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At least 613 records · Page 34Linked to original sources

PubMed2002

Glow curve analysis applied to the discrimination of X ray versus proton irradiation.

Three types of thermoluminescence dosemeters (TLDs): LiF:Mg,Ti (TLD-100), CaF2:Tm (TLD-300), and alpha-Al2O3:C (TLD-500), were investigated for their glow curve response to separate X ray and proton irradiations. The glow curve structure for each individual TLD's exposure to the X ray and proton irradiations was analysed and compared. Distinguishable differences between the glow curve structure characteristic of each type of radiation were observed. The proton TLD-100 glow curve has revealed a complex high-temperature peak structure that was used for the proton/X ray discrimination algorithm. Proton irradiation of TLD-300 resulted in an apparent switch in the relative heights of peaks 3 and 5 as compared to X ray. In TLD-500, proton irradiation produced a more subtle difference in the glow curve with an increase in the ratio between high- and low-temperature peaks. Results demonstrate promising differences in glow curve structure present allowing for discrimination between X ray and proton radiation field exposures.

Calcium Fluoride↗

PubMed2002

The unified interaction model applied to LiF:Mg,Ti (TLD-100): properties of the luminescent and competitive centres during sensitisation.

An attempt is made to predict/interpret theoretically the experimentally measured values of f(D) and S(Ds)/So for composite peak 5 in TLD-100. using the Unified Interaction Model (UNIM) with identical values of the UNIM parameters for both sets of experimental data. Although an excellent fit can be obtained to the experimental f(D) data over the entire dose region where f(D) is greater than unity. i.e. from 5 Gy to several thousand Gy, a satisfactory fit to both sets of data is found to require different values for at least one of the parameters. The lack of success in fining f(D) and S(Ds)/So with the same values of all the parameters, suggests that the sensitisation anneal (particularly the duration of the anneal) may somehow change the structure (S(LC)) and/or the total number of available LCs in an unknown manner.

Fluorides↗

PubMed2003

The response of lif thermoluminescence dosemeters to photon beams in the energy range from 30 kV x rays to 60Co gamma rays.

The energy response of standard (TLD-100) and high-sensitivity (TLD-100H) LiF thermoluminescence dosemeters (TLDs) has been studied for photon beams with mean energies from about 25 keV to 1100 keV. Canadian primary standards for air kerma were used to establish the air kerma rates for each of the photon beams. TLDs were mounted in a PMMA holder and the air kerma response was measured as a function of energy. The EGSnrc Monte Carlo code was used to model the TLD holder and calculate the absorbed dose to the TLD chip per unit air kerma for each beam. The measured and calculated results were combined to obtain the intrinsic dose response of the TLD chip. Broadly, our results are consistent with existing data, which show a marked difference in the energy dependence of the two materials. However, the precision of our measurements (standard uncertainty of about 0.6%) has permitted the identification of features that have not been noted before. In particular, the energy dependence of the two materials is quite different in the important energy region delimited by 137Cs and 60Co gamma rays.

Calibration↗

PubMed2003

On the use of LiF:Mg,Ti thermoluminescence dosemeters in space--a critical review.

The use of LiF:Mg,Ti thermoluminescence dosemeters (TLDs) in space radiation fields is reviewed. It is demonstrated in the context of modified track structure theory and microdosimetric track structure theory that there is no unique correlation between the relative thermoluminescence (TL) efficiency of heavy charged particles, neutrons of all energies and linear energy transfer (LET). Many experimental measurements dating back more than two decades also demonstrate the multivalued, non-universal, relationship between relative TL efficiency and LET. It is further demonstrated that the relative intensities of the dosimetric peaks and especially the high-temperature structure are dependent on a large number of variables, some controllable, some not. It is concluded that TL techniques employing the concept of LET (e.g. measurement of total dose, the high-temperature ratio (HTR) methods and other combinations of the relative TL efficiency of the various peaks used to estimate average Q or simulate Q-LET relationships) should be regarded as lacking a sound theoretical basis, highly prone to error and, as well, lack of reproducibility/universality due to the absence of a standardised experimental protocol essential to reliable experimental methodology.

Aircraft↗

PubMed2003

Energy dependence of new thermoluminescent detectors in terms of HP(10) values.

The aim of this work was to determine energy dependence characteristics in terms of values of the personal dose equivalent, HP(10). The following types of thermoluminescent detectors (TLDs) were investigated: (a) two new types based on lithium borate, Li2B4O7:Cu,In and Li2B4O7:Cu,In,Ag; (b) two types based on the highly sensitive material LiF:Mg,Cu,P, TLD-700H and GR 200A; (c) two well-known types of LiF:Mg,Ti detector, TLD-100 and TLD-700 and (d) highly sensitive Al2O3:C detectors. TLDs previously calibrated with 137Cs gamma rays were simultaneously irradiated with X ray beams in the range of mean energies between 33 and 116 keV. The irradiations were performed with detectors in polymethyl methacrylate (PMMA) holders placed on a 30 cm x 30 cm x 15 cm water phantom with PMMA walls (ISO phantom). Measured energy responses were compared with calculated data for HP(10) values. The results confirmed the satisfactory tissue equivalent characteristics of all investigated TLDs except Al2O3:C, which (due to its large energy dependence) is suitable for personal dosimetry only with an appropriate filter.

Borates↗

PubMed2001

A Monte Carlo investigation of electron backscattering.

Kearsley's, Haider's and Frujinoiu's cavity expressions depend upon the existence of reliable data on electron backscattering in different media. These data are not available in the literature. By using MCNP, backscatter distributions and their saturation values were obtained for electron beams with energies between 0.1 MeV and 9 MeV traversing different materials such as polyethylene, solid water, lithium fluoride, aluminium, copper and lead. The data obtained using MCNP show that electron backscatter probability most strongly depends on the scatterer's effective atomic number and electron energy. Backscatter probability becomes less dependent on energy and is mostly a function of the effective atomic number of the scatterer for electron energies below 0.5 MeV. For low atomic number materials MCNP data suggest that the backscatter saturation values are distributed linearly with the effective atomic number of the scatterer for all energies investigated.

Aluminum↗

PubMed2002

Response components of LiF:Mg,Ti around a moderated Am-Be neutron source.

The responses of TLD-1010, TLD-700 and TLD-600 thermoluminescence dosemeters to the radiation field inside a water tank enclosing an isotopic 241Am-Be neutron source are analysed. Separate contributions coming from thermal neutrons, neutrons with energies above thermal and gamma rays to the total response of the three types of TLD are obtained. This is accomplished by assuming that the gamma responses for materials with different 6Li enrichments are identical and that the neutron response of TLD-700 is negligible compared to TLD-100 and TLD-600. The last assumption is tested by Monte Carlo simulations of the neutron energy spectrum at the points where the TLDs are irradiated.

Americium↗

PubMed1999

Extra dose due to extravehicular activity during the NASA4 mission measured by an on-board TLD system.

A microprocessor-controlled on-board TLD system, 'Pille'96', was used during the NASA4 (1997) mission to monitor the cosmic radiation dose inside the Mir Space Station and to measure the extra dose to two astronauts in the course of their extravehicular activity (EVA). For the EVA dose measurements, CaSO4:Dy bulb dosemeters were located in specially designed pockets of the ORLAN spacesuits. During an EVA lasting 6 h, the dose ratio inside and outside Mir was measured. During the EVA, Mir crossed the South Atlantic Anomaly (SAA) three times. Taking into account the influence of these three crossings the mean EVA/internal dose rate ratio was 3.2. Internal dose mapping using CaSO4:Dy dosemeters gave mean dose rates ranging from 9.3 to 18.3 microGy h-1 at locations where the shielding effect was not the same. Evaluation results of the high temperature region of LiF dosemeters are given to estimate the mean LET.

Calcium Sulfate↗

PubMed2004

Developments in the synthesis of LiF:Mg,Cu,Na,Si TL material.

A procedure for synthesis of the highly sensitive pellet-type LiF:Mg,Cu,Na,Si thermoluminescent (TL) detector has been newly developed. It was found that the optimum concentrations of dopants for a pellet-type LiF:Mg,Cu,Na,Si TL detector were found to be Mg: 0.2 mol %, Cu: 0.05 mol %, Na: 0.9 mol%, and Si: 0.9 mol%. The TL sensitivity of this new detector was about 30 times higher than that of the TLD-100 by light integration measurements. Reusability study of the detector was carried out for 10 cycles. The results show that the coefficients of variation for each detector separately did not exceed 0.016, and that for all 10 detectors collectively was 0.0054.

Copper↗

PubMed2004

On fading corrections for LiF:Mg,Ti irradiated by thermal neutrons.

The phenomena of preirradiation and postirradiation fading of LiF:Mg,Ti phosphors are considered a significant practical problem in routine dosimetry because of the uncertainties introduced, especially for mixed neutron-gamma dosimetry, as different fading corrections may be necessary for the gamma and neutron contributions. We have investigated if the region of interest (ROI) method is applicable to minimizing the fading effect for thermal neutron irradiation as it is for gamma irradiation. By employing the ROI method, which consists of integration between channel 31 below the glow curve maximum and channel 16 above the glow curve maximum, a constant dose value was obtained for the period of 90 d. Thus, by employing the ROI method, a fading independent evaluation of the thermal neutron dose can be made.

Algorithms↗

PubMed2004

The effects of ionisation density on the thermoluminescence response (efficiency) of LiF:Mg,Ti and LiF:Mg,Cu,P.

In this paper, the various models dealing with the effects of ionisation density on the thermoluminescence (TL) response (efficiency) of TL LiF dosemeters are discussed. These include (i) the Unified Interaction Model (UNIM), which models photon/electron linear/supralinear dose response; (ii) the Extended Track Interaction Model (ETIM), which models heavy charged particle (HCP) TL fluence response; (iii) Modified Track Structure Theory (MTST), which models relative HCP TL efficiencies; and (iv) Microdosimetric Target Theory (MTT), which models both relative HCP efficiencies and photon energy response.

Copper↗

PubMed2004

Performance of different thermoluminescence dosimeters in 90SR+90Y radiation fields.

The dosimetry of beta radiation is a difficult process especially because of the low penetration of beta particles in matter. The dosemeter utilised for this kind of procedure needs to approximate an ideal point-like detector: it should be as thin as possible, and its area should be small. The thermoluminescence dosemeters (TLDs) meet with these requirement properties. The aim of this work was to study the dosimetric characteristics of different TLDs to verify the possibility of their use for the calibration of 90Sr+90Y plane applicators. The response reproducibility, calibration curves, TL response as a function of the source-detector distance, the transmission factors and the linearity of the sample response were obtained for several types of dosimetric pellets.

Beta Particles↗

PubMed2004

Thermoluminescence dosimetry of a thermal neutron field and comparison with Monte Carlo calculations.

The characteristics of thermoluminescence dosemeters (TLDs) regarding the determination of photon and neutron absorbed doses were investigated in a thermal neutron beam. Harshaw TLD-100 (LiF:Mg,Ti) and TLD-700 (7LiF:Mg,Ti) were compared with similar materials from Solid Dosimetric Detector and Method Laboratory (People's Republic of China). Harshaw TLD-700H (7LiF:Mg,Cu,P) and aluminium oxide (Al2O3:Mg,Y) from Hungary were also considered for photon dose measurement. The neutron sensitivity of the investigated materials was measured and found to be consistent with values reported by other authors. A comparison was made between the TL dose measurements and results obtained via conventional methods. An agreement within 20% was obtained, which demonstrates the ability of TLD for measuring neutron and photon doses in a mixed field, using careful calibration procedures and determining the neutron sensitivity for the usage conditions.

Aluminum Oxide↗

PubMed2004

Response of a lithium gadolinium borate scintillator in monoenergetic neutron fields.

Accurate estimation of neutron dose requires knowledge of the neutron energy distribution in the working environment. Existing neutron spectrometry systems, Bonner spheres for example, are large and bulky, and require long data acquisition times. A portable system that could indicate the approximate neutron energy spectrum in a short time would be extremely useful in radiation protection. A composite scintillator, consisting of lithium gadolinium borate crystals in a plastic scintillator matrix, produced by Photogenics is being tested for this purpose. A prototype device based on this scintillator and digital pulse processing electronics has been calibrated using quasi-monoenergetic neutron fields at the low-scatter facility of the UK National Physical Laboratory (NPL). Energies selected were 144, 250, 565, 1400, 2500 and 5000 keV, with correction for scattered neutrons being made using the shadow cone technique. Measurements were also made in the NPL thermal neutron field. Pulse distributions collected with the digitiser in capture-gated mode are presented, and detection efficiency and energy resolution derived. For comparison, neutron spectra were also collected using the commercially available Microspec N-Probe from Bubble Technology Industries, which consists of an NE213 scintillator and a 3He proportional counter.

Algorithms↗

PubMed2005

Studies on automatic hot gas reader used in the countrywide personnel monitoring programme.

In India, approximately 58,000 radiation workers are monitored using locally made CaSO4:Dy teflon embedded thermoluminescence dosemeter (TLD) badge system. The automatic hot gas readers developed locally are also used in TL measurements. The hot gas reader system has many advantages over the manual readers used previously and has completely replaced the manual reader system in all TLD personnel monitoring units in India. In the present study, the new reader system is studied and a theoretical attempt has been made to interpret the experimentally obtained results. The glow curves are generated theoretically and are also plotted experimentally. It has been found that the heat capacity of the heating gas, which is responsible for the transfer of heat, has a role in deciding the position of peak and is verified experimentally using different gas flow rates of nitrogen and argon as heating gases in the reader. The theoretical study may also be helpful in fitting the experimentally obtained glow curves and, therefore, the elimination of unwanted non-radiation-induced contributions, such as dark current, electronic spikes, light leakage and triboluminescence that generally distort the glow curve shape, can be achieved.

Automation↗

PubMed2005

On the roles of the dopants in LiF: Mg,Cu,Na,Si thermoluminescent material.

In this paper, some results of the study on the roles of the dopants in the LiF:Mg,Cu,Na,Si thermoluminescent (TL) material that was developed at the Korea Atomic Energy Research Institute for radiation protection are presented. Although there have been many studies to investigate the roles of the dopants in LiF:Mg,Cu,P TL material in the TL process, there are some discrepancies in the understanding of the roles of Cu and P between various researchers. In case of LiF:Mg,Cu,Na,Si TL material, there are a few studies on the roles of the dopants. Three kinds of samples in each of which one dopant is excluded, and the optimised sample, were prepared for this study. The measurements and analysis of the three-dimensional TL spectra, based on the temperature, wavelength and intensity, and the glow curves for those samples are used in this study. The results show that Mg plays a role in the trapping of the charge carriers and Cu plays a role in the luminescence recombination process; however, the effect of Na and Si on the glow curve structure and the TL emission spectra is much less than that of Mg and Cu. It is considered that Na and Si each plays a role in the improvement of the luminescence efficiency.

Dose-Response Relationship, Radiation↗

PubMed2005

Secondary photon fields produced in accelerator-based sources for neutron generation.

Neutrons can be produced with low-energy ion accelerators for many applications, such as the characterisation of neutron detectors, the irradiation of biological samples and the study of the radiation damage in electronic devices. Moreover, accelerator-based neutron sources are under development for boron neutron capture therapy (BNCT). Thin targets are used for generating monoenergetic neutrons, while thick targets are usually employed for producing more intense neutron fields. The associated photon field produced by the target nuclei may have a strong influence on the application under study. For instance, these photons can play a fundamental role in the design of an accelerator-based neutron source for BNCT. This work focuses on the measurement of the photon field associated with neutrons that are produced by 4.0-6.8 MeV protons striking both a thin 7LiF target (for generating monoenergetic neutrons) and a thick beryllium target. In both cases, very intense photon fields are generated with energy distribution extending up to several MeV.

Beryllium↗

PubMed2005

Energy response of LiF and Mg2SiO4 TLDs to 10-150 keV monoenergetic photons.

Energy response of LiF:Mg,Ti, LiF:Mg,Cu,P and Mg2SiO4:Tb thermoluminescence dosemeters (TLDs) was measured in the range 10-150 keV for monoenergetic photons at SPring-8 of an 8-GeV synchrotron radiation facility. The photon beam was monitored by a parallel-plate free-air ionisation chamber calibrated with an uncertainty of 3%. Owing to the small dimension of the beam, a rotating holder was designed in order to irradiate TLDs uniformly. The measured responses of LiF to energy were approximately in agreement with the calculated dose absorption dependence in the soft tissue. However, two types of LiF TLDs presented the different luminescent responses to the photon energy. The response of LiF:Mg,Ti had a smooth curve, and that of LiF:Mg,Cu,P presented a local maximum at 30 keV and a local minimum at 100 keV. The Mg2SiO4:Tb response was nearly bone equivalent. Linearity of dose responses was also confirmed up to 2 Gy on each TL material.

Dose-Response Relationship, Radiation↗