Download - In-field identification of neutron sources
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In-field identification of neutron-sources
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Vienna, February 19, 2010
In-field identification of neutron sources
C.T. Nguyen, J. Bagi, L. Lakosi, J. HusztiK. Szirmai, Z. Hlavathy, I. Almasi, J. Zsigrai
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In-field identification of neutron-sources Vienna, February 19, 20102
Contents
Categories of neutron sources Options for neutron-source identification Application of neutron-coincidence counting
for identification of neutron sources “Traditional” application of NCC vs. neutron
source identification Possible practical realizations Problems at high count rate and solution
NCC at the Institute of Isotopes
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In-field identification of neutron-sources Vienna, February 19, 20103
What is a neutron source?
Radioactive material emitting neutrons
Neutrons from Spontaneous fission Induced fission (,n) reactions …
Pu n
9Be
PuBe13Be(,n)Be(n,2n)Pu(n,f)
RANDOM NEUTRONS: S
n
n
TIME CORRELATED SPONTANEOUS-FISSION NEUTRONS : D1
TIME CORRELATEDINDUCED-FISSION AND Be(n,2n) NEUTRONS: D2
For example:
In this presentation we do not consider other sources of neutrons (e.g. nuclear reactors, neutron generators etc.)
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In-field identification of neutron-sources Vienna, February 19, 20104
Categories of neutron sources – according to neutron emission
Dominantly fission sources D1>>D2, DS
Pu metal Pu-oxide MOX Cf-252: Cm-244
Mixed D1 D2, D<S
PuF4 (,n) sources
D1 << D2, D<<S PuBe Am-Be Am-Li
S: Random neutronsD1: spontaneous fission neutronsD2: induced fission neutronsD=D1+D2
Pu n
9Be
PuBe13Be(,n)Be(n,2n)Pu(n,f)
RANDOM NEUTRONS: S
n
n
TIME CORRELATED SPONTANEOUS-FISSION NEUTRONS : D1
TIME CORRELATEDINDUCED-FISSION AND Be(n,2n) NEUTRONS: D2
For example:
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In-field identification of neutron-sources Vienna, February 19, 20105
Categories of neutron sources – according to threat
Pu in various forms Pu metal, Pu-oxide, MOX, PuF4, Pu-Be sources …..
Everything else Spontaneous-fission
sources Cf-252 Cm-244 …
(α,n) sources Am-Be Am-Li …
Proliferation hazard
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In-field identification of neutron-sources Vienna, February 19, 20106
How to identify and characterize neutron sources?
Neutronsource
Neutro
ns HeatG
amm
as
Gamma spectrometry
Neutron counting Calorimetry
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In-field identification of neutron-sources Vienna, February 19, 20107
How to identify and characterize neutron sources?
Neutronsource
Neutro
ns HeatG
amm
as
Gamma spectrometry+ Standalone technique
+++ Can be used anywhere- Shielding may cause problems
Neutron counting+Satisfactory accuracy++Shielding no problem+Standalone technique
+++Can be used anywhere
Calorimetry+++Very good accuracy
-Not a standalone method---Can be used only in the lab
-Shielding may cause problems
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In-field identification of neutron-sources Vienna, February 19, 20108
What can a first responder do?
Commonly used equipment: Personal Radiation Devices: gamma
and neutron rate display Radiation Identifiers: low-resolution
gamma spectrometry (mainly NaI) Background:
No scientific background Knowledge:
Basic training (1-2 weeks) Capability:
To handle simple cases
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In-field identification of neutron-sources Vienna, February 19, 20109
And the expert team? Commonly used equipment:
Portable HPGe: High-resolution gamma spectrometry
Background:Scientific
Capability: Case assessment Making decisions Implementing specific
approaches
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In-field identification of neutron-sources Vienna, February 19, 201010
Gamma spectrometryUnshielded sources
Neutron source typeIsotopic composition
Fissile content?
Shielded source spectrum
Shielded or masked sources
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In-field identification of neutron-sources Vienna, February 19, 201011
Gamma spectrometry
Detecting the presence of Be
Commercial applications stop here
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In-field identification of neutron-sources Vienna, February 19, 201012
Neutron measurements Gross neutron detection:
Equipment needed: personal radiation detector Neutron count rate Rough idea about neutron yield
Neutron coincidence counting: Equipment needed: neutron detector (3He) + electronics + software (!)
Gross count rate, S Coincidence rate, D And their ratio, D/S
Estimated neutron yield
Number of spontaneous fissions
and secondary reactions
Neutron source type,Neutron yield,
Fissile content,Estimated isot. comp. of Pu
Heavy–metal shielding is no problem for neutrons!
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In-field identification of neutron-sources Vienna, February 19, 201013
“Traditional” application of NCC vs. identification of neutron sources
“Traditional” application :
Determination of 240Pueffective mass, based on detection of time correlated neutrons (Dspontaneous) from spontaneous fission of Pu isotopes
m240effective = 238m238 + m240 + 242m242
Identification of N-sources:
Detection of both spontaneous and induced fission neutrons
For (,n) sources S>>Dinduced>>Dspontaneous
D/S: number of fissions induced by a one random neutron
Pun
Be
PuBe
RANDOM NEUTRONS: S
nn
SPONTANEOUS-FISSION NEUTRONS : D1
INDUCED-FISSION AND Be(n,2n) NEUTRONS: D2
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In-field identification of neutron-sources Vienna, February 19, 201014
Identification of neutron sources by neutron coincidence countingRatio of coincidences (“doubles”) to total counts (“singles”) as a function of total count rate
D/S
S
Different sources on different curves
Curve determined by: Specific neutron yield Isotopic composition
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In-field identification of neutron-sources Vienna, February 19, 201015
Identification of neutron sources by neutron coincidence countingRatio of coincidences (“doubles”) to total counts (“singles”) as a function of total count rate
D/S
S
Dominantly fission sources D1>>D2, DS
Pu metal Pu-oxide MOX Cf-252: Cm-244
Mixed D1 D2, D<S
PuF4 (,n) sources
D1 << D2, D<<S PuBe Am-Be Am-LiS: Random neutrons, D1: spontaneous fission neutrons
D2: induced fission and Be(n,2n) neutrons, D=D1+D2
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In-field identification of neutron-sources Vienna, February 19, 201016
Identification of neutron sources by neutron coincidence countingRatio of coincidences (“doubles”) to total counts (“singles”) as a function of total count rate
D/S
S
Plutonium E.g. pure Pu,
Pu-Be with various isotopic composition
Everything else Spontaneous-
fission sources (α,n) sources
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In-field identification of neutron-sources Vienna, February 19, 201017
Identification of neutron sources by neutron coincidence counting
D/S
S
Neutron source type Presence of Pu Isotopic composition
of Pu Mass of fissile isotope
Pu isotopic composition can be estimated also for high-burn-up Pu (with 239Pu < 70%), for which MGA fails!
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In-field identification of neutron-sources Vienna, February 19, 201018
Further characterization of (,n) sources Total Pu content of Pu-Be
sources
Analogously for other (,n) sources
Specific neutron yield
Important parameter for determining the origin of the source
MNY
Neutron yield
Specific neutron yield
Mass
MPu~D/SS>>Dinduced>>Dspontaneous
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In-field identification of neutron-sources Vienna, February 19, 201019
Possible realizationsCanberra HLNC Ortec fission meter
JSR-15 AMSR 150
IKI prototype
Detector
Electronics
Detector calibration
Software
PTR-II
Shift (multiplicity) registerList mode operationPulse train analysis
Die-away time calculation
Using neutron sources at IKI
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In-field identification of neutron-sources Vienna, February 19, 201020
Possible upgrades of the IKI prototype
Modules in Closed and open geometry
Real-time Monte-Carlo simulations for calibrating actual source-detector configuration
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In-field identification of neutron-sources Vienna, February 19, 201021
Problems at high count rates
Many neutron sources have neutron output >106 n/s Dead-time losses strongly influence accurate
measurement of D
JCC-13 (18 det./3 amp.) +JSR14 can not operate correctly with sources emitting > ~106 n/s
HLNC (JCC-31:18 det./6 amp.) +JSR14 can not operate correctly with sources emitting > 107 n/s
0.01 0.1 1 10 100 10001E-3
0.01
0.1
D/S
MPu
(g)
HLNC 18 dets.1 amp. / 3 dets.Efficiency 13 %
JCC-13 18 dets.1 amp / 6 dets.Efficiency 28 %
Sources with 106 -107 n/s
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In-field identification of neutron-sources Vienna, February 19, 201022
Problems at high count rates
Similar efforts at IAEA: Activities Supported Through Regular Budget in the IAEA R & D
Programme for Nuclear Verification 2010–2011 NDA Activity #7: Analysis and considerations of potential gaps in
the point model aiming at finding the methodological error sources in highly intensive neutron counting
NDA Activity #8: Analysis and consideration of possibilities to minimize and account correctly for dead time in the method of neutron coincidence counting using 3He in moderator
Possible solution: Separate amplifiersand separate data acquisition channelsfor each 3He tube (see next presentation)
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In-field identification of neutron-sources Vienna, February 19, 201023
Complex approach for characterization
Gamma and neutron measurements
Pure gamma methodCombination of neutron-gamma
methodPure neutron method
Neutron source type,Amount,
Precise isotopic comp. of Pu
Neutron source type,Neutron yield,
Amount,Precise isotopic comp. of Pu Neutron source type,
Neutron yield,Amount,
Estimated isotopic comp. of Pu
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In-field identification of neutron-sources Vienna, February 19, 201024
NCC at the Institute of Isotopes
A set of well characterized neutron sources is available at IKI: 1 AmLi, 3 AmBe, 7 Pu-Be, 2 242Cm, 5 252Cf (characterization by HRGS, calorimetry, NCC, neutron-radiography)
Field test of IKI prototype performed, in attendance of IAEA and JRC observers
Pu content of ~80 Pu-Be sources measured and safeguards accountancy corrected: total of 563±15 g of Pu, instead of 2050 g !
Development of nuclear electronics for list-mode data acquisition
Pu-Be neutron sources repackaged into new containers
Home-made neutron counter
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In-field identification of neutron-sources Vienna, February 19, 201025
Conclusion NCC can be successfully applied for
identification of neutron sources Pu in any form (pure Pu, Pu-Be …) can be
separated from pure fission and (,n) sources Appropriate hardware and software needed
Coincidence counter, List mode electronics, Multichanel data collection dealing with high count rates
Prototype readily available Help in testing and validation and
suggestions for improvement arewelcome!
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In-field identification of neutron-sources Vienna, February 19, 201026
Thank you for your attention!