Future Development and Needs for Low Background

Counting and Assay CapabilityRichard Ford (SNOLAB)

Future Project Planning Workshop25th August 2015

Brief Outline

• Reasons for Low background Counting and Assaying

• Current detectors and capabilities at SNOLAB

• The case for creating expanded and coordinated facilities

• Plans for SNOLAB’s new Low Background Counting facility

• Future counters and capabilities

• Global facilities co-ordination and web-portal

Reasons for Low Background Counting• Rare event detector experiments (eg. dark matter searches and neutrino

detector) require low radioactivity background. This requires that fabrication materials have low concentrations of radioactivity chain elements (232Th, 238U, and 40K), often well below ppt levels. These backgrounds can be due to manufacturing cleanliness (inclusion of mineral dust), chemical contaminations (eg. potassium), or intrinsic to materials (eg. steel).

• These levels are below that generally accessible by chemical analytical techniques, and assay method is often by radiation counting.

• Another application is counting of detector target fluids, either as part of a QC requirement, diagnostics, or purification testing.

• Backgrounds of interest can be alphas, betas, gammas or neutrons, depending on the experiment and the component in question. The radiation could be direct, or via leaching or emanation. Thus several detector technologies are used.

• Generally these counting detectors must themselves be very low background, which requires them to be clean and underground, and fabricated and shielded with low background materials.

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Uranium Decay Chain

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Thorium Decay Chain

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Other Interesting Isotopes

40K

1460.83 keV

137Cs

661.66 keV

60Co

60Ni

1173 keV

1332 keV137Cs

137Ba

137mBa 661.6 keV

1460.8 keV40K40Ar

e

235U

231Th 4´s

54Mn at 834.85 keV

7Be at 477.60 keV

138La and 176Lu

60Co 1173.2 keV

1332.5 keV

235U 143.76 keV 163.33 keV 185.22 keV 205.31 keV

Observed in Stainless Steel

Observed in Carbon based materials, due to neutron activation, samples are particularly affected after long flights.

Observed in rare earth samples such as Nd or Gd.

Usually Present:

Occasionally Present:

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SNOLAB PGT HPGe Counter(The workhorse detector at SNOLAB)

Additional lead used to dampen microseismic activity from blasting and rockbursts

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SNOLAB PGT HPGe Detector SpecificationsMotivation Survey materials for new, existing and proposed experiments for SNOLAB (such as

SNO/SNO+, DEAP/CLEAN, PICASSO/COUPP/PICO, EXO, and other externals).

Refurbished in 2005 with low background shielding Counter manufactured by PGT in 1992, stored UG from 1997, refurbished 2005 Endcap diameter: 83 mm, Crystal volume: 210 cm3

Relative Efficiency is 55% wrt a 7.62 cm dia x 7.62 cm NaI(Tl) detector, Resolution 1.8 keV FWHM.

Shielding

- 2 inches Cu + 8 inches Pb

- Nitrogen purge at 2L/min to keep radon out, as the lab radon levels are 150 Bq/m3.

Detection Region Energy: 90 – 3000 keV

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Unshielded and Shielded Spectra (PGT Coax Detector)

Shielding In Place

No Shielding

Counts

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PGT HPGe Typical Detector Sensitivity(for a standard 1L or 1 kg sample counted for one week)

Isotope Sensitivity for Standard

Size Samples

Sensitivity for Standard Size

Samples

238U 0.15 mBq/kg 12 ppt235U 0.15 mBq/kg 264 ppt

232Th 0.13 mBq/kg 32 ppt40K 1.70 mBq/kg 54 ppt

60Co 0.06 mBq/kg

137Cs 0.17 mBq/kg54Mn 0.06 mBq/kg

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Canberra Well Detector at SNOLAB

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Canberra Well Detector at SNOLAB

Sample Well

Typical Sample Bottle

Volume is 3 ml

Detector Volume:300 cm3

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SNOLAB Canberra Well Detector SpecificationsMotivation Survey very small quantities of materials, concentrated samples or very expensive

materials. Used by DAMIC, DEAP, PICO & SNO+ so far.

Constructed by Canberra using low activity materials and shielding. Counter manufactured by Canberra in 2011 and refurbished in 2012, the cold finger was

lengthened as it was too short to fit the shielding and the tail end and crystal holder were replaced to reduce radioactivity levels.

Crystal volume: 300 cm3.Installed and operational in 2013.Shielding Cylindrical shielding of 2 inches Cu + 8 inches Pb Nitrogen purge at 2L/min to keep radon out, as the lab radon levels are 150 Bq/m3.Detection Region Energy: 10 – 900 keV

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Unshielded and Shielded Spectra (Canberra Well Detector)

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Electrostatic Counting System (ESCs)

Originally built for SNO, now used primarily by EXO. However, these counters are owned by SNOLAB so samples can be measured for other experiments.Measures 222Rn, 224Ra and 226Ra levels.

The technique involves recirculation of low pressure gas from sample volume to the ESC.Sensitivity Levels are:222Rn: 10-14 gU/g224Ra: 10-15 gTh/g226Ra: 10-16 gU/gWork is ongoing to improve

sensitivity even further.9 counters located at SNOLAB, 1 on loan to LBL (EXO), 1 on loan to U of A (DEAP).

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Alpha Beta Counting System

Transparent liquid scintillator vials optically coupled to 2” PMTs.

The technique is combination of pulse shape discrimination and coincidence counting for identifying BiPo events.

Sensitivity for 238U and 232Th is ~1 mBq assuming that the chains are in equilibrium.

The case for Expanded Low Background Facilitiies

• One trait most of the current detectors/capabilities share, is that they are “left over” from previous experiments.

• Until now experiments had to develop low background techniques within collaboration for each experiment, often “re-inventing the wheel”, at large cost.

• It is desirable to have these low background counting methods and detectors as part of the underground lab facilities. As experiments typically need these facilities most during detector design and construction, it requires a lot of funding and development time for experiments to take this on themselves. Then this developed resource can be under utilized once the supporting experiment is in operation.

• Beyond this, a global sharing and networking of low background counting facilities and resources would further benefit experiments and collaborations, allowing faster experiment design and identification of suitable materials.

SNOLAB Underground Facilities

SNOCavern

SouthDrift

Personnel Facilities& Refuge

UtilityArea

Ladder Labs

HALOStub

Cube HallCryopit

J-Drift

RampSNO Utility SNO Drift

Over 53,000 sq.ft. of climate-controlled class-2000 cleanroom laboratory space

Four large experiment areas

SNOLAB Underground Facilities

SNOCavern

SouthDrift

Personnel Facilities& Refuge

UtilityArea

Ladder Labs

HALOStub

Cube HallCryopit

J-Drift

RampSNO Utility SNO Drift

South Drift, was refuge and shower rooms for original SNO detector. Now to be refurbished for Low Background Lab.

South Drift Today(assembly & storage area)

Refurbishing South Drift for low background facility

Preliminary detector layout plan

SuperCDMSGopher detector

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Additional Future Low Background Counters

Two additional high purity germanium detectors will be installed.

1. SNOLAB Canberra 400 cm3 coaxial detector acquired in 2011 and refurbished into an ultra-low counter in 2013 to be installed, the shielding apparatus is currently being designed.

2. Bern Coax detector, detector is currently at Bern and will be relocated to SNOLAB. This detector has been used extensively by the EXO experiment. It is expected to be shipped to SNOLAB this summer.

Soudan Gopher HPGe(to be relocated to SNOLAB)

2.0kg of Ge. P-type coaxial

Dedicated to SuperCDMSSensitivity of ~ 1 mBq/kg for 3 week runSample changes by mine crewQueue and Analysis by UM students

Options for SNOLAB Low Background Facilities

• We are currently surveying the community for input on capabilities that would best benefit future experiments at SNOLAB, and enhance SNOLAB’s position as leader in low background techniques.

• Items being investigated:– Low radon air supply– Low radon nitrogen supply– Emanation chambers with Rn cryotraps– XIA alpha screener (large area wire detector)

Low Radon Air Supply• To supply to assembly rooms,

detectors or gloveboxes

• General methods are low-pressure adsorption, or pressure/vacuum swing adsorption, or a hybrid or these.

• Flow rates over 50 m3/hr and radon levels below 100 mBq/m3 have been demonstrated.

• Maybe able to use Vale mine compressed air system as input air, which is surface air (3 – 9 Bq/m3), versus UG air ~130 Bq/m3.

Communication and Collaboration on common issues related to

Assay and Acquisition of Radiopure Materials

SNOLAB is a member of AARM:

AARM- Originally an NSF DUSEL S4 grant to characterize backgrounds

and design low background counting facility for DUSEL-Homestake.- Current NSF grant = “Integrative Tools for Underground

Science” Principle Investigators Priscilla Cushman (University of Minnesota) Jodi Cooley (Southern Methodist University) Toni Empl (University of Arkansas, Little Rock) Angela Reisetter (Evansville University) Richard Schnee (Syracuse University SDSM&T)

• Cosmogenic Simulation Group

• Universal Materials Database

• Radiogenic Cross Section Working Group

• FLUKA-Geant4 Comparative Study Group

• Neutron Benchmarking Data Group

AARM is Organized by working group.

Bi-annual workshops combine talks on new developments with Working Group sessions devoted to work and planning.

AARM Going Forward

Integrative Website witho All relevant publications and links organized in one place

Including all the AARM workshop talks and the LRT talks/proceedings

o Contact information and scheduling tools for woldwide assay centersIncluding HPGe, Surface assay, ICPMS, NAA etc

o Community Assay Database, including hooks from the assay centerso GEANT/FLUKA/MCNP code tools, code benchmarking and updateso Nuclear Databases, alpha-n, SOURCES4 etco Cleaning and Handling Protocols. Standardize Assay Prepo Cosmogenic Activation, underground storage, transport shieldingo Data on radon plateout and diffusion in various materials

This Website Content has been developed. The next step is to transfer it to SNOLAB and PNNL

with the resources to maintain and develop the user base

AARM will request resources in the next year to supportbiannual collaboration meetingscollaboration with labs in the continued development of infrastructure

http://www.hep.umn.edu/aarm/

The AARM Integration Website

Rotating picture and contact information for Labs & Experiments

Home Page

The AARM Integration Website

Facilities and Scheduling: Detector InfoWhat the Assay Facility Manager submits

Up to date information on screening available at labs.

Form defines relevant information and sorts it

The AARM Integration WebsiteFacilities and Scheduling: Assay or Storage RequestWhat the user submits

Check out the available assay from Detector InfoFill out request form – goes to the contact listed

Storage request also available

The AARM Integration WebsiteResources:

Easy reference for relevant papers

Links to LRT and AARM presentations

Add your own papers

The AARM Integration WebsiteStep 1: TENDL vs EMPIRE cross sections comparison TENDL 2011 and 2012 have been considered as the USD website inputs. TENDL is a nuclear data library (validated) which provides the output of the TALYS nuclear model code system.EMPIRE cross section are the input libraries of SOURCES4 Step 2: USD website vs SOURCES4 calculations: compare the radiogenic neutron spectra coming from both codes.

Compiled plots and data from AARM studiesPortals to other relevant websites

http://www.radiopurity.org/

AARM recognized 10 years ago the need for an Assay Database with an easy-to-use interface to enter new data and to search for radiopure materials, vendors, etc.

The Majorana database (J. Loach) was chosen as a template

The more globally used, the more useful for everyone.

• Began by entering legacy data: ~300 assays; data from ILIAS, EXO and XENON100

• Now have ~ 1000 assays, primarily historical.

• Database is being used by SuperCDMS and DarkSide, LZ evaluating it

• In the process of adding features to the software for easier distributed use.

The AARM Integration Website

Register your name and find others with common interests.

Summary• There is on-going and expanded need for low background

counting facilities.

• These are best located underground to improve sensitivities, and also to better server the underground laboratory community developing low background experiments.

• SNOLAB is expanding the underground low background counting area to increase capabilities.

• SNOLAB will join and host the AARM community integration website portal and community assay database.

• There is opportunity to expand the application of low background counting to other interdisciplinary areas (environmental, geophysics, ocean samples, space samples)