DSPEC 50 and DSPEC 502 salute the 50th year in which ORTEC has delivered innovative and quality nuclear instrumentation to scientists in a broad range of applications world wide. Fifteen years after the first ORTEC DSPEC® digital spectrometer received acclaim among spectroscopists for its performance and stability, the new DSPEC 50 and DSPEC 502 are landmark products which bring together our long design experience in digital spectrometers and the ongoing innovation skills of our developers.
The “retro” look front panel, which incorporates a built-in display, a reminder of earlier times in the evolution of multichannel analyzers, but inside, the DSPEC 50 is packed full of the latest digital signal processing technology and quality design.
Digital spectrometers are inherently more stable than the analog variety common in the past. In introducing the DSPEC 50, ORTEC has launched an all-new digital instrument platform, enhanced with a number of unique features and modes of operation which have distinct benefit in real-world applications.
DSPEC 50 Features at a Glance
For High-Rate Spectroscopy Applications
“Loss Free” or “Zero Dead Time” (ZDT)
The usual way to account for counting losses at high rates is by extending the acquisition time. The underlying assumption is that the sample count rate does not change during the total counting period. This is far from true when short half lives are encountered or the sample is in motion (e.g., flowing through a pipe). ORTEC has refined the loss-free counting technique in the digital domain. In this method, the spectrum itself is corrected pulse by pulse, and the ZDT method provides both an accurately corrected spectrum and correctly calculated statistical uncertainty.
“Enhanced Throughput” Mode
Accuracy at high input count-rates can be limited by the speed at which the spectrometer stores data to memory. It is said to be “throughput-limited.” Pulse pileup means that beyond a certain point, as input count-rate increases still further, the rate of data stored to memory DECREASES, reducing result quality. By developing a new kind of digital peak detection algorithm, ORTEC has increased the maximum throughput by up to 30% by removing some of the dead time associated with the process of pulse peak amplitude determination.
For Samples in Motion
For situations in which the sample is moving relative to the detector, it is often vitally important to be able to measure an activity profile as a function of time. Examples of such applications include aerial and land-based surveying and portal monitoring. It is usually a requirement that no “dead periods” occur, associated with the acquire-store-clear-restart cycle. In the list mode of operation, data are streamed directly to the computer, event by event. There is no associated “dead period.” In the DSPEC 50 implementation, each event is timestamped to an accuracy of 200 nanoseconds. Via the use of the A11 Programmer’s Toolkit, the data may be made into a spectrum for off-line analysis by one of ORTEC’s wide range of analysis software products or user-developed codes.
For Hostile Environments and Mechanical Coolers
Low-Frequency Rejector (LFR)
HPGe detectors do not always perform well in environments where there is mechanical vibration. Microphonic noise degrades energy resolution by adding low frequency periodic electrical noise to the primary signal. Electrical ground loops are also a source of low frequency electrical noise. The increasing use of mechanical coolers for HPGe detectors to eliminate the need for LN2 and increasing need to take HPGe detectors out of the laboratory environment mean an increase in mechanical vibration. DSPEC 50 incorporates a Low-Frequency Rejecter (LFR) Filter feature, which reduces the effects of such noise sources.
For Enhancement of Resolution in Large or Neutron Damaged Detectors
Ballistic Deficit and Charge Trapping Correction
The trapezoidal digital filter in the DSPEC 50 is the same as all other ORTEC DSPEC family members. It allows adjustment of the filter to optimize the resolution performance of large HPGe detectors which often have low-side peak tailing when ballistic deficit is present. These large detectors are increasing in use in low level counting applications. The adjustment is largely automated by the use of the “OPTIMIZE” feature and may be monitored by the InSightTM Virtual Oscilloscope mode.
The DSPEC 50 offers even further capability in the form of the Resolution Enhancer, a charge trapping corrector which can be used to reduce the peak degradation for neutron damaged detectors. The neutron damage to the crystal lattice causes “trapping” centers which hold some of the charge created by the gamma-ray interaction. This results in low-side tailing similar to ballistic deficit although the cause is different. The charge trapping corrector is calibrated or “trained” for the individual detector such that it adds back the pulse height deficit, event by event.