Scintillation detectors energy resolution

The temperature dependence of the light yield is a second important factor which could affect in a significant way its performance as a scintillation detector, in particular it directly affects the detector energy resolution. The Lanthanum Halide materials have an uncommon temperature stability in a veiy large temperature range which make them suitable to use also in very harsh or hostile environment. 

The recent general availability of solid state Ge(Li) gamma-ray detectors has made possible new applications of activation analysis to multielement trace analysis. A simplified schematic representation of a Ge(Li) detector is given in Fig. 6. The principal advantage of these detectors is their excellent energy resolution for gamma-ray spectrometry 52>. While a typical 3 X 3" NaI(Tl) scintillation crystal may have a photopeak resolution of 50 KeV fwhm (/ull width at Aalf maximum) for the 137Cs... 

It is also interesting to note that the limitations of most neutron systems lie not in the neutron source(s) but rather in the (gamma ray) detectors and subsequent data acquisition system. The obvious need is for development of detectors with higher rate capability and improved energy resolution. All modern digital data processing techniques have allowed significant improvement in the performance of conventional scintillation detectors with respect to rate and pileup rejection. 

An obvious extension to the CSCT technique as described so far is to replace the scintillator detectors with room temperature semiconductors, thus markedly improving the energy and thus the momentum transfer resolution [41],... 

Scintillation counters usually consist of a sodium iodide crystal doped with 1% thallium. The incident X-ray photons cause the crystal to fluoresce producing a flash of light for every photon absorbed. The size of the light pulse is proportional to the energy of the photon and is measured by a photomultiplier. A deficiency associated with scintillation counters is that they do not provide as good energy resolution as proportional or solid state detectors. 

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. 

Scintillation detectors with Nal(Tl) crystals may also be used for y spectrometry. Because Nal(Tl) crystals can be made in larger size than Ge crystals and because the atomic number of I is larger than that of Ge, the internal counting efficiency of Nal(Tl) detectors for y rays is higher than that of Ge crystals, as already discussed in section 7.5 (Fig. 7.16). On the other hand, the energy resolution is appreciably lower (5 to 7% for y energies of the order of 100 keV). Scintillation detectors are operated in a way similar to that used with Ge detectors, but without cooling. 

Many types of detectors, such as Geiger-Miiller counters, proportional counters and scintillation detectors, are used for charged particle detection. The selection is made on the basis of resolution and range of particle in the gas or scintillator. In some cases, the particles are not completely stopped within the detector for an energy measurement, but deposit only a portion of their energy. This is related to the relative ionization of the particle and can be used to identify different kinds of particles. 

In gas-filled as well as scintillation detectors, the observed count rate is typically less than the actual decay rate of the radionuclide. The efficiency of detection may differ from particle to particle under identical conditions using the same type of detector. The factors that affect the efficiency of detection are operating voltage, resolving time, geometry of the instrument used in relation to the position of the sample with respect to the detector, scaler, energy resolution, absorption by cells, and sometimes constituents of the sample itself. 

This type of detector is one of the oldest and most often used in X-ray diffraction. Its response time is extremely low (= 0.2 pS). This feature is its main advantage compared to proportional gas detectors. It is sensitive to the energy of X-rays but has a poor energy resolution. Its efficiency is almost 100%. Compared to proportional gas counters, the background noise is more significant and scintillating crystals deteriorate in a humid atmosphere. 

These are used on single counter four-circle diffractometers. The detector is often sodium iodide. The scintillator is used in conjunction with a photomultiplier tube. Thallium activated sodium iodide has an energy resolution of about 40% at lOkeV. Hence, the attractiveness of such a detector lies not only with its counting of individual photons but also its... 

Assume that the energy resolution of a scintillation counter is 9 percent and that of a semiconductor detector is 1 percent at energies around 900 keV. If a source emits gammas at 0.870 MeV and 0.980 MeV, can these peaks be resolved with a scintillator or a semiconductor detector ... 

Of all the scintillators existing in the market, the Nal crystal activated with thallium, NaI(Tl), is the most widely used for the detection of y-rays. Nal(Tl) scintillation counters are used when the energy resolution is not the most important factor of the measurement. They have the following advantages over Ge(Li) and Si(Li) detectors ... 

A disadvantage of all scintillation counters, in addition to their inferior energy resolution relative to Si(Li) and Ge(Li) detectors, is the necessary coupling to a photomultiplier tube. 

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