Compton scattering from ${}^6\mathrm{Li}$ at 86 MeV

Cross sections for ${}^6\mathrm{Li}(\gamma ,\gamma ){}^6\mathrm{Li}$ have been measured at the High Intensity Gamma-Ray Source $\mathrm{(HI}\vec{\gamma }\mathrm{S)}$ and the sensitivity of these cross sections to the nucleon isoscalar polarizabilities was studied. Data were collected using a quasimonoenergetic 86-MeV photon beam at photon scattering angles of ${40}^{\circ }–{160}^{\circ }$. These results are an extension of a previous measurement at a lower energy. The earlier work indicated that the ${}^6\mathrm{Li}(\gamma ,\gamma ){}^6\mathrm{Li}$ reaction at 60 MeV provides a means of extracting the nucleon polarizabilities; this work demonstrates that the sensitivity of the cross section to the polarizabilities is increased at 86 MeV. A full theoretical treatment is needed to verify this conclusion and produce values of the polarizabilities.

Figure 1

Diagram of the experimental setup showing the positions of the collimator, five-scintillator-paddle system, target, and NaI(Tl) detectors. Drawing is not to scale.

Figure 2

A representative TDC spectrum with the prompt and random windows shown.

Figure 3

The energy spectrum (with both random and empty-target contributions subtracted) at forward and backward angles for ${}^6\mathrm{Li}$. The dashed, vertical lines denote the region of interest (ROI). The red curves indicate the elastic peak determined by fitting the geant4 simulations. At forward angles, the atomic-related background is modeled by an exponential (dashed curve), and the total response is shown by the blue curve.

Figure 4

Comparison of scattering cross section for ${}^{16}\mathrm{O}$ obtained by [5] and present results. The statistical uncertainties are shown on the present results and the systematic uncertainties for this measurement are shown in the band beneath the data.

Figure 5

The ${}^6\mathrm{Li}$ Compton-scattering cross section from this experiment at 86 MeV (bottom) and measured previously at 60 MeV (top). The error bars shown on the data points are the statistical and systematic uncertainties added in quadrature. The curves are the results obtained from fitting the data to a phenomenological model [1].