Fast Neutron Dosimetry Employing Soft Error Detection in Dynamic Random Access Memories

During the mid 1970s it was found that the logic state of integrated circuits could be altered by the passage through them of ionising particles. The aim of this study was to use this phenomenon in dynamic random access memory (DRAM) chips, where it is known as soft error production, to detect neutrons and thus provide a means of neutron dosimetry.
The phenomenon is described, together with metal-oxide- Silicon (MOS) device operation, to show how soft errors can occur in MOS based DRAMs. The interactions of neutrons and protons in materials of interest are described, together with the current state of neutron dosimetric methods.
The experimental work involving a Van de Graaff accelerator and Californium-252 isotopic neutron sources together with various polyethylene radiators is described. An attempt was made to model the phenomena occurring within the radiators and DRAM using Monte Carlo methods. Several approaches were used to describe the chord length distribution within the sensitive volume. The modelling results are described and the FORTRAN programs developed are given.
It was found that detectors could be constructed with a sensitivity range of 70 to 2.7 mSv per soft error for the Van de Graaff source and between 2.2 and 0.8 Sv per error for the californium source. These results were within the range obtained from the modelling work.