|Title of Invention
"ELECTRONIC MODULE FOR GAMMA RAY SPECTROSCOPY SYSTEM"
|An electronic module for use in gamma rays spectroscopy system. The gamma rays spectroscopy system comprises a clover detector and an Anti-Compton Shield (ACS). The clover detector generates "ENERGY" signal and "TIME" signals. The electronic module comprises at least four shapers for shaping and magnifying the "ENERGY" signals, a plurality of Analog to Digital converters for generating accurate digital value proportional to "ENERGY" signals, a set of four Timing Filter Amplifier cum constant fraction discriminator (TFA+CFD) adapted for shaping, amplifying, and generating a corresponding logic pulse from "TIME" signals, a preamplifier connected to ACS for amplifying and shaping signals from the ACS, a timing filter amplifier cum constant fraction discriminator for amplifying and generating a prompt logic pulse from the signal received therefrom, and Anti-Coincidence logic unit connected to the TFA+CFD for processing raw timing logic signals generated from the clover detector and the ACS. FIG. 1
|BACKGROUND OF INVENTION
A clover detector is a multisegment (4) High purity Germanium detector (HPGe) used as a single Structure for gamma ray spectroscopy. Another detector comprising scintillation material with photo multiplier tubes surrounding the HPGe structure substantially and not covering detector aperture is an Anti Compton Shield (ACS). ACS is meant to convert and reject gamma rays that would scatter into if from Germanium detector segments. The gamma ray radiation induced signals in Germanium detector segments are processed with a of electronic circuit in module form. In order to have good signal to noise ratio, stability and linearity if essential to use sophisticated and state of the art electronic circuits. This would ensure good energy (amplitude) resolution and time (time of occurrence) . In gamma ray spectroscopy experiments many (50 to 100) such detectors are used, complicating the circuit with the use of many electronic modules (circuits) and interconnections. These can lead to interference between circuits, which can affect reliability of the circuit. There are various difficulties experienced while using conventional electronics setup for multisegment detectors.
Usually amplitude of signal (pulse) generated by the detector (proportional to amount of energy released in Detector) is processed in "ENERGY" channel and the time of radiation occurrence is processed by "TIME" channel. The "ENERGY" channel contains "Shaper" and ADC (analog to digital converter) to shape the fast rising and slowly decaying pulses into a near Gaussian shape pulses for digitisation in ADC. After digitisation the digital value is recorded and used to build histogram in computer display for visualization of nuclear radiation spectrum.
Typical "shaper" is available in single width NIM (Nuclear Instruments & Measurements standard) module having various controls such as Gain adjustments (0.5 to 1500), Shaping time constant adjustments (0.5us to lOus), BLR (manual/auto) selection, Bipolar outputs apart from Unipolar outputs, Busy and Pile Up Rejection (PUR) indications. In TIME channel the function of "Timing Filter Amplifier" (TFA) is to preserve the fast timing components and amplifying the signal with wideband amplifier while keeping base level constant. The function of " Constant Fraction Discriminator" (CFD) is to generate a fast logic signal to indicate the time of occurrence of radiation, independent of incoming signal amplitude variation from "TFA". The remaining complicated logic circuits (Anticoincidence Logic) are used to generate various time related signals to control ADCS and TDC (Time to Digital converter). Since these modules are general purpose, many features are not used in a typical experiment setup. Some of these modules are also available in multiple channels (independent), which make them attractive but often few channels are used. Thus they occupy large area, consume lot of power and involve huge cost. Moreover, the currently available modules are bulky use outdated electronic components . The panel adjusted mechanical parts make these module highly unreliable after certain number of adjustments.
Thus a compact module with all essential functions, controls at par with essential (minimum) interconnections has been developed that saves large real estate, power consumption, cost, altogether avoiding unreliable mechanical components, while providing flexibility and good performance than conventional setup. Remote controlling of various circuit parameters through computer is an added feature for controlling large number of
modules which are generally placed in radiation restricted areas.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be described in brief with reference to the accompanying drawings wherein:
Fig. 1 represents the Block Diagram of Clover Electronics Module
Fig. 2 represents the block diagram implemented as Anticoincidence logic
DETAILED DESCRIPTION OF THE DRAWINGS
The present invention relates to clover (multisegment) Detector Electronic Module (Fig 1) for use in various experiments with broad range of detector and radiation sources comprising shaping amplifiers, TFAs, CFDs and logic circuitry for processing signals from a clover detector with Anti Compton Shield (ACS) wherein the circuits are realised in high density daughter card form using SMD components.
Accordingly the present invention relates to multisegment clover detector electronic module for use in gamma rays spectroscopy comprising a four segment High purity Germanium (HPGe) clover detector (1) an AntiCompton Shield (2) with scintillation material with photomutiplier tubes, substantially surrounding the HPGe structure for converting and rejecting gamma rays leaking into it from Germanium detector segments, builtin preamplifiers in Germanium detector for processing the "ENERGY" and "TIME" signals, at least four SHAPERS (3) connected to the Clover detector for magnifying the amplitude of "ENERGY" signals, plurality of an Analog to Digital Convertor (8) connected in
sequence with SHAPER for processing and generating accurate digital word proportional to amplitude of "ENERGY" signals, Timing Filter Amplifiers (TFA) (4) for amplifying and shaping "TIME" signal, a discriminator (4) having an input from TFA for obtaining logic pulse by processing the amplified and shaped TIME signal, a preamplifier connected to AntiCompton Shield for amplifying and shaping signals from AntiCompton Shield and feeding into TFA and discriminator connected to a Logic circuit, an Anti Coincidence logic unit (Fig2) for processing raw timing logic signals received from Clover detector and ACS detector.
A typical commercial electronic setup would require a large no. of modules which occupy large area, interconnecting cables and connectors whereas NIM module of present invention comprises five channels of electronics to accommodate one clover with accompanying anti-compton shield. Surface mount tech (SMT) has been adopted for designing circuits like Mother Board, TFA + CFD and anticoincidence logic-unit to achieve compactness.
The main detector consists of 4 Germanium crystals to have good efficiency. Signals from all four crystals of one detector are recorded as they come from a single composite detector. When the gamma radiation deposits energy on GE crystals it creates hole and electrons which are attracted towards respective electrodes. The resulting current impulse is fed to a pre-amplifier which gives a voltage signal proportional to the gamma radiation energy. The signal also contains timing information related to time of energy deposition in its rise time.
The high resolution spectroscopy amplifier have fixed 3 us shaping constant and 3 fixed gain settings (2, 4 & 6 MeV) which are jumper selectable. The DC base line is stabilized with Gated BLR, while P/Z and BLR (manual) threshold adjustments can be
remotely voltage controlled. The unipolar output has the dynamic range of 8 volts across 50 ohms.
The 4 nos. of "ENERGY" signals and 4 nos. of "TIME" signals from 4 crystals of Germanium detector through built-in preamplifiers are taken out for further processing.
Each "ENERGY" pulse is fed to a "shaper" or shaping amplifier for further pulse processing. The major role of a shaping amplifier is to magnify the amplitude of preamplifier from millivolt level into 1 volt to 10 volts range in addition to shaping of pulse into a traditional Gaussian pulse shape that provides excellent signal to noise enhancement. This technique involves one pulse differentiation followed by several stages of active integrating filtering, all set to the same cut-off frequency (the shaping time constant). Thus the shaper acts as a narrow bandpass filter - amplifier.
The shaper current contains all required functions and controls like P_Z (Pole-Zero) Adjustment, P_Z and BUSY Monitoring, BLR (Base line Restorer) adjustment gain Adjustment (on board selectable)
Pile Up Rejection. All adjustments are voltage controllable either by manual or through remote computer. The state of the art active and passive components is SMT are adopted for low electronic noise, excellent thermal and baseline stability. The resulting each ENERGY signal is fed to ADC (Analog to Digital Converter) which generate accurate digital word proportional to the amplitude of ENERGY Signal which are stored in processor of data acquisition system for further analysis.
Each "TIME" pulse signal from, Germanium crystal and ACS detector are fed to timing Filter Amplifier (TFA) . Four TFAs with fixed constants and gain settings are provided for processing TIMING signals from clover detectors. They are wide band linear amplifiers (70Mh2, - 3dB) with high pass filler to remove any low frequency variations, which are required to derive, optimum timing resolution.
The TFA is designed with single CFA gain stage and baseline is stabilized with twin diode restorer and high input impedance buffer. These amplifiers have rise time of better than 10 nanoseconds across their dynamic range of +- 2.5 volts across 100 ohms. The Constant Fraction Discriminator (CFD) circuits with amplitude and rise time compensation (ARC) is realised with fixed delay of 25 ns and fraction of 0.3. The lower level threshold, WALK adjustment and monitoring are possible on front panel. The CFD outputs from the individual clover elements with width of 50 ns and dead time of 2 us are set internally. Each amplified and shaped TIME signal is fed to a discriminator to derive the logic pulse. Constant fraction discrimination technique is used as a discrimination technique. CFD circuit has features such as built-in Delay line, CFD/SRT (Slow rise time reject), Dead Time and Shaping circuits to process the signal to derive Time information.
In order to improve timing resolution, after the initial transition of logic pulse further timing information is blocked for 2 micro seconds.
Anti-compton shield signal from ACS Preamplifier (6) is processed with identical TFA + CFD (7) as mentioned above but without dead time. The raw timing logic signals received from CFDs from clover
detector and ACS detector are further processed to affect Anticoincidence, an important function provided by Anticoincidence Logic Unit.
The logic functions performed are Pile-Up Rejection, Individual ADC GATing , Anti-Coincidence output and delayed STOP signals are buffered and available in standard logic levels on the panel.
Whenever the radiation leaks into ACS detector through Germanium detector which is indicated by presence of logic pulse from both detector at the same time is called COINCIDENCE. Such signal coincidence is undesirable in order to provide better signal to noise ratio from Germanium Detector the desirable ANTICOINCIDENCE function is implemented with AND gate function whose inputes are logic pulses from Germanium detector and ACS detectors respectively.
Other control signals to Analog to digital connectors such s "ADC GATE", PUR signal to ADC (Analog Digital Converter) are derived from this ANTICOINCIDENCE signal.
1. An electronic module for use in gamma rays spectroscopy system, the gamma rays
spectroscopy system comprising a four segment High Purity Germanium (HPGe) clover detector (1)
having built-in preamplifiers and an Anti-Compton Shield (ACS) (2) comprising scintillation material
with photo-multiplier tubes, the clover detector (1) adapted to generate "ENERGY" signal
corresponding to energy generated by the clover detector (1) upon radiation by gamma rays and
generate "TIME" signals corresponding to timing of radiation by gamma rays, the ACS (2) configured
to surround the clover detector (1) and adapted to convert and reject gamma rays leaking into it from
the four segments of the clover detector (1), the electronic module comprising:
at least four shaping amplifiers (SHAPERS) (3) connected to the clover detector (1) for shaping and magnifying the "ENERGY" signals received from pre-amplifiers of the clover detector (1),
a plurality of Analog to Digital converters (ADCs) (8) connected in sequence with SHAPERS (3) for generating accurate digital value proportional to amplitude of "ENERGY" signals,
a set of four Timing Filter Amplifier (TFA) cum constant fraction discriminator (TFA+CFD (4)), the TFA+CFD (4) adapted for shaping, amplifying, and generating a corresponding logic pulse from "TIME" signals received from built-in preamplifiers of clover detector (1),
a preamplifier (6) connected to ACS (2) for amplifying and shaping signals from the ACS (2),
a timing filter amplifier cum constant fraction discriminator (TFA+CFD (7)) coupled to the preamplifier (6) for amplifying and generating a prompt logic pulse from the signal received from the preamplifier (6) without any built-in dead time, and
an Anti-Coincidence logic (ACL) unit (5) connected to the TFA+CFD (4, 7) for processing raw timing logic signals generated from the clover detector (1) and the ACS (2) through the corresponding TFA+CFD (4,7).
2. An electronic module as claimed in claim 1, wherein the ACL unit (5) is adapted to generate
Pile Up Rejection (PUR) logic signals and Anti-coincidence logic, and to generate ADC GATE signals
by processing "TIME" signals, the ADC GATE signals being provided to corresponding ADC(8) for permitting the ADC (8) to perform digital conversion of only qualified linear signal from the SHAPER (3) for better signal to noise ratio.
3. An electronic module as claimed in claim 1, wherein the said Constant Fraction Discriminator (CFD) of the TFA+CFD (4) circuit has features such as built-in Delay Line, CFD/SRT (Slow rise time reject) selection, Dead Time and Shaping circuits to derive "TIME" information for further processing at ACL (5).
4. An electronic module as claimed in claim 1, wherein the TEA of the TFA+CFD (4) is a wide band linear gain stage (fixed gain) amplifier with a compact high pass filter network, the wide band amplifier wired around a CFA and having baseline stabilized with twin diode restorer and buffer amplifier.
5. An electronic module as claimed in claim 1, wherein each of the Shaping amplifiers (3) is a compact band pass filter adapted to provide all required functions and controls like P_Z (Pole_Zero) Adjustment, P_Z and BUSY Monitoring, gated BLR (Base Line Restorer) threshold adjustment, Gain Adjustment, and Pile UP Rejection indication.
6. An electronic module as claimed in claim 1, wherein all the adjustments are voltage controllable either by manual or through remote computer.
7. An electronic module as claimed in claim 1, wherein all logic outputs are buffered, short-circuit proof and available in standard logic levels on panel of the electronic module.
8. An electronic module, substantially as hereinbefore described with reference to the accompanying drawings.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|INTER-UNIVERSITY ACCELERATOR CENTRE
|UGC, ARUNA ASAF ALI MARG, NEW DELHI-110 067, INDIA.
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date