Influence of the Mechanical Sample Treatment on the Thermally Stimulated Exoelectron Emission in Aspect of the Application for Sample Dating

Transcription

1 Applied Radiation and Isotopes 50 (1999) Influence of the Mechanical Sample Treatment on the Thermally Stimulated Exoelectron Emission in Aspect of the Application for Sample Dating Andrzej Zastawny and Jan Białoń Silesian Technical University, Institute of Physics, Gliwice, Poland Abstract The examination was focused on a typical, contemporarily produced ceramics, irradiated by the beta particles 90 Sr- 90 Y source. According to measurements, the mechanical treatment of the sample in the form of abrading and washing in alcohol did not affect the glow curve of the TSEE above the temperature 130 o C. Because the peaks of the TSEE, witch can be taken full advantage for the dating must lie above 300 o C, the mechanical and washing preparing of the samples should not affect the measurements. Introduction The exoelectron emission is well known phenomenon which has been widely investigated Robertson (1981), Scharmann (1982). The aim of this work is to examine if the sample preparing affects the phenomenon of TSE, because it is precondition for application of the TSEE to sample dating through analogy to theromoluminiscence method. Experimental As material for examination, the soft part (not glazing) of a typical tile produced in a neighbouring factory, was chosen. Its density was 1.75 g/cm 3. In analysis of the ceramic composition, made by means of the chemical and X-ray crystal analysis, supported by polarisation microscope method, gives the results presented in Tab.1. Samples were in the shape of disks 15 mm in diameter and from 1.5 to 1.8 mm thick.

2 Tab.1. The chemical and phase composition (in % of g/g ) of the examined ceramics. SiO 2 Al 2 O anorthite 54.8 CaO Fe 2 O quartz 22.0 MgO K 2 O glaze 13.4 H 2 O Na 2 O orthoclase 9.8 Exoelectrons were registered by a needle gas flow proportional counter Zastawny (1986), whose draft, with the heater, is shown in Figure 1. A mixture of propane -butane was used as counter gas. The thermoelement measuring the temperature was fixed at the contact of the heater and steel stable of the sample. In special calibration measurements the proportion between the samples and thermoelement temperature was established at about 0.5. Absolute error of the sample temperature measurements was estimated as less than 10 degrees, while relative error as about 4 degrees. Fig. 1. Drawing of the flow gas needle counter, with heater. 2

3 The samples were irradiated by the 90 Sr- 90 Y source delivering about 0.7 Gy/min. Values of the irradiation doses were controlled by measuring of the irradiation time (from 25 to 200 minutes), so the relative values of the doses were established with good accuracy, but the error of the absolute values of the doses was estimated as about 15 %. Considering the mean energy of the beta particles, irradiation of the sample was approximately homogeneously in layer of 200 µm thickness. Graininess of the phase texture was from 10 to 30 µm. Fig. 2. Examples of the glow curves (two from 20, two from 140 o C, of the sample irradiated to 34.8 Gy. The sample was heated from room temperature to about 244 o C, at the rate of 3.7 C/minute. The exoelectrons were counted at 1 minute intervals. The examples of a glow curves obtained are shown in Figure 2. Obviously, after heating of the irradiated sample, the next heating was made and a background glow curve was obtained - Figure 3. By subtracting the second curve from the first, the net effect was prepared. Considering the graininess of the samples phase texture in each measuring series was made with one sample and one surface prepared, besides a series for examining of the influence of surface preparing. 3

4 Fig. 3. Examples of the glow curves of the second heating, sample irradiated by different doses. Results Examples of the measured glow curves, presented in Figure 2 and Figure 3 show the reproducibility of the examined TSSE. The glow curves up to 130 o C are unreproducible, dependent upon the non identified agents. Attention has been focused on the reproducible, distinct peak between temperatures 140 and 220 o C. The examined peak seems to correspond with the glow curves of the Al 2 O 3 phase Akselrod (1991), Choon Ho Lee (1987), Fitting Von (1978), Iacconi (1993) In order to check if actually the electrons but not photons are registered, measurements, with a sample covered by a thin layer of mica, were made. The results, presented in Figure 4, confirm that TSEE but not TSL occurs. 4

5 Fig. 4. The glow curves of a sample covered by mica of the thickness 0.01 mm. The square points denote the mean background from results presented in Figure 3. The net glow curves for different radiation doses are shown in Figure 5. The total counts under peak were accepted as a gauge of the TSEE yield. The yields calculated in this way, versus irradiation dose, are presented in Figure 6. As it is seen, the level of the saturation effect in this material is rather low. Fig. 5. The glow curves of the TSEE net effect for different irradiation doses. Fig. 6. Calculated yield and specific yield of the TSEE counts under peak, versus the irradiation dose. 5

6 The main question was the influence of the mechanical treatment of the sample surface on the TSEE effect. Results of such an investigation are shown in Figure 7 and Figure 8. Always after abrading, the samples were washed in alcohol. As it is seen from both figures, in the region of the peak, the mechanical treatment in the form of abrading did not generate additional exoelectrons and also did not influence yield of the TSEE. Fig. 7. The glow curve of the non irradiated sample after abrading with paper No 250 and background glow curve. Fig. 8. The glow curves of the sample irradiated in the same doses, first abraded, then non abraded and abraded again. 6

7 Acknowledgement This work was performed within the framework of the Statute Researches, financed by the Committee of Scientific Researches of the Polish Government. References Akselrod M.S. and Kortov V.S. (1991) Combined aluminiuum oxide TSEE-TL detectors for skin. Radiation Protection Dosimetry, 39(1-3) Choon Ho Lee, Ha Yong Du, Pung Gil Lee, Kyung Nam Chon, Byung Ho Kim (1987) Thermally stimulated luminescence and exoelectron emission from X-ray irradiated Al 2 O 3 single crystal. New Physics (Korean Physical Society), 27(6) Fitting Von, H.J., Glaefeke, H., Wild, W. (1978) Energy and angular analysis of exoelectrons. Experimentelle Techni der Physik, 26(3), Iacconi P., Petel F., Lapraz D., Bindi R. (1993) Thermostimulated exoelectronic emission and thermoluminescence of various alpha-al 2 O 3 samples. Physica Status Solidi A, 139(2) Robertson, A.J.B. (1981) Exoelectron emission from solids. Int. J. Electronics 51(5) Scharmann, A. and Kriegseis, W. (1982) Exoelectron emission. In Microscopic aspect of adhesion and lubrication, eds Georges J. M., Elsevier Scientific Publishing Company, Amsterdam, Zastawny, A. and Rabsztyn, B. (1986) A double needle gas counter arrangement for measurements of low beta radioactivity solid emitters. Nucl. Instrum. Methods Phys. Res. B