Impact of ${}^7\mathrm{Be}$ breakup on the ${}^7\mathrm{Li}(p,n)$ neutron spectrum

The formation of continuum neutron distribution in ${}^7\mathrm{Li}(p,n)$ has been identified as due to the coupling of the ${}^7\mathrm{Be}$ breakup levels to the final state of the reaction. The continuum neutron spectra produced by the ${}^7\mathrm{Li}(p,n)$ reaction has been estimated by measuring the double differential cross sections for continuum and resonant breakup of ${}^7\mathrm{Be}$, through the ${}^7\mathrm{Li}(p,n){}^7\mathrm{Be}^{*}$ reaction at 21 MeV of proton energy. The breakup contributions from continuum and $5/2^{-}$, $7/2^{-}$ states of ${}^7\mathrm{Be}$ have been identified. The measured double differential cross sections have been reproduced through continuum-discretized coupled channel-coupled reaction channel calculations. The cross sections were projected to neutron spectrum using the Monte Carlo approach and validated using experimentally measured ${}^3\mathrm{He}$ gated neutron spectra. ${}^7\mathrm{Li}(p,n)$ neutron spectrum at 20 MeV incident proton energy measured by McNaughton et al. [Nucl. Instrum. Methods 130, 555 (1975)] has been reproduced by adapting estimated model parameters for the reaction.

Figure 1

Experimental setup.

Figure 2

$\mathrm{\Delta }E\text{−}E$ correlation spectra measured by $-{55}^{\circ }$ telescope.

Figure 3

An example energy correlation plot of the energy measured in $-{55}^{\circ }$ versus energy of resolved ${}^3\mathrm{He}$ in $+{55}^{\circ }$, for the coincidence events, used for reconstruction of $\alpha \mathrm{s}$ below the discrimination threshold. Red circle indicates the constant radius ($\mathrm{\Delta }$) window about kinematically defined query point

Figure 4

Neutron energy-efficiency plot for EJ301 liquid scintillator.

Figure 5

The true coincidence and reconstructed events comparison with three-body kinematics, projected to the fragments at $+{55}^{\circ }$ and $-{55}^{\circ }$

Figure 6

The measured double differential cross sections for ${}^7\mathrm{Li}(p,n){}^7\mathrm{Be}^{*}\to n+{}^3\mathrm{He}+\alpha$, and CDCC-CRC calculated continuum and resonant stare cross sections (for the laboratory folding angle of ${110}^{\circ }$).

Figure 7

The simulated $0^{\circ }$ breakup neutron spectrum at 21 MeV, having continuum and resonance contributions.

Figure 8

The comparison of ${}^3\mathrm{He}$ gated neutron spectra with theoretical spectra.

Figure 9

Comparison of evaluated neutron spectrum with the spectrum reported by McNaughton et al. for 20 MeV.