Effect of high-energy electron emission spectrum in monocrystal on photoneutron yield

The photoneutron yield from Be and C amorphous targets under the effect of coherent γ-radiation, due to the 1 GeV electrons when passing through Si monocrystal, is measured. The electron beam with the divergence of 2x104 rad and the energy scattering ΔE/E<=1 % is directed to a crystal 300 μm thick. γ-quanta emitting from the crystal in the angular span of 5x10-3 rad through a channel in the shield are transported to the target placed 12 m from the crystal to decrease the effect of the accelerator neutron background. Crystal orientation is carried out by measuring the intensity of crystal bremsstrahlung using an ionization chamber. Electron beam current monitoring is performed using an ionization chamber. Photoneutrons which generated from the target are registered by an ''all-wave'' BF3- counter. The investigation has shown that the neutron maximum yield Nsub(max) is observed in the case when the angle of disorientation of the crystal axis relatively to the electron beam direction is PHI=0. This is conditioned by the electron coherent radiation. The minimum neutron yield Nsub(min) is PHI approximately 150 mrad when due to electrons bremsstrahlung in a monocrystal takes place. The increase of neutron yield determined as the ratio Nsub(max)/Nsub(min) is 3.3 for a carbon target and 4.3 for a beryllium target. The conclusion is made that photoneutron yield in the cases studied depends on monocrystal orientation and threshold of (γ, n)- reaction