TLD Materials Research Articles

Effect of high-energy [formula omitted] ions on the TL behavior of LiF:Mg,Cu,P detectors

Thermoluminescence (TL) of LiF:Mg,Cu,P (TLD-700H) phosphor irradiated with 24 MeV 7 Li ions at different fluences in the range 5 × 10 9 – 1 × 10 12 ions / cm 2 (with corresponding doses in the range 620 Gy to 123.96 kGy) has been studied. The samples from the same batch were also exposed to γ -rays from a Co 60 source for comparative studies. It has been found that at low fluences ( 5 × 10 9 – 1 × 10 10 ions / cm 2 ) the TL glow curves of the samples irradiated with 7 Li ions have similar structures to that of γ -irradiated sample, while at higher fluences ( 5 × 10 10 – 1 × 10 12 ions / cm 2 ) the relative intensities and fluence responses of the TL glow peaks were observed to vary with fluences increasing. The TL intensity of the dosimetric peak at 481 K saturates at the fluence 5 × 10 11 ions / cm 2 , while that of the peak at 524 K increases till the maximum fluence 1 × 10 12 ions / cm 2 . All the TL glow peaks show nearly sublinear behavior except the peak at 524 K, which exhibits supralinear. This has been attributed to the formation of more defects (trapping centers (TC)/luminescence centers (LC)) due to 7 Li ions implantation, during ion beam irradiation. The implantation has been confirmed from TRIM calculations. Moreover, on ion beam irradiation, a shift in the peak positions toward lower temperature side by around 10 K was observed, comparing with those induced by Co 60 γ -rays. The TL efficiency of LiF:Mg,Cu,P to 24 MeV 7 Li ion beam has been measured relative to γ -rays of Co 60 . Further, theoretical analysis of the glow curves of the ion beam and γ -irradiated samples was done by glow curve deconvolution (GCD) method to determine trapping parameters of various peaks. As LiF:Mg,Cu,P is highly sensitive and tissue equivalent TLD material and its peak at 524 K does not saturate even at high fluences, this peak may be used for the dosimetry of ion beams in medical and other applications.

Commercial optical fibre as TLD material

This work presents a study of commercial SiO2 optical fibre thermoluminescence (TL) properties as part of the efforts within the Dosimetric Application Project at the Physics Institute of the University of Mexico to develop new radiation detection materials and technologies. The SiO2 commercial optical fibre studied demonstrates useful TL properties and is an excellent candidate for use in TL dosimetry of ionising radiation. The optical fibre's glow curve was observed between 30 and 400 degrees C after exposure to 60Co gamma radiation. One very well-defined glow peak has a maximum at 230 degrees C. The TL response between 100 and 350 degrees C increases monotonically over a wide dose range, from 0.1 Gy to several kGy. It is linear in the range 0.1-3 Gy, which is important for clinical high dose or accident dosimetry. The optical fibre demonstrated high data reproducibility, low residual signal and almost no fading in our study. Moreover, the optical fibre can be re-used several times, after thermal annealing, without any detriment in the dose-response. All these TL characteristics, plus the small size of the 150 microm diameter SiO2 optical fibre, the high flexibility, easy handling and low cost compared with other TL materials, make the commercial optical fibre a very promising TL material for use in research, medicine, industry, reactors, and a variety of other applications.

SU‐FF‐T‐191: Design and Construction of a Realistic Pelvic Phantom for a Level III Dosimetry Study

Purpose: Verification of dose delivery is a basic necessity of quality assurance in radiotherapy treatment, and is extremely valuable in determining uniformity of protocol adherence in the context of a multi‐centre trial. To verify the delivery of radiotherapy doses and dose distributions it is necessary to replicate the entire treatment process as accurately as possible in a way that allows the direct measurement of doses. A pelvic phantom was constructed to investigate the 3D delivery of radiotherapy (Level III dosimetry) for rectal and prostate cancer treatment in collaboration with the Trans‐Tasman Radiation Oncology Group. Method and Materials: A CT dataset of a male pelvis was used to define the geometric boundaries of principle tissues — bone, prostate, seminal vesicles, bladder, rectum and muscle. Points of interest were located throughout the dataset to identify appropriate placement of TLD materials. The centre of the prostate was identified as the location for point‐measurement with a small‐volume ionization chamber. Polyurethane materials for phantom construction were evaluated in terms of their durability, ability to be milled and radiographic qualities. Results: The pelvic phantom has been manufactured and has undergone commissioning. CT numbers for different density materials match well with typical tissues. TLD measurements in the phantom show a reproducibility of 2 %. The proposal for the inter‐centre study has led to a high (> 85 %) accrual of radiotherapy centres in Australasia. The phantom has now been used at a large number of participating centres. Conclusion: This study will provide estimates of variation in critical structure outlining, expansion algorithms and dose volume histograms across different planning systems. In addition local irradiation techniques, geometric and dosimetric accuracy dose distributions in realistic materials, and the feasibility of multi‐centre dosimetry studies is assessed.

The use of TLD-700H dosemeters in the assessment of external doses at the former Semipalatinsk nuclear test site.

The joint projects performed since 1995 by the Jülich Research Centre in co-operation with the Kazakh National Nuclear Centre in the area of the former nuclear test site near Semipalatinsk, in eastern Kazakhstan, have assessed the current dose rate of the population at and around the test site, as well as determining retrospectively the dose rate of persons affected by the atmospheric tests. Measurements of the population by personal dosemeters depend on reliably wearing these dosemeters over prolonged periods of time, and of a sufficient dosemeter return. In the past, such measurements have been particularly successful whenever short wearing times were possible. This requires high sensitivity of the dosemeters. The suitability of the highly sensitive TLD material of the BICRON TLD 700H type for such personal dosimetry measurements was investigated. It was tested in practical field application at the Semipalatinsk nuclear test site in September 2000. Initial results are available from individual doses received by a group of geologists and a group of herdsmen at the test site. For the first time, the individual dose was measured directly in these population groups. Detection limits below 1 microSv permit informative measurements for wearing times of less than two weeks. Most individual doses did not arise significantly out of local fluctuations of natural background. A conservative assessment from the aspect of practical health physics yielded a mean personal dose of 0.55 microSv per day for the herdsmen, whereas the geologists received a mean personal dose of 0.45 microSv per day. For an annual exposure period of typically, about three months, the radiation dose received by the persons investigated, in addition to the natural radiation exposure, is thus well below the international limit value of 1 mSv x a(-1) for the population dose.

Luminescence of CsGd2F7 crystals.

Optical and dosimetric properties of nominally pure CsGd2F7 crystals and of CsGd2F7 crystals doped with various concentrations of Pr3+ ions were investigated. Effects of X, beta and UV irradiation on these crystals were studied. Methods of optical absorption, X and UV excited luminescence, thermoluminescence (TL), phototransferred thermoluminescence and optically stimulated luminescence were used in these investigations. The dependence of the TL efficiency on the radiation dose was found to be linear up to 6 kGy for the 3 at.% Pr3+ doped samples. The crystals containing from 0.3 at.% to 1.0 at.% of Pr3+ ions were found to have the best TL sensitivity and the intensity of the main TL peak in these samples was more than two orders of magnitude higher than that of the pure crystals. The TL sensitivity of the CsGd,F7:Pr3+ crystals was also compared with that of other commonly used TLD materials.

Optically stimulated luminescence of some thermoluminescent detectors as an indicator of absorbed radiation dose.

Stimulation spectra of several TLD materials in the short-wave spectral region are measured using the optically stimulated afterglow (OSA) method for determination of absorbed dose. Optical stimulation spectra are studied in the region of wavelengths lower than those of emission spectra. The effective optical stimulation hands have been found for examined materials in the regions of wavelengths which overlap with fluorescence excitation bands. Application of short-wave OSA bands for determination of absorbed dose is analysed.

Development of NaCl : Tb(T) as gamma and beta radiation dosimetry material

The present work involves extensive study of thermoluminescent behaviour of untreated and thermally pre-treated, terbium-doped NaCl phosphors. It is found that NaCl : Tb (1000 ppm of terbium concentration) specimens, quenched from 750°C, designated as NaCl : Tb(T), display optimum TL output with a dominant and well-defined glow peak around 200°C. The study of this peak for beta and gamma radiation dosimetry indicates that the NaCl : Tb phosphors satisfy most of the basic requirements of an efficient TLD material. It is suggested that the present material can be used in beta and gamma dosimetry for the range 10 0–10 4 rad.

10.2172/10188235

This progress report concentrates on two major areas of dosimetry research: measurement of fast neutron kerma factors for several elements for monochromatic and white spectrum neutron fields and determination of the response of thermoluminescent phosphors to various ultra-soft X-ray energies and beta-rays. Dr. Zhixin Zhou from the Shanghai Institute of Radiation Medicine, People`s Republic of China brought with him special expertise in the fabrication and use of ultra-thin TLD materials. Such materials are not available in the USA. The rather unique properties of these materials were investigated during this grant period.

Dose Linearity of LiF:Mg,Ti and LiF:Mg,Cu,P in Radiotherapy: Effect of Time Between Dose and Evaluation

Clinical measurements using LiF dosemeters in radiotherapy are complicated by deviations from a linear dose response at typical doses per fraction (exceeding I Gy). In the present study, two TLD materials - LiF:Mg,Ti and LiF:Mg,Cu,P - were utilised to investigate the effect of time between irradiation and evaluation on dose linearity. TLDs were irradiated to doses of 0.01, 0.1, 0.5, 2, 5 and 20 Gy using a 6 MV photon beam from a medical linear accelerator and evaluated one hour, one week, one month and six months after irradiation. Assuming linear response at 0.1 Gy, the ratio of the response at 5 Gy and 0.1 Gy, R 5 0.1 , was taken as a measure of response variations with dose. LiF:Mg,Ti retained stability of dose response over time; however, LiF:Mg,Cu,P showed a 16% and 13% increase in R 5 0.1 for the slow and fast cool down, respectively. Overestimation could occur in clinical dose evaluation after storage longer than between one week and a month after the measurement was taken.

Evaluation of Bicron NE MCP DXT-RAD Passive Extremity Dosemeter

Passive extremity dosemeters currently used in dosimetry communities worldwide have shortcomings. In general, an extremity dosemeter has too thick a detector element, and the dosemeter response is highly energy dependent for beta rays with energies ranging from 200 keV to 2 MeV. It often does not have dosemeter identification, causing problems in the chain of custody. It is often read manually, rendering reading/packing operations very labour intensive. As a result of collaboration between AECL and BICRON ✦ NE, a new extremity dosemeter, incorporating a highly sensitive LiF:Mg,Cu,P TLD and tentatively code named MCP DXT-RAD, was developed. It has been evaluated for radiological performance against an ISO draft standard for extremity dosemeters in twelve categories: homogeneity, detection threshold, beta ray energy response, beta angular response, photon energy response, photon angular response, reproducibility, stability under various climatic conditions, linearity, residue, self irradiation, and effect of light exposure. Test results, as detailed in this paper, show that this extremity dosemeter meets the ISO draft standards requirement in all categories except residue. Its 2nd reading residue (7%) is much higher than other TLD materials (0.2%). However, it was found that an annealing in the oven at 240°C for 10 min prior to the 2nd reading reduces the residue to 0.4%, comparable to that of other TLD materials. The greatest advantage of this dosemeter is that it can measure beta skin dose accurately over a wide range of beta energies.

Glow Curve Analysis of Long-term Stability of LiF:Mg,Cu,P as Compared to LiF:Mg,Ti

Over a six month period, the long-term stability of LiF:Mg,Cu,P (GR-200A, Beijing China) was compared with LiF:Mg,Ti (GR-100, Beijing China). This is of particular interest in applications where there can be considerable variations in the time intervals between TLD preparation, irradiation and readout, such as environmental, accident personal and mailed dosimetry. For each TLD material, slow and fast cool-down anneals, characteristic of those used in the above-mentioned applications, were employed to study the effect of annealing procedure on long term stability. An analytical approximation based on the Randall-Wilkins model employing first order kinetics was used to fit individual peaks. Glow curve features unique for each TLD material and annealing condition were quantified and compared. From computerised glow curve analysis, annealing at 220°C, instead of the pre-set temperature of 240°C, caused an increase in the contribution from peak 3 in LiF:Mg,Cu,P, causing the material to be more susceptible to fading and peak area interchanges.

Thermally and Optically Stimulated Luminescence of AlN-Y2O3 Ceramics after Ionising Irradiation

Thermally (TL) and optically stimulated luminescence (OSL) were studied in AlN-Y2O3 ceramics after irradiation with ionising radiation. The extremely high TL sensitivity (approximately 60 times the sensitivity of LiF:Mg,Tl (TLD-100)) makes AlN-Y2O3 ceramics attractive as a TLD material. However, an essential drawback of AlN-Y2O3 is at its high fading rate. Special attention has been focused on understanding and improving the fading properties. In particular, the influence of the ceramics production conditions and the additive concentration on the fading rate have been studied. Experimental results on spectral properties and thermal evolution of OSL are also presented. The stimulation spectrum covers the spectral range from green to infrared light. A combination of thermal and optical stimulation allowed a correlation to be found between parameters of OSL and TL after the same irradiation dose. It is concluded that OSL occurs due to depopulation of shallower traps than TL traps.

Dose response of various radiation detectors to synchrotron radiation

Accurate dosimetry is particularly difficult for low- to medium-energy x-rays as various interaction processes with different dependences on material properties determine the dose distribution in tissue and radiation detectors. Monoenergetic x-rays from synchrotron radiation offer the unique opportunity to study the dose response variation with photon energy of radiation detectors without the compounding effect of the spectral distribution of x-rays from conventional sources. The variation of dose response with photon energies between 10 and 99.6 keV was studied for two TLD materials (LiF:Mg, Ti and LiF:Mg, Cu, P), MOSFET semiconductors, radiographic and radiochromic film. The dose response at synchrotron radiation energies was compared with the one for several superficial/orthovoltage radiation qualities (HVL 1.4 mm Al to 4 mm Cu) and megavoltage photons from a medical linear accelerator. A calibrated parallel plate ionization chamber was taken as the reference dosimeter. The variation of response with x-ray energy was modelled using a two-component model that allows determination of the energy for maximum response as well as its magnitude. MOSFET detectors and the radiographic film were found to overrespond to low-energy x-rays by up to a factor of 7 and 12 respectively, while the radiochromic film underestimated the dose by approximately a factor of 2 at 24 keV. The TLDs showed a slight overresponse with LiF:Mg, Cu, P demonstrating better tissue equivalence than LiF:Mg, Ti (maximum deviation from water less than 25%). The results of the present study demonstrate the usefulness of monoenergetic photons for the study of the energy response of radiation detectors. The variations in energy response observed for the MOSFET detectors and GAF chromic film emphasize the need for a correction for individual dosimeters if accurate dosimetry of low- to medium-energy x-rays is attempted.

A Monte Carlo study of the quality dependence factors of common TLD materials in photon and electron beams

A Monte Carlo simulation of the quality dependence of different TL materials, in the form of discs 3.61 mm in diameter and 0.9 mm thick, in radiotherapy photon beams relative to -rays has been performed. The beam qualities ranged from 50 kV to 25 MV x-rays. The TL materials were: , , LiF and . The effects of the dopants on energy deposition in the TL material have also been determined for the highly sensitive LiF:Mg:Cu:P (TLD-100H) and for :Mn. It was found that there was a significant difference in the quality dependence factor derived from Monte Carlo simulations between LiF and LiF:Mg:Cu:P but not between and :Mn. The quality dependence factors for varied from (1 sd) for 25 MV x-rays to (1 sd) for 50 kV x-rays relative to -rays; Monte Carlo simulations were also performed for in megavoltage electron beams. For , the quality dependence factor varied from (1 sd) for 25 MV x-rays to (1 sd) for 50 kV x-rays. The figure for ranged from (1 sd) for 25 MV x-rays to (1 sd) for 50 kV x-rays. The quality dependence factor for increases by up to 5% with depth and by up to 15% with field size for the kilovoltage x-ray beams. For LiF-TLD, however, there was no significant dependence on the field size or depth of irradiation in the kilovoltage energy range.

An EGS4 Monte Carlo examination of general cavity theory

EGS4 Monte Carlo simulations have been performed to examine general cavity theory for a number of TLD cavity materials irradiated in megavoltage photon and electron beams. The TLD materials were LiF, , and irradiated in Perspex, water, Al, Cu and Pb phantoms. For megavoltage photon beams, this has been done by determining the dose component (1-d) resulting from photon interactions in the cavity compared with the dose component resulting from photon interactions in the phantom material (d) by Monte Carlo simulations and analytical techniques. The results indicate that the Burlin exponential attenuation technique can overestimate the dose contribution from photon interactions in a 1 mm thick LiF cavity by up to 100% compared with the Monte Carlo results for LiF TLDs irradiated in a water or Perspex phantom. However, there is agreement to within 1% in the quality dependence factor, determined from Burlin's cavity theory, Monte Carlo simulations and experimental measurements for LiF and TLDs irradiated in a Perspex or a water phantom. The agreement was within 3% for TLDs. However there was disagreement between Monte Carlo simulations and Burlin's theory of 6 and 12% for LiF TLDs irradiated in copper and lead phantoms respectively. The adaptation of Burlin's photon cavity theory and other modifications to his photon general cavity theory for electrons have been shown to be seriously flawed.

Use of SSNTDs in neutron beam dosimetry

A new Biological Irradiation Facility (BIF) has been constructed at the Budapest Research Reactor Center. The 10 cm diameter beam is led through a variable filter and collimator system, providing different neutron spectra from the nearly pure fission one to a well moderated, 1/E spectrum. To use the irradiator for biological irradiation and for investigating the response of neutron detector materials one must know the neutron spectrum, the beam intensity and profile in advance, and moreover, each irradiation should be adequately monitored to be able to correct the dose conversion factors against the burnup of the fuel, change in the reactor thermal power etc. For the purpose, a set of track detectors were developed. All the detectors are chemically etched and evaluated by a new image analyzer system called VIRGINIA (also presented on this conference). Detectors developed are: CR-39 (TASTRAK) track detectors with proton converter (polyethylene, PE) turning this combination into a threshold detector when applying thin gold foils as proton energy degraders; fission track detectors using depleted uranium and thorium with LEXAN polycarbonate and CR-39 using the 6Li and 10B contents of commercially available TLD materials as alpha converters. We present the basic fundamentals of the proton recoil detector, including the response calculation model.

Radiation effects in organics and inorganics for ESR dosimetry

Models of radiation-induced lattice defects or radicals and elementary processes of their formation are discussed for both organics and inorganic materials used in practice for ESR dating and dosimetry. A hybrid material containing a stabilizer embedded in van der Waals type molecular crystal matrix is proposed considering the tissue equivalence of organic materials. Inorganic materials suitable for radiation dosimetry and dosimetric imaging should be developed taking into account the accumulated information on ESR dating and also on TLD materials.

Thermoluminescence studies on Sr 2+ doped cesium halides and their application to dosimetry

Thermoluminescence (TL) and optical absorption studies on Sr 2+ doped cesium halides have been carried out. The various glow peaks due to F, D 1D 2 and Z 1 centers are identified by means of TL and optical absorption studies. Z 1 centers are found to be formed on irradiation itself in both Sr 2+ doped CsBr and CsCl crystals. The study of the dosimetric properties of the TL glow peak at 403 K for irradiation indicated that the CsBr:Sr 2+ phosphor satisfies the most basic need of an efficient TLD material. It is proposed that the CsBr:Sr 2+ phosphor material can be used in dosimetry for the range 10 0 – 10 3 R.

The quality dependence of LiF TLD in megavoltage photon beams: Monte Carlo simulation and experiments

The quality dependence of LiF TLD in megavoltage photon beams with qualities from -rays to 25 MV x-rays has been studied experimentally against ion chamber measurements and theoretically by Monte Carlo simulation using the EGS4 Monte Carlo code system. The experimental findings are that the energy dependence of 1 mm thick TLD-100 (micro-rods and chips) on average decreases slowly from 1.0 for -rays to for 6 MV x-rays () and to for 25 MV x-rays () relative to -rays. The Monte Carlo results vary from for 6 MV x-rays to for 25 MV x-rays. Differences between chips and micro-rods were negligible and there was no difference in the energy dependence between TLDs irradiated in water or Perspex (PMMA). The Monte Carlo simulation shows that the contribution to the total absorbed dose from photon interactions in the 1 mm diameter and 6 mm long TLD material varies from 50% for -rays to 10% for 25 MV x-rays. When the diameter of the TLD micro-rod was increased from 1 mm to 5 mm there was no significant change in response computed by Monte Carlo even though the dose contribution to the total dose scored in the TLD material from photon interactions in the cavity increased to 85% for -rays and 30% for 25 MV x-rays.

Glow Curve Deconvolution of Various TLD Materials

Journal Article Glow Curve Deconvolution of Various TLD Materials Get access ................................ ................................ Search for other works by this author on: Oxford Academic PubMed Google Scholar Radiation Protection Dosimetry, Volume 60, Issue 1, 1 June 1995, Pages 21–35, https://doi.org/10.1093/oxfordjournals.rpd.a082705 Published: 01 June 1995