# Presentation: 359839

## 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
- 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

## 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.

## Different Types of Spectroscopic Radiation Detectors

- Plastic

- HPGE

- NaI(Tl)

- CZT

## How can we quantitatively compare resolution?

**All 3 Peaks have equal areas (counts)**

- 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.

## 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.

- Wide peaks mean bkg area is large

- Narrow peaks minimize bkg area

- 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!**

## 210Po

- 210Po

- 0.0000106 gamma rays per decay

- Time

- 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.

## High Resolution is required in gamma spectrometry

**NaI **
**133Ba, WG Pu**

**Energy range Approx 220-480KeV**

**HPGe**
**133Ba, WG Pu**

**High Resolution is required in gamma spectrometry**
** ****to resolve conflicting (overlapping) peaks.**

## 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

## Comparison of HPGe, NaI, and LaBr 

## Brief history of cooling technologyfor 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”)

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

## IDM Component Layout

- Detector

- Shielding

- USB Connector

- Cooler

- Detector Bias Supply

- Multi-channel Analyzer

- Universal Rack Mounting Brackets

- Universal Lines
- Power In

- Cryostat Assembly

**IDM Component Layout**

## 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

## 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

## 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: **Universal** **110/220 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.

## 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.)

## IDM Applications

**IDM Applications**

**Pedestrian**

**Search**

**Vehicle**

**Parcel**

**Parcel**

## 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

## 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**

## 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.**

## IDM Peak Shape

-  The peak shape is important for accurate spectrum analysis.
-  Resolution is 1.27 keV at 60 keV.
-  Resolution at 1173 keV** **is 2.0 keV.

## 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

## Multi energy efficiency vs horizontal position with collimation - Continued

-  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.** **

**Multi energy efficiency vs horizontal position with collimation - Continued**

## 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.

## Standoff Measurements

-  192Ir source** **used 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.

## Questions and Discussion