Scintillators Nal

As in the proportional counter, the pulses produced in a scintillation counter have sizes proportional to the energy of the x-ray quanta absorbed. But the pulse size corresponding to a certain quantum energy is much less sharply defined, as shown in Fig. 7-19 for typical proportional and scintillation (Nal Tl) counters. As a result, it is more difficult to discriminate, with a scintillation counter, between x-ray quanta of different wavelengths (energies) on the basis of pulse size. 

The concrete block walls of the cell housing the generator tube and associated components are 1.7 meters thick. The facility also includes a Kaman Nuclear dual-axis rotator assembly for simultaneous transfer and irradiation of reference and unknown sample, and a dual Na iodide (Nal) scintillation detector system designed for simultaneous counting of activated samples. Automatic transfer of samples between load station to the rotator assembly in front of the target, and back to the count station, is accomplished pneumatically by means of two 1.2cm (i.d.) polyethylene tubes which loop down at both ends of the system and pass underneath the concrete shielding thru a pipe duct. Total one-way traverse distance for the samples is approx 9 meters. In performing quantitative analysis for a particular element by neutron activation, the usual approach is to compare the count rates of an unknown sample with that of a reference standard of known compn irradiated under identical conditions... 

A sealed-tube neutron generator, utilizing the deuterium-tritium reaction is the source of fast (14 MeV) neutrons, and a 8 x 3 1 Nal scintillation detector, with three optically coupled photomultipliers, is used to measure the >ray signal... 

Some properties of the detectors most commonly used for transmission experiments are summarized in Table 3.2. Alternative counters are scintillation detectors based on Nal or plastic material that is attached to a photomultiplier, and solid-state detectors using silicon- or germanium-diodes. 

The sources most commonly used so far consisted of sintered disks containing about 100 mg ZnO enriched with 90% Zn. The disks were irradiated with 12 MeV deuterons or 30 MeV He particles, to yield the 78 h activity of Ga, and then annealed by heating in oxygen to 700-1,000 K for about 12 h and cooling down slowly (about 50 K h ) to room temperature. A Nal scintillation counter, 2-3 mm thick, is suitable for the detection of the 93 keV y-rays. Because of the relatively high transition energy, both source and absorber are generally kept at liquid helium temperature. 

The 99 keV y-quanta are usually counted with Nal(Tl) scintillation counters or Ge(Li) diodes in transmission geometry. A Cd absorber should be used to reduce the background counting rate of the K X-rays and to avoid pile-up of the different X- and y-rays (cf. Fig. 4 in [325]). 

Figure 9.3 The whole-body counter of University Medical Centre, Utrecht, The Netherlands. The counter has a mobile shadow shield with two Nal(Tl) scintillation detectors (4x6 in) placed at opposite sites of the subject. The lead shielding is 100 cm long with a diameter of 90 cm. The scanner moves on rails over a distance of 240 cm with an adjustable speed. Extreme variations in geometry yield practically the same value for 59Fe activity. The equipment can be used for measurements in man and small animals.

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 equipment used in gamma spectroscopy includes a detector, a pulse sorter (multichannel analyzer), and associated amplifiers and data readout devices. The detector is normally a sodium iodide (Nal) scintillation counter. Figure 27 shows a block diagram of a gamma spectrometer. 

A gamma spectrometer uses a scintillation counter, normally Nal. 

Working solutions (1 litre) which were 10 7 mol/1 in one of the elements to be studied were prepared by appropriate addition of the radioactive stock solutions to pH-adjusted artificial seawater. After the pH had been checked, 100 ml portions were transferred to the bottles to be tested. The filled bottles were shaken continuously and gently in an upright position, at room temperature and in the dark. At certain time intervals, ranging from 1 min to 28 d, 0.1 ml aliquots were taken. These aliquots were counted in a 3 x 3 in Nal (TI) well-type scintillation detector, coupled to a single-channel analyser with a window setting corresponding to the rays to be measured. 

The hematite with adsorbed Co-57 or Sb-119 along with the solution was subjected to emission Mossbauer measurement at 24 1°C with the experimental setup shown in Figure 2. The absorber, Fe-57-enriched potassium ferrocyanide (0.5 mg Fe-57/cm2) or barium stannate (0.9 mg Sn-119/cm2), was driven by a Hanger 700-series Mossbauer spectrometer connected to a Tracor-Northern TN-7200 multi-channel analyzer. The Mosssbauer gamma-rays of Co-57 and Sb-119 were detected respectively with a Kr(+3% carbon dioxide)-filled proportional counter and with a 2 mm-thick Nal(Tl) scintillation counter through 65 pm-thick Pd critical absorber for Sn K X-rays. The integral errors in the relative velocity were estimated to be of the order of 0.05 mm/s by repeated calibration measurements using standard absorbers. 

Unlike the problems associated with measuring alpha and beta activity in water in the field, the properties of gamma radiation allow it to be measured relatively well in water samples in the field. The standard instrumentation used to measure gamma radiation from water samples in the field is a sodium iodide (Nal) scintillator. 

Breakthrough. Eluate radionuclidic purity is determined by Nal scintillation spectrometry on 50 ml of eluate. Samples must be held at least one hour before measurement to allow full decay of Rb-82. To improve sensitivity of measurement, the most prominent 511+514 keV peak is counted. Computations are based upon comparison with an aliquot of Sr-82+Sr-85 solution used to prepare the generator.. Data are expressed in units of yCi Sr-82/ml of eluate/ mCi Rb-82 at end of elution. 

The distributions of americium on the fissure surfaces were then quantitatively determined by scanning the face of each fissure with a Nal scintillation crystal through a 0.3 cm slit in lead shielding. The 59 keV gamma ray emitted by Am was monitored. Histograms of the americium distributions on the fissure surfaces were produced and are presented in Figures 5, 7, and 9. 

A Nal well-type scintillation was used to count they emission... 

The sensor is a crystal of Nal(TI) that transforms the 7 photon into luminescence whose intensity is proportional to the energy of the photon (assuming that the 7 photon is entirely absorbed by the crystal). The principle is similar to that of liquid scintillators used to measure 14C. If a Ge(Li) crystal is used, it behaves like the support gas in a Geiger-Muller tube. 

Figure 1. Two spectra from the same air-filter sample (presumed Chinese test, Jan. 16,1968). Upper spectrum obtained with a 4 X 4 inch Nal(Tl) scintillator system. Lower spectrum obtained with our 8-cm.3 planar Ge(Li) detector...

---