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The GAMMA-RAD is a powerful, portable instrument combining a complete NaI Scintillation Probe with a Digital Pulse Processor that provides 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. |
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Includes
Features
Detector
Standard Performance
Applications
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The GAMMA-RAD is a complete, integrated gamma-ray spectrometer. It includes a scintillator and PMT, a digital pulse processor based on Amptek’s DP4, 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-RAD is ideally suited for a wide range of gamma-ray spectroscopy measurements, from lab applications to most harsh field homeland security applications.
Figure 2. GAMMA-RAD Architecture.
| Detector Properties | |
| 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 of standard 76 x 76 mm NaI(Tl) |  Figure 3. Efficiency of 76 x 76 mm NaI(Tl). |
| Pulse Processing Performance | |
| 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 >300,00 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. |
| MCA Performance | |
| 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 |
| External Connections | |
| USB | A standard USB interface, for USB 1.1 (2.0 compatible) at full-speed (12 mbps), is available. This provides both serial data and power for the entire GAMMA-RAD |
| Ethernet | 10Base-T/100Base-TX, TCP or UDP, DHCP or fixed IP. |
| DAC Output | Single pin LEMO connector |
| Power | |
| +5 V | Average current 150 mA USB*, 350 mA Ethernet. When using the USB port, the entire Gamma-Rad can be powered from USB. Ethernet requires the use of the external DC supply. *In order to achieve the stated USB power, the ethernet port must be disabled. This can be done only at the factory. Please specify at time of order whether low power USB operation is needed. |
| High Voltage | A stabilized, high efficiency Cockroft-Walton power supply provides PMT bias. The HV can be set by the HV Set potentiometer on the back panel. The HV can be monitored with a voltmeter at the HV Test point on the back panel. 1 mV = 1 V, e.g. 0.800 mV = 800 V |
| Physical | |
| Size | 35.5 cm x 8.3 cm (dia) |
| Mass | 3.6 kg (76 x 76 mm NaI(Tl)) |
| Interface Software | |
ADMCA is a standard data acquisition and control package for use with all of Amptek’s digital processors and MCAs, including the GAMMA-RAD. This package provides the capability to configure the GAMMA-RAD and acquire and save data. Amptek also provides a DLL library (API) of routines so that users can write their own interface software. Along with the DLL library are example routines, written in Visual Basic and Visual C++, which can be used to control data acquisition. These can be tailored for specific uses. This includes an example code which implements the gain stabilization algorithm, using the 40K peak in the background spectrum. | |
Figure 2 shows an application that takes full advantage of the ruggedization of the GAMMA-RAD. The GAMMA-RAD 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.
Presentation on this shipping container system.
Paper on this shipping container system.
Figure 4. Photo of VeriSpreader shipping container monitor.
An example program is provided with the GAMMA-RAD 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 GAMMARAD 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.
Figure 5.
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-RAD clearly detected it and identified the energy.
Figure 6.
Figure 7. Optional 4" x 4" x 16" NaI(Tl). The resolution with this "bar" is 6.9% FWHM at 662 keV.
Figure 8.
Figure 9. 60Co Spectrum
Figure 10. 137Cs Spectrum.
Figure 11. 22Na Spectrum.
Figure 12. 133Ba Spectrum.
Figure 13. 57Co Spectrum.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19. GAMMA-RAD 76B76 mechanical dimensions.
Please see the DP4 for more information on the Digital Pulse Processor and MCA inside of the GAMMA-RAD.
GAMMA-RAD Specifications PDF (810 k)
Glossary
Revised March 12, 2007
