Materials Assay & ICPMS for DUSEL R&D

Starting Points 238U and 232Th chains are primary concerns Are not always in equilibrium with progeny Other backgrounds are also important Surface contamination, cosmogenics Next-generation experiments require a range of materials purity levels, but the most stringent are <1 uBq/kg Full range of assay techniques will be needed – alpha, beta, gamma spectroscopy, mass spectroscopy, radiochemistry, neutron-activation analysis

Scope Look at examples favoring and disfavoring gamma spectroscopy vs ICPMS Simple look at what favors Gamma spectroscopy ICPMS ICPMS Detection and Overview Challenges for direct measurement R&D implications

Easy Example: Cable Desired budget for cable was a count/year (full spectrum) Initial assay (above-ground, low-background gamma spectrometer) of 500-foot spool of cleaned cable gave limits of <45 uBq/foot (<36 mBq/kg) Analysis of experiment efficiency showed this would contribute <1.0 count/year Done! Start using cable…(IGEX)

Hard Example: Electroformed Cu Stringent limits of <0.1 uBq/kg desired Best gamma spectrometry limits <6-8 uBq/kg 90-day count, Homestake or LNGS, ~10-kg sample Developed dissolution and Th tracer chemistry for Cu Developed adsorbent (column) chemistry to partition Cu from Th Used radiochemistry as front-end to ICPMS Electroformed copper sample result of 0.7 ± 0.6 uBq/kg (1-g sample, few-hour measurement, 7-fold replicate, 1 week of setup for campaign) Many months of radiochemistry R&D to enable measurement Not there yet, work continues! But already better than previous best gamma result. End in sight.

Unfinished Example: Resistor Desired radiopurity ~1 ppb 238U, 10 ppb 232Th Using LNGS screening detector (one of world’s best) as example, this would require 1 kg of material and a 100-day count Cost of 1 kg of chip resistors (about 1.7e6 units) would be $1.7M! Conclusion: Turn toward clean chemistry for chip resistors, FET ($27M/kg), etc. as front-end to ICPMS ICPMS will require <1g of material for assay

View from another angle…

What Favors Gamma Spectroscopy? Assembled commercial items (heterogeneous) Cables, electronic components, valves, etc. Used in small quantities = only moderate radiopurity limits Means many can be assayed for better limits per item Cheap and available Can afford to buy many more than needed to support assay of large quantities Modest volumes Needed to allow usable efficiency for reasonable number of items

What Favors ICPMS? Easy dissolution chemistry Can “dilute-’n-shoot” when only moderate limits needed Simple elements or compounds Best when radiochemistry is already developed for the system Existence of appropriate isotopic tracers Complex systems can be analyzed, but requires significant chemistry development

ICP-MS DETECTION RANGES Aqueous Standards WEIGHT PREFIX 238U ATOMS/ml 10-3 (ppt) Milli 2.53x1018 10-6 (ppm) Micro 2.53x1015 10-9 (ppb) Nano 2.53x1012 10-12 (ppt) Pico 2.53x109 10-15 (ppq) Femto 2.53x106 10-18 (pp?) Atto 2530 10-21 (pp??) Zepto 2.53 10-24 (pp???) Guaca 0.00253 NORMAL ICP-MS RANGE ULTRA TRACE

Direct Atto-gram/mL Detection 250 ag/mL Np-237 25000 MHz/ppm Response (cps) amu

ICPMS Generalities Elements/Isotopes in the environment that are not naturally occurring, easy to detect at instrument and method detection limits Pu239,240,242,242, Am241, Np237, Th230,229, Tc99, I129 However elements like Th and U are problematic Th and U at ppm levels in dirt Ultra-pure acids, reagents, lab supplies Sample introduction system of ICP/MS

Challenges for Direct Measurement Cosmogenics, e.g. 60Co in Cu, Ge Background limits more stringent than U, Th chains Each system has different challenges and opportunity for purification, e.g. electrochemistry for Cu, zone refinement for Ge May have to depend on measured production rates and process knowledge Disequilibrium in Th, U chains Hard to measure at necessary levels May have to depend on higher-level validation of equilibrium behavior for a particular system, then process knowledge

Common Theme: Radiochemistry Opportunity to sample larger masses, get sensitive results from smaller masses Ability to count atoms with MS Higher efficiencies for radiometric counting Alpha, beta measurement Requires Dissolution chemistry for system Tracer chemistry (radio or stable) Separation chemistry for system Challenge Clean chemistry Reproducible yielding Extremely high partition between analyte of interest and matrix

R&D Issues Newest instruments have plenty of raw sensitivity Radiochemistry for specific systems is needed (and requires significant effort) Dissolution Tracers Separation

Conclusions Gamma spectrometry when possible Inexpensive, non-destructive, nominal sample preparation, detailed information when signal is seen Radiochemistry when necessary (R&D priority) Front-end to ICPMS Front-end to LSC or direct alpha/beta In combination with NAA