The GAMMA-RAD5 is a powerful, portable gamma-ray spectrometer combining a complete NaI Scintillation Probe with a Digital Pulse Processor providing high quality detection and spectroscopic information.
To simplify its use, this detector system communicates and receives its power through the USB port. All that is needed is a laptop computer for control, display, and data storage. It also supports Ethernet, for distributed networks.
The GAMMA-RAD5 is a complete, integrated gamma-ray spectrometer. It includes a scintillator and PMT, a digital pulse processor based on Amptek’s DP5 called the DP5G, all the hardware and software necessary to control and communicate to a PC, and all power supplies. It is a single, integrated, portable module.
Several key innovations make this system ideal for field use. First, the scintillator and PMT are ruggedized to protect against mechanical shock and vibration. Second, the Ethernet interface permits operation over long distances: 100 m via Ethernet or, with Internet software, globally while the USB interface permits a single connection (power and data) to virtually any computer. Third, it has a flexible digital architecture so it can be easily tailored for specific applications. The GAMMA-RAD5 is ideally suited for a wide range of gamma-ray spectroscopy measurements, from lab applications to most harsh field homeland security applications.
|Detector||The detector is a ruggedized scintillator and PMT. The 76 x 76 mm NaI(Tl) is considered standard, but many different configurations are possible. Contact Amptek for details. The detector performance (resolution, stopping power, photofraction, etc.) are determined by the scintillation crystal.|
|Efficiency 76 and 152 mm NaI(Tl)||
Figure 4a. Efficiency of 76 x 76 mm Na(I)Tl.Figure 4b. Efficiency of 76 mm and 152 mm NaI(Tl) compared.
|Gain Settings||Two software selectable coarse gain settings are available: 3 MeV full scale and 750 keV full scale. Fine gain is adjustable between 0.75 and 1.25.|
|Pulse shape||Trapezoidal, typically set to 2.4 µs peaking time (equivalent to a 1 µs shaping time). Software commandable from 0.8 to 102.4 µs peaking time (0.3 to 40 µs equivalent shaping time).|
|Gain stabilization||The gain from the NaI(Tl) and PMT is well known to vary with temperature. A gain stabilization algorithm runs in software to compensate.|
|Maximum Count Rate, Dead Time, and Throughput||With the default configuration, the system operates to an input count rate of 150,000 sec-1 with a throughput >50% and good baseline stability and pile-up rejection. Configured for the shortest peaking time, 0.8 µs, it will sustain an input count rate of >300,000 sec-1 with throughput >50%. Unlike an analog system, there is no separate dead time for digitization and events can be processed when separated by less than a full pulse width, specifically by 1.25 times the peaking time. Pulse processing electronics have a cycle time of 1 µs so a 1 MHz periodic signal can be acquired. The fast channel (used for pile-up rejection and measuring the input count rate) has a 600 ns resolving time.|
|Custom Configuration||The DP5G is set at the factory for either 20 MHz or 80 MHz clock. For NaI(Tl), the standard 20 MHz is standard, yielding the specifications listed above. The 80 MHz setting allows for peaking times down to 0.1 µs in the slow channel and 0.05 µs in the fast channel but draws about 50% more power. The 80 MHz setting is recommended for custom scintillator materials with faster decay times, fast pulse shape discrimination, or other unique requirements.|
|Number of channels||Software commandable to 8k, 4k, 2k, 1k, 0.5k, or 0.25k channels.|
|Minimum acquisition time||<10 ms|
|Presets||Time, total counts, counts in an ROI, counts in a single channel|
|USB||A standard USB interface, for USB 1.1 (2.0 compatible) at full-speed (12 mbps), is available. This provides both data and power for the entire GAMMA-RAD5. No external power is needed.|
|Ethernet||10Base-T or UDP, DHCP or fixed IP. External power must be used with this interface (AC adapter included).|
|Aux 1||This is a primary auxiliary input/output connector. It can be configured as (1) the analog output, (2) the AUX_OUT_1 digital output, or (3) the AUX_IN_1 digital input. AUX-1 can be used for diagnostic purposes by displaying analog outputs, e.g. shaped pulses or the ADC input. It can be used as a digital input, e.g. to count pulses from a 3He neutron monitor. It can also be used to display digital outputs, e.g. as an output count indicator. A software controlled switch selects between the DAC output and a bidirectional digital transceiver (SN74LVC1T45) with 50 ohm series impedance and a 100 k pull-up resistor. It is a LEMO connector, P/N Lemo EPK 00.250.NTN.|
|Aux 2||This is a digital input/output connector. It can be configured as either (1) the AUX_OUT_2 digital output or (2) the AUX_IN_2 digital input. It is connected to a bidirectional transceiver (SN74LVC1T45) with a 50 ohm series resistance and 100 k pull-up. It is a LEMO connector, P/N Lemo EPK 00.250.NTN.|
|Aux 3||This is a 15 socket D connector which includes (a) the lines for a serial RS232 interface, (b) the AUX_OUT_1 and AUX_OUT_2 digital input/output lines, and (c) the 8 SCA outputs. The RS232 lines connect to a MAX3227. The AUX_OUT lines connect to SN74LVC1T45. The SCA lines connect to an SN74LVC245. Amptek sells an optional breakout cable which mates with AUX-3.
|Power Connector||A +5 V AC adapter is provided, which is needed only when using Ethernet or RS232. When using USB, the USB bus provides the power. If the Gamma-Rad5 is to be connected to an external power supply the connector information is below: Molex 39-30-1020, Digi-Key WM1351-ND
Mates with Housing: Molex 39-01-2020, Digi-Key WM3700-ND
Terminal: 16 ga. – Molex 44476-3112, Digi-Key WM1913-ND
18-24 ga. – Molex 44476-1112, Digi-Key WM1914-ND
Figure 5. Connectors.
|+5 V||Average current 150 mA USB, 350 mA Ethernet. When using the USB port, the entire Gamma-Rad5 can be powered from USB. Ethernet requires the use of the external DC supply. When the USB cable is plugged in and no Ethernet connection is detected, the Gamma-Rad5 will automatically disable the Ethernet port to save power.|
|Range||3 to 6.4 V|
|High Voltage||A stabilized, high efficiency Cockroft-Walton power supply provides PMT bias. The HV is software controlled.|
|Size||31.5 cm x 9.2 cm (dia)|
|Mass||3.35 kg (76 x 76 mm NaI(Tl) with handles)
5 kg (76 x 152 mm NaI(Tl) with handles)
|Operating Temperature||-25 °C to + 65 °C.
Maximum temperature gradient is 10 °C per hour.
|DPPMCA||The Gamma-Rad5 can be controlled by the Amptek DPPMCA display and acquisition software. This software completely controls and configures the Gamma-Rad5, and downloads and displays the data. It and supports regions of interest (ROI), calibrations, peak searching, and so on. Runs under Windows XP PRO SP3 or later. Click here for the software download page.|
|SDK||The Gamma-Rad5 comes with a free Software Developer’s Kit (SDK). The user can use this kit to easily write custom code to control the Gamma-Rad5 for custom applications or to interface it to a larger system. Examples are provided in VB, VC++, etc. Click here for the software download page.|
|VB Demonstration Software||The VB demonstration software runs on a personal computer and permits the user to set the Gamma-Rad5 parameters, to start and stop data acquisition, and to save data files. It is provided with source code and can be modified by the user. This software is intended as an example of how to manually control the Gamma-Rad5 through either the USB, RS-232, or Ethernet interface using the most basic calls without the SDK. This is primarily needed as an example when writing software for non-Windows platforms. Click here for the software download page.|
Figure 17 shows an application that takes full advantage of the ruggedization of the GAMMA-RAD5. The GAMMA-RAD5 modules are mounted on the VeriSpreaderTM bar of the crane that lifts shipping containers. Radiation detection is carried out during routine handling so there is no delay in processing. The spectroscopy performance keeps the false positive rate at a very low level, which is a vital concern.
*VeriSpreaderTM is a trademark of VeriTainer Corporation U.S. Patent 6,768,421.
An example program is provided with the GAMMA-RAD5 to aid in long term monitoring where weak sources are present. This program automatically saves a spectrum at user defined intervals, it provides gain stabilization using the 40K background peak, and it provides a simple ROI analysis capability to verify if suspect counts are present above preset thresholds. This software can run on a laptop, connected to the GAMMA-RAD5 by a USB cable. It can also run over an Ethernet link and the Internet, and be monitored on the other side of the world. The plot below shows a background spectrum and measurements from natural UO3 and a lantern mantle containing natural thorium.
The same software used for the environmental monitoring application can be used in a pedestrian or vehicle portal monitor using much shorter data acquisition intervals. The plot below shows the count rate, both total and in the 662 keV peak, when a pedestrian walked by the 76 X 76 mm detector at a distance of 10 feet with a 100 µCi 137Cs. A standard Geiger counter was unable to detect the source, since it registered a natural background of 0.02 mR/hr before and during the pedestrian incident, but the GAMMA-RAD5 clearly detected it and identified the energy.
Figure 21. Gamma-RAD5 units installed in a loading dock.
Figure 22. Gamma-RAD5 units installed as a pedestrian portal monitor.
With a custom detector, a single Gamma-Rad5 module can provide neutron detection while measuring the gamma-ray spectrum. The key is the use of a “Phoswich” detector, a sandwich of two scintillators mated to a single photomultiplier tube. A LiI(Eu) crystal is added to the standard NaI(Tl) scintillator. The NaI(Tl) measures the gamma-ray spectrum. The lithium is enriched in 6Li, providing for efficient detection of neutrons via the 6Li(n,a) reaction. The two scintillators produce different pulse shapes, so the DP5G’s pulse shape discrimination is used to distinguish between them.