Study of Two-Neutron Radioactivity in the Decay ofO26

Abstract

A new technique was developed to measure the lifetimes of neutron unbound nuclei in the picosecond range. The decay of 26 O→ 24 O + n + n was examined as it had been predicted to have an appreciable lifetime due to the unique structure of the neutron-rich oxygen isotopes. The half-life of 26 O was extracted as 4.5 +1.1 −1.5 (stat.) ± 3(sys.) ps. This corresponds to 26 O having a finite lifetime at an 82% confidence level and, thus, suggests the possibility of two-neutron radioactivity.

Beyond the neutron drip line: The unbound oxygen isotopes25O and26O

“…In the experimental work by the NSCL-MoNA group, a half-life T 1/2 = 4.5 +1.1 −1.5 (stat) ± 3(syst) ps has been extracted, corresponding to a lifetime of 6.5 ps. At an 82% confidence level, a finite lifetime of the 26 O ground state is claimed [37], suggesting the possibility of two-neutron radioactivity. Our upper limit of 5.7 ns (95% c.l.)…”

“…During the final stages of the refereeing process two Letters were published in Physical Review Letters discussing the lifetime of 26 O, one experimental [37] and the other theoretical [38]. In the experimental work by the NSCL-MoNA group, a half-life T 1/2 = 4.5 +1.1 −1.5 (stat) ± 3(syst) ps has been extracted, corresponding to a lifetime of 6.5 ps.…”

Three-body model for the two-neutron emission ofBe16

“…In one of the first theoretical studies of twoneutron decay, Grigorenko [12] discussed the existence of one-, two-, and four-neutron emitters, as well as comparisons of their widths in a three-body framework. Recently, a few cases of two-neutron decay have been observed [13,14,15]. The first of these was observed in a 2012 experiment at the National Superconducting Cyclotron Laboratory [13] through the decay of 16 Be to 14 Be plus two neutrons.…”

“…We use the definition of the spinorbit strengths of FaCE [25]. Potential depths for the various models included are as indicated in Table I. The lowest s-and p-orbitals in 14 Be are assumed to be full. In order to remove the effect of these occupied states in the 14 Be core, the 1s 1/2 , 1p 3/2 , and 1p 1/2 states were projected out through a supersymmetric transformation [25].…”

“…As the ground state energy of 16 Be was found to be 1.35 MeV (with a width of 0.8 MeV) and a lower limit of 1.54 MeV had previously been placed on the ground state of 15 Be [16], 16 Be is an ideal candidate for simultaneous two-neutron decay. Depending on the width of the ground state of 15 Be, sequential neutron de-cay from 16 Be to 14 Be could be energetically inaccessible. A later experiment [17] determined that the lowest state in 15 Be is an l = 2 state at 1.8 MeV with a width of 575 ± 200 keV.…”