Cross section measurement for the ${}^{10}\mathrm{B}(n,t2\alpha )$ three-body reaction at 4.0, 4.5, and 5.0 MeV. II. Experimental setup and results

Cross sections of the ${}^{10}\mathrm{B}(n,t2\alpha )$ three-body reaction were measured at $E_n=4.0$, 4.5, and 5.0 MeV using a twin gridded ionization chamber and a thin-film ${}^{10}\mathrm{B}$ sample. The present paper is the second part of the work. A digital data-acquisition system was developed for the gridded ionization chamber based on the waveform digitizer. A thin-film ${}^{10}\mathrm{B}$ sample was designed and prepared. The number of ${}^{10}\mathrm{B}$ atoms in the sample was determined by the relative method using the thermal neutron induced ${}^{10}\mathrm{B}(n_{th},\alpha ){}^7\mathrm{Li}$ and ${}^6\mathrm{Li}(n_{th},t){}^4\mathrm{He}$ reactions with a ${}^6\mathrm{LiF}$ sample as the reference. The measurement of the ${}^{10}\mathrm{B}(n,t2\alpha )$ reaction was performed at the 4.5 MV Van de Graaff accelerator of Peking University. In the measurement, the double-coincidence technique was used, which involves the forward-backward and the grid-anode coincidence. In the data processing, the effective event area in the forward two-dimensional spectrum and the time window in the drift-time spectrum were employed to reject the background events. Cross sections of the ${}^{10}\mathrm{B}(n,t2\alpha )$ and ${}^{10}\mathrm{B}(n,\alpha ){}^7\mathrm{Li}$ reactions were obtained. The present results are compared with the data of existing measurements and evaluations.

Figure 1

Block diagrams of the electronics of the GIC spectrometer: 1, cathode; 2, grid; 3, anode; 4, shield; PA, preamplifier; FIFO, quad fan in, fan out; SA, spectroscopy amplifier; LG, linear gate stretcher; SC, single-channel analyzer; CH, input channel; EXT, external trigger; WFDm, WFD master; and WFDs, WFD slave.

Figure 2

The tantalum supporter with the aluminum washer viewed from side A and side B.

Figure 3

The thin-film ${}^{10}\mathrm{B}$ sample viewed from side A and side B.

Figure 4

Schematics of the experimental setup viewed from top, based on (a) the accelerator $d\text{−}d$ neutron source and (b) the Am-Be neutron source.

Figure 5

Grid-anode two-dimensional spectrum obtained in the accelerator-based measurement (a) for the ${}^6\mathrm{Li}(n_{th},t){}^4\mathrm{He}$ reaction and (b) for the ${}^{10}\mathrm{B}(n_{th},\alpha ){}^7\mathrm{Li}$ reaction.

Figure 6

Anode spectrum obtained in the accelerator-based measurement (a) for the ${}^6\mathrm{Li}(n_{th},t){}^4\mathrm{He}$ reaction and (b) for the ${}^{10}\mathrm{B}(n_{th},\alpha ){}^7\mathrm{Li}$ reaction.

Figure 7

Two-dimensional spectrum of the $\alpha$ source at $E_n=4.0\mathrm{MeV}$: (a) the grid pulse height versus the anode pulse-height and (b) the drift time versus the anode pulse height.

Figure 8

Grid-anode two-dimensional spectrum of the ${}^{10}\mathrm{B}$ reaction induced by neutrons with $E_n=4.0\mathrm{MeV}$, (a) forward and (b) backward.

Figure 9

Drift-time spectrum for the foreground and background events in the effective event area at $E_n=4.0\mathrm{MeV}$.

Figure 10

The total-energy spectrum of the events selected by the effective event area and the time window at $E_n=4.0\mathrm{MeV}$.

Figure 11

Anode spectrum for the ${}^{10}\mathrm{B}(n,\alpha ){}^7\mathrm{Li}$ reaction at $E_n=4.0\mathrm{MeV}$: (a) forward $\alpha$-particle + leaking events and (b) backward $\alpha$-particle events.

Figure 12

Anode spectrum of the effective event area in the forward two-dimensional spectrum [as shown Fig. 8] at $E_n=4.0\mathrm{MeV}$.

Figure 13

Present cross sections compared with the existing measurements and evaluations (a) for the ${}^{10}\mathrm{B}(n,t2\alpha )$ reaction and (b) for the ${}^{10}\mathrm{B}(n,\alpha ){}^7\mathrm{Li}$ reaction.