Clustering in $^{18}$O - absolute determination of branching ratios via high-resolution particle spectroscopy

Abstract

The determination of absolute branching ratios for high-energy states in light nuclei is an important and useful tool for probing the underlying nuclear structure of individual resonances: for example, in establishing the tendency of an excited state towards α-cluster structure. Difficulty arises in measuring these branching ratios due to similarities in available decay channels, such as ( 18 O,n) and ( 18 O,2n), as well as differences in geometric efficiencies due to population of bound excited levels in daughter nuclei. Methods are presented using Monte Carlo techniques to overcome these issues.

Precision branching-ratio measurements in $$^{18}$$O

“…Just above the n-decay threshold of S n = 8.045 MeV, it is very difficult to distinguish between γ -decay and n-decay events due to the limited kinetic energy available to product 17 O nuclei. As γ -decay becomes suppressed above particle decay thresholds, it is very unlikely to find a significant value of γ/ tot for high-lying excitations, however, the states at 8126(3) MeV, 8219(1) MeV and 8280(1) MeV have been previously determined to γ -decay [16].…”

Search for evidence of rotational cluster bands in O18

“…In order to distinguish between these decay channels, a kinematic technique known as a Catania plot (also known as a Romano plot) [16,17,19,26] was employed. A FIG.…”

“…The in-house Monte-Carlo code, Resolution8.1 [19,27,28], was used to generate events for each observed excited state, simulating all available decay paths. Individual decay paths for each state were simulated using 10 7 events in order to determine the expected geometry efficiency of the DSSD array while limiting the associated statistical error.…”

“…The simulations were also used to determine the fraction of individual channel events in overlapping loci of the Catania plots, using the method detailed in Ref. [19].…”

“…An experimental method was used in order to extract branching ratios for the high-energy excited states in 18 O to allow for determination of γ 2 α/γ 2 W , utilizing high-resolution reconstruction of decay products detected in the Birmingham large-angular-coverage DSSD array through kinematic techniques [16]. Establishment of the detection efficiency of each decay channel, as well as distinguishing between population of excited levels in daughter nuclei and consequent further decays, was done through Monte-Carlo simulation [17][18][19]. The Monte-Carlo data were used to set gates on regions of the experimental data, allowing for measurement of many different decay channels.…”