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INTERNATIONAL WORKSHOP ON ADVANCED SENSORS FOR SAFEGUARDS Advancements in High Resolution Gamma-Ray Detector Deploymen

INTERNATIONAL WORKSHOP ON ADVANCED SENSORS FOR SAFEGUARDS Advancements in High Resolution Gamma-Ray Detector Deployment Sam Hitch, ORTEC. Agenda:. Need for high resolution gamma spectrometry Brief history of improvements in gamma detector technology

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INTERNATIONAL WORKSHOP ON ADVANCED SENSORS FOR SAFEGUARDS Advancements in High Resolution Gamma-Ray Detector Deploymen

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  1. INTERNATIONAL WORKSHOP ON ADVANCED SENSORS FOR SAFEGUARDSAdvancements in High Resolution Gamma-Ray Detector DeploymentSam Hitch, ORTEC

  2. Agenda: • Need for high resolution gamma spectrometry • Brief history of improvements in gamma detector technology • Brief history of cooling technology for Ge detectors • The ORTEC Interchangeable Detector Module (IDM) – The culmination of technical improvements driven by real-world measurement requirements. • Performance test results: • Efficiency in the IEEE point source geometry • Resolution as a function of energy (IEEE geometry) • IDM peak shape • Multi energy efficiency vs horizontal position with collimation • Multi energy efficiency vs vertical position with no collimation • Standoff measurements

  3. Need for high resolution gamma spectrometry • High Resolution is required in gamma spectrometry to resolve conflicting (overlapping) peaks. • High Resolution is required in gamma spectrometry to resolve peaks lost or distorted by high and/or changing background. • High Resolution is required in gamma spectrometry to resolve peaks hidden by natural, medical, or industrial radionuclides common in commerce. • High Resolution is required in gamma spectrometry when shielding reduce measured activity and distorts peak ratios.

  4. Different Types of Spectroscopic Radiation Detectors Plastic HPGE NaI(Tl) CZT

  5. 50x 10x 1x How can we quantitatively compare resolution? • Radionuclides are determined by their gamma spectra “finger print” which is made up of one or more “lines” or energy peaks. • HPGe (green) has 50 times better resolution than NaI (red). • Wider peaks cause interference with other peaks and frustrate identifications. All 3 Peaks have equal areas (counts)

  6. The other problem with low and medium resolution detectors Even if we ignore peak interference issues, higher resolution means less uncertainty in the background term and therefore faster identifications. The background and background uncertainty term are both equivalent to the trapezoidal area under the base of the peak. Recall that all peaks include the same number of net counts (the signal). A 50x improvement in resolution reduces the background area (the noise) by 50x. This improves the signal to noise ratio by 50x! Narrow peaks minimize bkg area Wide peaks mean bkg area is large

  7. The Detective reported Po-210 as Identified in this spectrum in less than one minute. Po-210 has been in all Detective and Detective-EX libraries since introduction. 210Po 0.0000106 gamma rays per decay Time

  8. High Resolution is required in gamma spectrometry to resolve conflicting (overlapping) peaks. HPGe 133Ba, WG Pu NaI 133Ba, WG Pu Energy range Approx 220-480KeV

  9. Brief history of improvements in gamma detector technology • Late 19th Century – Film and ionization based detection • 1930’s – Geiger-Muller Tube • 1940’s – Proportional Counters (first direct energy indicating detector) • 1950’s – Scintillator detectors: NaI (first real gamma energy spectroscopy detector) • 1960’s – Solid state detectors: GeLi and CdTe • 1970’s – HPGe, Plastic Scintillators, Mercuric Iodide • 1980’s – CZT • 1990’s – La Halide Scintillators

  10. Comparison of HPGe, NaI, and LaBr

  11. Brief history of cooling technologyfor Ge detectors • 1960’s – GeLi Required liquid nitrogen cooling. (Detector required re-drifting if allowed to warm) • 1970’s – HPGe replaces GeLi. Still cooled with LN2 but could be shipped and stored at ambient temperatures without deterioration. • 1980’s – First practical mechanical coolers -- large/fixed, expensive, and limited life. • 1990’s – First “portable” mechanical coolers attempted – never got beyond the proof of principle stage. • 1990’s – First low cost, long life, fixed mechanical coolers introduced (ORTEC “X-Cooler”). • 2000’s – First high reliability (> 50,000 hrs. MTBF) portable mechanical coolers introduced (ORTEC “DETECTIVE” and ORTEC “Interchangeable Detector Module – IDM”)

  12. The ORTEC Interchangeable Detector Module (IDM) The culmination of technical improvements driven by real-world measurement requirements.

  13. IDM Component Layout Universal Rack Mounting Brackets Detector Shielding Universal Lines Power In Detector Bias Supply Cryostat Assembly USB Connector Cooler Multi-channel Analyzer

  14. IDM Benefits • Fully integrated HPGe instrument • No field setup required • Installation requires only physical mounting, line power and computer (USB 2.0) connection • Large area 85 mm x 30 mm HPGe crystal • High-reliability Stirling cycle cooler • High capacity cooler provides excess cooling capacity for extreme conditions and rapid cool down to operating temperature • High performance, digitally stable signal processing • Hardened cryostat designed for long operational life • Can be temperature cycled at any time, even from partial warm up • Continuous data collection, no dead spots, using list mode • Low power consumption • Low Frequency Rejector (LFR) improves spectrum resolution in noisy environments • “Hot swap” of IDM modules while in operational state – reduced downtime for upgrade or repairs

  15. Proven reliability • Built with the same proven detector technology as used in the DETECTIVE • Several hundred DETECTIVEs have been deployed since 2004 with <0.5% detector or cooler failures total to date • Hardened detector encapsulation • Industrial cooler designed for 24/7 operation in cell towers • Design to meet ANSI N42.38 ruggedness requirements

  16. IDM Mechanical/Operating Specifications • Overall Dimensions: Depth - 47.31 cm (18.625”) from detector nose to back panel (48.58 cm including mounting brackets) Width - 45.55 cm (16.75”) (48.26 cm including mounting brackets) Height - 22.86 cm (9.0”) • Weight: 50 lb. (22.68 kg) without detector backshield 60 lb. (27.22 kg) with detector backshield • Input Power: Universal110/220 V ac 50/60 Hz • Temperature Operation (without external enclosure): Range: –20°C to +50°C Relative Humidity: 100%, noncondensing. • Cool Down Time: Initial cool down time depends on ambient temperature, but is typically <5 hours from ambient.

  17. IDM Spectroscopy Specifications • Detector Dimensions: 85 mm diameter x 30 mm deep • Digital MCA. 16k channel conversion gain • Linearity Integral Nonlinearity: <±0.025% over top 99.5% of spectrum, measured with a mixed source (55Fe @ 5.9 keV to 88Y @ 1836 keV). Differential Nonlinearity: <±1% (measured with a BNC pulser and ramp generator) over top 99% of range. • Digital Spectrum Stabilizer: Controlled via computer, stabilizes gain and zero errors. • System Temperature Coefficient Gain: <50 ppm/°C. [Typically <30 ppm/°C.] Offset: <3 ppm/°C of full scale, with Rise and Fall times of 12 µs, and Flat Top of 1 µs. (Similar to analog 6 µs shaping.)

  18. IDM Applications Parcel Vehicle Pedestrian Search Parcel

  19. Performance test results: • Efficiency in the IEEE point source geometry • Resolution as a function of energy (IEEE geometry) • Multi energy efficiency vs horizontal position with collimation • Multi energy efficiency vs vertical position with no collimation • Standoff performance

  20. Efficiency in the IEEE point source geometry • Efficiency was measured with a point source 60Co at 25 cm from end cap. • Ten nuclides measured to obtain the efficiency as a function of energy. • Four IDMs were measured and the average is shown below. • Results are typical for p-type detectors. • Variation IDM to IDM is not significant above about 80 keV

  21. Resolution as a function of energy (IEEE geometry) • The resolution was also measured using the same sources and the same geometry. • The FWHM for a typical IDM is shown below.

  22. IDM Peak Shape • The peak shape is important for accurate spectrum analysis. • Resolution is 1.27 keV at 60 keV. • Resolution at 1173 keVis 2.0 keV.

  23. Multi energy efficiency vs horizontal position with collimation • Side efficiency as well as the front efficiency is important for portal applications. • Each source was moved in 10 cm steps from 2 m before and 1 m after the center of the IDM at a distance of 50 cm. • 133Ba, 60Co, 57Co, and 137Cs (NIST traceable) were used

  24. Multi energy efficiency vs horizontal position with collimation - Continued • Integration width of the data can be adjusted to maximize the signal to noise ratio. • The previous figure shows data detected as a percent of the total data possible. • Note that the percentage is energy dependent with 83% of the 81 keV data and 65% of the 1.3 MeV data included in the 1.6 m width integration time. • At a speed of 8 kph, this is an integration time of 750 ms.

  25. Multi energy efficiency vs vertical position with no collimation • Relative efficiency in the vertical plane. • No collimation in the vertical plane, so the curve is wider. • No correction for attenuation in the air.

  26. Standoff Measurements • 192Ir sourceused to measure the ability of the IDM to detect sources at a distance • Measured at distances from 100 to 225 meters • 316 and 416 keV peak counts shown • Note that at a distance of 200 meters, the field of view at 5 kph is several minutes.

  27. Questions and Discussion

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