4D-imaging of drip-line radioactivity by detecting proton emission from 54mNi pictured with ACTAR TPC

Abstract

Proton radioactivity was discovered exactly 50 years ago. First, this nuclear decay mode sets the limit of existence on the nuclear landscape on the neutron-deficient side. Second, it comprises fundamental aspects of both quantum tunnelling as well as the coupling of (quasi)bound quantum states with the continuum in mesoscopic systems such as the atomic nucleus. Theoretical approaches can start either from bound-state nuclear shell-model theory or from resonance scattering. Thus, proton-radioactivity guides merging these types of theoretical approaches, which is of broader relevance for any few-body quantum system. Here, we report experimental measurements of proton-emission branches from an isomeric state in 54mNi, which were visualized in four dimensions in a newly developed detector. We show that these decays, which carry an unusually high angular momentum, ℓ = 5 and ℓ = 7, respectively, can be approximated theoretically with a potential model for the proton barrier penetration and a shell-model calculation for the overlap of the initial and final wave functions.

Elucidating the nature of the proton radioactivity and branching ratio on the first proton emitter discovered 53mCo

“…The signal for each pad is sampled at 25 MHz after being passed through a preamplifier and a shaper. The processing of the GET electronics is already described in the literature 44 , 45 , and more details for the present experiment can be found elsewhere 8 , 46 .…”

“…Since then, over 60 proton emitters have been discovered 5 , 6 , and the region near doubly-magic N = Z = 28, 56 Ni, has continued to exhibit discovery potential for exotic decay modes. For example, discrete-energy proton branches competing with γ -ray emission have been found stemming from the 10 + isomer in 54 Ni 7 , 8 and from a rotational state at about 10 MeV excitation energy in 56 Ni 9 , 10 .…”

Search for Weak Side Branches in the Electromagnetic Decay Paths of the 6526-keV 10+ Isomer in 54Fe

“…Interestingly, it took more than 50 years to disentangle the complete decay pattern of this isomeric state by means of a combination of Penning-trap-assisted decay spectroscopy and 4D imaging of charged-particle decays with a time-projection chamber [10]. In the same experimental campaign, both protonemission branches of 54m Ni were determined [11,12]. The new experimental results were compared to cutting-edge shell-model and barrier penetration calculations for these (very) high-protons with = 5, 7, and 9, all (very) far beyond the N = 3, f 7/2 shell [10,11].…”

“…In the same experimental campaign, both protonemission branches of 54m Ni were determined [11,12]. The new experimental results were compared to cutting-edge shell-model and barrier penetration calculations for these (very) high-protons with = 5, 7, and 9, all (very) far beyond the N = 3, f 7/2 shell [10,11]. Further, the complete decay pattern of 54m Ni allowed the derivation of reduced transition strengths, B(E2; 10 + 1 → 8 + 1 ) and B(E4; 10 + 1 → 6 + 1 ), for the two competing γ-ray transitions from 54m Ni [13].…”