Multichannel Analyzers Based on Digital Signal · PDF fileMultichannel Analyzers Based on...
Transcript of Multichannel Analyzers Based on Digital Signal · PDF fileMultichannel Analyzers Based on...
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Multichannel Analyzers Based on Digital Signal Processing
Valentin T. Jordanov
YANTEL, LLCDurham, NH 03824, USA
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INTRODUCTION• Early 1990s first practical DSP
based MCA proposed
• 1992-1994, Real Time, Time-Invariant DSP algorithms developed
• Communication/Internet tech revolution leads to High-Resolution, Fast ADC development in late 1990s
• FPGA technology progress also follows the communication bum
• 2000+ Radiation Instrumentation Industry switches almost entirely to DSP technology
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DET
PA
DIF
AMP
PKD
ADC
MCA
BASIC ANALOG SPECTROMETER
DET
PA
DIF
AMP
PKD
ADC
MCA
BASIC DIGITAL SPECTROMETER
FAST DISCRIMINATOR
FAST DISCRIMINATOR
PILE-UP REJECTOR
PILE-UP REJECTOR
RISE-TIME DISCRIMINATOR
RISE-TIME DISCRIMINATOR
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Pulse Shaping Goals
• Noise Suppression (Resolution)
– White Noise: parallel and series;
– 1/f Noise: parallel and series;
• Throughput Optimization (Dead Time)
– Finite Pulse Duration;
• Ballistic Deficit (Resolution, Peak Distortion)
– Flat Top;
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Optimum Shaping: White Noise
– Parallel
– Series
V. Radeka, IEEE Trans. Nucl. Sci. NS-15 (1968) p 455
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Optimum Shaping: 1/f Noise
E. Gatti and M. Sampietro, Nucl. Instr. and Meth., A287, (1990) p513.
E. Gatti et al., Nucl. Instr. and Meth., A394, (1997) p268.
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Digital Pulse Shape Synthesis
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Digital Pole-Zero Cancellation
X
ACC
M
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+
R
C
v(n)
p(n)
q(n)
s(n)Σ
τ 1
X - multiplierACC - accumulatorΣ - adder
M ≈ τ1 /Tclk - 0.5
Dig
itize
r
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τ 2
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Pile-up EffectsPeak Detection
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Real Time Operation
PA
DIF
SHP
PKD
ADC
MCA
DAC
DET
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DIGITAL PULSE-SHAPE DISCRIMINATION
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Pulse Processing for Pulse-Shape Discrimination
• Convolution of the Integrated Pulse with Impulse Response for Optimum Pulse-Shape Discrimination
• Amplitude Normalization
• Threshold Discrimination
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Ratio Spectra at Different Energies
100 200 300 400 500 600Channel
100 200 300 400 500 600Channel
20-30 keV ee
M=0.78
30-60 keV ee
M=1.14
60-100 keV ee
M=1.59
100-150 keV ee
M=2.16
M=3.39
300-400 keV ee
400-500 keV ee
M=3.46
200-300 keV ee
M=2.95
M=2.55
150-200 keV ee
n γ
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Neutron-Gamma Separation
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Digital MCA in the Near Future
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Miniaturization
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Spectrometer on a Programmable Chip
DIGITALPULSE
SHAPER
DIGITALGAIN
CONTROL
DIGITALFAST
SHAPER
MAINSHAPER
LLD
FASTDISCRIMINATOR
PILE-UPREJECTER
DUAL PORTMEMORY
CONTROLLER
REAL and LIVETIMERS
DIGITALBLR
RISE TIMEDISCRIMINATOR
AUTOMATICTHRESHOLDSCONTROLLER
DIGITALPEAK
DETECTOR
DEAD TIMEESTIMATOR
EXTERNAL ANDINTERNAL GATE
CONTROLLER
HOUSE KEEPINGAND INTERFACE
CIRCUITS
DATAACQUISITION
DIGITALOSCILLOSCOPE
COUNTERS
• High Density FPGA
• Low Power
• Flexible Design
• In Circuit Reprogram
• One Hardware Platform –Multiple Device Functions
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Small Size and Low Power Benefits
• Integration of the Detector and the MCA in one package.
• Elimination of signal and power cables.
• Low Power and the Integration reduce the external noise pickup and ground loop effects.
• MCA is completely tuned to the attached Detector which eliminates most of the traditional adjustments –Pole/Zero, Gain, Polarity, HV polarity etc.
• MCA is always calibrated – user chooses energy range. Efficiency, calibration and other data storage.
• Extra power and space allows the integration of analytical software.
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EXAMPLE: Niton XRF Analyzers
• Integrated Detector, MCA and X-Ray Source in One Package
• Ultra small, Ultra light
• Battery Operated
• Low Power
• Integrated Analytical Software
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Field Use of Portable Digital MCA
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CONCLUSION
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Digital Pulse Processing Benefits• Improved Spectroscopy Performance
• High Count Rate, High Resolution
• Temperature Stability
• Improved Pulse Shape Analysis
• Size and Weight of Instruments
• Battery Operation
• Overall Flexibility, Hardware and Software Integration