Future Development and Needs for Low Background Counting and Assay Capability Richard Ford (SNOLAB) Future Project Planning Workshop 25 th 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 ( 232 Th, 238 U, and 40 K), 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.

4 Uranium Decay Chain

5 Thorium Decay Chain

6 Other Interesting Isotopes  40 K keV  137 Cs keV 60 Co 60 Ni   1173 keV  1332 keV 137 Cs 137 Ba 137m Ba  keV   keV 40 K 40 Ar ee 235 U 231 Th 4  ´s  54 Mn at keV 7 Be at keV 138 La and 176 Lu  60 Co  keV  keV  235 U  keV  keV  keV  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:

7 SNOLAB PGT HPGe Counter (The workhorse detector at SNOLAB) Additional lead used to dampen microseismic activity from blasting and rockbursts

8 SNOLAB PGT HPGe Detector Specifications Motivation 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 cm 3 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/m 3. Detection Region Energy: 90 – 3000 keV

9 Unshielded and Shielded Spectra (PGT Coax Detector) Shielding In Place No Shielding Counts

10 PGT HPGe Typical Detector Sensitivity (for a standard 1L or 1 kg sample counted for one week) IsotopeSensitivity for Standard Size Samples 238 U0.15 mBq/kg12 ppt 235 U0.15 mBq/kg264 ppt 232 Th0.13 mBq/kg32 ppt 40 K1.70 mBq/kg54 ppt 60 Co0.06 mBq/kg 137 Cs0.17 mBq/kg 54 Mn0.06 mBq/kg

11 Canberra Well Detector at SNOLAB

12 Canberra Well Detector at SNOLAB Sample Well Typical Sample Bottle Volume is 3 ml Detector Volume: 300 cm 3

13 SNOLAB Canberra Well Detector Specifications Motivation 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 cm 3. Installed and operational in 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/m 3. Detection Region Energy: 10 – 900 keV

14 Unshielded and Shielded Spectra (Canberra Well Detector)

15 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 222 Rn, 224 Ra and 226 Ra levels. The technique involves recirculation of low pressure gas from sample volume to the ESC. Sensitivity Levels are: 222 Rn: gU/g 224 Ra: gTh/g 226 Ra: gU/g Work 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).

16 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 238 U and 232 Th 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 SNO Cavern South Drift Personnel Facilities & Refuge Utility Area Ladder Labs HALO Stub Cube Hall Cryopit J-Drift Ramp SNO Utility SNO Drift  Over 53,000 sq.ft. of climate-controlled class-2000 cleanroom laboratory space  Four large experiment areas

SNOLAB Underground Facilities SNO Cavern South Drift Personnel Facilities & Refuge Utility Area Ladder Labs HALO Stub Cube Hall Cryopit J-Drift Ramp SNO 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 SuperCDMS Gopher detector

23 Additional Future Low Background Counters Two additional high purity germanium detectors will be installed. 1. SNOLAB Canberra 400 cm 3 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 SuperCDMS Sensitivity of ~ 1 mBq/kg for 3 week run Sample changes by mine crew Queue 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 m 3 /hr and radon levels below 100 mBq/m 3 have been demonstrated. Maybe able to use Vale mine compressed air system as input air, which is surface air (3 – 9 Bq/m 3 ), versus UG air ~130 Bq/m 3.

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 with o 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 centers Including HPGe, Surface assay, ICPMS, NAA etc o Community Assay Database, including hooks from the assay centers o GEANT/FLUKA/MCNP code tools, code benchmarking and updates o Nuclear Databases, alpha-n, SOURCES4 etc o Cleaning and Handling Protocols. Standardize Assay Prep o Cosmogenic Activation, underground storage, transport shielding o 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 support biannual collaboration meetings collaboration with labs in the continued development of infrastructure

The AARM Integration Website Rotating picture and contact information for Labs & Experiments Home Page

The AARM Integration Website Facilities and Scheduling: Detector Info What the Assay Facility Manager submits Up to date information on screening available at labs. Form defines relevant information and sorts it

The AARM Integration Website Facilities and Scheduling: Assay or Storage Request What the user submits Check out the available assay from Detector Info Fill out request form – goes to the contact listed Storage request also available

The AARM Integration Website Resources: Easy reference for relevant papers Links to LRT and AARM presentations Add your own papers

The AARM Integration Website Step 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 studies Portals to other relevant websites

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)