Noble Gas Sampling and Detection Methods for On-Site Inspections in Support of CTBT

J.S. Elisabeth Wieslander, Kirill KhrustalevEquipment Officers, CTBTO

On-Site Inspection DivisionPreparatory Commission for the Comprehensive Nuclear-Test-BanA Treaty OrganizationProvisional Technical SecretariatVienna International CentreP.O. Box 1200A-1400 Vienna

Presentation at IAEA Symposium, Wien, 20-24 Oct 2014

The views expressed here are those of the authors and do not

necessarily reflect the views of the CTBTO Preparatory Commission

On-Site Inspections (OSI): Last step of the verification

OSI the final verification measure specified by the Treaty

guided by the OSI Operational Manual

Each State Party has the right to request an OSI

only AFTER the Treaty has entered into force

The Treaty, Article IV, Paragraph 35

The sole purpose of an on-site inspection shall be to clarify whether a nuclear weapon test explosion or any other nuclear explosion has been carried out in violation of Article I and, to the extent possible, to gather any facts which might assist in identifying any possible violator.

Context for radionuclide monitoring

Atmospheric, surface, near surface and some underwater explosions

can be identified via particulate monitoring

detections in the IMS will most likely suffice for verification of the Nuclear Event

Underground & underwater explosions:

low amount of aerosols escape

NG likely to be released via cracks and diffusion

NG are inert gases : stay in the atmosphere, seep times & concentrations vary

this is where an On-Site Inspection becomes of interest....

Detection of radionuclides from nuclear weapon testing

Detection of ACTIVATION & FISSION products

Both radioactive GAS and PARTICLES

Measurements supported by Atmospheric Transport Modelling (ATM)

RN detections in an OSI are supported by other verification methods:

VISUAL observations

GEOPHYSICS methods, active and passive SEISMIC monitoring

Multi spectral/infrared analysis (MSIR)

Verification methods

KEY RADIONUCLIDES the traces that indicate nuclear test

Table 1. Most abundant radionuclides after a 1 kt explosion. Table 2. Radionuclides relevant as nuclear test indicators. Courtesy of CTBTO/IDC

OSI permitted RN : DRAFT LIST

Not included below but in the DRAFT LIST: Tc-99m, I-132, Pr-144 Cal. sources: Co-60, Ba-133

Background: K-40, Natural Decay Chains from U-238 & Th-232, activation products from detectors & shielding material

Primary NG : - Xe-133, -133m, 131m, -135 and Ar-37

No Kr-85 : - too long half-life (10y) - production by civilian nuclear industry substantial global background : 1-1.5 Bq/m3

OSI NG Field Sampling- current status

Sub-soil GasXe & Ar-37Number of samples/day depends on Number of Sampling Stations and resourcesSampling Station = combination of sampling points, which provides volume & cover larger areaVariable sample volume according to soil typeRequirement = 0.4 – 4 m3/sample

Manual = Labour intensive

Bulk AirXe (currently no Ar-37 capability)Continuous monitoring 2 samples/dayVariable air volume up to ~10 m3/sample

Automatic, ~unattended = ~no Labour after installation

Xe & Ar-37Selected atm. bulk air samples taken in the field as background comparison to subsoil gas samples0.4-2 m3/sample

Manual = some daily Labour

SSSS

2233

4455

11S = points

Getting enough gas per sample in the Field

Newtonian search = faster screening in the Lab

S1S1 S2S2

S3S3 S4S4

S5S5 S6S6

S7S7 S8S8

Sscrening = (S1-S8)fractions

OSI NG Field Sampling

• Continuous low sampling flow overnight / several days• Compressed into high-pressure transportation bottles

• Tampering control• Chain of Custody

OSI NG Field Laboratory

can be assemblied by 2 persons

Laboratory equipment housed in two 20-feet shipping containers with climate control, UPS and back-up generator.

OSI NG Field Laboratory- premiere in 2014

OSI NG Field Laboratory- premiere in 2014

SAUNA-OSI 2014MARDS and SAUNA-OSI 2014

WITHOUT cryogenics & large amounts of consumables, can be mounted by 2 pers.

• A set of equipment from several manufacturers• Partly Unattended Systems

Name Manufacturer Nucl. Gas Separation & Processing

Detection Systems

Analysis Software

SAUNA-OSI FOI, Sweden Xe Y Y Y

XESPM NINT, China Xe Y N N

Si-Pin Detector LARES, Russia Xe N/A Y Y

MARDS INPC, China Ar-37 Y Y Y

Pre-Processing FOI, Sweden Xe Y N/A N/A

Support equipment & consumables• Gas detectors (CO2, H2O, Methane etc)• Carrier gases He, N2, CO2• H&S equipment (Oxygen alarm, comms, fire alarm)

OSI NG Field Laboratory- premiere in 2014

integrated into one OSI NG Lab

OSI NG Lab Process

SAMPLE INPUT high pressure bottle to low pressure Lab syst.

Quantification 1

ANALYSISvarious software

EVALUATIONratios, historical data, local bkg, atm, data

fusion with other OSI techniques…

Quantification 2

Ar-37 Processingseveral steps

Xe Processingseveral steps

Decay Measurementvarious equipment

Exhaust incl. Argon,

N2, O2 CO2, H2O etc

• State of Health• Data quality, integrity, security• Chain of custody, managed access

Xe Processing Example

Processing

Quantification 1

- coincidence measurements

Quantification 2

OSI NG detection capability vs background

(*1) Limiting factors: one detector & manual sample change

(*2) Limiting factors: manual sample change

(*3) Heavy items are mainly leadshield modules

(*4) Data from CEP, University of Bern (Dr. R. Purtschert)

Ar-37 Xe-133

Bkg subsoil gas < 100 mBq/m3air (*4) TBD (*5)

Bkg atm air 1-5 mBq/m3 (*4) 0.087 ppm

IMS MDC (mBq/m3) N/A ~ 0.2 (12h)

OSI MDC (mBq/m3) ~25 (10h) ~ 0.2-1 (24h)

Sample volume 0.4 m3 2-4 m3

System throughput 4-6 / 24 h (*1)6 / 24 h (SAUNA)4 / 24 h (XESPM)

LAB total throughput for 10 h workday

2-4depends on counting time

6-8depends on sample change

System foot print (WxL) ~ 2.1 x 3 m ~0.85 x 1.6 m (SAUNA)~ 1 x 3 m (XESPM)

System module weight 20-60 kg (*3) 20-80 kg (*3)

(*2)

(*5) No data set yet available, indications of initial measurements show in the range of <10 of mBq/m3. Work in progress.

OSI NG Detectors : Xe

Typical detectors for Xe detection

kBq NaI det. syst.

Bq HPGe det. syst.

mBq - coincidence det. syst.

Si-Pin- coincidence systems with Digital Pulse Processing

Detectors optimized for • low count rates• high sensitivity (~4 geometry), • focus on metastable isotopes isotopic ratios for source discrimination• modularized lead shields

Si-Pin: High-resolution - NaI coupled with SiPin diodes

SAUNA-OSI: Low-resolution - NaI coupled with plastic scintillator

- Al oxide coated to reduce memory effect

- Clover design – 4 detectors in one shield with

individual compartments incl. lead separator

Calibration process is complicated• QC sources (Cs-137) : Energy and Resolution• Gas spikes : Efficiency

SAUNA

OSI NG Detectors : Ar-37

Proportional counter with veto system

• Copper tube inside a NaI well-type crystal (muon veto)• Analog NIM electronics• Volume 500 ml at ~2 bar• Filling gas : 90% Ar, 5% CO2 and 5% He• HV ~2500 V• 100 kg lead shield in modules

Single Ar-37 X-ray 2.38 keV

Calibration• straight-forward using external Am-241 source• BUT: very sensitive to the impurities from the

gas processing

NG coincidence spectrum-Spike test

Xenon Isotopes: Xe-131m, -133m, -133 and -135

Thank you!