength inNi60,62,64(n,p) reactions at 198 MeV

Measurements of the ([ital n],[ital p]) reaction cross section on [sup 60,62,64]Ni have been made at 198 MeV for [theta][sub lab]=0--20[degree] in 4[degree] steps. Multipole analyses have been performed on the resulting spectra and Gamow-Teller (GT) strength distributions have been obtained. These GT distributions have been found to occur as strong peaks at low excitation energy in the final Co nuclei and extend weakly upwards to 30 MeV of excitation. Comparisons of the data with renormalized shell-model calculations show reasonable agreement at low excitation, though the calculations predict very little strength at excitation energies above about 6 MeV.

Gamow-Teller strength in Ni 6 0 , 6 2 , 6 4 ( n , p ) reactions at 198 MeV

Measurements of the ([ital n],[ital p]) reaction cross section on [sup 60,62,64]Ni have been made at 198 MeV for [theta][sub lab]=0--20[degree] in 4[degree] steps. Multipole analyses have been performed on the resulting spectra and Gamow-Teller (GT) strength distributions have been obtained. These GT distributions have been found to occur as strong peaks at low excitation energy in the final Co nuclei and extend weakly upwards to 30 MeV of excitation. Comparisons of the data with renormalized shell-model calculations show reasonable agreement at low excitation, though the calculations predict very little strength at excitation energies above about 6 MeV.

Gamow-Teller strength in [sup 60,62,64]Ni([ital n],[ital p]) reactions at 198 MeV

Measurements of the ([ital n],[ital p]) reaction cross section on [sup 60,62,64]Ni have been made at 198 MeV for [theta][sub lab]=0--20[degree] in 4[degree] steps. Multipole analyses have been performed on the resulting spectra and Gamow-Teller (GT) strength distributions have been obtained. These GT distributions have been found to occur as strong peaks at low excitation energy in the final Co nuclei and extend weakly upwards to 30 MeV of excitation. Comparisons of the data with renormalized shell-model calculations show reasonable agreement at low excitation, though the calculations predict very little strength at excitation energies above about 6 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.

Elastic Scattering of Polarized Protons from Polarized 3He at Intermediate Energies

A new laser polarized 3He target was constructed at TRIUMF with a volume of 18 cm3. The 3He gas is polarized through spin exchange with optically pumped Rb vapour. In a new development the pressure at room temperature was increased from 3.5 atm to 7 atm. The 3He polarization typically had a value of 0.45. This result was verified by polarized proton induced pion production at 300 MeV and 400 MeV for which reaction the analyzing power is equal to 1 due to strong interaction symmetries.