Semimicroscopic description of basic modes of relaxation of the Gamow-Teller resonance
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CLEI Theory
Semimicroscopic Description of Basic Modes of Relaxation of the Gamow–Teller Resonance I. V. Safonov* and M. H. Urin National Research Nuclear University MEPhI, Kashirskoe sh. 31, Moscow, 115409 Russia Received December 23, 2011; in final form, April 22, 2012
Abstract—Semimicroscopic approach based on the continuum version of the random-phase approximation and on a phenomenological method for taking into account the fragmentation effect is used to describe quantitatively basic relaxation parameters of the Gamow–Teller resonance in magic and nearmagic nuclei. For the 208 Bi nucleus, the results obtained by calculating the resonance parameters in question are compared with respective experimental data. DOI: 10.1134/S1063778812120113
1. INTRODUCTION Being a spin-flip partner of the isobaric analog resonance (IAR), the Gamow–Teller resonance (GTR) corresponds to monopole 1+ collective excitations associated with a proton-to-neutron transition, basically without a change in the radial quantum number. Numerous experimental and theoretical investigations of properties of the Gamow–Teller resonance and its satellites were devoted, as a rule, to studying the distribution of the Gamow–Teller strength. Along with this distribution (Landau damping), there are other modes of relaxation of the Gamow–Teller resonance. These include the fragmentation effect and direct protonic decay. Quite a lot of experimental data have been obtained for the total width of the Gamow– Teller resonance—it is associated primarily with the fragmentation effect—but a detailed experimental investigation of direct protonic decay was performed only for the Gamow–Teller resonance in the 208 Bi nucleus by using the direct reactions 208 Pb(3 He, t) and 208 Pb(3 He, tp) [1]. Later, a similar investigation was performed for the isovector giant spin-monopole resonance (IVSGMR(−) ) [2], which is an overtone of this Gamow–Teller resonance. For energies lower than the energy of the Gamow–Teller resonance, the experimental distribution of the Gamow–Teller strength (with respect to the strength of the main maximum) in the 208 Bi nucleus was studied in [3] also by using the reaction 208 Pb(3 He, t). A radically different means for exciting the Gamow–Teller resonance in [4] via the resonance reaction 117 Sn(p, n) is worthy of special note. The results obtained in that experiment are at odds with respective data extracted *
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from an analysis of the direct reaction 118 Sn(3 He, t) in [5]. The reasons behind this discrepancy have yet to be clarified. In the present study, a semimicroscopic description of basic modes of relaxation of the Gamow–Teller resonance is proposed and is implemented for the example of the parent nucleus 208 Pb. The semimicroscopic approach to describing the relaxation of giant resonances (for a detailed description of the modern version of this approach, we refer the interested reader to [6]) relies on the continuum version of the random phase approximation (cRPA) and on a phenomenological description of the
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