Characterization of the Risø TL/OSL DA-20 reader for application in TL dosimetry

The automated Risø TL/OSL Reader Model DA-20, often used in dating and retrospective dosimetry, was examined for possible applications in thermoluminescent dosimetry related to radiation protection. The investigations revealed that performance of the DA-20 is comparable with that of the Harshaw 3500 manual reader, which was used as a reference instrument. All studied parameters, like stability, reproducibility, low-dose measuring capabilities, were at the same level or only somewhat inferior to those of Harshaw 3500. In particular, using the highly-sensitive LiF:Mg,Cu,P dosimeters, it is possible to measure doses at the microgray level.The DA-20 reader possesses built-in alpha and beta sources, which cause an increased radiation background. At positions just under the closed sources the dose-rate rises to about 50 μGy/h. When the ⁹⁰Sr/⁹⁰Y source is open a quite high dose-rate of 100 mGy/h was measured at the position adjacent to the one being irradiated. Additionally the TLD response to the background radiation significantly depends on the TLD type (atomic number), as the radiation leaking through shielding is composed of low-energy photons. The dose-rate under the closed ²⁴¹Am source was over 10 times higher, when measured with CaF₂ dosimeters, than with LiF.In spite of these problems, the DA-20 reader due to its good stability, reproducibility and sensitivity, combined with such obvious benefits as a 48-dosimeter carousel, temperatures up to 700 °C and full automatics of measurements control, encourages the opinion that the DA-20 Risø reader can be successfully used in practical dosimetric measurements.     

New luminescence measurement facilities in retrospective dosimetry

This paper gives a review of recent developments in luminescence measurement facilities on the Risø TL/OSL reader including radio-luminescence (RL), exo-electron and violet stimulation attachments, and a method for characterising and if necessary correcting for beta irradiation source non-uniformity.We first describe improvements to the existing RL option to allow near infra-red detection (NIR) during irradiation by the built-in ⁹⁰Sr/⁹⁰Y beta source. The RL optical signal is collected by a liquid light guide through an F34-901 interference filter and detection is based on a dedicated thermoelectrically cooled NIR sensitive PMT (detection window peak at 855 nm, FWHM 27 nm). Software and electronics have been modified to allow standard TL and OSL measurements in the same sequence as RL measurements. Together with a new bleaching source based on a high-power UV LED (395 nm; 700 mW/cm²), this facility has been used to measure natural doses in feldspar using the decaying NIR RL signal.Secondly, we present a method for mapping radiation field of the built-in ⁹⁰Sr/⁹⁰Y β-source and estimating grain-location specific dose-rates. This is important for the accuracy of single grain results, when radiation field is spatially non-uniform across the sample area. We document the effect of this correction method and further investigate on the effect of lifting the source to achieve a better dose-rate uniformity.Finally we summarise two recently-developed novel facilities to help investigate (i) the time scales involved in OSL processes (time-resolved exo-electron detection) and (ii) extending the age range (violet stimulated signals from deep quartz OSL traps).     

Impact of measurement approach on the quality of gamma scanning density profile in a tray type lab-scale column

This article presents a study for investigating impact of the measurement approach on the quality of gamma scanning density profile in tray type columns using experimental and computational evaluations. Experimental density profiles from the total and the photopeak count measurements, as two approaches in gamma ray column scanning technique, has been compared with the computational density profile from Monte Carlo simulation results. We used a laboratory distillation column of 51 cm diameter as an illustrative example for this investigation. ¹³⁷Cs was used as a gamma ray source with the activity of 296 MBq (8 mCi), with a NaI(Tl) detector. MCNP4C Monte Carlo code has been used for simulations. The quality of the density profile in the photopeak count approach is relatively within 155–204% better than that of the total count approach for experimental results. The same comparison for simulation results leads to a relative difference within 100–135% for the density profile.     

Characterisation of 32P beta source for external radiation protection

Custom-made design of ³²P patch sources are used in brachytherapy applications. Use of this source requires external radiation protection. This implies measurement of absorbed dose rate to tissue at a depth of 0.07 mm. Towards this goal, 2.75 mCi ³²P patch source was locally developed. Characterization of this source has been carried out by measuring source parameters such as uniformity in the activity distribution and beam uniformity. The characterization also includes output measurements in terms of absorbed dose rate to air using an extrapolation chamber at 11, 20 and 30 cm from the source. Various correction factors which are dependent on the cavity length as well as independent of the cavity length were also determined in this study. The backscatter correction and Bragg–Grapy stopping power ratio were calculated using the Monte Carlo techniques. Using these correction factors and the measured absorbed dose rate to air, absorbed dose rate to tissue at a depth of 0.07 mm was determined. The study also includes measurements of H_p(0.07) and H_p(10) at different source-to-detector distances using an electronic pocket dosimeter.     

Investigation of a fibre-coupled beryllium oxide (BeO) ceramic luminescence dosimetry system

The purpose of this study is to investigate the potential use of a beryllium oxide (BeO) ceramic as a radioluminescence (RL) and optically stimulated luminescence (OSL) probe material for fibre-coupled luminescence dosimetry. A portable dosimetry system, named RL/OSL BeO FOD was developed, consisting of a 1 mm diameter, 1 mm long BeO ceramic cylinder coupled to a silica/silica optical fibre. The reader measures the RL signal and also uses a 450 nm laser diode to stimulate the BeO ceramic. A second background optical fibre is used to remove the stem effect. The RL/OSL BeO FOD was characterised in a solid water phantom, using a 6 MV x-ray beam. The RL was found to be reproducible and have a linear response to doses ranging from 30 cGy–15 Gy and dose rates from 100 cGy/min – 600 cGy/min. The OSL response was linear to doses of 10 Gy, becoming supralinear at higher doses. Measured percentage depth curves using the RL/OSL BeO FOD agreed with those measured using an IC15 ion chamber to within 5%, beyond the build up region. It was also found that the RL from BeO ceramic is unaffected by the delivered dose to the probe and hence, it remains constant for a given dose-rate. The insensitivity of the RL to accumulated dose makes BeO ceramic potentially capable of accurate dose-rate measurements without any corrections for the accumulated dose. This study demonstrates the feasibility of BeO ceramic as a versatile fibre-coupled luminescence dosimeter probe.     

The use of the TL and OSL phenomena for determination of absorbed dose rates of 90Sr + 90Y sources by a postal method

International recommendations establish that ⁹⁰Sr + ⁹⁰Y clinical applicators have to be calibrated in order to determine the absorbed dose rates in the case of the sources that do not have original calibration certificates, or to update the absorbed dose rates presented in the source certificates. Following these recommendations, a postal dosimetric system was developed to calibrate clinical applicators using two luminescent techniques: thermoluminescence (TL) and optically stimulated luminescence (OSL). In this work, Al₂O₃:C commercial detectors were characterized and their TL and OSL responses were analyzed. The results showed the efficiency and the optimal behavior of this material in beta radiation beams. After characterization, the system was sent to the Federal University of Sergipe (UFS), Brazil, for calibration of five ⁹⁰Sr + ⁹⁰Y clinical applicators, where the detectors were irradiated and returned to IPEN, for their evaluation and determination of the absorbed dose rates. A comparison between these absorbed dose rates and those adopted by the UFS as original was made; the differences obtained were within those of other studies, and they demonstrated the usefulness of the system.     

Study on the Separation of Carrier-Free Yttrium-90 from Strontium-90

The separation of carrier-free ⁹⁰Y from ⁹⁰Sr by solvent extraction with di-(2-ethylhexyl) phosphoric acid (HDEHP) in dodecane has been investigated in this study. The extraction equilibrium time, the effect of temperature, concentration of extractant, and hydrochloric acid concentration on this extraction system were examined. Based on the studies, the chemical procedure for the separation of carrier-free ⁹⁰ Y from its parent ⁹⁰Sr have been established. The chemical yield of ⁹⁰Y is about 80%. Meanwhile, the ⁹⁰Sr impurity is less than 1×10^?6% and the trace of extractant presented in the final product can be removed by fumed with HNO₃. Consequently, the preparation of millicurie of ⁹⁰Y is quite satisfactory for the adsorption in microsphere resin for radiotherapy applications.     

Performance parameters and uncertainty of the method for assessment of Sr concentration in small powder samples using α-Al2O3:C beta detectors

Non-destructive detection of very low concentrations of ⁹⁰Sr (about 0.4 Bq g⁻¹) inside powdered samples with masses below 200 mg (such as tooth enamel prepared for EPR measurements) is not a trivial task. Most of the conventional measurement techniques require a special chemical treatment or an enrichment process. Thin-layer α-Al₂O₃:C passive luminescence beta detectors have been successfully used for measuring dose rates due to beta decay of ⁹⁰Sr inside small samples. In this paper, a new refinement is introduced for the assessment of ⁹⁰Sr concentration in dental tissue using thin-layer α-Al₂O₃:C passive luminescence beta detectors. The performance parameters of passive luminescence beta detection (such as detection and quantification limits) have been evaluated using statistical analysis of the experimental results. The sources of uncertainty have been analyzed and the total uncertainty calculated using Monte Carlo simulations. The results of TL passive beta detection for measurement of ⁹⁰Sr concentrations are shown to be in good agreement with those obtained using low-level beta counting.     

Synthesis of titanium boride nanoparticles and fabrication of flexible material for radiation shielding

A numerical simulation for a radio frequency (RF) thermal plasma torch was carried out to identify the temperature and velocity distributions and determine the optimal design of a plasma system based on the coil turn and torch inner diameter parameters. Then, the optimized conditions of five coil turns and a torch inner diameter of 64 mm were applied to synthesize titanium boride nanoparticles. The major crystal structure of the synthesized titanium boride nanoparticles was TiB₂, with TiB as a minor phase and an average particle size of 42 nm. Subsequently, the gamma-ray shielding performance was analyzed using synthesized titanium boride nanoparticles. Flexible shielding materials were fabricated using a hydrogel to load the synthesized nanoparticles. The attenuation coefficient of the titanium boride nanoparticle flexible material was 0.238 cm⁻¹, and the half-value layer was 2.91 cm.     

2<Emphasis Type="Italic">π</Emphasis> proportional counting chamber for large-area-coated <Emphasis Type="Italic">β</Emphasis> sources

Detection system for measuring absolute emission rate from large-area-coated β sources has been indigenously developed. The system consists of a multiwire-based proportional counter with gas flow and a source mounted within the sensitive volume of the detector. Design of the counter enables efficient counting of emissions in 2π solid angle. A provision is made for change of the source and immediate measurement of source activity. These sources are used to calibrate the efficiency of contamination monitors at radiological facilities. Sensitive area of the detector covers 165^° solid angle nearing 2 π of emission from the source of size 100 × 150 mm. Performance of the chamber is tested using collimated ⁵⁵Fe X-ray source and ⁹⁰Sr / ⁹⁰Y coated β sources of various activities. The activity measurement system is established as a national primary standard for calibration of coated β sources at Radiological Laboratory at BARC. Design and performance of the chamber are presented.     

Development of a compact on-beam SEOP neutron spin filter

We have designed and demonstrated a prototype on-beam spin-exchange optical pumping (SEOP) ³He neutron spin filter (NSF). It is designed as the incident neutron polarizer for spallation neutron sources, where the installation space is limited due to thick radiation shielding. The size of the NSF is roughly 50 cm×50 cm×25 cm including the diode-laser optics with a frequency narrowing external cavity, and a cylindrical ³He cell as large as a diameter of 5 cm and a length of 10 cm can fit. A neutron beam test was performed at the NOP beamline of JRR-3 to see the performance of the NSF.     

Study on bubble formation in non-Newtonian fluids by laser image technique

A laser image system for studying bubble formation at the orifice submerged in liquid was established. The process of bubble formation can be directly visualized and real-time recorded through computer by means of He–Ne laser as light source using the beam expanding and light amplification technique. The behaviors of bubble formation in polyacrylamide (PAM) aqueous solutions were investigated at temperature 293.15 K and orifice diameters 1, 1.5 and 2 mm, respectively, the chamber volume was 90 cm³ and the gas flowrate from 0.1 to 0.6 cm³/s. The influences of mass concentration of solution and orifice diameter on bubble detachment volume were investigated experimentally and the results show that bubble detachment volume increases with solution concentration and orifice diameter in the experimental range of this work.     

Ball lens based lensed patch cord probes for optical coherence tomography in the field of dentistry

A lensed patch cord probe has been made with a ball lens packaged in a metal cylinder. By simply placing a ball lens directly in front of a fiber patch cord, a compact and potentially disposable sampling probe for optical coherence tomography (OCT) could be implemented. To achieve a sufficiently long working distance and a good transverse resolution simultaneously, the proper ball lens diameter and the distance between the ball lens and the fiber patch cord were investigated. Experimentally, a working distance of up to 5.2 mm, 3 dB bandwidth of 2 mm, and transverse resolution of 16 μm were achieved. With the patch cord probe, a common path swept source OCT system was implemented and used to demonstrate the feasibility as the dedicated probe for dentistry.     

Verschiebung des radioaktiven Gleichgewichtes 90Sr- 90Y im Organismus von Ratten nach oraler Verabfolgung

Bei unseren Stoffwechseluntersuchungen mit ⁹⁰Sr an Ratten und Kaninchen stellten wir wiederholt fest, daß sich die Aktivität einer Kot- oder Harnprobe verändert. Diese Veränderung der meßbaren Zählraten kann nur auf eine Verschiebung des radioaktiven Gleichgewichtes zwischen ⁹⁰Sr und ⁹⁰Y infolge der Stoffwechselvorgänge im Organismus zurückgefuhrt werden. Auf Grund der unterschiedlichen chemischen und physikalischen Eigenschaften von Strontium und Yttrium tritt bei jedem chemischen Eingriff eine Verschiebung des radioaktiven Gleichgewichtes zwischen ⁹⁰Sr und ⁹⁰Y ein. So bleibt beispielsweise bei der Fällung von Sr als Sulfat das ⁹⁰Y in Lösung und kann unter Einsatz von Trägermaterial fast quantitativ abgetrennt werden.     

Applicability of an X-ray and gamma-ray portable spectrometer for activity measurement of environmental soil samples

This paper presents a study on the applicability of a commercial X-ray and gamma-ray portable spectrometer (Rover) for in situ gamma-ray spectrometry. This portable spectrometer consists of a 3 × 3 × 1 mm (CdTe) Cadmium Telluride detector and a 30 × 30 mm [NaI (Tl)] Sodium Iodide detector. The radioactive sources used were ²⁴¹Am, ¹³³Ba, ¹⁵²Eu and ¹³⁷Cs tablet type, sealed with aluminum and polyethylene, as well as soil samples contaminated with ¹³⁷Cs. With the aid of these radioactive sources, this study determined the efficiency curve for both detectors. In addition, measurements were carried out to identify the minimum detectable activity (MDA) for both detectors, using time acquisition change ranging from 900 s to 138 h, depending on which detector was utilized and the sample distance. The results for the tablet-type sources were as follows: The MDA for the CdTe detector, while positioned 4.15 cm from the ¹³⁷Cs source, was 15 kBq and 6 kBq for energy lines 32 keV and 661.65 keV, respectively. However, when the distance between the source and detector was 100 cm, the 661.65 keV line presented a MDA of 68 kBq. Results for the soil samples were as follows: Using the CdTe detector, positioned 4.15 cm from the source, the MDA was 73 Bq for the ¹³⁷Cs 32 keV line. In relation to the ⁷Be soil samples, the MDA was 301 Bq when the detector was 4.15 cm from the source. Using the NaI (Tl) detector to analyze the ¹³⁷Cs 661.65 keV line, the MDA was 8 kBq when the detector was 100 cm from the tablet-type source. For the soil sample containing ¹³⁷Cs, the MDA was 7.4 Bq when the source was 2.8 cm from the NaI (Tl) detector. For those samples containing ⁷Be, and measured at the same distance (2.8 cm), the MDA was of 9.6 Bq. Based on the minimum detected activities obtained for both detectors, it is concluded that the in situ gamma-ray spectrometric system used to quantify soil sample activities with ¹³⁷Cs and ⁷Be is only appropriate when those activities are around one or more orders of magnitude larger than the usual radioactivity levels found in the environment. Even though it is a commercialized machine, the Rover system’s manufacturer does not provide the information cited in this abstract.     

Determination of90Sr in environmental samples with resonance ionization spectroscopy in collinear geometry

A new, fast technique for trace analysis of the radioactive isotopes⁸⁹Sr and⁹⁰Sr in environmental samples has been developed. Conventional mass separation is combined with resonance ionization spectroscopy in collinear geometry, which provides high selectivity and sensitivity. In addition, a chemical separation procedure for sample preparation has been developed. The described technique was used to determine the⁹⁰Sr content in 870 m³ air samples collected near Munich during and shortly after the Chernobyl reactor accident in April 1986. The content of⁹⁰Sr was measured to be 1.4 mBq per m³, corresponding to 1.6 × 10⁹ atoms of⁹⁰Sr per sample. This value is in good agreement with the results of radiochemical measurements.This publication comprises part of the Dissertations of J. Stenner and K. Zimmer     

Experimental investigation on the measurement deviations in recording brush discharges from insulating surfaces by Coulombmeters

The total charge on a charged sheet before and after a provoked brush discharge, their difference “C”, the induced charge “A” on different probes immediately before the discharge and their transferred charge “B” measured by commercially available Coulombmeters have been measured for probes from 2 mm to 25 mm in diameter including human thumb and shielded probe. The brush discharges were provoked on PTFE discs 10 cm–20 cm. The results obtained can be used for correct estimation of the incendivity of brush discharges between 10 nC and 90 nC.     

Proton-neutron interactions in nuclei withA∼90

An extension of the cluster-(quadrupole-octupole) phonon model is proposed for nuclei withA～90 to describe simultaneously positive- and negative-parity states, in which quadrupole as well as octupole vibrations of the⁸⁸Sr core are allowed. The cluster states include particle and particle-hole core excitations. The residual interaction is a delta-function force with spin-spin exchange plus a quadrupole-quadrupole force. The model is applied to⁸⁷Sr,⁸⁹Sr,⁸⁸Y, and⁹⁰Y nuclei. For each case, energy levels, spectroscopic factors, and electromagnetic properties are calculated and compared with experiment.     

External bremsstrahlung spectra of the Sr source in some lead compounds measured using NaI detector

The spectral distributions of external bremsstrahlung (EB) excited by beta particles from a ⁹⁰Sr/⁹⁰Y source in thick target compounds PbCl₂, PbF₂, Pb(NO₃)₂ and CdO were measured using a 3.8 cm × 3.8 cm NaI(Tl) crystal. The spectra, unfolded using the Liden-Starfelt procedure, showed fairly good agreement with theory (Tseng and Pratt) at low energies and some deviation (less than 15%) at higher energies. The discrepancy between theory and experiment increases with modified atomic number of the target compound and photon energy. The application of the measured/theoretical spectrum to estimate the bremsstrahlung dose is also discussed.     

High-intensity and high-brightness source of moderated positrons using a brilliant γ beam

Presently, large efforts are conducted toward the development of highly brilliant γ beams via Compton back scattering of photons from a high-brilliance electron beam, either on the basis of a normal-conducting electron linac or a (super-conducting) Energy Recovery Linac (ERL). Particularly, ERLs provide an extremely brilliant electron beam, thus enabling the generation of highest-quality γ beams. A 2.5 MeV γ beam with an envisaged intensity of 10¹⁵ photons s⁻¹, as ultimately envisaged for an ERL-based γ-beam facility, narrow band width (10⁻³), and extremely low emittance (10⁻⁴ mm² mrad²) offers the possibility to produce a high-intensity bright polarized positron beam. Pair production in a face-on irradiated W converter foil (200 μm thick, 10 mm long) would lead to the emission of 2×10¹³ (fast) positrons per second, which is four orders of magnitude higher compared to strong radioactive ²²Na sources conventionally used in the laboratory. Using a stack of converter foils and subsequent positron moderation, a high-intensity low-energy beam of moderated positrons can be produced. Two different source setups are presented: a high-brightness positron beam with a diameter as low as 0.2 mm, and a high-intensity beam of 3×10¹¹ moderated positrons per second. Hence, profiting from an improved moderation efficiency, the envisaged positron intensity would exceed that of present high-intensity positron sources by a factor of 100.