New experimental results for the triple-alpha reaction

Abstract

The triple-alpha reaction is one of the key reactions in nuclear astrophysics. The reaction rate is primarily needed at temperatures of some 10 8 K typical for Helium burning in red giant stars, but the rate at very low and very high temperatures is also needed for various specialized applications. Here we discuss new experimental results relevant for determining the rate of the 3α reaction. First, we present a new improved upper limit for direct α-decay of the Hoyle state, which effectively removes this issue from the error budget of the reaction rate at Helium burning temperatures. We use the reaction 11 B(3 He,d)3α to populate the Hoyle state, and measure its decay in complete kinematics. Second, we present a new method for studying broad resonances in 12 C. We populate a resonance above the region of interest and select γ-decays of this resonance to lower lying resonances. The γ-decay is identified by measuring the final state in complete kinematics, which makes it possible to identify γ-decay to broad resonances, which is otherwise very difficult due to either background from overlapping states with different spin-parity, or due to the response of conventional gamma-detectors. By choosing the first resonance appropriately one can enhance the selectivity for each state of interest by using the selection rules of γ-decay. Our first case using this method is a search for the first 2 + resonance in 12 C, which has been the object of countless studies throughout the years. We will present clear evidence for a 2 + resonance near 11-12 MeV and tentative evidence also for a resonance at 9-10 MeV. These resonances will enhance the 3α-reaction rate at elevated temperatures.

Cosmic nucleosynthesis: A multi-messenger challenge

“…These can be explained by the operation of the first and second dredge-up during the red giant phase prior to the AGB phase. However, the origin of Group 2 grains, which also show a strong depletion in 18 A 16 O isotopic ratios in the envelope of solar metallicity stars at FDU ith mass from 1 to 2 M and at SDU for masses from 4.5 to 6 M , t cyan points are group 1 oxide grains, while darker dots are those ending from the 1.2 M , and the 1.5 M markers refer to magnetic tars for different values of k (see the text for details). The maximum mposition that can be produced by CBP during the RGB phase is d curves starting from 4.5, 5, and 6 M SDU abundances deal with O/ 16 O isotopic ratios in the envelope of AGB stars affected by HBB.…”

“…The maximum mposition that can be produced by CBP during the RGB phase is d curves starting from 4.5, 5, and 6 M SDU abundances deal with O/ 16 O isotopic ratios in the envelope of AGB stars affected by HBB. un with reaction rates of set A and Panel (B) to calculations run with the 17 O/ 16 O and the 18 O/ 16 O solar values.…”

“…The maximum modification of the envelope composition that can be produced by CBP during the RGB phase is indicated by the gray curve. Red curves starting from 4.5, 5, and 6 M SDU abundances deal with the evolution of 17 O/ 16 O and 18 O/ 16 O isotopic ratios in the envelope of AGB stars affected by HBB. Panel (A) refers to calculations run with reaction rates of set A and Panel (B) to calculations run with the set B.…”

“…Panel (A) refers to calculations run with reaction rates of set A and Panel (B) to calculations run with the set B. The dashed lines mark the 17 O/ 16 O and the 18 O/ 16 O solar values.…”

Broad resonances in light nuclei studied withβ- andγ-spectroscopy

“…The implications for the nuclear synthesis of 12 C for various astrophysical processes is discussed in [7,[19][20][21], and references therein.…”