[Triumf-seminars] TRIUMF ISAC Seminar, Thu 2005-04-07 at 14:00

[postmaster@ADMIN.TRIUMF.CA]

Date/Time: Thu 2005-04-07 at 14:00  

Location: Auditorium  

Speaker: Hans O.U. Fynbo (University of Århus)  

Title: 12B, 12C and the Red Giants - 50 years later  

Abstract: There is a fascinating interplay between subatomic physics and astrophysics in the history of the exploration of nuclear properties of the isotope 12C - the fourth most abundant nuclear species in the Universe. In 1953 Fred Hoyle predicted the existence of a 0+ nuclear resonance at 7.6 MeV in 12C in order to understand the observed abundances of 12C and 16O. Due to this resonance the reaction rate of the Salpeter process 4He + 8Be -> 12C is much enhanced. He also helped to provide experimental support for his prediction using the transfer reaction 14N(d,4He)12C. Already in 1955, as part of a more general work on n.alpha nuclei (e.g. 8Be, 12C, 16O, 20Ne, ...), Morinaga suggested that the Hoyle resonance should have the structure of a linear chain of three alpha particles. He further conjectured the existence of a 2+ resonance at higher energy - a rotational excitation of Hoyle's resonance.   

In 1957 Cook, Fowler, Lauritsen and Lauritsen used the beta decay of 12B to establish the energy and spin-parity of Hoyle's important resonance. They also found evidence for another resonance at higher energy, but they could only establish that the spin-parity of this new resonance was either 0+ or 2+, and therefore could not settle if it was Morinaga's predicted resonance or not.  

For nearly 50 years surprisingly little new information has come to light to clarify these questions, despite numerous experimental and theoretical studies. Theoretically the existence of Morinaga's conjectured 2+ resonance is strongly enough believed in for it to be included in the most recent Nuclear Astrophysics Compilation of Reaction rates (NACRE), where it enhances the rate of the Salpeter process by more than an order of magnitude for temperatures above 10^9 K.

In our recent work, we have performed a series of experiments using the beta decays of both 12B and 12N at the ISOLDE facility at CERN and the IGISOL beam line of the Jyväskylä accelerator centre in Finland to clarify the question of 0+ or 2+ states in 12C. In this talk I will present results from these experiments along with plans for future work.
   

Stimulants available 15 minutes before the talk.