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

[email protected]

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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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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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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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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

http://de.wikipedia.org/w/index.php?title=Datei:Radiation_warning_symbol.svg&filetimestamp=20071202091307

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How to identify and characterize neutron sources?

Neutronsource

Neutro

ns HeatG

amm

as

Gamma spectrometry

Neutron counting Calorimetry

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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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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

http://www.polimaster.eu/products/personal_radiation_detectors/pm1703gn/

http://www.polimaster.eu/products/hand_held_radionuclide_identification_devices_rids_/pm1401k_identifier/

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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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Gamma spectrometryUnshielded sources

Neutron source typeIsotopic composition

Fissile content?

Shielded source spectrum

Shielded or masked sources

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Gamma spectrometry

Detecting the presence of Be

Commercial applications stop here

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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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“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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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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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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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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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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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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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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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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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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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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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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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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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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Thank you for your attention!

[email protected]

http://www.iki.kfki.hu/

in-field identification of neutron sources

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