Nuclear Seminar

A new study of low energy (p, gamma) resonances on Magnesium isotopes

Dr. Gianluca Imbriani
University of Naples, Italy

Monday, October 19, 2009   4:00 p.m.   NSH 124
(Refreshments served prior to seminar in NSH 124)

Proton captures on Mg isotopes play an important role in Mg-Al cycle active in stellar H shell burning. In particular, the strength of low energy resonances (Ep<190 keV) in ²⁵Mg (p, gamma) ²⁶Al determine the production of ²⁶Al.

Observations from satellites have discovered a gamma-ray line at keV which arises from the beta-decay of ²⁶Al to ²⁶Mg (T{1/2} = 7*10⁵ yr). Moreover, the presence of ²⁶Al in the interstellar medium has been determined from the observation of ²⁶Mg isotopic enrighment (extinct ²⁶Al) in carbonaceous meteorites. While the observations from COMPTEL and INTEGRAL provided evidence that ²⁶Al nucleosynthesis is still active on a large scale, the Mg isotopic variations show that ²⁶Mg must have been produced within the last 4.6 billion years (time of the condensation of solar-system material). Any astrophysical scenario for ²⁶Al nucleosynthesis must be concordant with both observations. A more precise knowledge of these nuclear data is highly desirable whereby this determination depends strongly on the availability of intense beams, on one side, and on the possibility to produce oxygen free targets. The latter problem can be circumvented by use of higher energy resonance strengths in the same reaction.

In this seminar I will report on the measurement of the strengths of the resonances at 224, 304 and 338 KeV in ^{24, 25, 26}Mg(p, gamma) reactions and of the strengths of lower energy resonances of ²⁵Mg (p, gamma) performed using different experimental techniques and setups.