Scintillation detector requirements

Completely isolating the element to be determined from all other radioactive indicators is rarely necessary, and several group separation schemes have been developed that improve the determination of most trace elements with adequate precision. Particularly simple separations may be carried out by adsorption on active carbon or by eliminating only Na from the sample [4]. Such incomplete separations require the use of high-resolution detectors for y radiation the use of scintillation detectors requires the best possible separation. 

The X-ray instrumentation requires a commercial small angle X-ray camera, a standard fine structure X-ray generator and a sample manipulator if scanning is requested. The essential signal is the relative difference between the refraction level Ir and the absorption level Ia. Both levels are measured simultaneously by two scintillation detectors. At fixed angles of deflection this signal depends solely on the inner surface density factor C and thickness d of the sample [2] ... 

Position Sensitive Detectors. By replacing the scintillation detector in a conventional powder diffractometer with a Position Sensitive Detector (PSD), it is possible to speed data collection. For each x-ray photon received a PSD records the angle at which it was detected. Typically, a conventional scintillation detector records x-ray photons in a range of a few hundredths of a degree at a time. A PSD can measure many degrees (in 20) of a powder pattern simultaneously. Thus, for small samples, data collection, which could require hours with a conventional detector, could take minutes or even seconds with a PSD. 

The experimental equipment requires a standard fine structure X-ray generator operated usually with monochromatic K -radiation. The measurements of the refraction effect are taken by using a commercial small angle X-ray camera of the Kratky type in combination with two scintillation detectors for simultaneous detection of X-ray refraction intensity Ir and sample absorption U- A standard DOS-computer handles the scattering intensity data acquisition and the micromanipulator scanning-system. Figure 1 shows the experimental setup. 

For the measurement of y emitters in solids Nal(Tl) scintillation detectors or Ge detectors are most suitable, depending upon whether high counting efficiency or high energy resolution is required. For comparison, the spectra of Co taken with a Nal(Tl) scintillation detector and with a Ge(Li) detector are plotted in Fig. 7.16. 

The properties of a scintillation material required for good detectors are transparency, availability in large size, and large light output proportional to gamma ray energy. Relatively few materials have good properties for detectors. Thallium activated Nal and Csl crystals are commonly used, as well as a wide variety of plastics. Both Nal and Csl require an activator such as Thallium for proper operation. Nal is the dominant... 

E. Because of the weak beta radiation, tritium is NOT readily measured by the Geiger-Mueller counter used with most fielded radiac instruments and requires wipe testing swipes and a liquid scintillation detector to determine the level of contamination. 

For a similar Ge lithium-drifted detector, the energy required for ionization is 2.96 eV. This is much less than the energy required for ionization in a proportional counter or a Nal(Tl) scintillation detector. 

Instruments for measuring ionized radiation typically include a sensing device and a readout device. Some are usefiil for field measurement whereas other combinations come in small packages useful for dosimetry. Sensors are very critical. Different types of radiation require different types of sensors. Sensors include Geiger-MueUer tubes (used in Geiger counters), ionization chambers, luminescent detectors, scintillation detectors, and photographic emulsions. 

Industrial applications require durable, shock-and vibration-resistant, easy-to-use equipment, which may be operated in a wide range of temperature, humidity, and pressure environments (Johansen and Jackson 2004). These criteria can be better satisfied by scintillation detectors, and such detectors may also be satisfactory for monitoring the composition of nearly identical objects. 

DCEMS together with low-temperature and in-field measurements require much more sophisticated experimental equipment. Gas counters, scintillation detectors, electron multipliers (Channeltron, Ceratron), surface barrier silicon semiconductor detector, and electron energy analyzers belong to the most frequently used detectors applied in CEMS and CXMS, respectively. Differences among individual constructions can be found in Ref. 123. Commercially available version of CEMS/CXMS spectrometer is depicted in Fig. 18.36 [127]. Device is based on 27t proportional continuous gas flow counter for room-temperature zero-magnetic field measurements. 

The length of the column used in the analysis was 7.1 cm, with a calculated volume of 0.25 ml. The time required to automatically pack the microcolumn was 4.5 min, including washing steps. After elution, online detection was carried out by a flow-through liquid scintillation detector, configured with a 0.5 ml flow cell. The detector integration time to accumulate counts for each data point reported... 

---