Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Observation of oscillations and near-barrier suppression in the fusion of $^{20}$O + p

H. Desilets, Rohit Kumar, R. T. deSouza, S. Hudan, C. Ciampi, A. Chbihi, K. W. Brown, Varinderjit Singh, B. Pinheiro, J. L. Ferreira, J. Lubian

TL;DR

This work investigates how entrance-channel structure governs near-barrier fusion in a neutron-rich light system by measuring $^{20}$O+$p$ fusion with an active-target detector. It combines angle-integrated fusion data with CC/R-matrix calculations that include the first excited $2^+$ state of $^{20}$O to reveal oscillatory structures in the cross-section and a sub-barrier suppression trend. The three broad peaks, each about $50$–$100$ keV wide, are consistent with coupling to low-$\ell$ quasibound states in $^{21}$F near the proton threshold, and the results underscore the need for dynamical, time-dependent treatments to fully describe fusion in this quasibound regime. The study demonstrates the diagnostic power of proton fusion for probing evolving nuclear structure in neutron-rich systems and the barrier itself.

Abstract

Using an active target detector, the fusion excitation function for $^{20}$O + $^1$H was measured for the first time. Near the barrier, the fusion cross section manifests an oscillatory behavior with broad peaks $\sim$50-100 keV wide. The presence of these peaks likely reflects the low density of low-angular-momentum states in the quasibound regime. R-matrix coupled channel (CC) calculations that include the first excited 2$^+$ state in $^{20}$O are able to reproduce the observed oscillations. However, one channel CC calculations fail to reproduce the decrease in the sub-barrier cross section experimentally observed.

Observation of oscillations and near-barrier suppression in the fusion of $^{20}$O + p

TL;DR

This work investigates how entrance-channel structure governs near-barrier fusion in a neutron-rich light system by measuring O+ fusion with an active-target detector. It combines angle-integrated fusion data with CC/R-matrix calculations that include the first excited state of O to reveal oscillatory structures in the cross-section and a sub-barrier suppression trend. The three broad peaks, each about – keV wide, are consistent with coupling to low- quasibound states in F near the proton threshold, and the results underscore the need for dynamical, time-dependent treatments to fully describe fusion in this quasibound regime. The study demonstrates the diagnostic power of proton fusion for probing evolving nuclear structure in neutron-rich systems and the barrier itself.

Abstract

Using an active target detector, the fusion excitation function for O + H was measured for the first time. Near the barrier, the fusion cross section manifests an oscillatory behavior with broad peaks 50-100 keV wide. The presence of these peaks likely reflects the low density of low-angular-momentum states in the quasibound regime. R-matrix coupled channel (CC) calculations that include the first excited 2 state in O are able to reproduce the observed oscillations. However, one channel CC calculations fail to reproduce the decrease in the sub-barrier cross section experimentally observed.

Paper Structure

This paper contains 6 sections, 2 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Experimental details
  3. Experimental Results
  4. Theoretical Calculations
  5. Conclusions
  6. Acknowledgements

Figures (5)

  • Figure 1: Schematic illustration of the potential between a proton and a $^{20}$O nucleus. The short-range attractive part is assumed to have a Woods-Saxon form with the parameters indicated. The cross-hatch regions indicate quasibound states.
  • Figure 2: Putative proton fusion trace (solid, black) is compared to a few beam traces (solid, magenta). The average of the beam traces used as the reference beam trace is depicted by the dotted (black) line. Based upon a Z$^2$ scaling from the average beam trace, the reference line for F ions is indicated by the solid (red) line.
  • Figure 3: For putative proton fusion traces in anode 4, one-dimensional distribution of $\langle$E$\rangle$$_{after}$. Events to the left of the red line are rejected.
  • Figure 4: Fusion cross section for the reaction $^{20}$O + p. Incident energies at the middle of A0 along with the various pressures used are indicated.
  • Figure 5: Comparison of the experimental fusion cross section with one channel and R-matrix coupled channel calculations.