institute of isotopes hungarian academy of sciences nuclear electronics for ncc measurements and...
TRANSCRIPT
In
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Nuclear electronics for NCC measurements and
training
J. Bagi, J. Huszti, K. Szirmai
Department of Radiation Safety
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IAEA, 19th February 2010NCC measurements & training
Contents
IKI list mode equipment
Neutron coincidence counting
IKI instruments and software
Comparison with JSR-14
Virtual source
Concept
Applications
Educational use
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Neutron coincidence counting
Basic assumption: Spontaneous fission rate is proportional to plutonium mass
Spontaneous fission produces multiple neutrons per event
(α,n) processes are more frequent
Fission neutrons are not detected coincidently but they are time correlated
Rossi-alpha distribution Event probability after a trigger Time correlated events are in the near field Far field events are not correlated with
trigger
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Multiplicity counting
Multiplicity distribution
Probability of event numbers in a time interval
Building event number distribution in a near and far gate
Difference of near and far gate describes coincident neutrons
Point model
Uses first three multiplicity moments
Solution for effective plutonium mass, neutron multiplication factor and (α,n) contribution
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IKI list mode equipment
Virtual instrument Hardware box connected to a PC All controls and display are on the PC monitor
Instrument family Based on the same hardware platform: uniform look Control and data transfer is made via USB line Hardware identifies itself
Handles impulse rates up to 3∙106 cps
List mode Saving follow-up times Evaluating with different parameters
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IAEA, 19th February 2010NCC measurements & training
IKI instruments
Single channel list mode hardware High voltage option
Virtual source
Multichannel list mode hardware Simple model Model with channel
number handling
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Multichannel device
Multichannel device
Detectors contain several amplifiers
Amplifier outputs are merged for data acquisition
Deadtime loss due to merging is growing with count rate
Correction may be greater than measured value
Multichannel operation reduces deadtime correction considerably at high count rates
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Channel information handling
Saves channel number with each follow-up value
Channel information handling extends PTR by several new features
Increased reliability by checking individual channels
Coincidence rates and Rossi-alpha distribution for individual channels
Data of defect channel can be subtracted after acquisition
By grouping of channels ring ratios can be calculated
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Data acquisition software
• Handles single channel and multichannel units
• Displays channel and ring rates
• Repeated measurements• Graph expandable and
collapsible even while data acquisition
• Displaying previously recorded data files
• Channel operations on list mode files
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Coincidence rate calculation
• Very fast processing
• Predelay, gate width and long delay can be set
• The same data set can be evaluated with different parameters
• Program performed well at ESARDA NDA Benchmark test
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Rossi-α distribution
• Detection probability after a trigger event in function of time
• Random events have a uniform distribution whereas fission neutrons are time correlated
• Dieaway calculation by fitting
t
eRAtN
)(
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Comparison with JSR-14
PTR-02
JSR-14
CopyJCC-31
JSR-14JCC-
31
PTR-16
For multichannel measurements preamplifier outputs of detector were used
JCC-31 has only six preamplifiers
Single channel version in parallel with JSR-14
Copy output of PTR-02 used
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Comparison results
Good agreement with JSR-14 results
Data without deadtime correction
At high count rate multichannel version compensates for impulse loss resulting from merging of preamplifier signals
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Virtual source
Computer with impulse train
library
Virtual source
Data acquisition
unit
Replaces real source and detector
Can feed any standard data acquisition unit e.g. JSR-14, AMSR, PTR
Replays list mode data and software-generated artificial pulse trains
Virtual source is a tool for replaying impulse trains recorded with a list mode device. It opens new
possibilities for NCC
Extendable impulse train library
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Replacing real source and detector
With a virtual source neither a source nor a
detector nor paperwork is needed for neutron
coincidence training.
The virtual source system can be transported like a laptop and no paperwork is needed
Great freedom in establishing training sites because some training can be performed without any real sources
High efficiency detectors are difficult to move because of their large mass
Transporting radioactive sources especially nuclear ones involves a lot of administration
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IAEA, 19th February 2010NCC measurements & training
Virtual source applications
Service generator
Signal generator and virtual neutron detector in one small unit
No real sources are needed for instrument testing
The same random pulse train can be reproduced many times
Training and Educational Tool for NCC
Demonstrating basic features of coincidence spectra by artificially generated impulse trains
Easy transport gives more freedom in selecting and preparing training sites
Virtual source library gives the possibility of investigating sources that trainees would not have access to or not present at the training site
No radiation hazard
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Classroom use of virtual source
Four identical output channels
Teams connected in star topology are independent of each other
Additional teams can be lined up through the copy output of PTR-02
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Exercises with virtual source
Demonstrating the basics of neutron coincidence counting
Three-stage exercise plan with software-generated periodic, burst and random impulse trains
Several simple tasks at each stage
Analyzing real spectra
Introduction to most frequent sources
Application of basic knowledge to real measurements
Determining the type of unknown source
Application of D/S-method of IKI
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Distribution basics
Pe
riod
icB
urst
Ra
nd
om
Follow-up Multiplicity Rossi-alpha
Every stage demonstrates some basic characteristics of the distributions
Periodic: multiplicity depends on gate width, building-up of Rossi-alpha
Burst: interpreting follow-up distribution, predelay
Random: variants of multiplicity spectrum
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Analyzing real spectra
Getting familiar with basic source types
Basic impulse train library
Impulse trains measured in other laboratories can be added to library
PuBe Cf-252
Fo
llow
-up
Mu
ltiplicity
Ro
ssi-α
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Identifying unknown source
Reference sources
Data acquisition
Calculation of coincidence rates
Setting up classification diagram
Unknown sample
Data acquisition
Calculation of coincidence rates
Determining source kind from D/S value
Application of D/S method developed in IKI
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Exercises – completion
Virtual source reduces training costs
Basic training can be held in a simple classroom
Training in the laboratory is shorter
Trainees are better prepared when measuring with real sources
Real source handling is required
No sample handling exercise
Using of detector
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Conclusion
List mode measuring is emphasized in IAEA R&D objectives
Laboratory prototype available
Multichannel prototype extends measuring capability into million cps range
Virtual source is a spin-off product of list mode
Application of virtual source in training
Cost reducing
No radiation hazard
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IAEA, 19th February 2010NCC measurements & training
Thank you for your attention!
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