Abstract
To investigate the spectator role of the d5/2 unpaired proton outside the Z=50 closed shell, the 120Sn(p,α) 117In and 121Sb(p,α)118 Sn reactions have been measured in high resolution experiments, performed with the 23 MeV proton beam of the Munich MP Tandem, using the Stern-Gerlach type polarized hydrogen ion source and the Q3D magnetic spectrograph.
Highlights
We have observed [1] an interesting behaviour for a number of transitions induced by (p,α) reactions on near magic target nuclei having one proton outside a completely filled magic shell. In this case the outside, slightly bound nucleon acts as a spectator in the process and some distinctive features are displayed: a) at lower excitation energies weak population of residual nucleus levels, fed by the pickup of the spectator proton together with a neutron pair of the core; b) at higher excitation energies population of multiplets of states. In this high excitation energy region the dominant contribution arises from a process in which the incident proton picks up a proton and a pair of neutrons from the core, while the valence proton outside the Z=50 shell acts as a spectator
The configurations of these multiplets result from the coupling of the spectator proton with the low-lying states excited in the core that we call parent states
In the case of weak coupling between the parent state and the spectator nucleon it is expected that: a) the angular distributions of cross sections and analyzing powers for transitions to homologous states are very similar in shape because the processes exciting these states are essentially the same; b) the differential cross section for populating a parent state is approximately equal in magnitude to the sum of the cross sections of the transitions a e-mail: luisa.zetta@mi.infn.it to the multiplet of homologous states corresponding to the given parent state; c) the relative cross section for the population of a homologous state with spin Ji in a given multiplet is proportional to (2Ji + 1)
Summary
We have observed [1] an interesting behaviour for a number of transitions induced by (p,α) reactions on near magic target nuclei (odd-A nuclei) having one proton outside a completely filled magic shell (core) In this case the outside, slightly bound nucleon acts as a spectator in the process and some distinctive features are displayed: a) at lower excitation energies weak population of residual nucleus levels, fed by the pickup of the spectator proton together with a neutron pair of the core; b) at higher excitation energies population of multiplets of states. Sn(p,α)117 In and 121 Sb(p,α)118 Sn reactions have been measured
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