Main Glow Peak Research Articles

A hole trapped centre responsible for high temperature thermoluminescence in sodium borate glass

Thermoluminescence (TL) is now widely used for radiation dosimetry and B203 glass is no doubt one of the most advantageous materials for this purpose from the point of view that its effective atomic number is very close to that of human tissue. However, according to our previous investigation [1], pure B~O3 glass has fatal shortages: (a) The temperature of the main glow peak is too low to keep the radiation memory against preservation at room temperature (RT). (b) Pure B~O3 is very hygroscopic and cannot be used in wet air. These problems can be solved by the addition of alkali oxides into borate. According to Nasipuri et aL [2], sodium borate glasses containing less than about 33 mol% Na20 showed better characteristics for TL materials, though the effective atomic number slightly increased. Also though they mentioned that the TL output of the glasses is much weaker compared to commercial phosphors, and this shortage can be easily overcome by the addition of luminescent impurities, such as copper ions. Therefore, to explore the mechanisms of TL, or to find out the trapping centres responsible for-the TL in these base materials without impurities seems to be required. This is the reason why the following investigation on a borate glass containing sodium was undertaken. Samples were made from a mixture of reagent grade orthoboric acid (H3BO3) and the corresponding sodium carbonate calculated to form 80mo1% B203-20mol% NazO. They were melted at 1100 ° C for 1 bin a platinum crucible and cast into a brass mould and annealed at 250 ° C for 1 h to remove strain. Samples 7 mm x 7 mmx 2 mm were polished for TL measurement. Smaller samples of about 2 mmx 2 mm x 3 mm was used for ESR measurement. After the samples were irradiated by 7-rays up to 10 v R at RT, they were kept at RT for 60 days before the TL and ESR measurements. Fig. I shows the TL glow curves of a 7-irradiated Na~O (20 tool %)-B203 (80 mol %) glass measured with a heating rate of 20°Cmin -1. A real line indicates the whole glow curve which starts at about 350 K and finishes at about 515 K. The glow curve consists of at least three components. The dotted line shows the last component, which was obtained by the second heating after the sample was heated firstly up to 450 K followed by cooling to RT. The peak temperature, Tin, of this last component is 477.5 K, and the two half-maximum temperatures are T 1 = 452.0 K and T2 = 496.0 K, respectively. The activation energy for the last glow peak can be determined by using the Chen's formula [3]

UV excitation spectra of thermoluminescence in quartz

Thermoluminescence was excited at 300 K in natural quartz crystals by monochromatic ultraviolet radiation. The excitation spectra of the main glow peaks were measured in the spectral region 1150–2000 Å. A strong excitation maximum appeared for all measured glow peaks in the region of high absorbance on the long wavelength tail of a sharp reflectance peak at 1275 Å. Some glow peaks showed excitation maxima also at photon energies smaller than the absorption edge of the material. The dependence of the TL intensities on the dose of the exciting radiation was investigated for various glow peaks and excitation wavelengths. A sublinear dependence was recorded for some peaks by excitation at 1275 Å, while the same peaks showed a strictly linear dependence up to relatively high radiation doses, when excited at 1600 Å.

Thermoluminescence and optical absorption studies rubidium bromide doped with barium

AbstractThermoluminescence (TL) and optical absorption studies are made on RbBr:Ba2+. An absorption band due to Z1‐centres appears at 1.58 eV on F‐light bleaching subsequent to γ‐irradiation. A TL glow peak attributable to Z1‐centres is identified. TL emission under the main glow peak shows a broad emission at 2.65 eV with a shoulder at 1.95 eV. This 1.95 eV emission is attributed to VM2‐centres which give rise to an absorption band around 4.1 eV. A tentative energy band scheme is suggested explaining the various TL processes.

Thermoluminescence and optical absorption studies in γ‐irradiated KClxBr1–x mixed crystals

AbstractThermoluminescence (TL) and optical absorption measurements have been carried in γ‐irradiated KCl, KBr and various compositions of KClxBr1–x mixed crystals as a function of irradiation time and composition. The position of the main glow peak (high temperature peak) and F‐band position are found to vary non‐linearly with composition, showing a correlation between colour centers and TL. The TL peaks have been analysed by numerical fitting and the trap depths and frequency factors have been calculated for different compositions of the mixed crystals. The thermal ionisation energy of F‐centers has been calculated for the mixed crystals and it is found to vary non‐linearly with composition. The results obtained in mixed crystals have been discussed in terms of high disorder present in them.

Exoelectron Emission during the Thermal Annihilation of VK Centers in Pure and Cu-Doped NaCl

Thermally stimulated exoelectron emission (TSEE) in pure and Cu-doped NaCl crystals, which are cleaved in a clean high vacuum and X-irradiated at 77 K, is measured simultaneously with thermoluminescence (TL). The emission and absorption spectra, the decay of the TSEE and TL intensities and the change in the glow curves by the F-light stimulation, are also measured. The main TSEE glow peaks are ascribed to reaction of color centers as well as the TL glow peaks. Among them, the TSEE glow peak at about 160 K in these crystals is due to the diffusion of V K centers and the subsequent reaction of them with F' centers. The release-process of the electrons in this case may be interpreted in terms of a kind of Auger effect.

Thermally Stimulated Exoelectron Emission in KCl: Tl, KCl: Cu and Undoped KCl

Thermally stimulated exoelectron emission (TSEE) in KCl: Tl, KCl: Cu and undoped KCl cleaved in a clean high vacuum and X-rayed at liquid nitrogen temperature, is measured simultaneously with thermoluminescence (TL). On the basis of F-light stimulation experiments and close correlations between TSEE and TL, the main TSEE glow peaks are ascribed to the thermal annihilation of color centers. Among these, the TSEE glow peak at about 210 K in KCl: Tl and KCl: Cu is ascribed to the diffusion of VK centers and the subsequent reaction of these centers with electron-excess centers such as F' centers, while the TSEE glow peak at 207 K in undoped KCl is due to the thermal release of electrons from F' centers. The mechanism of the exoelectron emission due to the annihilation of VK centers may be interpreted in terms of a kind of Auger effect.

Thermoluminescence and recovery processes in pure and doped NaCl after 20 K irradiation

The thermoluminescence (TL) spectra after X-ray irradiation at 20 K have been investigated for pure as well as divalent cation doped NaCl. The F-centre decay has also been determined in pure and Ca and Mg doped NaCl for comparison purposes. A clear decrease in F-centre concentration appears to correlate with glow peaks at 44 and 50 K for pure and Ca-doped samples. Main glow peak appearing at 69 K is not associated to any appreciable F-centre decay step. Below liquid nitrogen temperature (LNT) all peaks show both σ and π exciton emission bands. Above LNT, the glow peaks for doped samples show the σ emission together with another band at 410 nm, whereas pure samples still present the intrinsic emission bands.

The Role of Cu+ in the Thermoluminescence of X-Irradiated NaCl

A detailed investigation of the thermoluminescence and the trapping centers related with the main glow peak centered at 327 K have been carried out. The luminescence center of the peak is confirmed to be the substitutional Cu+ ion, whereas those of the other peaks observed at higher temperatures are not related to it. The 327 K peak is ascribed to the electrons released from the F- centers, which are considered to be formed from the F centers by trapping the electrons released from Cu0 centers.

銅と銀で活性化したLi<sub>2</sub>B<sub>4</sub>O<sub>7</sub>TLD

Lithium borate (Li2B4O7) is known as one of the most promising thermoluminescence materials because of its low dependence on photon energy. A new phosphor, Li2B4O7 activated with copper and silver (0.02_??_Cu, 0.02_??_Ag), has been developed and found to have the following thermoluminescence characteristics.(1) Its thermoluminescence emission bands lie in the near ultraviolet region; a dominant peak appears at 368 mμ (by Cu) and another smaller one at 268 mμ.(2) The main thermoluminescence glow peak appears at 185°C (by Ag), and another smaller one at 110°C.(3) The thermoluminescence output detected by a widely used photomultiplier (1P21) is about 3 times larger than that of Li2B4O7: Mn, and the expoure response is linear in an exposure range from 10 mR to 300R.(4) Fading is less than 9% in 2 months.

Les phenomenes de relaxation non isotherme dans les copolymeres ethylene-acetate de vinyle—II. Thermoluminescence

Thermoluminescence glow curves displayed by ethylene-vinyl acetate copolymers after u.v. irradiation at low temperature have been compared to the depolarization thermocurrents (DTC) described in a previous publication, in order to establish a possible correlation between the thermal liberation of the trapped carriers and the intrinsic relaxation phenomena. The detailed analysis of these glow curves has been carried out, either by studying their spectral distributions between 300 and 650 nm, or by the systematic application of the classical method of partial glow and by a method of partial irradiation which consists in irradiating the sample isothermally at different temperatures in several experiments. Two main glow peaks corresponding to distinct spectral emission zones were found. These peaks occur in temperature zones similar to those of appearance of the DTC peaks; the latter were assigned to primary and secondary dipolar relaxations, i.e. α and β type relaxations, respectively. In addition, the β glow peak presents properties comparable with those of the DTC β peak and hence results probably from thermal untrapping, this untrapping being at least partly assisted by short range chain motions in the polymer. The α glow peak, on the other hand, shows little correspondence with the DTC peak and has essentially a superficial origin; it probably arises from two distinct traps associated with impurities or with interface between amorphous and crystalline regions rather than from the polymeric chains themselves.

The application of thermoluminescence theory to natural semiconducting diamond

The main thermoluminescence glow peak at ~ 250°K in natural semiconducting diamond has been analysed by methods proposed by several authors, using the model of the thermoluminescence process developed in the preceding paper as a guide. Kinetic equations appropriate to two conditions of recombination are developed and discussed in the light of the recombination processes in natural semiconducting diamond. A summary of several methods of analysis is given. The various methods are then applied in turn to the 250°K glow peak. The method of initial rise is shown to be appropriate to the model of trapping and recombination given in the preceding paper, and gives a value 0.35 ± 0.02 eV for the trap depth. Halperin and Braner's method for the trap depth is unsuitable owing to the high value of their correction term 2 kT m/ E, although their analysis suggests that the order of the kinetics changes from nearly 1st to nearly 2nd as the glow progresses. The methods of Grossweiner, Keating and Luschik apply only when 1st order processes are selected. An estimation of the trapping cross-section gives S T ~ 10 -20 cm 2.

Mixed radiation dosimetry with LiF (TLD-100)

The LiF dosemeter presents two main glow peaks, one at 210 degrees C and the other at a temperature between 250 and 300 degrees C. It is shown that the two-peak ratio depends on the type of incident radiation. This characteristic makes it possible to use LiF to measure doses in mixed fields (slow neutrons and electromagnetic radiations). The method is reliable for personal dosimetry.