Different mechanism of two-proton emission from proton-rich nuclei 23Al and 22Mg

Yugang Ma ,K Okada,J.S Wang,N Aoi,H Baba,S Shimoura,M Wang,W Guo,H.W Wang,K Ieki,H Ooishi,T Motobayashi,A Ozawa,K Yoneda,Y Yamada,Y Togano,R Shioda,S Ota,G.Q Zhang,Y Kondo,T Moriguchi,N Iwasa,T Kawabata,K Kurita,S Kanno,M Kurokawa,J.G Chen,Toshio Honda ,X G Cao ,Yuta Ito ,Yusuke Yasuda ,Yunlong Fu ,Zhengguo Hu ,Hiroyuki Kimura ,Cai Xiang-Zhou ,Satoshi Takeuchi ,H Sakuraï ,Yuji Ishibashi ,Dq Fang ,Eri Takeshita ,Wenlong Tian ,Kazunari Yamada ,Hiroshi Murakami ,X Y Sun ,Yasuo Hara ,Pei Zhou

doi:10.1016/j.physletb.2015.02.066

Abstract

Two-proton relative momentum (qpp) and opening angle (θpp) distributions from the three-body decay of two excited proton-rich nuclei, namely Al23→p+p+Na21 and Mg22→p+p+Ne20, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at qpp∼20 MeV/c as well as a peak in θpp around 30° are seen in the two-proton break-up channel from a highly-excited 22Mg. In contrast, such peaks are absent for the 23Al case. It is concluded that the two-proton emission mechanism of excited 22Mg is quite different from the 23Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process.

Highlights

The decay of proton-rich nuclei, especially the two-proton (2p) radioactivity [1], is an interesting process that may be observed in nuclei beyond or close to the proton dripline [2,3,4]
A broad qpp spectrum and structure-less θpp distribution are observed as shown in the insets of Fig. 1(a) and Fig. 1(b). These results indicate that the dominant mechanism of two proton emission from 23Al and 22Mg are sequential or simultaneous decay with weak correlation between the two protons
A clear peak should appear at relative momentum around ∼20 MeV/c as well as small opening angle

Summary

Introduction

The decay of proton-rich nuclei, especially the two-proton (2p) radioactivity [1], is an interesting process that may be observed in nuclei beyond or close to the proton dripline [2,3,4]. The diproton emission is basically two protons constrained by the pair correlation in a quasi-bound s-singlet, i.e., 1 S0 configuration. Studying the two-proton correlation provides a good tool to understand the nucleon–nucleon pair-correlation (p–p correlation in particular) inside a nucleus and other related topics like the BCS-BEC crossover [5]. It is a good way for investigating the astro-nuclear (2p, γ ) and (γ , 2p) processes which are closely related to the waiting point nuclei [6,7,8]. Some experimental investigations on the 2p emitter have been done [9,10,11,12,13,14,15,16,17], the two-proton decay mechanism is still not well understood and further experimental and theoretical studies are required

Methods

Results

Conclusion