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Features

• Automatic gain stabilization, using built in LED
• Extended range probe and current modes
• Excellent linearity and accuracy
• Calibration cycles of up to two years
• Detectors are packaged in a water resistant O-ring sealed NEMA-4 cylinder with a mu-metal shield
• Operated with PA300E preamplifier with three single channel analyzer channels

Quality

• Commitment to meet or exceed your quality expectations
• One year guarantee against defects in material and workmanship
• Cost-effective for safety and compliance

Description

The MD Series of standard scintillation detectors provides customers with the capability of measuring gamma and beta emitting radionuclide for a wide variety of applications. The detectors consist of one or two scintillators (gamma or beta) optically coupled to a photomultiplier (PM) tube via a Lucite light pipe. A reference Light Emitting Diode (LED) and a temperature sensor are imbedded in the Lucite pipe.

These detectors operate with a unique gain stabilization circuitry for temperature-compensated drift-free operation, resulting in improved accuracy and extended calibration cycles.

The MD455E, MD55EB1, MD55EV1, MD55EV2 and MD55EV5 are capable of measuring extended operating ranges of up to 11 decades of linear activity from environmental effluent release levels to accident range.

The MD Series detectors operate in conjunction with a preamplifier, Model PA300E. This unit contains the circuitry that compares the LED pulses with a reference to provide closed loop feedback for automatic gain compensation. The preamplifier amplifies the detector output signal and generates shaped digital pulses to the remotely located ratemeter. When configured to work with MD455 Series Beta-Gamma detectors, the PA300E also separates pulses of interest for gamma and beta radiation from the composite signal, by pulse shape discrimination.

The MD Series can be connected to multifunction control and display unit such as ADM600, ADM606, ADM606M, ADM616, and ADM616S.

Principle of Operation
CANBERRA's MD Series consists of scintillation detectors used for gamma radiation monitoring such as the MD55EB1, MD55EV1, MD55EV2 and MD55EV5 and for beta and gamma radiation monitoring such as MD455E, MD455V5 and MD455V6. Most of these detectors are designed for use over an extended operating range. (Exceptions are MD455V5 and MD455V6).

The Thallium activated Sodium Iodide (NaI), Bismuth Germanate Oxide (BGO) crystals or plastic phosphors emit pulses of light when bombarded with certain radiation. In fact, the amount of light given off is proportional to the energy of the absorbed photons. The light pulses are viewed by a photomultiplier (PM) tube which converts them to electrical pulses. A traditional problem associated with scintillation detectors has been gain shifts, such as short and long term changes in amplitude of pulses contributing to drift and photo peak shift, caused by changes in PM tube gain due to hysteresis, fatigue, and temperature effects.

The MD Series detectors operate with a unique gain stabilization circuitry for temperature-compensated, drift-free operation, resulting in improved accuracy and extended calibration cycles. This gain compensation methodology using a thermally compensated light emitting diode (LED) offers several advantages over designs based upon using a radioactive seed. The radioactive seed adds significant cost to the crystal and poses potential disposal problems when the crystal is no longer usable.

In the MD Series the scintillator(s) are optically coupled to a photomultiplier (PM) tube via a Lucite light pipe. The PM tube fits into a tube socket mounted on the Socket PC board with a voltage divider network to provide the dynode voltages. The LED, the temperature sensor connections and the signal from the PM tube are brought out of the detector via the PC board. A mu-metal shield surrounds the PM tube to protect it from gain changes due to stray magnetic fields or from changes in orientation with respect to the earth's magnetic field. The entire assembly is contained in a moisture proof stainless steel housing, with an integral cable assembly which carries the high voltage into and signals out of the detector.

The MD Series detectors operate in conjunction with the CANBERRA Preamplifier PA300E. The preamplifier takes the voltage from the ratemeter and generates a stable high voltage supply required by the PM tube.

The PA300E also drives the LED in the detector and takes the signal from the temperature sensor. It then compares the LED signal from the PM tube with a temperature compensated reference signal and generates a correction voltage to automatically adjust the high voltage to provide gain stabilization.

The PA300E amplifies the detector output signal, separates the beta and gamma pulses (where applicable) from the composite signal by pulse shape discrimination (based on the different decay constants of the two scintillators), and transmits the digital pulse output.

At low concentrations, the PA300E amplifies the detector output pulses before transmitting the signal to the ratemeter. At high concentrations, the PM tube current is converted into a proportional frequency. In very high gamma fields, the high voltage to the detector is automatically lowered to bring the PM tube into its linear range.