Hungarian Academy of Sciences
Institute of Isotopes
Nuclear electronics for
NCC measurements and
training
J. Bagi, J. Huszti, K. Szirmai
Department of Radiation Safety
huszti@iki.kfki.hu
IKI list mode equipment
Hungarian Academy of Sciences
Institute of Isotopes
Contents
 Neutron coincidence counting
 IKI instruments and software
 Comparison with JSR-14
Virtual source
 Concept
 Applications
 Educational use
NCC measurements & training
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IAEA, 19th February 2010
Neutron coincidence counting
Hungarian Academy of Sciences
Institute of Isotopes
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
NCC measurements & training
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Multiplicity distribution
Hungarian Academy of Sciences
Institute of Isotopes
Multiplicity counting
 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
NCC measurements & training
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IAEA, 19th February 2010
Hungarian Academy of Sciences
Institute of Isotopes
IKI list mode equipment
Virtual instrument
 Hardware box connected to a PC
 All controls and display are on the PC monitor
List mode
 Saving follow-up times
 Evaluating with different parameters
Instrument family
 Based on the same hardware platform: uniform look
 Control and data transfer is made via USB line
 Hardware identifies itself
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 Handles impulse rates up to 3∙10 cps
NCC measurements & training
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IAEA, 19th February 2010
Hungarian Academy of Sciences
Institute of Isotopes
IKI instruments
NCC measurements & training
Single channel list mode
hardware
 High voltage option
Multichannel list mode
hardware
 Simple model
 Model with channel
number handling
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Virtual source
IAEA, 19th February 2010
Multichannel device
Hungarian Academy of Sciences
Institute of Isotopes
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
NCC measurements & training
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 Saves channel number with each follow-up value
Hungarian Academy of Sciences
Institute of Isotopes
Channel information handling
 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
NCC measurements & training
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• 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
Hungarian Academy of Sciences
Institute of Isotopes
Data acquisition software
NCC measurements & training
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• Very fast processing
• Predelay, gate width
and long delay can
be set
Hungarian Academy of Sciences
Institute of Isotopes
Coincidence rate calculation
• The same data set
can be evaluated
with different
parameters
• Program performed
well at ESARDA
NDA Benchmark test
NCC measurements & training
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• Detection probability after
a trigger event in function
of time
Hungarian Academy of Sciences
Institute of Isotopes
Rossi-α distribution
• Random events have a
uniform distribution
whereas fission neutrons
are time correlated
• Dieaway calculation by
fitting
N (t )  A  R  e
NCC measurements & training
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t

IAEA, 19th February 2010
Hungarian Academy of Sciences
Institute of Isotopes
Comparison with JSR-14
 For multichannel
measurements preamplifier
outputs of detector were used
 JCC-31 has only six
preamplifiers
JSR-14
JCC31
Copy
PTR-02
PTR-16
 Single channel version in
parallel with JSR-14
 Copy output of PTR-02 used
NCC measurements & training
JSR-14
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JCC31
IAEA, 19th February 2010
Hungarian Academy of Sciences
Institute of Isotopes
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
NCC measurements & training
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IAEA, 19th February 2010
Virtual source is a tool for replaying impulse trains
recorded with a list mode device. It opens new
possibilities for NCC
Virtual
source
Hungarian Academy of Sciences
Institute of Isotopes
Virtual source
Computer with
impulse train
library
Can feed any
standard data
acquisition unit
e.g. JSR-14,
AMSR, PTR
Replaces real
source and detector
Extendable impulse
train library
Replays list mode data and software-generated
artificial pulse trains
NCC measurements & training
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Data
acquisition
unit
IAEA, 19th February 2010
Hungarian Academy of Sciences
Institute of Isotopes
Replacing real source and
detector
 High efficiency detectors are difficult to move because of
their large mass
 Transporting radioactive sources especially nuclear ones
involves a lot of administration
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
NCC measurements & training
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Virtual source applications
Hungarian Academy of Sciences
Institute of Isotopes
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
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
NCC measurements & training
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 Four identical output channels
Hungarian Academy of Sciences
Institute of Isotopes
Classroom use of virtual source
 Teams connected
in star topology are
independent of
each other
 Additional teams can be lined up through
the copy output of PTR-02
NCC measurements & training
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Demonstrating the basics of neutron coincidence counting
Hungarian Academy of Sciences
Institute of Isotopes
Exercises with virtual source
 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
NCC measurements & training
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Distribution basics
Periodic: multiplicity
depends on gate width,
building-up of Rossialpha
Burst: interpreting
follow-up distribution,
predelay
Burst
Random: variants of
multiplicity spectrum
Random
Hungarian Academy of Sciences
Follow-up
Periodic
Institute of Isotopes
Every stage demonstrates some basic characteristics of the distributions
NCC measurements & training
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Multiplicity
Rossi-alpha
IAEA, 19th February 2010
PuBe
Cf-252
 Basic impulse train library
 Impulse trains measured in
other laboratories can be
added to library
Multiplicity
Hungarian Academy of Sciences
 Getting familiar with basic
source types
Follow-up
Institute of Isotopes
Analyzing real spectra
Rossi-α
NCC measurements & training
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Identifying unknown source
Hungarian Academy of Sciences
Institute of Isotopes
Application of D/S method developed in IKI
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
NCC measurements & training
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Real source handling is required
Hungarian Academy of Sciences
Institute of Isotopes
Exercises – completion
 No sample handling exercise
 Using of detector
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
NCC measurements & training
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IAEA, 19th February 2010
List mode measuring is emphasized in IAEA R&D objectives
Hungarian Academy of Sciences
Institute of Isotopes
Conclusion
 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
NCC measurements & training
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IAEA, 19th February 2010
Hungarian Academy of Sciences
Institute of Isotopes
Thank you for your attention!
www.iki.kfki.hu/radsec/research
huszti@iki.kfki.hu
NCC measurements & training
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