GEOPHYSICAL GAMMA-RAY SPECTROMETER
Brno, October 2001
Technical specifications 1. Theory 2. Operating Instructions 2.1. GRM-260 Preparation 2.2. Measurement 2.2.1. Spectrum 2.2.2. Dose Rate 2.2.3. Viewer 2.2.4. Calibration 2.3. Measurement using external PC 2.3.1. Single Spectrum 2.3.2. Profile Measurement 2.3.3. DoseRate Indication 2.3.4. Working Settings 2.3.5. Spectrum Viewer 2.3.6. Calibration 2.3.7. Data Transfer to PC 3. Maintenance 4. Trouble Shooting 8
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NaI(Tl) or BGO 2”x2” with shielded photomultiplier geometrical center is placed in the middle of the casing at 45 mm distance from the front sideEnergy resolution Energy range Reference source Pulse shaping Analyzer
better than 8.5% for NaI(Tl) (at 0.662 MeV) better than 13.0% for BGO (at 0.662 MeV) to 3 MeV
Cs, activity 10 kBq
Semi-Gaussian, 1 µs 256 channels, up to 70.000 pulses per second 4 ROIs K, U, Th assays calibrated in %, ppm, ppm dose rate measurement in nGy/h or U equiv
single spectrum profilemeasurement dose rate indication
Control unit PC interface Power supply Dimensions Weight Ambient conditions
numeric keyboard with graphic backlit screen or user’s PC RS 232C rechargeable batteries (min. 15 hours life time) 270 x 130 x 180 mm (length, width, height) 3.1 kg -10 to +60 oC dropping water resistant
battery charger cable for PC connection software for PCcontrol and data transfer operating manual transport case
Strong mechanic shocks may damage the detector inside the instrument.
The GRM-260 gamma-ray spectrometer is designed for spectral measurements of natural and artificial radionuclides in field and laboratory conditions giving the information about the kind and the concentration of radionuclides present in rocks,soil and water. The gamma-ray spectrometry as the most common nuclear method is useful for raw material exploration, environmental radiation monitoring, geological studies of lithology and stratigraphy, geophysical mapping, borehole logging, laboratory assays of rocks and building materials. The measurement is based on the capture of emitted gamma quanta in the scintillation detector. The gammaquanta of characteristic energies are transformed into electric pulses with heights that are proportional to those energies. The queue of electric pulses is analyzed consequently and separate pulses are sorted into individual channels of the measured spectrum. The spectrum of the GRM-260 consists of 256 channels with the channel width of 12 keV. The spectrum is divided into four parts – groups ofchannels called ROI (Region Of Interest) – with the respect to the peak positions of studied radionuclides and due to the real resolution of the scintillation detector. Radioactivity of rocks is usually caused by one of three natural sources of gammaradiation: potassium (K), uranium (U) and thorium (Th). Each of those elements in natural conditions contains a fraction of a radionuclide that can bedetected in either direct or indirect way. The isotope 40K emits gamma-rays with the energy of 1.461 MeV thus the determination of K is direct one. The concentration of K is given in mass percentage. The determination of U is based on the detection of 214Bi radionuclide, which is a member of 238 U decay series emitting the energy of 1.764 MeV. In the case of U the detection is indirect and theconcentration is given in ppm eU (equivalent of uranium). The determination of Th contents is indirect as well – the 208Tl radionuclide with the energy of 2.615 MeV originating from the 232Th decay series is detected. The concentration of Th is given in ppm eTh. Other sources of gamma-radiation may come from artificial activities as power stations, industrial enterprises, nuclear weapons. Those...
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