Ultraviolet sensitivity and photo-transferred thermoluminescence of the Harshaw and Panasonic used TLDs—a comparison

The intrinsic u.v. sensitivity and the photo-transferred thermoluminescence (PTTL) of three Harshaw (LiF:Mg, Ti, CaF₂:Dy and CaF₂:Tm) and two Panasonic (Li₂B₄O₇:Cu and CaSO₄:Tm) TL phosphors were evaluated. It was found that all the TLDs, except Li₂B₄O₇:Cu, have a low intrinsic u.v. sensitivity. The CaSO₄:Tm was found to possess PTTL, being one order of magnitude greater than the intrinsic u.v. and nearly independent of previous γ-irradiations ranging between 5 and 100 mgGy.     

High level γ-dosimetry using CaSO4: Dy phosphor with high dy-concentration

It has been observed that the thermoluminescent traps in CaSO₄:Dy phosphor with a high concentration of activator (2.0 mol% Dy) compared to that of normal samples (containing 0.05 mol% Dy) show a better stability and a lesser tendency towards saturation to γ-radiation. This effect has been observed for the main dosimetric peak (∼225°C) as well as for the high temperature peak (∼390°C). Thus by using 390°C TL peak in CaSO₄:Dy (2.0 mol%) we were able to make high level γ dose measurements in the range from 2 × 10² to 3 × 10⁶ Gy. The 390°C TL peak in CaSO₄:Dy (2.0 mol%) samples increases non-linearly with dose and does not show any tendency towards saturation at least up to 3 × 10⁶ Gy— the dose level studied. However, the corresponding high temperature peak in the normal samples (0.05 mol% Dy) shows saturation in its TL response above a γ-dose of 1.18 × 10⁶ Gy. In addition, a high temperature TL peak at 572°C which is only observed for the high activator concentration sample (as reported in our earlier work⁽¹¹⁾ increases non-linearly with dose and does not show saturation up to the γ-dose of 3 × 10⁶ Gy. Investigations on photo-transferred TL of high temperature peaks as a function of γ-dose were also carried out for both the types of samples.     

The gamma-ray response of clear polymethylmethacrylate dosimeter radix RN15®

Basic characteristics of different batches of Radix RN15® dosimeter, a commercially available undyed polymethylmethacrylate dosimeter, was studied for its application to process control of radiation sterilization. Radix has relatively small deviation of thickness, optical absorption spectrum, and optical density values before irradiation. The response curves, in terms of net optical density per unit thickness (ΔOD/mm) as a function of absorbed dose, D_PMMA, are nearly linear up to 15 kGy and become sublinear at higher doses. Scattering of dose response in 5 dosimeter replicates is ± 1% (1 σ). The dose-response slope at 25 kGy while held at irradiation temperatures in the range 0–60°C, relative to those under 25°C, increases with temperature up to 40°C, the maximum point, and decreases at higher temperatures. Over the temperature range of 10–50°C, the variation with temperature of evaluated dose derived from the calibration curve at 25°C is less than 5% when using a dose rate of 6 kGy/h. At lower dose rates (e.g. 0.7 kGy/h) the irradiation temperature dependence is negligible over this temperature range. The temperature dependence at 40 kGy is less severe than that at 25 kGy. The post-irradiation stability of dose response is less than 5% for more than 100 h after 25 kGy irradiation and storage at 0–35°C. The change in optical density of unirradiated dosimeters 3 years after manufacturing is negligible when the dosimeters are stored at controlled laboratory conditions of temperature (25°C) and relative humidity (40%). The 3-year-old dosimeters by irradiation to a dose of 25 kGy show about 2% lower response than that at 25 kGy at the beginning of the 3-year period.     

Some dosimetric parameters of MgB4O7:Dy sintered pellets and CaSO4:Dy Teflon discs—A comparative study

The effect of u.v. and sunlight exposures on MgB₄O₇:Dy and CaSO₄:Dy have been studied. Both phosphors are found to have intrinsic sensitivity to u.v. radiation and their γ ray induced TL fades faster if exposed to sunlight. The intrinsic TL response for an u.v. (253.7 nm) exposure of 1500 Jm⁻² was found equivalent to that caused by 1 and 5 mGy of ⁶⁰Co γ rays for MgB₄O₇:Dy and CaSO₄:Dy, respectively. The fading caused by 48000 lx of sunlight exposure was 99.7% and 56% in MgB₄O₇:Dy pellets and CaSO₄:Dy Teflon TLD discs respectively. MgB₄O₇:Dy pellets did not exhibit any added advantage over CaSO₄:Dy Teflon discs except its near tissue equivalence.     

The influence of temperature and humidity on the stability of the response of different thermoluminescent detectors

Fading results are presented for thermoluminescent detectors for temperatures of 20, 35 and 50°C and for relative humidities of 50 and 90% during storage periods of up to 30 days. The thermoluminescent detectors investigated were LiF:Mg,Ti(TLD-100 and TLD-700), CaF₂:Dy(TLD-200) and Li₂B₄O₇:Mn,Si. These detectors are very commonly used in personnel monitoring.     

Thermoluminescent response of single crystal Al2O3:Fe

Thermoluminescence characteristics of iron doped aluminum oxide (Al₂O₃:Fe) single crystals were studied. The glow curve of x- and γ-ray irradiated Al₂O₃:Fe single crystals while being heated up to 375°C consisted essentially of an intense isolated single peak at 193°C and small peaks at 250° and 285°C. But the study was carried out on 193°C peak because of the accuracy of measurements and the possibility of using it a thermoluminescence dosimeter. The trap depth and escape frequency factor were calculated to be 1.156 eV and 3.1 × 10¹¹ s⁻¹ respectively. Dose-response was investigated between dose ranges of 5 × 10² mR and 10⁴R for ¹³⁷Cs γ-rays. Dose-response was found to be linear in this range. The energy dependence was 5% between 33 and 662 keV when the thermoluminescent responses were normalized to ¹³⁷Cs γ-rays. It is suggested that Al₂O₃:Fe may be used as a γ radiation dosimeter in high dose environments such as oncology hospitals, radiobiological centers, nuclear reactors.     

Fading characteristics of an alanine-polystyrene dosimeter

Alanine dosimetry is useful for transfer dosimetry by long distance mailing, because of its stability. It has the advantage that the measurement of electron spin resonance (ESR) spectral signal is non-destructive to the dosimeter, with the promise that the method may supply archival dosimetry data, depending on the degree of post-irradiation stability of the signal. The effects of temperature during irradiation and storage on fading of the ESR signal were studied using an alanine dosimeter molded with polystyrene (alanine-PS dosimeter). This investigation covered a long range of storage time (up to 160 days) after irradiation to absorbed doses in the range 1 to 100 kGy, for application to transfer dosimetry between Japan and neighboring Asian countries.Dose response of an alanine-PS dosimeter depends on the temperature during irradiation. The same temperature coefficient of +0.24%/°C was measured at different dose levels of 1, 10 and 100 kGy administered at a constant dose rate of 7 kGy/h. Fading of the dose response was measured under storage at various temperatures (5–40°C). The fading curve generally has two phases with fast and slow fading rates. The response of an alanine dosimeter is relatively stable for doses of 1.4 and 14 kGy, when stored at temperatures below 25°C. However, the degree of fading was roughly 3 and 5% under a storage temperature of 40°C for 5 and 100 days, respectively, after irradiation to 14 kGy. The fading percentages at 100 kGy were 2 and 4% (after 5 days) and 6 and 15% (after 100 days) under the storage temperature of 25 and 40°C, respectively. The fading rates have a relatively small dependence on irradiation temperature. This is observed even when irradiation are made at high temperatures (60°C) and for the doses 100 kGy and above. The mechanism of decay of radicals is discussed to explain the fading characteristics of the two phases of fading. The alanine-PS dosimeter is useful for transfer standard dosimetry up to a dose level of 10 kGy when stored after irradiation at temperature below 40°C. However, consideration of temperature effects during and after irradiation is vital for accurate transfer dosimetry of high doses, especially in the southern Asian countries.     

Chromatin‐ and temperature‐dependent modulation of radiation‐induced double‐strand breaks

Purpose: To investigate the influence of chromatin organization and scavenging capacity in relation to irradiation temperature on the induction of double‐strand breaks (DSB) in structures derived from human diploid fibroblasts.

Materials and methods: Agarose plugs with different chromatin structures (intact cells±wortmannin, permeabilized cells with condensed chromatin, nucleoids and DNA) were prepared and irradiated with X‐rays at 2 or 37°C and lysed using two different lysis protocols (new ice‐cold lysis or standard lysis at 37°C). Induction of DSB was determined by constant‐field gel electrophoresis.

Results: The dose‐modifying factor (DMF_temp) for irradiation at 37 compared with 2°C was 0.92 in intact cells (i.e. more DSB induced at 2°C), but gradually increased to 1.5 in permeabilized cells, 2.2 in nucleoids and 2.6 in naked DNA, suggesting a role of chromatin organization for temperature modulation of DNA damage. In addition, DMF_temp was influenced by the presence of 0.1?M DMSO or 30?mM glutathione, but not by post‐irradiation temperature.

Conclusion: The protective effect of low temperature was correlated to the indirect effects of ionizing radiation and was not dependent on post‐irradiation temperature. Reasons for a dose modifying factor <1 in intact cells are discussed.     

Effects of temperature,relative humidity,and dose rate on the sensitivity of cellulose triacetate dosimeters to electrons and γ-rays

Cellulose triacetate (CTA) films are useful dosimeters for radiation processing with γ rays and electron beams, and are usually analyzed by u.v. spectrophotometry. The radiation sensitivity of CTA film material increases linearly with both temperature (around room temperature) and relative humidity (between 20 and 80% r.h.) when irradiated at lower dose rates typical for ⁶⁰Co γ-ray irradiation (< 100 kGy h⁻¹). On the other hand, the response depends neither on temperature up to 45°C nor on relative humidity of the surrounding atmosphere during irradiation at high dose rates above 1 MGy h⁻¹, which are typical for electron irradiation. In fact, the extent of temperature dependence and humidity of response are markedly influenced by dose rate. There are also appreciable influences of temperature and relative humidity changes during the post-irradiation storage, but in this case there is no difference of storage effect for different dose levels. The thickness of CTA film influences the dose-rate dependence in the range between 10 kGy h⁻¹ and 1 MGy h⁻¹, but not the dependence on temperature during irradiation. Other environmental influences on the sensitivity were also examined, for the purpose of evaluating systematic uncertainties due to these effects in practical dosimetry.     

Characterization of the glow-peak fading properties of six common thermoluminescent materials

The pre-irradiation and post-irradiation fading rates of the thermoluminescent glow peaks of six commonly used thermoluminescent dosimeters under controlled environmental conditions over approximately 30 d are examined. Glow peaks were fit to the first-order kinetics model using a computerized glow curve deconvolution program. Dosimeters studied were LiF:Mg,Ti, CaF₂:Dy, CaF₂:Tm, CaF₂:Mn, LiF:Mg,Cu,P, and CaSO₄:Dy. LiF:Mg,Ti and LiF:Mg,Cu,P experienced significant pre-irradiation fading. All types except CaF₂:Mn experienced post-irradiation fading. Ratios of glow-peak areas were fit to exponential decay functions when possible.     

Dose control in the semi-industrial irradiation plant at Ezeiza Atomic Center

High-dose dosimetry is carried out at Ezeiza Atomic Center (CAE) on a routine basis, within the absorbed dose range 10²–10⁵ Gy using potassium nitrate dosimeters (Dorda and Muñoz, 1985). The reference dosimeter is Fricke and Super Fricke. The next inauguration of a private irradiation plant and the increasing interest for a new technology in the industry led us to use a dosimeter easy to be read, without need for wet chemical analysis: the alanine dosimeter (Regulla and Deffner, 1982). Under the influence of ionizing radiation, the alanine in the crystalline state forms stable paramagnetic free radicals. The radical concentration of irradiated alanine, which is proportional to the absorbed dose, can be measured using electron spin resonance (ESR) spectroscopy. The pellets are made of 90% alanine and 10% paraffin. The procedure for mixing is not simple: temperature control is used to get an homogenous mass. The dose evaluation is performed for the ESR signal by measuring the maximum peak-to-peak amplitude. Intercomparison studies were made between the alanine and potassium nitrate dosimeter with good results. The relative standard deviation of our alanine dosimeter at doses of 25 and 32 kGy and 25°C temperature is 4%.     

Effect of different climatic conditions on the performance of CaSO4: Dy. thermoluminescent dosimeters

Performance of Teflon embedded thermoluminescent CaSO₄: Dy discs manufactured by the Division of Radiological Protection, Bhabha Atomic Research centre, Bombay has been studied under extreme climatic conditions prevailing in India to obtain the maximum effect of the variables; in actual practice the effect will be less than that revealed during experiments. Significant fading to the extent of 20% has been observed under ambient storage temperature range of 25°C to 34°C and 99% relative humidity after one month from the date of radiation exposure.     

Thermoluminescent dosimeters for exposure assessment in gamma or x radiation fields with unknown spectral distribution

The determination of the effective energy of a radiation field using the energy dependence of the response ratio of two dosimeters with different energy dependences is called the “Tandem Method”. Having in view the choice of the best pair of dosimeters to be used, the energy response characteristics of LiF: Mg, Ti; CaSO₄: Dy; CaF₂: Dy and CaF₂: Mn thermoluminescent (TL) dosimeters were studied. Two different physical forms of TL dosimeters were investigated: hot pressed chips and Teflon disc dosimeters. The calibration factors were obtained for the energy of ⁶⁰Co γ rays and their energy dependence, normalized to ⁶⁰Co γ-radiation, was determined using spectral width as a parameter. Tandem systems formed by all TL dosimeters evaluated were compared. It was concuded that the Tandem DCaSO₄: Dy−0.4/ LiF: Mg, Ti (TLD-100) determines the effective energy with a maximum uncertainty of only 10 keV and permits the assessment of the energy correction factor for the TLD-100 with a precision of better than 1.7% for the spectral distribution studied in the effective energy range from 30 to 100 keV.     

The response of the thermoluminescent dosimeter CaF2:Tm to protons in the energy range 15–30 MeV

This study describes the response of the thermoluminescent dosimeter CaF₂:Tm to protons from a compact cyclotron with energies between 15 and 30 MeV. Glow curve analysis indicates that the response of CaF₂:Tm to protons depends on proton energy and proton current.     

In-phantom dosimetry using CaF2: Tm (TLD-300) ribbons

Parameters of calibrating CaF₂ : Tm for in-phantom dosimetry of therapeutically used fast neutron and ⁶⁰Co γ-ray beams have been studied. For ⁶⁰Co γ-ray beams the over-response, outside the main beam and at depths in phantom for large fields of irradiations is significant, and is higher for its 240°C glow peak than for its 150°C peak. The difference in the photon energy dependences of the two peaks of CaF₂ : Tm (Z_eff = 16.3), which is responsible for the above effect, is discussed. For therapeutically used cyclotron-produced fast neutron beams, the γ-ray absorbed dose component from photons of energy less than 200 keV is negligible.     

Response of TL materials to diagnostic radiology X radiation beams

The main objective of this study was to carry out a direct performance comparison among some known types of TLDs—three types of CaSO₄:Dy pellets, sintered Al₂O₃ pellets, LiF:Mg,Ti (Harshaw TLD-100), CaF₂:Dy (Harshaw TLD-200) and CaF₂:Mn (Harshaw TLD-400)—in the energy and dose ranges of diagnostic radiology beams. Several dosimetric characteristics were evaluated, such as reproducibility, sensitivity, calibration curves, lower dose limits and energy dependence.     

X-ray excited optical luminescence studies of rare earth activated thermoluminescent phosphors

XEOL spectra of CaSO₄:Dy, MgF₂:Dy, and CaO:Dy are typical of Dy³⁺ and similar to that of TL emission spectra. However, the studies fail to reveal the charge conversion state of the RE ion on irradiation. Minor differences, as regards the intensity ratio of various lines are observed depending upon the host matrix and the radiation history.     

Preparation of CaSO4:Dy by precipitation method to gamma radiation dosimetry

This paper presents the results of the preparation and characterization of dysprosium-doped calcium sulfate (CaSO₄:Dy) phosphor, which was obtained by homogeneous precipitation from calcium acetate Ca(CH₃COO^?)₂. Structural and morphological characteristics were studied using a scanning electronic microscope (SEM). The structure of all compounds was determined by X-ray diffraction method too. Thermoluminescence (TL) emission properties of CaSO₄:Dy under gamma radiation effects were studied. This phosphor powder presented a TL glow curve with two peaks (Tmax) centered at around of 180 and 300 °C, respectively. The TL response of CaSO₄:Dy as a function of gamma absorbed dose was linear in a wide range. Both emission and excitation spectra were also obtained. Results showed that this new preparation method of CaSO₄:Dy TL phosphor is less expensive, cleaner and safer than the conventional preparation method.     

Thermal stability of 240Pu alpha damage trails in CR-39 polymeric detectors sensitized by ultraviolet irradiations

Environmental conditions affect the track registration and revelation response of the solid state nuclear track detectors. In the present work, the annealing of the tracks both with and without u.v. treatment has been studied. Bulk etching rate (V_g), evolution of the diameters of the ²⁴⁰Pu α damage trails and optical transmission characteristics have been investigated in CR-39 polycarbonate detectors. It has been found that half hour annealing at 140°C results in an abrupt increase in the diameters of α tracks. Prior to annealing, ultraviolet treatment to the detectors reduces the track dimensions around the critical annealing temperature of 140°C.