R.F. Casten

A study of the neutron-rich isotopes near A = 100 by means of the (t, p) reaction

Abstract The (t, p) reaction has been used to study the nuclides 102 Mo, 106 Ru and 112 Pd, all of which are two neutrons beyond the stable isotopes. A (t, p) spectrum of the 102 Ru(t, p) 104 Ru process was also obtained. The incident triton energy was 15 MeV in all cases and a magnetic spectrograph was used for momentum analysis of the reaction protons with an energy resolution of ≈ 20 keV FWHM resulting. Differential cross sections were measured for many transitions and spin and parity assignments have been made for a number of states. Examination of the results indicates that only 102 Mo shows characteristics of being a transitional nucleus between regions of different nuclear shape whereas the other nuclei studied appear to be in regions where the coupling scheme changes more slowly. The first 2 + state of 102 Mo is markedly lower in excitation energy than in the lighter isotopes and a low-lying 0 + state is excited with large intensity relative to the ground state. The present results agree with previous results from the Berkeley group on the decay of fission fragments and in a qualitative way support several recent theoretical predictions.

Energy levels in even actinide isotopes from (t, p) reactions

Abstract Energy levels in 232, 234 Th, 236, 238, 240 U and in 250 Cm have been measured using the (t, p) reaction. Angular distributions were obtained for the 234, 238 U targets and evidence for second order effects in the direct reaction mechanism was found.

The (t, p) reaction on 36, 38, 40Ar

Abstract The 36, 38, 40 Ar(t, p) reactions have been investigated at 20 MeV incident energy with an energy resolution of ≈ 35 keV FWHM. Proton spectra were measured at seven angles from 12.5° to 57.5°. The differential cross sections were analyzed by distorted wave calculations and values of the transferred orbital angular momentum were assigned for many transitions. A discussion of the observed cross sections for L = 0 transitions leads to the conclusion that the role of the pairing force in the Ar isotopes is midway between a vibrational and a superfluid case. It is demonstrated through an analysis of the low-lying 0 + → 2 + transitions that the extra degree of freedom, associated with the two proton holes, mixes with the neutron shell model and the multiparticle-multihole degrees of freedom.

Proton-hole states in 209Bi From the 210Po (t, α) reaction

Abstract The 210 Po(t, α) 209 Bi reaction has been studied at 20 MeV triton energy with an overall resolution of 20 keV FWHM. Absolute cross sections were established by a comparison of the (t, α) intensities to elastic triton scattering. The three lowest single-proton states in 209 Bi were observed and spectroscopic factors were extracted from the measured cross sections by DWBA analysis. Starting at 2.43 MeV, six levels were strongly excited. These states have large 2p-1h proton components. The spectroscopic factors were extracted by a comparison of 210 Po(t, α) cross sections to 208 Pb(t, α) 207 T1 single-proton-hole cross sections measured previously at the same bombarding energy. The observed states and their properties were analyzed within the framework of the particle- (or hole) vibration coupling model. Surface vibrational states in 208 Pb coupled to single protons as well as the proton pair addition modes (states in 210 Po) coupled to a proton-hole were included in the analysis.

Levels of 11Be from a study of the 9Be(t, p)11Be reaction

Abstract The reaction 9 Be(t, p) 11 Be has been studied with 20 MeV tritons and an Elbek-type spectrograph. Four previously unreported proton groups were observed corresponding to E x = 5.25, 6.51, 6.72 and 8.84 MeV in 11 Be, and two broader groups.

0+ states near the N = 20 neutron shell from Ar(t, p) reactions☆

Abstract The (t, p) reactions leading to 38,40,42 Ar and 42 Ca have been used to study the 0 + level spectrum near the N = 20 neutron closed shell. The Ar isotopes show a significant reduction and fragmentation of the L = 0 (t, p) strength relative to Ca. A major change in the structure of the 0 + levels thus takes place between Ca and Ar.

The 209Pb single-neutron states and the l = 4 levels of 205Pb studied by the (d, p) reaction

Abstract Differential cross sections and vector and tensor analyzing powers have been measured for the ( d ,p) reaction to the single-particle states of 209Pb with spins ranging from 1 2 to 15 2 . Distorted-wave calculations are compared to all of these results and reasonable agreement is obtained with the cross sections and vector analyzing powers but not the tensor analyzing powers. The d and g vector analyzing powers for the spin-orbit partners are found to have opposite signs and this fact is used to assign g 9 2 spin to three l = 4 states seen near 2.6 MeV in 2205Pb.

One- and three-quasiparticle states in 121Sn

Abstract The reactions 119 Sn(t, p) 121 Sn and 120 Sn(t, d) 121 Sn have been studied at 13 MeV bombarding energy with energy resolutions of 15 keV and 11 keV, respectively. Angular distributions were measured from 12° to 66° in 6° steps and values of the transferred orbital angular momentum were derived. In the (t, d) case, spectroscopic factors are presented. Considerable f-strength from the (t, d) reaction is found near 2.5 MeV, which is about 2 MeV lower than expected from the single-particle model. One- and three-quasiparticle components of the 121 Sn states are examined in some detail. It is concluded that in spite of considerable mixing, the low-lying levels seem amenable to a core-particle description.

Structure of 205Hg from T = 452 states in 205Tl

Abstract The elastic and inelastic proton scattering excitation functions were measured from a 204 Hg target at bombarding energies from 14.0 MeV to 16.4 MeV, and at scattering angles of 30.5°, 125°, 149.5° and 165°. The elastic scattering data show T = 45 2 , l = 4 resonances in 205 Tl at 14.72 and 15.43 MeV, an l = 2 resonance at 15.81 MeV, and another possible l = 2 resonance apparently at 16.5 MeV, which is near the upper limit of the experiment. The inelastic scattering to the first excited 2 + state does not exhibit sharp distinct resonances at the first three of these energies, whereas evidence for a strong resonance structure is found corresponding to the 16.5 MeV elastic resonance. The elastic data are analysed to yield resonance parameters: E res , Γ total and Γ p for each resonance. The observed splitting of the g 9 2 and d 5 2 strength interpreted in terms of the structure of 205 Hg based on the particle-core coupling model.

The asymmetry in the 176Yb(p, t)174Yb reaction using polarized protons at 16 MeV

Abstract The vector analyzing power, as well as the differential cross sections, were measured for the 176 Yb(p, t) 174 Yb reaction with E p = 16 MeV, leading to the 0 + , 2 + , and 4 + states of the ground band. It was found that the CCBA explains both measurements rather well, while the DWBA also explains the data for the analyzing power, but not the (p, t) angular distributions particularly those for the excited states.