See shell model analyses in: 1983Va31,1984Va06,1985Po10, 1987Sa15, 1992Go17, 1996Wa35, 2007Gu03

See Mean Field model analyses in: 1996Su24, 1997Ba23, 1997Ba54, 1997Re07, 2005Ar12, 2006Sh20, 2020Al27

See Cluster Model and AMD analyses in: 1981Se06, 1994De32, 1995De31, 2005Ne03, 2005Th06, 2012Ka10, 2013Ma53, 2021Co07

See other analyses in: 1995Ta32, 1999Ka67, 2000Bh07, 2004De60, 2004La24, 2004Ne16, 2004Sa50, 2006Ko02, 2007Bl02

See discussion on low-lying ¹³Be levels and possible level inversion in: 1985Po10, 1995De31, 1997Re07, 1999La20, 2004Ta03, 2008Ha16, 2009BlZZ, 2010Bl12, 2012Bo15, 2012Fo22, 2013Fo03, 2014Fo21, 2014Ho08, 2015Fo06, 2018Fo07, 2019Fo02.

In the present analysis the data are somewhat discrepant. The experimental approaches often provide incomplete measurements of the reaction observables and result in what appear as incompatible observations. The ¹⁴C(¹¹B,¹²N) and ¹⁴C(π^-,p) results have been used to guide an initial level scheme since these results are insensitive to ambiguities present in level energy determination based on n+¹²Be momentum reconstruction. The modern results where n+¹²Be kinematics are measured provide meritous information on levels energies and decay modes and have been heavily consulted.

In surveying the results a trend appears where two groups around E_rel( n+¹²Be)≈0.5-0.7 MeV and 2.3-2.5 MeV can reasonably fit the energy spectrum. However in studies utilizing γ+n+¹²Be coincidence events, where ¹²Be excited states are considered, evidence is found for a larger number of neutron groups corresponding to levels at E_res(n+¹²Be_g.s.)≈0.4, 0.8, 2.0 and 3.0 MeV. The importance of including γ emission in analyzing the n+¹²Be spectra is highlighted below with comments on two mesurements. First, in (2001Th01) the ⁹Be(¹⁸O,¹³Be|)¹²Be+n) reaction was measured; evidence for two components, at E_res≈0 and 2.0 MeV, was found in the relative energy spectrum; however subsequent understanding supports the interpretation that these groups are connected to a E_res(n+¹²Be)≈2 MeV level that decays to ¹²Be_g.s. with E_n≈2 MeV and also decays to the high energy tail of ¹²Be^*(2.1 MeV) . Second, in the initial analysis of the ¹H(¹⁴Be,¹³Be|)¹²Be+n) resonance spectrum of (2010Ko17), resonances at E_res=0.51 MeV 1 with Γ=0.45 MeV 3 and E_res=2.39 MeV 5 with Γ=2.4 MeV 2 were found, but the discussion indicated the E_res=2.39 MeV region could also be reproduced with groups at E_res=2.0 MeV and E_res=2.9 MeV as suggested by (1992Os04,1998Be28). α reanalysis of (2010Ko17) in (2013Ak02) found evidence for 5 levels that decay to ¹²Be ground and excited states.

Lastly, the virtual play-by-play analysis of experimental results given in the discussion of Fortune’s (2012-2019) articles provides insight into the evolution of our understanding of this nucleus. In these articles, extensive discussion on experimental work is given along-side a simple potential model analysis. Early on, the statement is made that, "The (lowest) s state in ¹³Be is unbound, and unbound neutron s states are notoriously hard to handle. " Throughout the series of articles, listed above, the discussion focuses on likely structure configurations, the order of low-lying level spins and reasonable widths, and decay modes that can reasonably explain the data. See related discussion in (2021Co07).

Q-value: S_2n=2720 keV 10.