New Measurement of the Direct 3α Decay from the C12 Hoyle State

A new high-precision upper limit of direct α-decays from the Hoyle state in 12C

“…This result, recently published in [26], has a precision of about a factor 5 better than any other previous investigation. An analogous result has been also obtained by a very recent experiment performed by the group of Birmingham [27].…”

Report on scipost_201911_00026v1

“…It was demonstrated that due to the effect of the Coulomb barrier in the decay of 16 O → 4α, this decay mode is suppressed up until ∼ 18 MeV (in agreement with previous experiments [37][38][39][40][41]). This means that even with the reduced Coulomb barrier from a dilute 0 + 6 state, the decay of this state into 4α is heavily suppressed.…”

“…The resulting energy surface for 12 C, calculated with the F1 nuclear interaction [12], is given in figure 1. Equivalent surfaces have been determined for other α-conjugate nuclei, 8 Be, 16 O and 20 Ne.…”

“…Much experimental effort has been devoted to measuring the 3α direct decay width of the Hoyle state in recent years [15][16][17][18]. The current section focuses on the data of reference [16], first published as a letter in 2017. A major issue in determining the 3α direct decay width is that the phase space for direct decay (5) is so much smaller than for the sequential decay (3).…”

“…In the 12 C( 16 O, 28 Si ) study [36], to overcome the limitations of the 4α penetrability, populating this state in the 12 C( 16 O, 12 C(0 + 2 )) 16 O reaction was attempted, by reconstruct- ing the 16 O from measuring the 12 C(0 + 2 ). From the compound nucleus, if one decay product ( 12 C(0 + 2 )) is produced which is heavily clustered, one would expect the other decay product to also be preferentially populated by heavily-clustered states.…”