Materials Assay & ICPMS for DUSEL R&D

Starting Points

• 238 U and analysis 232 Th 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

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

from Th

1-g sample

, , Homestake or LNGS,

~10-kg sample

• Developed dissolution and Th tracer chemistry for Cu • Developed adsorbent (column) chemistry to partition Cu • Used radiochemistry as front-end to ICPMS • Electroformed copper sample result of 0.7 ± 0.6 uBq/kg

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 238 U, 10 ppb 232 Th • 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 238 U ATOMS/ml 10 -3 (ppt) Milli 2.53x10

18 10 -6 (ppm) Micro 2.53x10

15 10 10 -9 -12 (ppb) (ppt) Nano Pico 10 -15 (ppq) 10 -18 (pp?) Femto Atto 10 -21 (pp??) Zepto 10 -24 (pp???) Guaca 2.53x10

12 2.53x10

9 2.53x10

6 2530 2.53

0.00253

NORMAL ICP-MS RANGE ULTRA TRACE

Direct Atto-gram/mL Detection

1E4 250 ag/mL Np-237 1 . 8 E + 0 5 1E3 25000 MHz/ppm 1 . 2 E + 0 4 1E2 1 . 2 E + 0 3 1E1 2 . 0 E + 0 2 1 . 0 E + 0 2 4 . 0 E + 0 1 2 . 5 E + 0 2 4 . 6 E + 0 1 2 . 2 E + 0 1 2 . 9 E + 0 1 1 . 9 E + 0 1 7 . 2 E + 0 1 5 . 6 E + 0 1 2 . 7 E + 0 1 1E0 1E-1 1E-2 230 232 234 236 amu 238 240 242 244

ICPMS Generalities

• Elements/Isotopes in the environment that are not naturally occurring, easy to detect at instrument and method detection limits – Pu 239,240,242,242 , Am 241 , Np 237 , Th 230,229 , Tc 99 , I 129 • 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. refinement for Ge 60 Co 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 – 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