12C(6Li, d)16O at E(Li) = 90 MeV

Abstract

The 12C(6Li, d)160 reaction has been studied at E(~Li)= 90.2 MeV with a magnetic spectrometer. Spectra up to E x ~ 30 MeV in 160 have been obtained and decay line widths, F~ .... have been extracted for broad levels. Known a-cluster states (J" = 2 +, E x = 6.9 MeV; J~= 4 +, E x = 10.35 MeV) are preferentially populated and exhibit sharply forward peaked angular distributions in contrast with (eLi, d) data obtained at lower bombarding energies. These features are well reproduced by reaction calculations assuming direct alpha-particle transfer provided one utilizes realistic optical model, target, and projectile wave functions. Alpha spectroscopic factors and reduced alpha widths have been extracted for levels E~ < 12 MeV including J~ = 1-levels of astrophysical interest. The results are compared with other recent measurements and theoretical calculations. There is generally at least qualitative agreement (within × 2) between the various experiments and theories. The analysis indicates a non-negligible alpha width for the J" = 1 -level at E, = 7.1 MeV in 160 (which determines the ~ 2C ~ 160 stellar helium burning rate) with 0.3 < 0~ 2 (7.1 MeV)/0~ (9.6 MeV) < 0.6 and 0.1 < 02 (7.1 MeV)/0~ (6.9 MeV) < 0.4. E NUCLEAR REACTION IzC(6Li, d), E = 90.2 MeV: measured a(Ed, 0~). 160 deduced e-cluster states, a-reduced widths, S~, resonances, F. Optical model, direct e-transfer mechanism, realistic target, projectile wave functions. Magnetic spectrometer.

The4He(12C, ?)16O reaction at stellar energies

“…It should also be pointed out that attempts to determine the reduced alpha-particle widths of the two J~= 1-states ( Fig. 1) by a-transfer reactions [11] do not agree well with the direct determination [9] through the 12C(a, 7)160 reaction. In addition, the c~-transfer reactions imply 0~z(6.92 MeV)~I.0 [11], so that the E2 resonant capture through the high-energy tail of the J~=2 + state at 6.92 MeV (Fig.…”

The 12C(a,g)16O Cross Section at Low Energies

“…These values of e~ are given in Table 7, where their ratios are compared with those of Becchetti et al (1989). Probably one should not take the agreement between the values of e~(7 ·12)/e~(6· 92) too seriously, as Plaga et al (1987) also pointed out the excellent agreement between the value of this ratio deduced from their fits to 12C(OC,y)160 and phase shift data and that obtained from oc-transfer reactions (Becchetti et al 1980); these values were, however, 0·42 and 0·41 respectively.…”

“…Becchetti et al (1989) Tables 5 and 6); nevertheless, it is prudent to compare ratios at the same value of a. The oc-transfer values of Becchetti et al are based on a channel radius of 5·4 fm.…”

Nuclear clustering using a modern shell model approach

“…On the other hand, the values of θ 2 α vary a lot from state to state, which makes its interpretation easier. For sub-threshold states the SFs are obtained using the ( 6 Li,d) reaction [71], those SFs are measured relative to 4 + 1 10.356 MeV. Therefore some error is introduced by the rescaling of this data using the reduced width of the over-threshold reference state.…”