Beta-decay of 20Mg

Revalidation of the isobaric multiplet mass equation for theA=20quintet

“…The present excitation energy of the lowest T = 2 state is 27 keV (1.9 standard deviations) lower than the value of 6525±14 keV from the most recent data evaluation [3], which was based on several measurements of 20 Mg betadelayed proton emission [18,24,25]. The present value is also 28 times more precise.…”

“…This peak was confirmed to be from a highlying level of 20 Na by placing a coincidence condition on the well known 984-keV 20 Na gamma-ray transition ( Figure 3) [25], showing that the 5514-keV gamma ray feeds the 984-keV level. The latter peak was observed at a laboratory energy of 983.70 ± 0.00 stat ± 0.10 syst keV (Figure 4).…”

“…The largest uncertainty, by far, is the 14 keV uncertainty associated with the mass excess of the lowest T = 2 state in 20 Na [3], which is based on measurements of the energies of 20 Mg beta-delayed protons [18,24,25]. Although T = 1/2 proton emission from a T = 2 state to produce T = 1/2 19 Ne is forbidden by conservation of isospin, the 20 Na state is sufficiently proton-unbound (by > 4 MeV) that the proton emission proceeds anyways and is, in fact, the dominant decay mode.…”

“…Adding the excitation energy to the recently determined precise ground-state mass of 20 Na [22,26] would provide the mass of the lowest T = 2 state, which could then be used for an improved IMME test. We measured the excitation energy of the lowest T = 2 state in 20 Na using the beta-delayed gamma decay of 20 Mg (Figure 1), which has only been measured once before yielding a single 20 Na gamma-ray transition from a low-lying bound state [25].…”

Constraining the 19Ne(p,γ)20Na Reaction Rate Using a Direct Measurement at DRAGON

“…However, for over twenty years, the exact strength and energy of this resonance state have been a subject of intense debate [8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”