Anatomy of three-body decay II: decay mechanism and resonance structure

Abstract

We use the hyperspherical adiabatic expansion method to discuss the the two mechanisms of sequential and direct three-body decay. Both short-range and Coulomb interactions are included. Resonances are assumed initially populated by a process independent of the subsequent decay. The lowest adiabatic potentials describe the resonances rather accurately at distances smaller than the outer turning point of the confining barrier. We illustrate with realistic examples of nuclei from neutron ( 6 He) and proton ( 17 Ne) driplines as well as excited states of beta-stable nuclei ( 12 C).

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

“…If the Hoyle state is a structureless α gas or condensate, then the decay should have equal probabilities for all of the possible partitions involving α-condensed subsystems [25]. However, the width of the Hoyle state has previously been calculated to be around 60 eV using the WKB approximation [26]. This is 3 times larger than the full computation and about 7 times larger than the experimentally measured value of 8.5 eV [27].…”

Two-proton radioactivity

“…This process which goes through the tail of an energetically inaccessible state, is called the virtual sequential two-body decay [134]. For its study, it is important to separate 1p-and 2p-decays in the effective Hamiltonian:…”

“…If crossings of various adiabatic potentials occur along the way through the barrier, the system is supposed to follow a path corresponding to the smoothest adiabatic potential. The Hyperspherical Adiabatic Expansion (HAE) method has been extensively used to study different possible situations in three-body decay resulting from various combinations of short and long-range interactions and different binding-energy situations of all two-body subsystems [134,153,154]. In particular, it has been applied for the description of the Borromean nucleus 17 Ne( 15 O + p + p) [134,38].…”

“…This mechanism which resembles the virtual sequential decay process discussed above (see Sect. 8.2.1) leads to a significant reduction of the 2p partial half-life of the 3/2 − state in 17 Ne [134,38]. Principal assumptions of the HAE approach are (i) the adiabatic motion in the three-body system, and (ii) the cluster ansatz for the many-body wave function of the total system.…”

First Observation of the Unbound NucleusNe15

“…2, since it is not strongly populated in inelastic scattering. The observed peak may therefore exclusively be assigned to the decay of the 5=2 − state at E Ã ¼ 1.764ð12Þ MeV, which has a negligible width compared to the experimental resolution [9,11]. The corresponding energy of the peak in the E fpp spectrum is expected at 831(12) keV.…”