Experimental study ofβ-delayed proton decay ofAl23for nucleosynthesis in novae

Abstract

The β-delayed γ and proton decay of 23 Al has been studied with a novel detector setup at the focal plane of the MARS separator at Texas A&M University. We could detect protons down to an energy of 200 keV and determine the corresponding branching ratios. Contrary to results of previous β-decay studies, no strong proton intensity from the decay of the isobaric analog state (IAS) of the 23 Al ground state at Ex = 7803 keV in 23 Mg, was observed. Instead we assign the observed low energy group Ep,cm = 206 keV to the decay from a state 16 keV below the IAS. We measured both proton and gamma branches from the decay of this state at Ex = 7787 keV in 23 Mg, a very rare case in the literature. Combining our data with its measured lifetime, we determine its resonance strength to be ωγ = 1.4 +0.5 −0.4 meV. The value is in agreement with older direct measurements, but disagrees with a new direct measurement. This state is the most important resonance for the radiative proton capture 22 Na(p,γ) 23 Mg in some astrophysical environments, such as novae.

Simultaneous measurement ofβ-delayed proton andγdecay ofP27

“…An upper limit of 0.16% on the absolute proton branch for 27 P was estimated in this study. This is much lower than anything previously measured with this experimental setup, as 23 Al had a 1.22% and 31 Cl had a 0.70% proton branch respectively [11,17]. The lower the proton branch, the more likely it is that β particles dominate the spectrum, negatively affecting the proton signal-tonoise ration.…”

“…This insured that the 27 P and the low-energy protons of interest were fully contained within the proton detector. The technique used in this experiment was similar to experiments done previously at TAMU [17][18][19][20]. The beam from the cyclotron was pulsed by sending electronic signals (beam-on and beam-off requests) to the cyclotron, with the 27 P implanted for 503 ms into the proton detector, the cyclotron was then turned off for a 3 ms wait (to give the cyclotron time to process the beamoff request), then the decay was measured for 500 ms, roughly twice the half-life value 260(80) ms [11].…”

“…This was somewhat mitigated by the fact that 28 P was created about 5 times more abundantly than 27 P in this experiment. What was measured in the detector was not the true proton energy in the lab system, but because of the implantation process, a combination of the proton energy, the recoil energy of the daughter heavy-ion (after the proton decay) and the small amount of energy deposited in the detector from the β particles [15,17]. Limited statistics resulted in only the ability to confirm the proton energies from the previous measurement [12].…”

Storage ring at HIE-ISOLDE

“…Besides the cases cited above, other examples of this behaviour are in the α + d decay of 6 He [31,32], or the β-delayed proton emission of 23 Al [33]. Theoretical studies have been recently performed on a possible proton-emission channel in the decay of 11 Li [34], and the β-delayed proton emission by one-neutron halo nuclei [35] such as 11 Be, 19 C and 31 Ne; such β-delayed proton decays in neutron-rich nuclei have not been observed so far.…”

The Beta Delayed Proton and Gamma Decay of 27P For Nuclear Astrophysics

“…We see the higher energy protons that were identified by a Berkeley group [2] but, in the low energy region we saw a background larger than expected. We have determined that it was not due to technical difficulties, but we were being relatively overwhelmed by β's, because the proton branching ratio was being much lower than in the cases of 23 Al and 31 Cl studied before (about 10-100 times lower) [3][4][5]. However, it can be seen in Figure 3, that there is a clear structure above a continuous background in the low energy region 2-400 keV.…”