Oak Ridge National Laboratory

Physics Division

Physics Division Seminars

Physics Division Seminars bring us speakers on a variety of physics related subjects. Usually these are held in the Building 6008 large Conference Room, at 3:00 pm on the chosen day, but times and locations may vary. For more information, contact our seminar chairman,

Alfredo Galindo-Uribarri
Tel (Office): (865) 574-6124  (FAX): (865) 574-1268

Tue., March 27, 2012, at 3:00 p.m. (refreshments at 2:40 p.m.)

Direct Capture in Nuclear Astrophysics: The cases of ¹⁷O (p, ) ¹⁸F and ³He ( ) ⁷Be

Antonio Kontos, NSCL, Michigan State University
Building 6008 Conference Room

Direct radiative capture is a non-resonant one-step nuclear reaction mechanism that in principle does not involve the formation of a compound nucleus. In the absence of strong resonances inside the Gamow window, direct capture can be the dominant contribution to astrophysical important reaction rates. The present work studies two such reactions, ¹⁷O(p, ) ¹⁸F and ³He () ⁷Be. The first reaction influences hydrogen-burning nucleosynthesis in several stellar sites, such as red giants, asymptotic giant branch (AGB) stars, massive stars and classical novae. In the relevant temperature range for these environments (Τ₉= 0.01 – 0.4) the main contributions to the rate of this reaction are the direct capture process, two low lying narrow resonances ЕR = 70 and 193 keV, and the low energy tails of two broad resonances ER = 587 and 714 keV. In this work we present a measurement of the reaction at a wide proton energy range Elab = 360 – 1625 keV and at several angles Θlab= 0˚, 45˚, 90˚, 135˚, in order to address discrepancies and uncertainties in the literature data, especially in the direct capture component. 3He () 7Be is important for the neutrino production in the sun’s core and the production of 7Li during the big band nucleosynthesis. Recent experiments have improved the uncertainty of the reaction but some discrepancies still exist. In the present work, a relatively wide energy window was measured, E CM= 0.300 – 1.450 MeV, by detecting the prompt gamma-rays from the reaction. The use of a compact helium jet gas target ensured high gamma-ray detection efficiency. Contact: A. Galindo-Uribarri (uribarri@ornl.gov; 574-6124)