## 3 Results
### Thermoluminescence (TL) Characteristics of Irradiated Glasses
#### 3.2.1 Electron Accelerator, Pulse Duration 4 \(\upmu\)s  
At first, the native (undoped) and terbium-doped phosphate glass samples were irradiated using electron accelerator with pulse duration of 4 \(\upmu\)s. The range of radiation doses delivered to the samples was 1-30 kGy. The results of these experiments are depicted in Figure 2, where TL glow curves for each sample is presented for different radiation doses. The undoped phosphate glass already exhibits thermoluminescent properties. The irradiated samples of PPG glass show wide, complex TL signals with maximum emission at ca. 125 \({}^{\circ}\)C (cf. Figure 2a). For the higher radiation doses, it is also possible to identify higher temperature peak, which in TL curves is located at ca. 180 \({}^{\circ}\)C (Figure 2a). For all terbium-doped samples, special shutter was installed to decrease amount of light reaching PMT tube (ca. 100 times). As one can see in Figure 2b, 0.1% addition of terbium oxide increases the yield of thermoluminescence significantly in comparison with native phosphate glass. Higher contribution of terbium results in further increasing of TL intensity, which can be clearly observed in Figure 2c,d. For the glass samples doped with 0.5% of terbium oxide, the maximum of signals appears at ca. 225 \({}^{\circ}\)C (Figure 2b,c). Further increasing of terbium concentration in glass, to 3%, is followed by formation of additional signal at higher temperatures. This is clearly presented in Figure 2d, where one can observe low temperature signal at ca. 125 \({}^{\circ}\)C with easily recognized signal at 275 \({}^{\circ}\)C. Signal at 125 \({}^{\circ}\)C is common for all samples irradiated with different doses, whereas peak at 275 \({}^{\circ}\)C appears for radiation doses higher than 8 kGy. Moreover, for radiation dose of 31 kGy one can observed partial degradation of the low temperature signal. Additionally PPG_Tb01 and PPG_Tb30 shows an extensive change in the peak positions at higher radiation dose than in PPG_Tb05. Such effect may be due to the intensity of glass network modification process caused by introduction of terbium dopant. In case of low content of terbium, one deals only with slight modification of the glass network, whereas when increasing terbium oxide concentration one can expect more significant change of glass matrix structure and weakening of the glass-network-forming bonds. Such processes may lead to formation of additional trap centers, which can be more easily bleached when irradiated with higher doses. For the presented glow curves, one can also observe the slight distortions of the signal shape related to the increasing radiation dose. Nevertheless, the overall character of the presented glow curves remains similar for each glass sample. This effect may be related to the possible thermal and geometrical conditions during readout and/or imperfect grain  
Figure 1: XRD patterns (**a**) and DSC traces (**b**) of synthesized phosphate glasses. size distribution of the material used for detectors preparation, which was already observed previously [39]. As one can see in Figure 2, introduction of terbium ions into the glass matrix significantly modifies thermoluminescence signals, both in terms of their shapes and intensity. Thermoluminescence signals at 125 and 180 \({}^{\circ}\)C may have their origins from pure glass lattice. For doped glasses, one can observe additional signals at 225 and 275 \({}^{\circ}\)C that are clearly caused by presence of Tb. The more detailed explanation for these effects is presumably related to the facts--that aluminophosphate glasses contain PO\({}_{4}\) tetrahedra as well as AlO\({}_{4}\) units, which are able to induce point defects owing to the fact of mismatching in bonding as well as formation links with neighboring phosphorous elements. Due to the presence of point defects, the simultaneous occurrence of localized energy levels within the band gap is possible [40]. Rare earth metals, such as terbium, induce higher sensitivity in TL materials [21].