Observation of γ-delayed 3α breakup of the 15.11 and 12.71 MeV states in 12C

Abstract

Deduced γ transitionThe reactions 10 B( 3 He, pααα) at 4.9 MeV and 11 B( 3 He, dααα) at 8.5 MeV have been used to investigate the γ decay of states in 12 C. By measuring the four-body final state in complete kinematics we are able to detect γ transitions indirectly. We find γ transitions from the 15.11 MeV state in 12 C to the 12.71, 11.83, 10.3 and 7.65 MeV states followed by their breakup into three α particles. The relative γ -ray branching ratios obtained are (1.2 ± 0.3), (0.32 ± 0.12), (1.4 ± 0.2) and (4.4 ± 0.8)%, respectively, with the remaining (92.7 ± 1.0)% of the γ decays going to the bound states. We obtain Γ α /Γ = (2.8 ± 1.2)% for the isospinforbidden α decay of the 15.11 MeV state. From the 12.71 MeV state we find γ transitions to the 10.3 and 7.65 MeV states. The relative γ -ray branching ratios are (0.9 +0.6 −0.5 ) and (2.6 +1.6 −1.2 )%, respectively, with the remaining (96.6 +1.7 −1.3 )% of the γ decays going to the bound states. Finally, we discuss the relation between the β decay of 12 N and 12 B to states in 12 C and the γ decay of the 15.11 MeV analog in 12 C to the same states.

Breakup ofC12resonances into threeαparticles

“…To avoid four-body correlations all together, alternative ways of populating excited states in 12 C must be found, e.g., through the β decay of 12 B and 12 N [29] or γ decays from higher-lying states in 12 C [30].…”

Observation ofαdecay from a state in10B at 11.48 MeV

“…[17,18] for details. We note that the detectors are insensitive to γ rays and neutrons; only charged particles are measured, but γ -ray and neutron energies can still be determined indirectly by use of energy and momentum conservation [19].…”

Search for rotational state of Hoyle state in complete kinematic experiment12C(α, α′) 3α

“…Recent inelastic α-scattering angular distribution studies also indicated the presence of a 2 + state at 9.84 ± 0.06 MeV of width 1.01 ± 0.15 MeV [5]. On the other hand, the study of 12 C * , produced in the β-decay of 12 N and 12 B, decaying into 3α continuum has however, not found clear evidence about the existence and nature of the 2 + states at excitations ∼10-12MeV [6] and also no evidence found in recent measurement of 3 He induced reactions on 10,11 B target [7]. In contrast, more recently, the γ induced 12 Be + α → α + α + α decay.…”

“…So, complete kinematical measurement of all outgoing particles in each event may be helpful in reconstructing the events originating from the decay of the excited states of the Hoyle state using missing energy (due to the emission of γ-ray) criterion. However, a recent experiment performed in this line [10], where complete kinematical measurement of all outgoing particles emitted from the reactions 10 2 2 + state. Since the spin and isospin zero α-particle is a very good projectile for the excitation of the nuclear IS states [9], we studied the decay of 12 C * into 3-body final states (3α) using inelastic α scattering from 12 C target to study the excited states of 12 C which are predominantly excitable through isoscalar transitions in general, and to look for a cleaner signature of the elusive 2 2 + state in particular.…”