Helium burning and the death of massive stars from the beta-delayed alpha-particle emission of {sup 16}N

Journal Article · Thu Apr 01 04:00:00 EST 1993 · Bulletin of the American Physical Society

OSTI ID:243778

Gai, M

Helium burning in massive stars and red giants (at {approximately}200 MK) allows for the nucleo-synthesis of {sup 12}C and {sup 16}O via the {sup 8}Be({alpha},{gamma}){sup 12}C triple alpha capture reaction and the {sup 12}C({alpha},{gamma}) {sup 16}O capture reaction. At 300 keV, the most efficient energy for burning of helium, the resonant triple alpha-capture reaction is well understood but the {sup 12}C({alpha},{gamma}){sup 16}O reaction is poorly understood, due to the fact that it is a non-resonant reaction governed by the bound 1{sup {minus}} and 2{sup +} states of {sup 16}O. The results of helium burning--the {sup 12}C/{sup 16}O ratio, determines the abundance of heavy elements and the dynamics of a massive star at its last stages before a supernova. Attempts to measure the cross section of the {sup 12}C({alpha},{gamma}){sup 16}O reaction lead to values of the E1 S-factor ranging from 0-500 keV-b. The author has measured the astrophysical p-wave S(300)-factor of the {sup 12}C({alpha},{gamma}){sup 16}O reaction by measuring the inverse process of the beta-delayed alpha-particle emission of {sup 16}N, with an increased sensitivity to the (virtual) reduced alpha-particle width of the bound 1{sup {minus}} state at 7.12 MeV in {sup 16}O. The enhanced sensitivity is due to a kinematical factor and matrix elements of the beta decay of {sup 16}N. An experiment performed at Yale University and at the MSU radioactive beam facility with a sensitivity for {sup 16}N beta-decay branching ratio on the order of 10{sup {minus}9} to 10{sup {minus}10} will be discussed. These data (together with other data) were used to extract the S-factor from an R-matrix theory and the author quotes S{sub E1}(300) = 95 {+-} 6(stat){+-}28(syst) keV-b, in agreement with a concurrent experiment at TRIUMF and the one deduced from stellar models of 12 to 40 solar masses stars.

• DOE Contract Number: FG02-91ER40609
• OSTI ID: 243778
• Report Number(s): CONF-9304297--
• Journal Information: Bulletin of the American Physical Society, Journal Name: Bulletin of the American Physical Society Journal Issue: 2 Vol. 38; ISSN BAPSA6; ISSN 0003-0503
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ALPHA PARTICLES
ALPHA REACTIONS
BETA DECAY
CARBON 12
HELIUM BURNING
NITROGEN 16
NUCLEOSYNTHESIS
OXYGEN 16
S PROCESS