Dopant Concentration and Effective Atomic Number of Copper-Doped Potassium Borate Glasses

Copper-doped (0.5mol%) and undoped potassium borate glasses have been prepared by the composition of (100-x)H 3 BO 3 + xK 2 CO 3 , where 10 ≤ x ≤ 30mol % by the traditional melting quenching method. The structural pattern of glasses with different composition has been identified by X-ray diffraction (XRD).The glow curves were analysed to determine various characterizations of the TLDs. Identification of the compositions and concentrations and effective atomic number of undoped and doped potassium borate glass was carried out using scanning electron microscope analysis (SEM). The dopant concentrations are found to be 0.25mol%, while Zeff are 11.42 and 10.48 for Cu-doped and undoped potassium borate glasses, respectively.


Introduction
Borate compounds have been widely studied due to their features as glass formers and also on account of being very advantageous materials for radiation dosimetry application as discussed elsewhere [1,2].The main advantages of these compounds are an effective atomic number which is very close to that of human tissue ( eff = 7.42), low cost, and easy preparation.This fact leads to use some borates ideal materials to develop medical and environmental dosimeter as discussed by Rao et al. [3].
A number of researchers investigated the thermoluminescence (TL) properties of lithium tetraborate: Li 2 B 4 O 7 (LTB) doped materials with different activators such as Mn as discussed by Annalakshmi et al. [4] and Cu as discussed by Corradi et al. [5].Kinetic parameters of some tissue equivalent TL materials were investigated "as discussed by Kitis et al. [6]".Calcium-doped and undoped borate glass system for TL dosimeter were studied by Rojas et al. [2].The electron paramagnetic resonance spectroscopy of the Mn 2+ and Cu 2+ centers in the glasses with Li 2 B 4 O 7 and KLiB 4 O 7 compositions was investigated by Padlyak et al. [7].TL and optical absorption properties of neodymiumdoped yttrium aluminoborate and yttrium calcium borate glasses were studied by Yoshimura et al. [8].Recently, we have investigated the high dose (range: 0.5-4.0Gy) photon irradiation response of K 2 B 4 O 7 , Cu system, aiming to develop new host materials for thermoluminescence dosimeter (TLD) [9].To date, to the best of our knowledge, no report has been published on dopant concentration, effective atomic number, and a TL study of copper-doped potassium borate glasses.

Sample Preparation.
The samples of potassium borate and Cu-doped potassium borate glass were prepared by a melt quenching technique.These five samples have been made by mixing different compositions of potassium carbonate (mole 10%, 15%, 20%, 25%, and 30%) and boric acid (mole 90%, 85%, 80%, 75%, and 70%) after they were weighed.The mass of each sample was measured using an electronic balance (PAG, Switzerland).The best copper-dopped potassium borate glasses was formed using potassium borate samples (mole 20% potassium carbonate and mole 80% boric acid) and doped with 0.5 mole% of pure copper (Cu).Before the melting process, the powders were mixed and homogenized by milling the powders for 30 minutes.Then, the samples (undoped) were melted in an alumina crucible in an electric furnace at a temperature of 1000 ∘ C for 30 minutes depending on composition until a clear homogenous melt was obtained.
The Cu-doped potassium borate samples were prepared by using high temperature furnace with a temperature of 1200 ∘ C for 30 minutes.Then the molten samples were poured onto a steel plate into another furnace to be annealed at a temperature of 300 ∘ C for 3 hours.This furnace was used with a different temperature for melting.The samples were left to be cooled inside the furnace until they reached room temperature to avoid thermal stress.

Annealing and Exposure to Radiation.
In the current investigation a Perspex sheet (tough transparent plastic material) contains 100 wells was covered by a thick black cover to avoid any light signal during transportation and storage or ultraviolet radiation from sunlight which can give rise to the TL signal.Finally the Perspex sheet which contains the Cu-doped and undoped potassium borate glass all together was placed on the beam axis at a depth of 10 cm in a solid phantom.The glass samples were exposed to 6 MV photon irradiation emitted from Linear Accelerator (LINAC) Primus MLC 3339 provided by the Department of Radiotherapy and Oncology, Hospital Sultan Ismail, Johor Bahru, Malaysia.The beam field size was set to 10 × 10 cm 2 and placed at the standard source surface distance (SSD) of 100 cm.The dose delivered by LINAC machine was 20 to 400 MU (Monitor Unit) using a constant dose rate of 200 MU/min.Each 50 MU dose is equivalent to 0.5 Gy and it took 15 seconds for complete exposure.The readout of the dosimeters was done 24 hours after irradiation.This period of time is very useful to eliminate the lower traps deliberately and also allows time for the lower energy thermoluminescence to decay away.The TL response was read out by using TLD Reader 4500 in Ibnu Sina Institute.The preheat temperature was 50 ∘ C for 10 seconds and the used readout temperature was 300 ∘ C for 33 seconds with a heating rate of 25 ∘ C S −1 and finally an annealing temperature of 300 ∘ C was applied for 10 seconds [9].Consequently, the characteristics of TLD were discussed and analyzed as follows.

Results and Discussions
3.1.X-Ray Diffraction (XRD) Analysis.In this experiment, XRD technique has been done for all the different compositions of samples previously prepared of undoped potassium borate.The measurements were carried out using Siemens Diffractometer D5000 system to analyze the structure of the samples whether amorphous or crystalline state.Two samples composed of 90% H 3 BO 3 (boric acid) + 10% K 2 CO 3 (potassium carbonate) and 85% H 3 BO 3 (boric acid) + 15% K 2 CO 3 (potassium carbonate) are firmly crystalline by XRD analysis.Figure 1 shows XRD pattern of polycrystalline by the composition of 90% boric acid and 10% potassium carbonates.On the other hand the XRD analysis showed that the other three samples which are composed of 80% boric acid and 20% potassium carbonate; 75% boric acid and 25% potassium carbonate; 70% boric acid and 30% potassium carbonate are glasses since there are broad peaks appearing on the spectra pattern as shown in Figure 2.

TL Glow Curve.
Thermoluminescence light emission which is known as the thermoluminescence glow curve is defined as the intensity of luminescence as a function of temperature, which is possible to exhibit several maxima.This glow curve varies with the mode of heating and heating temperature.The area under the curve represents the radiation energy deposited.Figures 3 and 4 present the glow curve for Cu-doped and undoped potassium borate glass.The red line which appears in the graph is the readout temperature which represents 300 ∘ C from the time-temperature profile set up for the TLD reader.It is clear that the glow curve of Cu-dopped potassium borate glasses is better than undoped potassium borate glasses.other contaminated material which may affect the glass samples.The result showed that all the glass samples were contaminated by either silica (SiO 2 ) or alumina (AL 2 O 3 ) or both except the third glass which was composed of 80% boric acid + 20% potassium carbonate.Table 1 shows the actual composition of the glass sample.The former glass samples were chosen to be doped with copper (Cu) in order to study its TLD characterization.SEM technique also has been done for the Cu-doped potassium borate glass to identify the elemental compositions of the sample and the concentration of each composition as shown in Table 2.   found to be 0.25 mol% as shown in Table 2.The effective atomic number of undoped glass was found to be 10.48 by the following formula:

Dopant Concentration in
where  1 ,  2 ,  3 , . . .  are the weight fraction contributions of each element in the glass depend on the total number of electrons in the mixture and   is the atomic number of the element-.The value of  adopted for photon purposes is 2.94.Moreover the Cu-doped potassium borate glass was found to have  eff = 11.42.This study indicates that the effective atomic numbers of Cu-doped and undoped potassium borate glasses were higher than the soft tissue which is 7.4.These results indicated that Cu-doped and undoped potassium borate glasses were not tissue equivalent.

Conclusions
Out of five different compositions, we have found three glass samples composed of 80% boric acid and 20% potassium carbonate; 75% boric acid and 25% potassium carbonate; 70% boric acid and 30% potassium carbonate by XRD technique.The glow curve of Cu-doped potassium borates glass is better than undoped sample.The effective atomic numbers are 11.42 and 10.48 for Cu-doped and undoped potassium borate glasses, respectively, which are higher than  eff in soft tissue 7.4.The Cu-doped potassium borate glass has been evaluated to have dopant concentration of 0.25 mol% and this dopant of Cu-doped glass has the capability of producing luminescence as well as good TL response on irradiation.

Figure 3 :Figure 4 :
Figure 3: The glow curve for the Cu-doped potassium borate glass following 6 MV photon irradiations.
: the atomic weight, : the atomic number of the element,   : the fractional weight, and At%: the atomic percentage.

Table 1 :
Identification of the compositions and concentrations of undoped potassium borate glass by SEM.
: the atomic weight, : the atomic number of the element, and   : the fractional weight.
Mol% and  eff .The SEM technique was used to determine the dopant concentration.The dopant concentration of copper (Cu) on the Cu-doped potassium borate glass was presented by At% which was

Table 2 :
Identification of the compositions and concentrations of Cu-doped potassium borate glass by SEM.