The electrical characteristics and neutron dosimetry properties of silicon based p-i-n diodes are presented in support of applications of the sensors in beam monitoring and medical physics. Both the current-voltage and capacitance-voltage characteristics of silicon planar p-i-n diode sensors with cylindrical geometry have been calculated and experimentally measured. Dependencies of the shift of the forward and reverse diode characteristics of the sensors versus neutron dose were obtained. It is shown that the forward voltage shift measured at a constant current of the p-i-n diodes under neutron irradiation is proportional to the measurement current in the case of the low injection level or to the square root of the current in the case of the high injection level. The capacitance-voltage characteristics and full depletion voltages of the diodes were calculated and experimentally verified. The use of planar cylindrical structures as neutron sensors allows optimization in the sensor sensitivity through the selection of the geometry on the device and the measurement current. ©2008 IEEE.