Gamma spectrometers and radiameters - frequently asked questions
GAMMA SURVEYOR VARIO determines concentrations of natural radioactive elements K, U, Th (%, ppm, ppm) and natural dose rate (nGy/h). Natural dose rate is given as spectrum depending quantity (derived from K, U, Th concentrations according to IAEA formula).
GAMMA SURVEYOR VARIO is calibrated on high volume standards made according to IAEA rules. The basic calibration corresponds with conditions of infinite homogenous half space (large flat surface of mass with uniform distribution of radioactive elements). For measurement in borehole mode calibration factor is automatically switched to well geometry.
Historical way of radiometry based on cps evaluation in ROIs cannot be considered as absolute. Various instruments are equipped with different kinds of detectors (regarding used size and material) so their cps responses can differ significantly and such simple measurement cannot replace calibrated values of K, U, Th concentrations and of dose rate.
Measuring time determines quality of K, U, Th assays and dose rate measurements. Its proper choice depends on requested accuracy of results, total level of gamma activity, used size and kind of detector.
In most cases it represents very incorrect measuring procedure giving only informative and relative results. Size, shape and homogeneity of the sample together with its distance from the detector can influence results in many hundreds of percents. If such samples are measured near to ground surface, results are influenced rather by ground than by sample.
GAMMA SURVEYOR VARIO allows performing laboratory assays of drill core or other samples of specific shape and volume. For this purpose it is necessary to perform user calibration of the instrument using a set of calibration standards of the same shape and volume like analyzed samples (using instrument stand and shielding box).
This procedure eliminates spectrum drift before its next processing. GAMMA SURVEYOR VARIO provides energy stabilization by means of natural or artificial isotopes. Use of the artificial isotope makes stabilizing phase shorter and more reliable especially if measurement is performed on materials with extra low gamma activities.
The GS CAR probe is to be mounted on rear side of a car or onto a sledge. The speed of movement (e.g. 10-20 km/h) is determined by requested resolution.