SRAM neutron detector

 

This invention is about a sensor for detecting the neutron fluence doses over a wide range in real time. The small and compact design, a user-friendly handling and connectivity with a PC via a USB interface are the special characteristics of the portable neutron fluence detector. The radiation sensor of the detector is based on commercially available SRAM (Static Random Access Memory) memory chips whose responsivity is immune against interfering background gamma-radiation. The detector provides perfect solution for neutron fluence measurement in environments with high gamma background.

Neutron fluence (neutrons*cm-2), measured in FLASH accelerator tunnel with SRAM-based neutron detector

Problem

Conventional SRAM chips contain boron (doping) in the ppb range. The boron indicates a high neutron capture for thermal neutrons. If such a SRAM chip is exposed to neutrons, high-energy alpha particles are released (by the nuclear reaction) from the boron atom. The released alpha particles cause local interferences, the so-called “bit-flips”, when striking sensitive junctions in the chip. These may be measured electronically and the detector read-out is directly proportional to measured neutron fluence.

 

Innovation

By using an innovative neutron moderator from composite materials (polyethylene and lead), the inventors have obtained the following properties:

  • increasing the sensitivity by 2 orders of magnitude
  • independency from the angle of incidence of the neutron radiation
  • absolute in-situ calibration possibility in the accelerator (eg, FLASH tunnel)

Benefits

The neutron fluence measurement and dosimetry at high-energy electron and proton accelerators are possible fields of application for this invention. Companies may also be interested in low cost monitoring devices for medical accelerators (medical linacs). However, this would require the development of electronics which are compliant with ISO 9000.

In addition, the following properties shall also be applied:

  • improvement of real-time measurement of neutron radiation in accelerators
  • immune against pulsed neutrons
  • system for use as neutron dosimeters, fluence monitor and spectrometer by means of Bonner sphere

Development status

The first prototype of the SRAM neutron detector has successfully been tested in FLASH accelerator tunnel at DESY (Fig. 1) and patent application has been granted.