API PUBL 7102:1997 pdf download

API PUBL 7102:1997 pdf download.Methods for Measuring Naturally Occurring Radioactive Materials (NORM) in Petroleum Production Equipment.
The most common radiation detectors used in the oil and gas industry are one- inch Nat scintillation detectors and Geiger-Mueller (G-M) tubes. Because the Nat detector is significantly more sensitive than the G.M tube, and because the majority of industry data are taken with the Nat detectors, it is the main instrument used in the present study. The calibration procedure for a one-inch Nat detector is described in this chapter. Also discussed are factors that affect the response of Nat detectors. Detector responses can vary by up to 10 percent for different detectors of the same type and for temperature variations.
2.1 INSTRUMENT CALIBRATION
The one-inch Nat detectors commonly used for radiological surveys display significant calibration variability, both among different detectors of the same model, and in different operating configurations and conditions. However, steps can be taken to minimize the effects of these variabilities. For example, the electronic variability can be minimized by setting the operating voltage of the instrument on the detector’s high voltage plateau and setting the threshold at the recommended value. For a one-inch Nat probe with a Ludium Model 3 survey meter, the recommended threshold value is 40 mA.
The operating voltage plateau of the detector is determined by placing the NORM source and detector in a fixed configuration, and then measuring the detector count rate at a series of different oeraung voltages. A typical curve that results from these measurements with a Ludium one-inch Nat detector is shown in Figure 2-1. Because a Ludlum model 2200 survey meter was used with the Nat probe, a threshold value of 30 mA was used in generating the curve in the figure. In general, the detector count rate increases with increasing voltage. However, there is a voltage range in which the count rate remains relatively constant or increases much less rapidly than for other operating voltages. This is the operating voltage plateau for the detector. The operating detector voltage should be near the midpoint of the plateau. This corresponds to a voltage of about 900 volts for the detector used to generate Figure 2-1.