DSPEC Pro 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 through extending the acquisition time. The underlying assumption must be that the sample does not change during the extended period. This is far from true when short half lives are encountered or the sample is not stationary (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 detector 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 radiation 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 Pro implementation, each event is time-stamped to an accuracy of 200 nanoseconds. Via the use of a programmers toolkit, data may be re-constituted 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 radiation detectors do not, as a rule, 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. There is increasing use of mechanical coolers for HPGe detectors (to eliminate the need for LN2) and the increasing need to take HPGe detectors out of the laboratory environment.
DSPEC Pro incorporates a Low-Frequency Rejector (LFR) Filter feature, which reduces the effects of such noise sources. Combined with high performance list mode, the DSPEC Pro is the instrument of choice for mobile vehicle survey systems.
For Enhancement of Resolution in Large or Neutron Damaged Detectors
Ballistic Deficit and Charge Trapping Correction
The trapezoidal digital filter in the DSPEC Pro is held in common with all other ORTEC DSPEC family members. It allows adjustment of the filter to optimize the resolution performance of large HPGe radiation detectors which can often suffer low-side peak tailing if ballistic deficit is present. These large detectors are finding increasing use in low level counting applications.
The adjustment is largely automated by the use of the "OPTIMIZE" feature and may be monitored by the InSIGHT digital oscilloscope mode.
The DSPEC Pro offers even further capability in the form of a charge trapping corrector which can be used to mitigate the peak degradation in the case of a neutron damaged radiation detector. The neutron damage to the crystal lattice causes "trapping" centers which "hold onto" 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" such that it adds back the pulse height deficit, event by event.