Spin-dependent cross sections from the three-body photodisintegration of ${}^3\mathrm{He}$ at incident energies of 12.8 and 14.7 MeV

The first measurement of the three-body photodisintegration of polarized ${}^3\mathrm{He}$ using a circularly polarized photon beam has been performed at incident energies of 12.8 and 14.7 MeV. This measurement was carried out at the high-intensity $\gamma$-ray source located at Triangle Universities Nuclear Laboratory. A high-pressure ${}^3\mathrm{He}$ target, polarized via spin exchange optical pumping with alkali metals, was used in the experiment. The spin-dependent double- and single-differential cross sections from $\overrightarrow{{}^3\text{He}}(\vec{\gamma },n)pp$ for laboratory angles varying from ${30}^{\circ }$ to ${165}^{\circ }$ are presented and compared with state-of-the-art three-body calculations. The data reveal the importance of including the Coulomb interaction between protons in the three-body calculations.

Figure 1

Schematic of the experimental apparatus. The movable target system (yellow [light gray]) that was used to cycle between the ${}^3\mathrm{He}$ target and the N${}_2$ reference cell is surrounded by 16 liquid scintillator detectors placed inside $\mu$-metal tubes (gray). The Helmholtz coils (red [dark gray]) provided the holding field. The movable support of the optics that was employed to polarize the ${}^3\mathrm{He}$ target and the D${}_2$O flux monitor can be seen in the bottom right corner of the figure, next to the flux monitor.

Figure 2

A PSD vs PH spectrum for a detector placed at ${90}^{\circ }$. The data were acquired at $E_{\gamma }=14.7$ MeV. The neutron events are well separated from the $\gamma$-ray events. The PH cut location is indicated by the long-dashed line.

Figure 3

The TOF spectra of ${}^3\mathrm{He}$ target in comparison to the N${}_2$ reference cell target normalized to the same flux for a detector placed at ${90}^{\circ }$. The data were acquired at $E_{\gamma }=14.7$ MeV.

Figure 4

Experimental spin-dependent double-differential cross sections for both parallel (two top rows) and antiparallel (two bottom rows) spin-helicity states as a function of the neutron energy, $E_n$, at $E_{\gamma }=12.8$ MeV. They are compared with the calculations of Deltuva et al. (solid curve) and Skibiński et al. (dashed curve). The neutron energy bin width is 0.2 MeV. The band at the bottom of each histogram shows the combined systematic uncertainties.

Figure 5

As in Fig. 4 at $E_{\gamma }=14.7$ MeV.

Figure 6

Spin-dependent double-differential cross sections corrected for the acceptance effect, for parallel (two top rows) and antiparallel (two bottom rows) spin-helicity states as a function of the neutron energy, $E$${}_n$, compared with the calculations based on Ref. [16] (solid curve) and Ref. [24] (dashed curve) at the incident photon energy of 12.8 MeV. The neutron energy bin width is 0.2 MeV. The band at the bottom of each histogram shows the combined systematic uncertainties.

Figure 7

As in Fig. 6 but for the incident photon energy of 14.7 MeV.

Figure 8

The double-differential cross section as a function of the outgoing neutron energy for the unpolarized three-body photodisintegration of ${}^3\mathrm{He}$ at $E_{\gamma }=14.7$ MeV and neutron scattering angle of ${90}^{\circ }$. The short-dashed (black) curve is the calculation from Ref. [24] including AV18 + UIX + seagull + pion-in-flight-terms. The second group of calculations from Ref. [16] are (from top to bottom) dotted (green online) curve, CD Bonn + RC; long-dashed dotted (red online) curve (nearly invisible behind the solid curve), CD Bonn + RC + Coulomb force; and solid (blue online) curve, CD Bonn + $\Delta$-isobar + RC + Coulomb force.

Figure 9

The double-differential cross sections of the three-body photodisintegration of ${}^3\mathrm{He}$ as a function of the outgoing neutron energy for both parallel (two top curves) and antiparallel (two bottom curves) spin-helicity states at $E_{\gamma }=14.7$ MeV and neutron scattering angle of ${90}^{\circ }$. The calculations from Ref. [16] are solid (blue online) curves, CD Bonn + $\Delta$-isobar + RC + Coulomb; and long-dashed (black) curves, CD Bonn + RC + Coulomb force. The CD Bonn + Coulomb force alone do not have any significant contribution to the difference of the cross sections between the spin-helicity states, and the corresponding curves—if plotted—would be in the middle of the long-dashed curves.

Figure 10

Spin-dependent single-differential cross sections for parallel (filled squares) and antiparallel (open squares) spin-helicity states with statistical and systematic uncertainties as a function of the neutron scattering angle, ${\theta }_{\mathrm{lab}}$ at $E_{\gamma }=12.8$ MeV. The data are compared with the calculations based on Ref. [16] (red [gray] curves) and Ref. [24] (black curves). The solid and the long-dashed curves are the calculations for the parallel and antiparallel spin-helicity states, respectively. (The statistical uncertainties in most of the angles are small and cannot be seen in the figure.)

Figure 11

As in Fig. 10 at $E_{\gamma }=14.7$ MeV.

Figure 12

All currently available total cross section data for the ${}^3\text{He}(\gamma ,n)pp$ reaction up to 30 MeV: Ref. [59] (open diamonds), Ref. [60] (open circles), Ref. [61] (open squares), Ref. [58] (open crosses), Ref. [62] (open upward triangles), Ref. [63] (filled downward triangles), Ref. [52] (filled stars), Ref. [53] (filled upward triangle), and present data (filled circles) in comparison with two calculations based on Ref. [16] (solid curve) and Ref. [24] (dash-dotted curve) theories. In the insert, the data of Ref. [52], which are hidden behind the results of the present work, are shown and compared with the theories. Very good agreement is found between the present results, the data of Ref. [52], and the calculations of Ref. [16].