A. Trudel

A study of spin isovector giant resonances with the208Pb(n, p)208Tl reaction

Abstract The 208 Pb(n, p) 208 Tl reaction was studied at 198 and 458 MeV in a search for isovector spin giant resonances. Peaks at 5.1 MeV and 13.6 MeV excitation in 208 Tl are observed and discussed as candidates for the T > spin giant dipole resonance (SGDR), the spin isovector monopole resonance (SIVM), and the spin isovector quadrupole resonance (SIVQ).

Vector analyzing powers for 1H(d

The vector analyzing powers for the /sup 1/H(d-italic-arrow-right,/gamma/)/sup 3/He and /sup 2/H(p-arrow-right,/gamma/) /sup 3/He reactions have been measured near threshold (E/sub /gamma// = 7.5 MeV). The angular distribution of the cross section was also measured for the /sup 2/H(p,/gamma/)/sup 3/He reaction. The ratio of the analyzing powers is sensitive to the presence of S = (3/2 capture strength. It was found that a 10% contribution to the capture by M1 radiation (predominantly S = (3/2) is required to explain the data.

Elastic scattering of polarized protons from polarized 3He

Abstract A polarized 3 He gas target of 6.44 atm pressure has been used to measure beam-and target-related asymmetries, A 00 N 0 and A 000 N , and spin correlation parameters, A 00 NN , for proton elastic scattering from 3 He. Between 200 and 500 MeV, and in the range of momentum transfers q = 2–5.1 fm −1 , differences between A 000 N and A 00 N 0 are found which provide unambiguous evidence for a significant f amplitude in p- 3 He scattering even though this amplitude vanishes for the NN system. The new target-related observables are only in fair agreement with results of two model calculations based on a non-relativistic momentum space optical potential and on a nonrelativistic distorted wave Born approximation model.

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.

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.

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.

Vector analyzing powers for /sup 1/H(d-italic-arrow-right,/gamma/)/sup 3/He and /sup 2/H(p-arrow-right,/gamma/)/sup 3/He

The vector analyzing powers for the /sup 1/H(d-italic-arrow-right,/gamma/)/sup 3/He and /sup 2/H(p-arrow-right,/gamma/) /sup 3/He reactions have been measured near threshold (E/sub /gamma// = 7.5 MeV). The angular distribution of the cross section was also measured for the /sup 2/H(p,/gamma/)/sup 3/He reaction. The ratio of the analyzing powers is sensitive to the presence of S = (3/2 capture strength. It was found that a 10% contribution to the capture by M1 radiation (predominantly S = (3/2) is required to explain the data.