Overview

The RADSiP™ II gamma-ray sensor is a small, inexpensive, filely passive hardware system designed for individual-item monitoring of radioactive materials. The system provides a method for maintaining 24-hour surveillance of stored radioactive items and recording any gamma-ray change. The system can be retrofitted into existing storage configurations and operated in either a fixed or mobile mode. Applications include nonproliferation monitoring, spent fuel safeguards, and long-term monitoring of stored radioactive wastes.

Features

• Gamma-ray attribute measurement of each item in storage
• Selectable gamma-ray energy band from 20 keV to 100 keV
• Automatic indication of system problems
• Pulse height discrimination of unwanted noise
• Standard transistor-transistor logic, pulse discriminator output
• Single +12 V supply requirement for electronics power
• Stable low-cost preamplifier-amplifier electronics

System Operation

RADSiP™ II sensors monitor the gamma-ray emission from special nuclear materials (SNMs). The sensors are affected by source (SNM) distance, collimation of the source, and the SNM container thickness and material. The count-rate is maximized by placing the sensors as close as possible to the source.

Main elements within the sensor unit are a Silicon-PIN photodiode, a low-noise preamplifier, and a pulse-shaping amplifier. Signal levels can be selected by a pulse height discriminator, lower-level adjustment for precise gamma-ray energy band monitoring of uranium-235. The Surface Mount Technology (SMT) circuit board is designed for use with either a silicon-PIN photodiode or a CdZnTe gamma-ray radiation detector (RADTELL™ II).

Pulses resulting from the photon interactions in the silicon detector are produced at an approximate rate of 500 counts per second per R per hour. Filters in the pulse-shaping amplifier provide an impulse response having a pulse-width of 20 to 50 microseconds. After leaving the pulse-shaping amplifier, the output signals go to a pulse height discriminator where the discriminator lower level is adjusted to correspond to an energy peak of americium-241 (60 keV). The gamma-ray energy band from either the calibrated americium-241 peak to the highest energy from the Compton interaction pulses generated in silicon provide a sensitivity band with a precise region for monitoring uranium enrichment.

The SMT circuit board is 1.5 cm wide by 8.75 cm long.

Hardware/Software Requirements

• ORSENS Sensor Concentrator
• ORSENS Common Sensor Interface Unit
• An Intel Pentium II based computer (or higher)
• At least 32 MB of RAM
• A minimum of 15 MB of free hard disk space