Alpha Spectrometer

Features

• Stainless steel vacuum chamber
• Accommodates samples up to 50 mm (2 in.) diameter
• Supports the use of alpha detectors up to 1200 mm 2
• Optional reverse sample bias (standard with 7401VR)
• Built-in counter/timer
• Integral vacuum gauge with vacuum/bias interlock
• Bias supply variable to 198 V dc, positive or negative
• Digital display of:

  Counter/Timer, Chamber Pressure, Detector Bias, Leakage Current, Pulser Energy, Discriminator Energy

Description

The CANBERRA Model 7401 is a comprehensive alpha spectrometer that can accommodate samples up to two inches in diameter in a double- width NIM package. The versatile sample chamber and instrument electronics support CANBERRA's own PIPS Detectors, which combine high resolution and low backgrounds in a rugged alpha detector with active areas up to 1200 mm 2 . In addition, the alternative use of most charged particle detectors is also supported. The Model 7401 fully integrates into one package a stainless steel vacuum chamber for low backgrounds and ease of cleaning, a vacuum gauge, detector bias supply, preamp/amplifier, pulser, discriminator, counter, and digital display. A stainless steel shelf and sample holder are included with each spectrometer, for reproducible detector/sample spacing, which is user selectable from 1 to 49 mm, in 4 mm increments.

The full functionality of the 7401 is enhanced by a microprocessor- managed user interface. Front panel controls allow the user to quickly set and easily display the bias voltage on the detector, the energy value of the calibrated internal pulser, the energy value of the discriminator and the preset time for the built-in counter. Additionally, the front panel display also monitors chamber pressure, detector leakage current, accumulated counts and elapsed time. To facilitate routine work and quick setup, the detector bias voltage, discriminator energy and pulser settings are retained in memory when the 7401 is switched off. For gross alpha counting, the counter can be started, stopped and reset using the simple front panel switches. For added convenience, the time display can be internally configured for either seconds or hours.

To support a variety of alpha detectors, the built-in detector bias supply is adjustable from 2 to 198 V dc, positive or negative. Premature and possibly damaging application of bias to the detector is avoided by a user-configured interlock. The interlock safely inhibits the bias supply until proper vacuum is attained, then the bias voltage is gradually ramped to the predetermined setting, over approximately one minute.

The precision preamp and amplifier provide the optimal pulse shaping and signal conditioning required for detectors used in alpha spectrometry. Gain and offset of the amplifier can be adjusted by means of front panel access to multi-turn controls. For reference, the internal test pulser can be set to mark energies from 0.1 to 10 MeV and can be used to calibrate the spectrometry system without the use of alpha emitting sources. The counter discriminator also is calibrated in energy units and is fully variable between 0.1 and 10 MeV. The discriminator output, indicating activity above the selected setting, is available at the rear panel counts output. The rear panel also has a connector for signal input from an optional external test pulser. When combined with appropriate CANBERRA Mixer/Routers, Multiplexers and software products, a single multichannel analyzer (MCA) can easily support multiple 7401 Alpha Spectrometers in a complete data acquisition and analysis system.

Each Model 7401 Alpha Spectrometer has a pressure gauge with an operating range of 0-1000 mmHg (0-133 Pa). For those who need to operate at higher chamber pressures, the Model 7401VR Alpha Spec-trometer has a pressure gauge range of 0-20 mm Hg (0-2.67 kPa). Chamber pressure is manually controlled by a three-position mechanical valve. To provide reliable performance with little maintenance, the stainless steel door of the chamber is equipped with hinges which automatically adjusts to and compensates for proper gasket compression. For added confidence, the vacuum chamber is helium leak tested to 10^-10 cc/s during manufacture.

Reverse sample bias is available as an option in the 7401 Alpha Spectrometer as Model 7401-RSB. In applications requiring this option, re-verse bias is provided by four 3-volt batteries. The Model 7401VR Alpha Spectrometer includes the 7401-RSB Reverse Sample Bias option.