Digital Gamma-Ray Spectrometer简介

ORTEC®DSPEC PLUS ™The next generation in . . .Digital Gamma SpectroscopyFigure 1.Peak Shift and Resolution Stability Over 9 Month Operation Period Using DSPEC.DSPEC PLUS™Figure 2.Throughput Measurements of the DSPEC line of34Timothy R.Twomey, Ronald M.Keyser, Michael L.Simpson, and Sanford E.Wagner, “High-Count-Rate Spectroscopy with Ge Detectors:Quantitative Evaluation of the Performance of High-Rate Systems.”5Multi-Group Analysis++ Licensed from Lawrence Livermore National Laboratory and F ixed-Energy R esponse Function A nalysis with M ultiple Efficiency (PC/FRAM) licensed from Los Alamos National Laboratory.6T.A.Kelley, T.E.Sampson, Los Alamos National Lab and R.M.Keyser, T.R.T womey, ORTEC, “Recent Developments of LANL PC/FRAM Code,”(1999 ESARDA Conference).4Don’t worry ...we still include the automated "Optimize"feature in the control panel to allow you to choose the best fit! This means that improvements for the resolutioncapability of your detector and better throughput are just a click of a mouse button away.D S PE C P l u s f o r L o w C o u n t R a t e A p p l i c a t i o n sDSPEC Plus is just as powerful in low level countingapplications such as environmental monitoring.Getting the best resolution and throughput means lower detection limits and better statistical accuracy.We have already shown that "Bigger is Better" for reducing the background in counting systems through the improved peak-to-Compton (pC) ratio.7By combining the benefits of better resolution using the DSPEC Plus with the obvious advantages of a super-large HPGe detector, a counting lab can lower its detection limits quite substantially byimproving all three critical factors in the MDA equation!√BackgroundMDA ∝(Livetime)(Efficiency)The high peak-to-Compton value of large detectors lowers sample induced background contributions for isotopes,such as K-40 or Tl-208.The higher throughput increases the live time for a given measurement.Obviously, the higher efficiency of a detector — like our world record holding 207% detector — adds the final piece to the MDA puzzle.When put together by ORTEC, the puzzle is easily solved!Figure 5 shows a comparison of data taken using the best analog amplifier available and the DSPEC Plus for a large coaxial detector.This detector measures 207% efficient relative to a 3" x 3" NaI.In previous systems a tradeoff was made between high and low count rate performance when using large detectors.At the short shaping times necessary to get higher count rate performance, the 672-based system, the best analog system available, yields poor resolution due to the ballistic deficit of this large detector.A 973-based system would have better resolution at these shorter shaping times than a 672 only to lose that performance advantage at longer shaping times (i.e.low count rate) because of its gated integrator design.The DSPEC Plus,however, offers low count rate performance as good as the 672 and high count rate performance b e t t e r than the 973.With notrade off at either end, the DSPEC Plus becomes THE universal instrument for HPGe spectroscopy.Figure 4.Gain and Rise Time Settings.7R.M.Keyser, T .R.T womey, and S.E.Wagner, “The Benefits of Using Super-Large Germanium Gamma-Ray Detectors for the Quantitative Determination of Environmental Radionuclides.”Figure parison of Analog Amplifier and DSPEC Plus Used with a 207% Coaxial Detector.5DSPECPLUS™M u l t iN u c l i d e M D A P r e s e tThe DSPEC Plus now has an additional preset mode for low count rate applications:Multi Nuclide MDA Preset.This preset allows the operator to select up to 20 library nuclides and set the activity (in Bq or µCi) for each individual nuclide — the activities can be different as in Figure 6 — for any of 10 MDA equations such as the Curie Method, NUREG 4.16,and others.The DSPEC Plus then calculates the activity during the acquisition based on the number of counts in the peak regions, selected units, current live time, and stored efficiency value at the peak.When all 20 peak regions are below the limits set by the operator, the count is terminated.This preset is in addition to the other presets (Live Time, RealTime, Peak Uncertainty, and others) all of which can be turned on for any acquisition.The DSPEC Plus automatically stops when the first preset limit is reached.This allows the user to select not only an MDA preset but also the maximum time to acquire data if the MDA's are not met.Z e r o D e a d T i m e (Z D T ) — L o s s F r e e C o u n t i n g C o r r e c t i o nThe conventional method for correction of dead time exhibited in the gamma spectroscopy system is known as Live Time Extension.The DSPEC Plus includes the Gedcke-Hale method 8for live time correction as in many of ORTEC's advanced multichannel buffers.ZDT is an alternative means to correcting for dead time.It is especially beneficial to applications where the count rate is significantly decaying during the acquisition, such as in Neutron Activation Analysis, or where there is a rapid spike of activity during a long acquisition, as in the case of hot particles in stack monitoring.Live-Time Clocks expand the counting time of the electronics to compensate for dead time.Loss-free counting methods, like our ZDT, correct the actual number of counts in the spectrum for those counts "lost" while the system was processing other pulses.The ZDT method uses ORTEC’s highly accurate Gedcke-Hale clock to determine how many events should be added for the time that the electronics were "dead."In the ZDT Mode, the DSPEC Plus automatically stores both spectra (corrected and uncorrected) with the system so that viewing and analysis can be made.Both spectra are also stored in the ORTEC SPC format file structure to allow comparisons to be made at anytime in the future.The user can easily switch between the corrected and uncorrected spectra through simple menu commands in GammaVision-32 and MAESTRO-32.ORTEC now includes an uncertainty estimation algorithm to further enhance our ZDT method.1Unlike other "loss-free counting" methods which cannot calculate the uncertainty associated with counts added to the spectrum, the ZDT mode in the DSPEC Plus simultaneously generates the corrected spectrum and the uncertainty as data is collected.See Application Note 56, "Loss-Free Counting with Uncertainty Analysis Using ORTEC’s Innovative Zero Dead-Time T echnique" for more information on ZDT.Figure 6.MDA Preset.6...And Still as Easy to Set Up as Ever!The DSPEC instruments are easy to set up and use.With the intelligent MCA control, no manual configurations or even so-called Wizards are needed.Simply install the software (such as GammaVision-32 or MAESTRO-32)and the software "just knows" what control panels to show.The tabular design of the panels uses logical groupings of the controls and features available on the DSPEC Plus (as shown in Figures 4 and 7).The DSPEC Plus includes the ORTEC patented Digital Automatic Pole Zero 9circuit, Digital Automatic Baseline Restorer 10, and the Optimize feature 11which chooses the optimum flat top/tilt settings for the detector currently connected to the DSPEC Plus, making setup andenhancement of your spectroscopy system as easy as possible.Of course, the most innovative feature provided in ourproducts is InSight™, the built-in virtual digital oscilloscope.With the InSight feature, you can easily see the effects of changing the flat top width, baseline restore setting, or check the effects ofBallistic Deficit Correction (see side bar).No longer is it necessary to have a heavy, cumbersome,external oscilloscope around.No special software is necessary.Simply open the control panel and turn InSight mode on.V o i l a ...troubleshooting made easy!9U.S.Patent No.5,872,36310U.S.Patent No.5,912,82511U.S.Patent No.5,821,533Figure 7.Advanced Settings Control Panel.Figure 8.InSight Oscilloscope Mode.Ballistic Deficit CorrectionIn larger HPGe detectors, a characteristic known as ballistic deficit is sometimes exhibited.This typically results in poorresolution especially for high energy peaks.In analog systems, the ballistic deficit is corrected with either a gated integrator amplifier or through a resolution enhancer module.In digital systems, however, a simple adjustment to the flat top width of the digital filter is all that is necessary.Using the InSight mode in the DSPEC Plus allows the operator to make adjustments to the flat top width (and tilt) and immediately see the effects of the signal processing.In most cases with extremely large detectors (such as the 207% efficient one used in this example!), a flat top setting of 0.8 µs is more than sufficient to recover excellent resolution.See Figure 5 for comparison of the best analog amplifier and the DSPEC Plus .7DSPEC PLUS™SpecificationsDSPEC Plus is unlike analog systems, consisting of discrete components such as an amplifier or ADC. Whereas it is conventional in an analog system to specify the Gain instability of the ADC in ppm/°C, in DSPEC Plus, many of these conventional functions are emulated in the digital world by firmware;therefore, such specifications are meaningless.The specifications are DSPEC Plus SYSTEM parison should be made ONL Y with SYSTEM specifications in the analog world.System Gain0.35 to 100, continuously computer adjustable;minimum gain step is 1/85,000.Coarse Gain Computer selectable as 1, 2, 5, 10, 20, 50, and 100.Fine Gain Computer adjustable from 0.35 to 1.00. Shaping-Time ConstantsRise and Fall115 rise and fall times ranging from 0.2 to 23.0 µs in 0.2-µs steps;computer selectable.Flat Top22 flat top times ranging from 0.3 to 2.4 µs in 0.1-µs steps;computer selectable.Cusp Parameter7 values, ranging from 0.4 to <1; computer selectable.(Adjusts the curvature of the rise and fall time.)Memory Segment Size Computer selectable as 16,384, 8192, 4096, 2048, 1024, or 512 channels full scale. System Conversion Gain The overall gain of the system is appropriate for use with all types of Ge detectors. Coaxial GEM (P-type) and GAMMA-X (N-type).Low Energy LO-AX (low-energy coaxial), GLP (planar Ge), IGLET and IGLET-X (ultra-thin window planar Ge), and SLP [Si(Li)].Dead-Time Correction Extended live-time correction according to Gedcke-Hale Live-Time Clock (LTC). Accuracy:Area of reference peak changes <±3% from 0 to 50,000 counts per second.ZDT Loss Free Counting Correction Zero dead time correction for varying count rate conditions.Two modes include collection and storage of LTC and ZDT spectra or ZDT and uncertainty spectra.LinearityIntegral Nonlinearity <±0.025% over top 99.5% of spectrum, measured with a mixed source (55Fe @ 5.9 keV to 88Y @ 1836 keV).12Note that this performance is superior to that of typical analog systems whose specification is 70 ppm/°C (50 ppm for the amplifier in quadraturewith 50 ppm for the ADC).Figure parison of DSPEC and DSPEC Plus 8DSPEC PLUS™913Repetitive Acquire Mode currently supported through the A11-B32 Programmer’s Toolkit. 10ORDERING INFORMATIONT o order, specify:Model DescriptionDSPEC-PLUSDSPEC Plus Digital Gamma-Ray Spectrometer, including MAESTRO-32 and FullShot software.Under Windows 32-bit operating systems, the DSPEC Plus built-in Ethernet port allows single or multiple EtherNIM units to be connected directly into existing thinwire Ethernet installations.Automated setup routines make installation trivial.Many Ethernet adapters may be used successfully.Adapters tested at ORTEC include 3COM, IBM, Xircom PocketLan, and 3COM PCMCIA.ETHRJ45EtherNIM 10Base2 to 10BaseT Adapter Kit (BNC to RJ45).A65-N32Additional network copy of the MAESTRO-32 MCA Emulator;allows the DSPEC Plus to be controlled from a second networked PC.A66-B32GammaVision-32 MCA Emulator with comprehensive analysis, QA, and reporting capabilities.CHANGE SAMPLE/CRM OUT Dual function, rear-panel BNC:Change sample mode:provides TTL signal level to control an external device such as a Sample Changer.(CHANGE SAMPLE can be set for either TTL level via software command.)CRM mode:(software selectable), functions as an output connection for the Input count rate monitor.Provides 100ns-wide, +5 V , TTL compatible, logic signal for every linear input pulse that exceeds the pileup inspector threshold.Output impedance is 50 Ω.SAMPLE READY INPUT Rear-panel BNC accepts TTL signal level from an external device such as a Sample Changer.SAMPLE READY can be set to read either TTL level via software control.PREAMP POWER OUTPUT Rear-panel, 9-pin D connector;provides ±24 V and ±12 V for preamplifier power.INTERFACE CONNECTORSRS-232-C Rear-panel standard RS-232-C, 9-pin D connector, male, wired as DTE to run at 19.2k baud maximum, with modem control.ETHERNET Rear-panel BNC connector accepts IEEE 802.3 10BASE2 (thin coax).ELECTRICAL AND MECHANICALDimensions 32.5 cm W x 34.8 cm D x 14.5 cm H (12.80 in.W x 13.70 in.D x 5.70 in.H).Weight 7.7 kg (17 lbs).Power Consumption 110 watts.Operating Environment 0°to 50°C.PREREQUISITESAny IBM-compatible PC capable of running Windows 2000/XP , with an appropriate Ethernet adapter.11DSPECPLUS™C O N N E C T I O N S Software is Built into the DSPEC PlusC ONNECTIONS provides the following enhancements to personal-computer-based DSPEC Plus workstations for spectroscopy:•Easy installation and automatic setup, from a single unit to multiple DSPEC Plus units •High-speed, high reliability communications between DSPEC Plus and the control PC •System-wide detector access and control from any connected workstation •Detector-locking password security•Live spectrum display from remote detectors •Multiple simultaneous access to detector data•PC-to-PC file and printer sharing, with access protection •Identical user interface for local and remote detectors•Easily added to exiting installation;automatic system configurationDSPEC PLUS . . .unlike existing gamma-ray spectrometersTel.(865) 482-4411 • Fax (865) 483-0396 • @801 South Illinois Ave.,Oak Ridge,TN 37831-0895 U.S.A.For International Office Locations,Visit Our WebsiteSpecifications subject to change043009ORTEC®DSPECPLUS™。