2+ States of 8Be

Abstract

SummaryAnalysis by many-level R-matrix theory of the d-wave "'-'" scattering phase shift suggests the existence of broad 2+ excited states of 8Be, but their properties depend sensitively on the assumed channel radius a2. A simultaneous fit to the 9Be(p, d)8Be deuteron spectrum near the 2, 9 MeV peak requires a2 "'" 7·1 fm, while a simultaneous fit to the ",-particle spectra following 8Li and 8B p-decays requires a2 "'" 6· 7 fm. For the best overall fit with a2 = 6·75 fm, the first 2+ excited state is at 2· 84 MeV excitation energy with a width at half maximum of 1·30 MeV. It is shown that data from other reactions which appeared to give much larger widths for this level can be fitted using the same R-matrix parameters. A second 2+ excited state is obtained at about 9 MeV with a width of about 10 MeV. Properties of the narrow 2+ states at 16·6 and 16·9 MeV are also discussed.

Further measurement of the beta-delayed alpha-particle emission of 16N

“…Barker [4,5] proposed the use of the β-delayed α-particle emission spectrum of 16 N to constrain S E1 , the p-wave component of the astrophysical cross section factor. At the time of these calculations [4,5], a single β-delayed α-particle emission spectrum with very high statistics ( > 36 million counts) existed. These data were measured at Mainz [8,9,10] in a successful measurement of the parity violating 1.281 MeV α-particle decay.…”

“…α-particles emitted from the continuum of 16 O populated by the β-decay of 16 N) has been predicted to provide a constraint on the cross section of this reaction [4,5,6,7], but it requires a measurement of a β-decay of 16 N with a sensitivity for a Branching Ratio (BR) of the order of 10 −9 . In particular, the low energy portion of the alpha-particle spectrum has been predicted to be sensitive to the reduced α-particle width of the bound 1 − state in 16 O; however, it cannot directly determine the mixing phase in the 12 C(α, γ) 16 O reaction of the two interfering states at 7.12 MeV and 9.58 MeV in 16 O.…”

The Ghost Anomaly in the 9Be(p, d)8Be Reaction

“…Simultaneous fits to these data and to the IX-IX s~wave phase shift, using a three-level R-matrix formalism, enabled properties of 0+ states of 8Be to be obtained, and required the s-wave IX-IX channel radius a o to be about 7 fm (Barker et al 1968). Similar fits to data involving 2 + levels of 8Be gave a 2 :::::: 6·75 fm (Barker 1969).…”

8Lielectron spectrum versus8Bneutrino spectrum: Implications for measuring solar

“…In addition, there are two narrow states at E x = 16.6 and 16.9 MeV, which are isospin mixtures of T = 0 and T = 1 2 + states, the latter being the analogue of the ground states of 8 Li and 8 B and is fed by Fermi beta decay, (M F ) 1 ′ = √ 2. The method of handling this isospin mixing is described in Barker [12] and Warburton [13].…”

“…Attempts to fit the α-spectra assuming only one state in 8 Be is operative fail to give enough yield at high energies. Barker [12] proposed R-matrix formulae in the many-level, one-channel approximation and used them to fit the β-delayed α-spectra. More recent fits have been given by Warburton [13] and Barker [9].…”