nist surface and microanalysis science division low-level counting (llc) at nist george a. klouda...

NIST Surface and Microanalysis Science Division

Low-Level Counting (llc) At NIST

George A. Klouda

Surface and Microanalysis Science DivisionNational Institute of Standards and Technology

Gaithersburg, MD

“Synergies in Low Background , Ultra-Sensitive Radiation Techniques,” University of Minnesota, 25-26 July 2005


Outline• Beta Counting (37Ar, 14C and 85Kr)

– 1970’s – 2002: BNL Logic Interface, + Waveform (Davis et al., 1972; Cleveland et al., 1998; Currie et al., 1983; 1998) – 2002 – Present: NIST Interrupt Driven System, + Waveform (A. Band)

• Accelerator Mass Spectrometry Atom Counting (14C)– 1980 – 2002: Collaborations with Many AMS Groups, e.g., Univ. of Rochester, Univ. Arizona and Woods Hole Oceanographic Institute– Source Attribution of Atmospheric Particulate and Volatile Carbon (L.A. Currie, J. Res. Natl. Inst. Stand. Technol. 109, 185, 2004)

• Neutron Activation Analysis– UltraPure Materials Analysis (R. Lindstrom)


Shielding and Counters• Passive Shield: World War I Iron Gun Barrel

– 20 cm Thickness; 147 cm Length– Location: Basement, ca. 2 m of Concrete Floor Above

• Active Shield– OFHC Cu Proportional Annulus– NaI(Tl) Annulus and Plugs (Bicron)

• Proportional and Geiger Muller Counters– NIST Miniature Quartz Proportional Counters (5 and 15 mL)– LND GM Counter (45 mL)

Counting Hardware

LND 45 mL GM Counter

NIST 5 mL Quartz Proportional Counter

Bicron NaI(Tl) Annulus & Plugs(61 cm Length; 14.5 cm ID; 26 cm OD; 5.7 cm Thickness; 10 cm Plugs)

Iron Gun Barrel

Gun Barrel with NaI(Tl)

Bkg = 0.1 cpm

Bkg = 0.02 cpm

Low Background Quartz Proportional Counter (5 mL)



Parameters Monitored by llc Electronics• Time-of-Arrival (TOA)• Rise Time (ADP) and Amplitude (E)• Digitized Waveform• Barometric Pressure• Live Display: Counts, Rates, ADP vs. E Plot and Waveform• Post Data Analysis

– ADP v. E, E Distrib., ADP Distrib.– TOA and dt Distrib.– Wave–Browser (–Filter)

AfterPulses

Commercial GM Counter


NIST llc Electronics Schematic

Hybricon 3-Slot Pizza BoxVMEbus Enclosure


Analog Pulse Processing

• GM and Proportional Counter– BNL Fast Preamp for PC– Linear Amplifier: Tennelec 213, Canberra 814A– Timing Filter Amplifier: Ortec 454, Canberra 2111– Fast Stretcher: BNL NIM

• NaI(Tl) Photomultiplier Tubes (n = 14)– Three Separate Circuits: Annulus Left & Right Bank, Plugs– Canberra 2005 Preamps

SBS 620 VMEbus – PCI Adapter with DMA, High Speed (35 M byte/sec) Fiber-Optic Connection

SIS 3300, 8 Channel, 100 MHz, 12-bitA/D, VMEbus Digitizer for Pulse HeightAnd Rise Time Signals

VME Enclosure Modules

NuPRO-770 PICMG Single Board Computer,800 MHz Pentium III Processor, BridgesISA bus and PCI bus Boards

Industrial PC

SBS 620 VMEbus – PCI Adapter with DMA,High Speed Fiber-Optic Connection

GT657 Time Interval Analyzer, RecordsTime of Event with 25 ns Resolution


NIST llc Facility


Post Data Analysis – GM Pulses

Overlay of CoincidenceWaveforms from GM Tube:Expected Constant PulseAmplitude and a Rare SaturatedEvent

Snapshot of Pulse Stream: - Amplitude - dt Between Coinc. and Antic. - Saturated Event - DT Between Antic. and Next Antic.

(Currie et al., Radiocarbon, 40(1), 113, 1998)


Dual Distribution Plot of dt v. Time of Arrival

Afterpulses, FairlyUniformly DistributedIn Time

(Currie et al., Radiocarbon, 40(1), 113, 1998)


85Kr Measurement Precision (RSD):Dependence on Counter Size and Shielding

Projections assume 2 Liter air sample at 1.4 Bq m-3 and a non-Poisson background variability of 5% rsd.

(Currie and Klouda, J. Radioanal. & Nucl. Chem., 248(1), 239, 2001)


Atmospheric 85Kr in Northern Mid-Latitude(Wilhelmova et al., 1994)


85Kr Measurement Capabilities:Detection and Quantification Limits in Bq m-3

(Currie and Klouda, J. Radioanal. & Nucl. Chem., 248(1), 239, 2001)


14C Accelerator Mass Spectrometry (AMS)

• Comparative Study of Small Targets, 10 – 1000 g (Klindinst et al., NIM B 92, 166, 1994)• Woods Hole Oceanographic Institute (NOSAMS) Small Target Preparation, 25 g (Pearson et al., Radiocarbon, 40, 61, 1998)• NIST Combustion – Dilution Facility for Small Samples Approaches the Limit of AMS, 1 g Modern Carbon, e.g. Black Carbon in Greenland Snow (Currie et al., NIM B 172, 440, 2000)

(Tandem Accelerator at ETH, Zurich)


14C Modern Carbon Standard vs. Carbon Mass(Klinedinst et al., Nucl. Instr. Meth. B 92, 166, 1994)


AMS 14C Precision, Accuracy and Mass Dependence

(Klinedinst et al., Nucl. Instr. Meth. B 92, 166, 1994)

Atmospheric Volatile Organic Carbon (VOC): Source Attribution Using 14C/13C Ratio

SCOS97 – Azusa, CA

Canister Sample w/ CO2 Removal

Biogenic VOC Summary

• Median Percentage: 18 11% (95% CI)• Median Mixing Ratio: 80 50 nmol mol-1 (95% CI)• Source Region for High Biogenics: North to East

(Klouda et al., JGR, 107(D8) 2002; Klouda et al., ES&T, 30 (4) 1996)

Acknowledgements

Alan Band (NIST Electron Physics Group) - for design andconfiguration of new electronics system hardware and softwarefor processing and storage of individual pulses to replaceexisting BNL Interface

Stephen Pheiffer (Contractor) - for software development tosupport new electronics system


BNL llc Electronics Schematic, + Waveform

NIST Counting Electronics

Electronics/Software Capabilities- Time of Arrival to 25 ns Resolution (GT675 Time Interval Analyzer)- Energy and Rise Time (Canberra PAD 814A & TFA 2111- Digitized Waveforms (SIS 3300 Digitizer)- Mu-meson Spectrum- Inter-Channel Events

Captured Pulses

Risetime v. Energy Distribution

AfterPulses

(Alan Band and Stephen Pheiffer, 2002)


nist surface and microanalysis science division low-level counting (llc) at nist george a. klouda...

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