Neutron signal features of Nb-based kinetic inductance detector with ¹⁰B convertor

In our preceding works, we demonstrated successful neutron detection using a superconducting current-biased kinetic inductance detector (CB-KID), which is composed of two Nb-based superconducting meanderlines and the ¹⁰B neutron absorption layer. The CB-KID with a ¹⁰B absorption layer outputs the voltage pulses when it is irradiated by pulsed neutrons. We expected that the voltage V is proportional to a product of the bias current I_b and a time derivative of the local kinetic inductance dΔL_k/dt, and a pair of signals propagate along the Nb stripline as an electromagnetic wave at a certain fraction of the light velocity c toward end electrodes. It still remains to be revealed why the signal voltage shows such a continuum in the histogram of the signal height even if the incident energy of the light ion is apparently monochromatic. In the present work, we investigated the distribution of the height and width of the signal. We found a clear correlation between height and width, which might be a key of understanding the operating principle of our detector. We consider that the origin of the signal distribution is due to the positional dependence of the light ion bombardment with respect to the meandering Nb nanowire.