Advanced Hand-Held Radiation Detection and Identification RIID: The Micro-Detective-HX

The “-HX” is the commercial example of the HPRDS development performed under contract between AMETEK and the U.S. Department of Homeland Security.

  • Portable - Light weight, long battery life, "one-hand" operation with GPS location
  • Wireless remote monitoring - Remotely control and monitor from a central location
  • Rugged - High or low temperatures, dust proof, water proof, and drop hardened
  • Simple to operate - Touchscreen or push button with audible and visual alarm indicators
  • Superior algorithms - Low false alarm rates, over 170 nuclide IDs and excellent SNM search
  • Detects and identifies X-rays and gamma rays from any radioactive source (liquid, solid, or gas)
  • Gamma and neutron detection - Identification, count rate, and dose rate
  • Detective-remote compatible - Use as a mobile, transportable or choke point monitor
  • Auto calibration - Continuous real-time detector stabilization

Hardware

The Micro-Detective-HX features light-weight, compact, and rugged hardware. A 50 mm diameter HPGe crystal in a “hardened” cryostat is cooled by an in-built low-power Stirling-cycle cryocooler. The newest version Micro-Detective-HX features a new cooler, offering lower levels of acoustic noise and vibration, and extended operation life. The hardened cryostat is completely free of conventional molecular sieve, allowing the instrument to be switched off or on at any point in the detector cool down or warm up cycle without hazard. This is impossible with conventional HPGe cryostat systems which need careful temperature cycling processes to avoid damage.

An integral digital MCA system and powerful data processor are added. All models feature the same clear and bright VGA resolution display with a touch sensitive operator screen. The display is readable in direct sunlight. Menu navigation is very intuitive. The radionuclide gamma-ray spectrum may be revealed and manipulated (e.g., zoom, vertical scale) like a conventional multichannel analyzer.

Gamma and neutron count rate and gamma dose rate are showed continuously both in bar graph form and numerically.

In the newest version, the Micro-Detective-HX internal battery offers sufficient power for up to five hours of operation and is easily swapped in seconds, allowing nonstop in-field operation. Measuring less than 16 lbs. in weight, the Micro-Detective sets a world record for portable, high resolution nuclide identifiers, by a broad margin.

-HX Software Approach

HPGe is already recognized as the “ideal” detector for a radioisotope identifier. It has ~40 times increased energy resolution (selectivity) than the closest alternative. In contrast to lower-resolution detector types, HPGe crystals must function at cryogenic temperatures — an engineering problem ORTEC solved 25 years ago. Several hundred detective series instruments in the field validate the reliability of today’s miniature Stirling cycle coolers used for this purpose.

Beyond the fundamental selectivity of the HPGe detector type, the ultimate performance with regards to its fidelity of identification (zero false positives or false negatives is the goal) depends on the software algorithms. Its practicality in use relies on reliable hardware and a user interface which is simple to learn and interpret.

The Micro-Detective-HX performance has been improved with the launch of the new Detective-Pro user interface. Additional reductions in both false positive and false negative results have been attained, combined with a new design user interface and new modes of operation.

The Micro-Detective-HX in Use: Overview

From the hardware standpoint the user interface comprises:

  • Two buttons on the front of the handle, Select (S) and Navigate (N) with which all survey and sampling operations can be done
  • A sunlight readable, high-resolution, color touchscreen offers an alternative way to select menu options and enter data such as alarm limits and passwords.
  • Audio-visual feedback:
    • Menus are designed to be operated with N and S buttons only, but if desired, the touchscreen is always available
    • On-screen help messages show radiation and system error alarms. The messages tell the user what the next press of the N and S buttons will achieve.
    • An audio alarm with three volume settings can be used with headphones and a vibration alarm is incorporated in the handle. Either, both, or neither can be enabled.
    • A four-LED panel is used to additionally inform the operator of alarm conditions
    • Color coding of the screen borders and LEDs match so as to make the instrument as intuitive as possible: green for innocent, red for threat, and yellow for suspect
    • Indicators at the top of the screen exhibit the current dose rate in mrem/hr, the number of spectra that can be stored on the SD card, battery time remaining, the power source (external power or battery), GPS co-ordinates, and the on/off state of the audio and vibration alerts. The storage-space and battery-time-remaining readouts alternate every few seconds.

When radiation is detected and identified, the identification is displayed at the real-time identification area of the screen. This area lists the names of any radioisotopes presently being detected and their classification as suspect (S), a threat (T), or innocent (I). It can also optionally display whether the identification is at low (L) or high (H) confidence.

The Micro-Detective-HX in Use: Modes of Operation

How the -HX Collects and Analyzes Data

  • Adaptable to the chosen CONOPS design
  • A flexible approach to reduce time and increase effectiveness
  • Continuous running and fixed time modes with “end survey summary”
  • Maximum sensitivity, maximum flexibility

The -HX monitors for radiation throughout. It gathers one spectrum per second, and then starts analyzing a rolling window of the eight most recent one-second spectra for radioisotope identification and alarms.

  • “Home” or “Passive Monitor” mode is the most basic form of operation. In this mode, the -HX is unceasingly “looking,” but not storing data
  • In “Detect” or “Survey” mode, the instrument stores the one-second data slices and tries to make an ID based on the 8-second rolling windows
  • Optional “Fixed Samples,” or “Long Samples” performed during the “Detect” mode survey, add longer spectrum acquisitions to the data stream of eight-second rolling-window analyses
  • The “End Survey Report” is a cumulative analysis of all one-second data slices in the survey, providing better detection sensitivity for weak or distant sources

Modes of Operation: Home (Passive Monitor) Mode: “Always Looking”

In Home (Passive Monitor) mode, the instrument is nonstop “looking” but not storing data. Gamma dose-rate, storage space, battery life, and GPS co-ordinates are shown. In this mode, the -HX acts like a survey meter, such that if it is moved away from the source, the ID will be taken off from the screen. However, any alarm posted persists and must be cleared. Data is collected and processed in one-second time slices. The -HX analyzes an 8-second rolling window of these slices and tries to make an ID. Nuclide IDs are posted to the Real Time ID area.

Modes of Operation: Detect Mode (The Survey Concept)

The Detect mode is used to locate and identify sources in a better manner. A survey always starts with a Detect mode measurement, and can include long and fixed sample mode operations also. The -HX can be fixed to automatically begin a survey instantaneously after it is removed from charge or a survey may be started manually. One-second data slices are stored in an ICD1/ICD2 file pair on the removable SD card. As in the Passive Monitor mode, the -HX tries to make an ID based on an eight-second rolling window. At the upper part of the screen, the color-coded strip chart records signal index (cumulative activity of all nuclides identified). The chart peaks at the location of maximum activity. The lower chart shows the Threat Material Index akin to the Signal Index, but only for threat material. To the right of each strip chart, a vertical bar and numeric value is used to reveal the current value of the signal and threat indices. If suitable to the measurement, alarm IDs are shown in the Real Time ID area and must be cleared.

Modes of Operation: Long and Fixed Sample Modes

A source may have been located and closer scrutiny desired during a Survey, in the Detect mode measurement. Fixed or Long Sample modes may be used to attain this. In Long Sample mode, a single spectrum is attained for 30 or more seconds and examined once per second for alarms. Fixed Samples are treated in the same manner but have preset durations of 5, 10, 15, 20, 25, 30, 60, 120, or 300 seconds. It is possible to view the live spectral display in the Long Sample mode. For the Survey, Long and Fixed Sample spectra and analyses are saved in the ICD1/ICD2 file pair, along with the rolling-window and cumulative-analysis data.

“End Survey Report”

A Survey is started automatically or manually, as described above. Besides the Detect mode operation, a survey can also include either single or multiple fixed or long sample mode measurements. When a Survey is terminated by the operator, an “End Survey” summary report is displayed containing the following:

  • Any alarms obtained from the 8-second rolling window mode of operation which starts every survey
  • Any alarms derived from those Long and Fixed Sample measurements included in the survey
  • Any alarms derived from an analysis of a cumulative spectrum representing the summation of all the 1-second slices gathered during the survey, thus attempting to ID any low intensity components which the rolling window analysis might have missed; the cumulative spectrum and analysis data are included to the ICD1/ICD2 file pair for the survey.

Modes of Operation: HX-LCX Operation — For the Expert

The LCX mode is “Low Confidence Expert” mode that is password protected. This mode displays threat alarms and identifications at an about 30% lower confidence level than normal. This leads to more “hits” on suspected threat nuclides, and is recommended for use by experienced personnel. Normal mode operation, in contrast, would either simply post an elevated radiation or beta alarm rather than listing a specific radionuclide, or would just not post a threat alarm as the confidence level is very low.

The -HX and Background Radiation — No more NORM alarms

The -HX is capable of distinguishing between radioactive materials in the environment and the sample, hence it does not indicate the presence of activity which is actually due to background. This is carried out by making periodic background measurements according to a schedule. It is possible for a user with password access to choose the number of days between required background checks. The -HX allows unlimited passive monitoring if the required background update is not performed, but will not enter Survey Mode. The -HX provides proper, real-time identifications of SNM, RDD, and other threats even with an expired background.

The -HX and Digital Stabilization — Making the best of it

Although a digital germanium spectrometer is a highly stable instrument, even with changing temperatures, the -HX is designed for use in extreme conditions (which definitely are not recommended but, within the specified environmental and mechanical limits, are not a barrier to correct operation). An automatic gain stabilizer system “locks onto” the natural background K-40 peak (if present) in order to ensure “perfect” calibration is maintained even in conditions of harsh handling. The stabilizer is “smart.” The stabilizer will be held at a constant setting if either the K-40 is determined as being absent, or if a potential gamma-ray interference with the K-40 peak is determined to be present.

Micro-Detective-HX Offline Analysis Program

  • Views the spectral contents of -HX data files, real time and live time for each spectrum contained in each, radioactive sources identified (if any), and alarm types associated with each identification.
  • Reanalyzes the data set with varied nuclide libraries
  • Exports all spectra in an -HX file to a set of ORTEC .CHN format spectrum files. The .CHN files can then be viewed and examined in more detail with ORTEC applications such as the MCA Emulator and GammaVision Gamma-Ray Spectrum Analysis.

The Micro Detective-HX Offline Analysis Program is a utility supplied with all instruments. It is operated on a PC and offers extended functionality for use post-analysis.

The key features of the program are listed below.

  • Toolbar — Click to issue the main program commands
  • Spectra List — Lists all the component spectra in the current ICD1/ICD2 file pair, including the background spectrum, any Long or Fixed Sample spectra, any 8-second “rolling window” Detect Mode spectra, and the final cumulative spectrum
  • File Information Section — Displays the name of the ICD1/ICD2 file pair currently open; its Location; and the instrument with which it was acquired, including the unit serial number (ID) and firmware version
  • Analysis Results Section — Lists the nuclides found (if any), including the dose rate in mrem/hr, threat type (innocent, suspect, or threat), and confidence level (H — high or L — low). In conjunction with this list, the three simulated LED readouts “light” according to the suspect (yellow), innocent (green), and/or red (threat) nuclides identified
  • Export Button — Exports all the component spectra in the current ICD1/ICD2 file pair to a set of ORTEC .CHN format spectrum files
  • Marker Information Line — Shows the energy, in keV, and counts per channel for the current marker position
  • Spectrum Window — A full-scale display (0 to 8191 channels) of the presently selected spectrum, in counts per channel, with logarithmic vertical scaling. This window comprises of a vertical marker line capable of being moved with the mouse.

Specifications

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Dose Rate Visual over range indication and continuous audible alarm, user settable. Over-ride alarm at dose rates >10,000 µSv/hr.
Internal HPGe Detector P-type high-purity germanium. Coaxial construction. Crystal Nominal Dimensions 50 mm diameter x 33 mm (±10%) length.
Cryostat and Cooler Hardened” cryostat, with high-reliability, low-power Stirling cooler. The cryostat design is such that the Micro-Detective-HX may be switched off at any time and power subsequently re-applied, without having to wait for a full thermal cycle (full warm up before cool down), as is normal practice with a HPGe detector system. This feature greatly increases system availability during measurement campaigns
Gamma Dose Rate Detector Two detectors determine the gamma dose rate over a wide range from <0.05 µSv/h to >10000 µSv/h, a dose-rate range of around six decades. For low dose rates, below ~20 µSv/h, the dose rate is determined from the Ge detector spectrum. For dose rates above this value, the internal compensated GM tube is used. Instrument switches between the two automatically.
Dose Rate Uncertainty <(–50% to +100%); continuous audible alarm at dose rates >10,000 µSv/h (fixed maximum threshold), user settable threshold below this.
Internal Neutron Detector Module Single tube: 4" active length, 0.5" diameter. High density Polyethylene moderator.
Digital MCA and Data Processor Display: VGA 640 x 480 TFT sunlight readable, touch sensitive, operate with finger or stylus.

Data Processor: Marvel 806 MHz XScale.
Data Storage Media: To internal RAM and removable SD card.

Storage Scheme: In passive monitor mode, no data files are saved. In Survey mode and Long and Fixed sample mode, ICD1 and ICD2 files are stored.

File Format: DNDO ICD format (similar to ANSI N42.42) for data and results.

These files may be read, reanalyzed and exported to the Micro-Detective-HX Offline Analysis Program, which is included with the instrument. Exported files are in the well known ORTEC “.CHN” format and may be read by many programs used by Reachback teams such as CAMBIO and by ORTEC products such as MAESTRO and GammaVision.
Computer Interfacing Computer Interfacing USB connection to laptop. Data transfer by Microsoft® ActiveSync. Wi-Fi (802.11) communication software.
Wireless Mobile MCB Server software.
GPS Internal NMEA compliant WAAS capable.
Digital MCA with Internal Storage of Multiple Spectral Data Digital Noise Suppression: "LFR Filter" ORTEC Patent Pending.
Conversion Gain: 8k channel.
Maximum Number of Stored Spectra: Unlimited on removable media.
Maximum Overall Dimensions (including handle, Ge detector endcap and shock absorbers) 14.7 in L x 5.75 in W x 11 in H (37.4 cm L x 14.6 cm W x 27.9 cm H).
Weight 16 lbs (7.25 kg)
Internal Battery Lithium Ion. 14.4 V, 6.2 Ah, 89 Wh, nominal. Up to 5 hours of battery life at 25 °C when HPGe detector is cold. <4 hour time to charge. Internal battery is easily swapped through removal of snap shut battery door.
External Battery Battery lifetime may be extended indefinitely by the use of external battery packs. DETECTIVE-OPT-15 is recommended, weighs less than 3.25 lbs and extends lifetime to >10 hrs.
Input Power 10 to 17 V DC from battery or DC power supply (universal mains supply included). Battery charger circuit is inside instrument.
Power Usage Strongest during cool down: <100 Watt. While charging Battery: 5A nominal. Cold with fully charged battery <2A
External Power DC Input and battery Charge Input. 2.5 mm coaxial connector with locking screw on collar.
Temperature Operation Range: –10 °C to 40 °C.
Relative Humidity: <90% at 35 °C, non-condensing.
Instrument Enclosure Sealed against ingress of dust and water. All perforations are sealed by rubber plugs (connectors, memory cards, etc.). Instrument is not designed to tolerate immersion.
External Connectivity to System 1 SD (Secure Digital) card slot (3.3 V).
1 USB connection for "ActiveSync" capability or MCA operation with external computer (ActiveSync and remote display software included).
Wi-Fi 802.11 communication software.
Wireless Mobile MCB Server software
1 Audio headphone jack.
Cool Down Time The high reliability cooler is designed for continuous operation. Between making measurements the unit is powered from a DC supply, car battery or other high capacity device. Initial cool down time depends on ambient temperature, but is typically <12 hours at 25 °C

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