Hardware
The Micro-Detective-HX features compact, light weight and rugged hardware. A 50 mm diameter HPGe crystal in a “hardened” cryostat is cooled by an integrated low-power Stirling-cycle cryocooler. The latest version Micro-Detective-HX features a new cooler, offering reduced levels of accoustic noise and vibration, and longer operation life. The hardened cryostat is entirely free of conventional molecular sieve, allowing the instrument to be turned off or on at any point in the detector cool down or warm up cycle without risk. This is impossible with conventional HPGe cryostat systems which require careful temperature cycling procedures to avoid damage.
A built-in digital MCA system and powerful data processor are included. All models feature the same bright and clear VGA resolution display, readable in direct sunlight, with a touch sensitive operator screen. Menu navigation is highly intuitive. The radionuclide gamma-ray spectrum may be displayed and manipulated (e.g., vertical scale, zoom) like a conventional multichannel analyzer.
Gamma and neutron count rate and gamma dose rate are displayed continuously both numerically and in bar graph form.
In the latest version, the Micro-Detective-HX internal battery provides enough power for up to 5 hours of operation and is easily replaced in seconds, allowing continuous in-field operation. At just under 16 lbs. in weight, the Micro-Detective sets a world record for portable, high resolution nuclide identifiers, by a wide margin.
-HX Software Approach
HPGe is already acknowledged as the “perfect” detector for a radioisotope identifier. It has ~40 times better energy resolution (selectivity) than the nearest alternative. Unlike lower-resolution detector types, HPGe crystals must operate at cryogenic temperatures — an engineering issue ORTEC solved 25 years ago. Several hundred Detective family instruments in the field attest to the reliability of today’s miniature Stirling cycle coolers used for this purpose.
Beyond the intrinsic selectivity of the HPGe detector type, the ultimate performance in terms of its fidelity of identification (zero false positives or false negatives is the goal) depends on the software algorithms. Its practicality in use depends on reliable hardware and a user interface which is easy to learn and interpret.
The Micro-Detective-HX performance has been enhanced with the introduction of the new Detective-Pro user interface. Further reductions in both false positive and false negative results have been achieved, 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, Navigate (N) and Select (S), with which all survey and sampling operations can be performed.
- A high-resolution, sunlight readable, color touchscreen provides an alternative way to choose menu options and enter data such as passwords and alarm limits.
- Audio-visual feedback:
- Menus are designed to be operated with N and S buttons only, but if preferred, the touchscreen is always available.
- On-screen help messages display radiation and system error alarms. The messages tell the user what the next press of the N and S buttons will do.
- An audio alarm with three volume settings can be used with headphones and a vibration alarm is provided in the handle. Either, both, or neither can be enabled.
- A 4-LED panel is used to further inform the operator of alarm conditions.
- Color coding of the LEDs and screen borders match in order to make the instrument as intuitive as possible: red for threat, yellow for suspect and green for innocent.
- Indicators at the top of the screen show the current dose rate in mrem/hr, the number of spectra that can be stored on the SD card, GPS co-ordinates, the power source (external power or battery), battery time remaining, 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 posted to the real-time identification area of the screen. This area lists the names of any radioisotopes currently being detected and their classification as a threat (T), suspect (S), or innocent (I). It can also optionally show whether the identification is at high (H) or low (L) confidence.
The Micro-Detective-HX in Use: Modes of Operation
How the -HX Collects and Analyzes Data
- A flexible approach to minimize time and maximize effectiveness.
- Continuous running and fixed time modes with “end survey summary.”
- Maximum flexibility, maximum sensitivity.
- Adaptable to the chosen CONOPS design.
The -HX monitors for radiation at all times. It collects one spectrum per second, then begins analyzing a rolling window of the eight most recent 1-second spectra for radioisotope identification and alarms.
- “Home” or “Passive Monitor” mode is the simplest form of operation. In this mode, the -HX is continuously “looking,” but not storing data.
- In “Detect” or “Survey” mode, the instrument stores the 1-second data slices and attempts to make an ID based on the 8-second rolling windows.
- Optional “Long Samples” or “Fixed Samples,” performed during the “Detect” mode survey, add longer spectrum acquisitions to the data stream of 8-second rolling-window analyses.
- The “End Survey Report” is a cumulative analysis of all 1-second data slices in the survey, providing increased detection sensitivity for weak or distant sources.
Modes of Operation: Home (Passive Monitor) Mode: “Always Looking”
In Home (Passive Monitor) mode, the instrument is continuously “looking” but not storing data. Gamma dose-rate, battery life, storage space, and GPS co-ordinates are displayed. In this mode, the -HX acts like a survey meter in that if it is moved away from the source, the ID will be removed from the screen. However, any alarm posted persists and must be acknowledged (cleared). Data is gathered and processed in 1-second time slices. The -HX analyzes an 8-second rolling window of these slices and attempts to make an ID. Nuclide IDs are posted to the Real Time ID area.
Modes of Operation: Detect Mode (The Survey Concept)
Detect mode is used to better locate and identify sources. A Survey always begins with a Detect mode measurement, and can include Long and Fixed Sample mode (see below) operations also. The -HX can be set to automatically start a survey immediately after it is removed from charge or a survey may be started manually. 1-second data slices are saved to an ICD1/ICD2 file pair (see specification section) on the removable SD card. As in the Passive Monitor mode, the -HX attempts to make an ID based on an 8-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 greatest activity. The lower chart shows the Threat Material Index similar to the Signal Index, but for threat material only. To the right of each strip chart, a vertical bar and numeric value is used to show the current value of the signal and threat indices. If appropriate to the measurement, alarm IDs are displayed in the Real Time ID area and must be acknowledged.
Modes of Operation: Long and Fixed Sample Modes
During a Survey, in the Detect mode measurement, a source may have been located and closer scrutiny desired. Long or Fixed Sample modes may be used to achieve this. In Long Sample mode, a single spectrum is acquired for 30 or more seconds and analyzed once per second for alarms. Fixed Samples are treated similarly but have preset durations of 5, 10, 15, 20, 25, 30, 60, 120, or 300 seconds. In Long Sample mode, the live spectral display can be viewed. Long and Fixed Sample spectra and analyses are saved in the ICD1/ICD2 file pair for the Survey, along with the rolling-window and cumulative-analysis data.
“End Survey Report”
A Survey is started manually or automatically, as described above. Apart from the Detect mode operation, a survey may include either single or multiple long or fixed sample mode measurements. When a Survey is terminated by the operator, an “End Survey” summary report is displayed containing the following:
- Any alarms derived from the 8-second rolling window mode of operation which starts every survey,
- Any alarms derived from an analysis of a cumulative spectrum representing the summation of all the 1-second slices gathered during the survey, thereby attempting to ID any low intensity components which the rolling window analysis might have missed; the cumulative spectrum and analysis data are added to the ICD1/ICD2 file pair for the survey.
- Any alarms derived from those Long and Fixed Sample measurements included in the survey.
Modes of Operation: HX-LCX Operation — For the Expert
The LCX mode is “Low Confidence Expert” mode. This mode is password protected, and displays threat alarms and identifications at an approximately 30% lower confidence level than normal. This results in more “hits” on suspected threat nuclides, and is recommended for use by experienced personnel. Normal mode operation, in contrast, would either not post a threat alarm because the confidence level is too low, or would simply post an elevated radiation or beta alarm rather than listing a specific radionuclide.
The -HX and Background Radiation — No more NORM alarms
The -HX can distinguish between radioactive materials in the environment and the sample, so it does not indicate the presence of activity which is actually due to background. It does this by making periodic background measurements according to a schedule. A user with password access can choose the number of days between required background checks. If the required background update is not performed, the -HX permits unlimited passive monitoring but will not enter Survey Mode. However, even with an expired background, the -HX provides proper, real-time identifications of SNM, RDD, and other threats.
The -HX and Digital Stabilization — Making the best of it
Although a digital germanium spectrometer is a highly stable instrument, even with varying temperatures, the -HX is designed for use in conditions that could be considered extreme (which certainly are not recommended but, within the specified mechanical and environmental limits, are not a barrier to correct operation). An automatic gain stabilizer system “locks onto” the natural background K-40 peak (if present) to ensure “perfect” calibration is maintained even in conditions of harsh handling. The stabilizer is “smart.” 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, the stabilizer will be held at a constant setting.
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 different 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 analyzed in more detail with ORTEC applications such as the GammaVision Gamma-Ray Spectrum Analysis and MCA Emulator.
The Micro Detective-HX Offline Analysis Program is a utility supplied with every instrument. It is run on a PC and provides extended functionality for use post-analysis.
The key features of the program are listed below.
- Toolbar — Click to issue the main program commands.
- 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 firmware version and the unit serial number (ID).
- Spectra List — Lists all the component spectra in the current ICD1/ICD2 file pair, including the background spectrum, any 8-second “rolling window” Detect Mode spectra, any Long or Fixed Sample spectra, and the final cumulative spectrum.
- Export Button — Exports all the component spectra in the current ICD1/ICD2 file pair to a set of ORTEC .CHN format spectrum files.
- Analysis Results Section — Lists the nuclides found (if any), including the threat type (innocent, suspect, or threat), dose rate in mrem/hr, and confidence level (H — high or L — low). In conjunction with this list, the three simulated LED readouts “light” according to the innocent (green), suspect (yellow), and/or red (threat) nuclides identified.
- Spectrum Window — A full-scale display (0 to 8191 channels) of the currently selected spectrum, in counts per channel, with logarithmic vertical scaling. This window includes a vertical marker line which can be moved with the mouse.
- Marker Information Line — Shows the energy, in keV, and counts per channel for the current marker position.