Spectroscopic study of 26Si for application to nova gamma-ray emission.

Abstract

26 Al was the first cosmic radioactivity ever detected in the galaxy. Its nucleosynthesis in novae outbursts is still uncertain mainly due to the lack of nuclear information concerning the 25 Al(p,γ) 26 Si reaction. We report here on a neutron-gamma coincidence measurement of the 24 Mg( 3 He,nγ) 26 Si reaction performed at the Orsay TANDEM facility aiming at the spectroscopic study of astrophysically important 26 Si states. A new level in the Gamow peak is observed at E X = 5.888 MeV and the gamma-ray decay scheme of all levels below the proton threshold is confirmed.11th Symposium on Nuclei in the Cosmos, NIC XI

Progress on nuclear reaction rates affecting the stellar production of 26Al

“…An additional open question has been recently highlighted by studies of the 24 Mg( 3 He, nγ) 26 Si reaction [268,269,271]. Population of a new level at 5890 keV has been observed and conclusively identified as a 0 + state [269].…”

“…Note that in [258], the 5928 keV state was labeled as 5916 keV as a result of the uncertain calibration of lower-lying levels [273], and it would be worthwhile to revisit the data from that measurement in light of the more precise energy measurements currently available. Another question is why is the 5890 keV 0 + state so readily observable in the 24 Mg( 3 He, nγ) 26 Si studies [266,268,269,271], but no neutrons were observed populating the state in the 24 Mg( 3 He, n) 26 Si measurement [261], which seemingly had the resolution to observe it? Finally, the question as to whether we are seeing too many 0 + levels and the assertion in [263] of a missing 1 − level clearly strains our ability to claim complete knowledge of the relevant 26 Si level structure.…”

26Si excited states via one-neutron removal from a27Si radioactive ion beam

“…As mentioned earlier, a potential new level at 5888(2) keV was recently reported in a study of the 24 Mg( 3 He, nγ) 26 Si reaction by de Séréville et al [36]. Its excitation energy was re-constructed from the observation of coincident γ-ray transitions of 1749(2), 3102(2) and 4091(2) keV to the bound 2 + states at 4139, 2785 and 1797 keV, respectively.…”

“…Furthermore, Bell et al [11] 26 Si in which neutrons were detected in coincidence with decay γ-rays [36], a potentially important new state was found at 5888 keV via its decay cascade, which was not observed in either Ref. [20] or Ref.…”