Octete Plus Alpha Spectroscopy Workstation

The Octęte Plus contains eight identical alpha spectroscopy channels with an eight-input multichannel buffer. Each alpha spectroscopy channel includes a vacuum gauge, variable detector bias supply (switchable positive or negative), a preamplifier, a shaping amplifier with adjustable gain, a test pulse generator with variable amplitude, and a leakage current monitor.

The Octęte Plus may be either rack mounted or left in the table-top mounting enclosure in which it is supplied.

Vacuum Chambers

• Cast brass, nickel-plated for ease of decontamination.

• Maximum Sample Size  51 mm (2.030 in.).

• Maximum Sample-to-Detector Spacing  44 mm, in increments of 4 mm.

• Maximum Detector Size  1200 mm².

• High-Performance O-Ring Seal  Spare package of 10 seals (ORTEC part OCT-CG) included.

• Detector Connector Type  Rear Microdot (ORTEC B-Mount).

• 3-Position Pump/Vent/Hold Valve  Front-panel mounted for each chamber.

• Vacuum Manifold Connector  Rear-panel NW25 ISO-KF.

• Vacuum Pump Requirements  Rotary vacuum pump, 6.7 CFM (190 L/min) displacement, with oil mist trap. The ORTEC 576A/676A-PPS-115 (or -230) is available for this application.

System Performance

• Based on use with a BU-017-450-100 ULTRA™ Series detector with a good-quality 241Am point source.

• Energy Resolution  ≤20 keV (FWHM) with a detector-to-source spacing equal to the detector diameter.

• Detector Efficiency  ≥25% for detector-to source spacing of less than 10 mm.

• Background  Above 3 MeV, ≤1 count/hour.

Electronics Performance

BIAS SUPPLY

• Range  0 ± 100 V, 10 µA; voltage can be read by the computer.

• Bias  Front-panel control continuously variable via one-turn screwdriver potentiometer for each channel.

• Pos/Neg  Polarity can be selected independently with PWB slide switches (factory set for positive bias voltage).

• Vacuum/Bias Interlock Control  Rear-panel locking toggle switch enables or disables bias voltage inhibit; inhibit occurs when chamber pressure exceeds threshold.

• Vacuum/Bias Interlock Set Point  Dual-position internal jumper chooses vacuum level at which bias is enabled: nominal trip level 75 Torr.

• Enable/Disable  By computer control.

• Indicator  Front-panel, red LED for each channel shows if the bias is on.

CALIBRATION PULSER

• Range  4 to 10 MeV.

• Pulser  Front-panel, 15-turn screwdriver potentiometer controls the internal pulser amplitude; set to a nominal 8-MeV pulse when shipped.

• Instability  <50 ppm/°C.

• ON/OFF  Front-panel, two-position toggle switch for each pulse generator.

DETECTOR CURRENT MONITOR

• Range  0 to 10,000 nA; read by computer.

• Display Resolution  3 nA.

VACUUM GAUGE

• Range  10 mTorr to 30 Torr, read by computer.

PREAMPLIFIER/AMPLIFIER

• Shaping  1 µs unipolar, dc restored.

• Integral Nonlinearity  <±0.1% of full scale.

• Gain  5 to 12 MeV full scale (factory set to 10 MeV full scale).

• Gain Instability ≤150 ppm/°C.

• E_cal  Front-panel, continuously variable potentiometer to adjust the amplifier gain.

• E_out  Front-panel test point for monitoring amplifier output pulses that are internally connected to the ADC through the multiplexer.

• Pos/Neg  Polarity can be selected independently with PWB slide switches.

MULTIPLEXER/ROUTER

• Inputs  One to 16, software selectable.

• Signal Isolation  Typically >72 db rejection of unselected inputs.

• Input Threshold  Set by front-panel screwdriver adjustment. Range is from 100 to 500 mV and is common to all inputs.

• Gain  Nominally unity.

• DC Level Instability  ≤20 µV/°C.

• Integral Linearity  0.05%.

• Gain Instability  ≤50 ppm/°C.

• Controls (rear panel)
  MUX DISC  Screwdriver potentiometer from 100 to 500 mV.

• Indicators (front panel)
  MUX BUSY  Red LED’s intensity indicates the relative activity of the multiplexer/router.

ADC

• Successive-Approximation-Type ADC  With sliding-scale linearization.

• Maximum Resolution  4096 channels, software-selectable as 64, 128, 256, 512, 1024, 2048, or 4096, independent for each segment.

• Digital Offset  Independent for each segment in increments of 1 channel from 0 to 4096.

• Conversion Time Per Event  15 µs (fixed).

• Integral Nonlinearity  ≤±0.025% over top 97% of dynamic range.

• Differential Nonlinearity  ≤±1% over top 97% of dynamic range.

• Gain Instability  ≤50 ppm/°C.

• Dead-Time Correction  Extended live-time correction according to the Gedcke-Hale method.¹

• Connectors
  Internal  Connections are made between each amplifier and each multiplexer input to the ADC.
  AUX INPUT  Eight rear-panel BNCs numbered 1–8.
  ADC GATE  Optional, slow-positive NIM input. Computer-selectable coincidence or anticoincidence. Signal must occur prior to and extend 0.5 µs beyond peak detect. Rear-panel BNC connector. Gate control for all active inputs.

• Controls (rear panel)
  ADC ZERO  Screwdriver potentiometer adjusts the ADC zero offset ±250 mV.
  ADC LLD  Screwdriver potentiometer adjusts the lower-level discriminator from 0 to 50% full scale.

• Indicators (front panel)
  CPU BUSY  Red LED’s intensity indicates the relative activity of the microprocessor.
  ADC BUSY  Red LED flashes once for each pulse digitized by ADC.

Presets

• Real Time/Live Time  Multiples of 20 ms.

• Region of Interest  Peak count/Integral count.

• Data Overflow  Terminates acquisition when any channel exceeds 2 billion.

Microprocessor System

Intel® 80386  64k RAM with battery backup; 6k “scratchpad” memory with battery backup; 64k mailbox memory (EPROM); and time-of-day clock with battery backup.

Interface Connectors

• ETHERNET  Rear-panel BNC connector, accepts IEEE 802.3 10BASE2 (thin-wire coax).

• RS-232C  Standard RS-232-C, 25 pin; male connector wired as DTE to run under model control at 38.4k baud maximum.

• USB 2.0  Rear panel standard "B" type USB connector.

Electrical and Mechanical

• Dimensions  19.5 in. W x 16 in. D x 11.6 in. H enclosure. Rack mountable without enclosure.

• Weight  25 kg (55 lb).

• Power Input  120/240 V ac, 50/60 Hz.

• Power Consumption  120-W input power.

• Operating Environment  Same as for IBM PC: 16° to 32°C (60° to 90°F), 8% to 80% relative humidity.

Computer Prerequisites

Any computer capable of running any of the following operating systems:  Windows 2000/XP. Ethernet interface is also required.

Ordering Information

¹Ron Jenkins, R.W. Gould, and Dale Gedcke, Quantitative X-Ray Spectrometry (New York: Marcel Dekker, Inc.), 1981, pp 266-267.