β-delayed proton decay ofMg20and its astrophysical implications

Abstract

We have studied the P-delayed proton decay of 2OMg to search for the 2645 keV state in t Na. This state is of astrophysical interest, because any proton capture through this state would dominate the stellar reaction rate of the reaction ' Ne(p, y) Na. This reaction determines the break out from the hot CNO cycle. Several proton groups have been observed and their logft values have been determined. No protons from the 2645 keV state were seen and a lower limit of logft~5. 85 has been established. The impact of this result on the ' Ne(p, y) rate is discussed. PACS number(s): 23.40.s, 23.90.+w, 27.30.+t, 97.10.Cv

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.…”

“…For example, we anticipate that this method could be applied to the decays of 24 Si, 28 S, 36 Ca, and so on, given sufficient rare-isotope production and a sufficiently sensitive gamma-ray spectrometer.…”

“…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.…”

“…The experiment was carried out at Michigan State University's National Superconducting Cyclotron Laboratory (NSCL), which provided a fast radioactive 20 Mg beam using projectile fragmentation of a 170 MeV/u, 60 pnA 24 Mg primary beam from the Coupled Cyclotron Facility, incident upon a 961 mg/cm 2 9 Be transmission target. The 20 Mg ions were separated from other fragmentation products by momentum/charge using the A1900 fragment separator, which incorporated a 594 mg/cm 2 Al wedge [27].…”

Spectroscopic studies of the βp and β2p decay of 23Si

“…It turned out that, due to the low implantation rate of about one 20 Na per second and of about three of each of the other isotopes per second, only a small contamination from the 20 Na activity might be possible due to its long half-life and its high branching ratios of its main α groups. The energy spectra of β-delayed protons were calibrated with the known β-delayed proton or α emitters 20 Na [15], 24 Si [16], 21 Mg [17], and 20 Mg [18,19]. 23 Si β-delayed protons have been measured in both the last silicon detector and the MSGC.…”