Systematic trends in beta-delayed particle emitting nuclei: The case ofβpαemission from 21 Mg

Abstract

We have observed β + -delayed α and pα emission from the proton-rich nucleus 21 Mg produced at the ISOLDE facility at CERN. The assignments were cross-checked with a time distribution analysis. This is the third identified case of βpα emission. We discuss the systematic of beta-delayed particle emission decays, show that our observed decays fit naturally into the existing pattern, and argue that the patterns are to a large extent caused by odd-even effects.

Beta-delayed proton emission from 20Mg

“…The beta decay of 21 Mg is well known, see e.g. [18][19][20], and it exhibits several high intensity βp transitions, which we have used for the calibration. However, for the very thin front detectors of 20 µm and 40 µm most proton lines punch through the detector.…”

“…The beta-delayed proton emission from 20 Mg feeds resonances in 19 Ne. The ground state of 19 Ne (plus proton mass) is located 2190.1(1.1) keV [6] above the ground state of 20 Na and the known excited states are located at 238.27 (11) keV, 275.09 (13) keV, 1507.56(30) keV, 1536.0(4) keV, 1615.6(5) keV, 2794.7 (6) keV, and 4032.9(2.4) keV [10]. The four lowest excited states are known to be populated by the beta decay of 20 Mg.…”

“…At an excitation energy of 4032.9(2.4) keV the seventh excited state in 19 Ne is located in the Gamow window of the 15 O(α, γ) 19 Ne reaction. This is the first reaction in the first breakout sequence from the HCNO-cycles [11] with the second reaction being 19 Ne(p, γ) 20 Na. The breakout sequence is leaking C, N and O seed nuclei into the A > 20 region and it is followed by the αp-and the rpprocesses.…”

“…The 2647(3) keV resonance in 20 Na is located just above the threshold for proton emission, S p = 2190.1(1.1) keV [6]. It is the most important resonance for determining the 19 Ne(p, γ) 20 Na reaction rate in X-ray bursters, as it is located in the Gamow window of the reaction. The spin and parity of this resonance have been the subject of some debate in the past.…”

Measurements of Thermal and Resonance Neutron Fluence and Induced Radioactivity Inside Bunkers of Medical Linear Accelerators in the Center of Oncology in Opole, Poland

“…Strong support to this assignment comes from the observation in the DSSSD detector of a proton peak in coincidence with this α peak. In this way, one can establish a new decay mode in 21 Mg with a branch of 1.6(3) × 10 −4 from the isobaric analog state in 21 Na to the 8.054 MeV state in 20 Ne with subsequent α emission to the ground state of 16 O [18]. The βpα decay mode is very rare and it has only been observed previously in 9 C and 17 Ne.…”