Scintillation detectors calibration

The detector can be either a gas-filled tube detector or a scintillation detector, which is systematically swept over the sample, and which measures the x-ray intensity as a function of the 26 scattering angle. Through suitable calibration, each 26 angle is converted into a wavelength value for display. The major drawback associated with WDX... 

When the energy of the charged particle beam is too large to easily stop the beam in a Faraday cup, the beam intensity is frequently monitored by a secondary ionization chamber. These ion chambers have thin entrance and exit windows and measure the differential energy loss when the beam traverses them. They must be calibrated to give absolute beam intensities. If the charged particle beam intensity is very low (<106 particles/s), then individual particles can be counted in a plastic scintillator detector mounted on a photomultiplier tube. 

Calibration of a liquid scintillation detector for beta-particle counting is discussed in Experiment 9. 

A plastic scintillation detector was to be calibrated for absolute measurements of /3-radiation. For this purpose a 2.13 X 10 M TlCl3 solution was available with a specific activity of 13.93 iCi ml T1 emits iS-particles with 0.77 MeV. Of this solution 0.1 ml is evaporated over an area of exactly 0.1 cm on a platinum foil. The sample is counted in an evacuated vessel at a distaiKe of 15.3 cm from the detector, which has a sensitive area of 1.72 cm. The detector registers 2052 cpm with a background of 6 cpm. What is (a) the surface weight of the sample, (b) the backscattering factor, and (c) the detector efficiency for the particular /3 s ... 

Several papers present reviews of measurement methods or improvements in existing methods. Yamashita et al. (1987) present the description of a portable liquid scintillation system that can be used for thoron (Rn-220) as well as radon (Rn-222) in water samples. Thoron measurements have not been made for houses where radon in water may be a significant source. Such an instrument could be useful in making such determinations as well as in studying geochemical problems as described in this report. A review of measurement methods by Shimo et al. (1987) and of development and calibration of track-etch detectors (Yonehara et al., 1987) are also included. Samuelsson... 

In order to assess the accuracy of the present method, we compared it with two other methods. One was the Track Etch detector manufactured by the Terradex Corp. (type SF). Simultaneous measurements with our detectors and the Terradex detectors in 207 locations were made over 10 months. The correlation coefficient between radon concentrations derived from these methods was 0.875, but the mean value by the Terradex method was about twice that by our detectors. The other method used was the passive integrated detector using activated charcoal which is in a canister (Iwata, 1986). After 24 hour exposure, the amount of radon absorbed in the charcoal was measured with Nal (Tl) scintillation counter. The method was calibrated with the grab sampling method using activated charcoal in the coolant and cross-calibrated with other methods. Measurements for comparison with the bare track detector were made in 57 indoor locations. The correlation coefficient between the results by the two methods was 0.323. In the case of comparisons in five locations where frequent measurements with the charcoal method were made or where the radon concentration was approximately constant, the correlation coefficient was 0.996 and mean value by the charcoal method was higher by only 12% than that by the present method. 

The standard sources have been designed in order to allow the calibration of all the classical detectors of a, p, e, y, n, X radiation (ionisation chambers, Geiger-Miiller or proportional counters, scintillation or solid-state counters, etc.). They are classified as alpha sources, electron sources, beta sources, gamma sources, neutron sources. X-ray sources, heat flux sources, and sources for radiation protection dose meters. 

A solvent module (Varian model No. 5000) with a UV detector coupled to an on-line Nal(Tl) detector was used for high performance liquid chromatography (HPLC) analysis. For radioactive measurements, a dose calibrator (Capintec CRC-7, USA), a solid scintillation counter (ORTEC, USA) with a plane (7.62 cm x 7.62 cm) Nal(Tl) detector, an automatic well type gamma counter (Compac-120, Picker, USA) and a multichannel analyser coupled to a Nal(Tl) detector (7.62 cm x 7.62 cm) were used. 

Under most circumstances, it is not convenient to measure the incident and reflected beams directly with the same detector because scintillator counters have a substantially smaller dynamic range than the 105- to 1010-fold difference between the direct beam flux and reflected beam flux. Instead, direct knowledge of the detector resolution, A(20), and the conversion factor between the monitor signal and the incident beam flux, amon, can be used to estimate the absolute reflectivity. Furthermore, the absolute reflectivity is well constrained by measurements close to bulk Bragg features or at the total external reflection condition near 20 0°. These intensities are dominated by bulk properties of the substrate and provide an independent calibration on the absolute reflectivity scale. 

Fig. 3a-c Experimental set-ups for measuring X-ray absorption spectra, a Standard transmission experiment b set-up for fluorescence yield measurements c set-up for electron yield measurements placed in an ultra-high vacuum (UHV). So Synchrotron X-ray source, M double-crystal monochromator IC ionization chamber Sa sample RS reference sample for energy calibration, x fluorescence X-rays FD fluorescence detector (typically an energy-dispersive solid-state X-ray detector) e electrons emanated from the sample eD detector for electrons (typically a scintillation counter) s/scattering foil which scatters a small part of the X-ray beams into the X-ray detector (xD), so that the intensity of the incoming beam can be measured... 

Using this pulse-shape spectrum, the cross-over point between the two detectors was set at a rise-time of 3/ s, shown by the dotted line in the figure. Events with faster rise-times were analysed as coming from the photodiode and were essentially all due to 60 keV events all others were assumed to come from the caesium iodide scintillator. The two types of event were analysed individually in order to obtain raw energy spectra from each detector (also shown in Figure 2). The peaks in the energy spectra were then used to calibrate the energy scales for the two systems. 

Such neutron detectors are simple to construct. For purposes of pulse height calibration, it is desirable to avoid leaving the photomultiplier surface in contact with the scintillating liquid. 

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