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X Ortega

Publications and source records attributed to X Ortega.

15 recordsLinked to original sources
PubMed2006

Influence of environmental changes on integrating radon detectors: results of an intercomparison exercise.

An intercomparison exercise for passive integrating radon detectors has been carried out with the participation of 12 detection systems from 10 laboratories. The detection systems comprise three commonly used in radon integrating measurements, tracks, activated charcoal canisters and electrets. The exposures were carried out in the radon and thoron chambers at the Institute of Energy Techniques (INTE) of the Technical University of Catalonia (UPC), which is considered to be the Spanish reference chamber. The detectors were exposed to three different temperatures (10, 20 and 30 degrees C) and relative humidities (30, 45 and 80%). Furthermore, in three exposures radon concentration was drastically changed during the exposure period in order to study the efficiency of canister collection. The results indicated that only the charcoal canister response was found to be significantly influenced by external climatic conditions and radon fluctuations. Those track detectors, which are unable to measure thoron concentrations show thoron sensitivity and thus interfere with precise measurement of radon. Detectors for measuring thoron concentration show quite a different response, which could be related to their traceability.

Air Pollutants, Radioactive↗
PubMed2006

Influence of environmental changes on continuous radon monitors. Results of a Spanish intercomparison exercise.

The first Spanish intercomparison exercise for continuous radon monitors was carried out with the participation of nine monitoring systems from eight laboratories. The exposures were carried out in the radon and thoron chambers at the Institute of Energy Techniques (INTE) of the Technical University of Catalonia (UPC), which is considered to be the Spanish reference chamber. The monitors were exposed to three different temperatures (13, 20 and 30 degrees C), relative humidities (30, 45 and 80%) and radon concentrations (450, 2000 and 9000 Bq m(-3)). Exposures in the thoron chamber were carried out at concentrations of approximately 450 Bq m(-3). The response of the ionisation chambers and scintillation monitors was acceptable. However, the response of monitors based on electrostatic collection was found to be influenced by external climatic conditions. Moreover, all radon monitors were sensitive to thoron concentration, which was especially significant for scintillation monitors.

Air Pollutants, Radioactive↗
PubMed2006

Comparison of two extremity dosemeters based on LiF:Mg,Cu,P thin detectors for mixed beta-gamma fields.

Two types of thin LiF:Mg,Cu,P detectors, GR-200F and MCP-Ns, have been characterised for use in the design of an extremity dosemeter for mixed beta-photon radiation fields. Both detectors consist of an extremely thin layer of sensitive material with effective thicknesses of 5 and 8 mg cm(-2), respectively, held in a 5 mg cm(-2) PVC ring holder. Dosimetric performance was analysed according to the ISO 12794 standard and compared with 240 mg cm(-2) TLD-100 measurements. In particular, the energy response was obtained for ISO narrow X-ray spectra, (137)Cs, (60)Co, (204)Tl and (90)Sr/(90)Y. From these measurements a mean calibration factor was calculated to estimate H(p)(0.07). Subsequently, the performance of the dosemeters was checked for a set of 10 different mixed photon and beta-photon fields. The study shows that the proposed dosemeters can estimate H(p)(0.07) in a wide range of mixed beta-photon fields with a maximum deviation from the given dose of 30% and an overall uncertainty of the order of 25% (k = 1). However, the results also highlight a large variability among the different thin detectors and, thus, the standard TLD-100 material is recommended whenever the workplace does not include low-energy beta radiation.

Beta Particles↗
PubMed2006

Dose evaluation in lung-equivalent media in high-energy photon external radiotherapy.

In high-energy photon external radiotherapy treatment planning systems (TPSs) are used to calculate the dose to the target volume and the dose distribution around it. Commonly used TPSs include algorithms based on measurements in water and often fail in the estimate of dose in the presence of heterogeneities. In this study TL detectors were used to study the reliability of the Cadplan (Varian) TPS in the presence of low-density heterogeneities such as the lung for 6 and 18 MV photon beams at different field sizes. TL measurements were compared with TPS calculations and Monte Carlo simulations performed with the PENELOPE MC code. In a phantom with lung heterogeneity, TL measurements and MC simulations agreed, with an average deviation inside the lung of 2%. In contrast, TPS results overestimated the dose inside the lung, with a maximum deviation of 39% for the 18 MV photon beam and a field size of 2 x 2 cm(2).

Algorithms↗
PubMed2006

Radon activity concentration--a Euromet and BIPM supplementary comparison.

For the first time, a comparison of radon activity concentration in air has been performed within the scope of Euromet. In the project 657, 'Comparison of calibration facilities for the radon activity concentration,' 12 participants from 9 countries compared different radon reference atmospheres at 1, 3 and 10 k Bq m-3 via a transfer standard. The comparison was listed as BIPM supplementary comparison EUROMET.RI(II)-S1. The results of most participants are correlated due to common traceability to one single radon gas standard producer. This makes a careful correlation analysis necessary to achieve an appropriate comparison reference value. The results of the comparison as well as the complex analysis of the correlated set of data is presented and discussed.

Air Pollutants, Radioactive↗
PubMed2002

Extremity and whole-body dosemeters for beta and beta gamma fields based on LiF:Mg,Cu,P thin detectors.

This study aims at proposing two TL dosemeters: one for the whole body and another for the extremities, for beta and gamma fields. Selected sensible material consists of 5 mg x cm(-2) LiF:Mg,Cu,P film (GR-200F) manufactured in China. Calibration was carried out according to ISO 4037-3, in terms of Hp(0.07), and dosimetric performance was analysed on the basis of IEC-1066 and ISO-12794 Standards. Experiments showed a satisfactory sensitivity of the proposed dosemeters for detecting beta radiation at protection levels and a very good energy response; thus, highly recommending their use for weakly penetrating radiation measurements. However, the homogeneity and the reproducibility of GR-200F are not found to be as reliable as in standard materials.

Arm↗
PubMed2002

Uncertainty analysis of the weighted equivalent lung dose per unit exposure to radon progeny in the home.

A parameter uncertainty analysis has been performed to derive the probability distribution of the weighted equivalent dose to lung for an adult (w(lung) H(lung)) per unit exposure to radon progeny in the home. The analysis was performed using the ICRP Publication 66 human respiratory tract model (HRTM) with tissue weighting factor for the lung, w(lung) = 0.12 and the radiation weighting factor for alpha particles, wR = 20. It is assumed that the HRTM is a realistic representation of the physical and biological processes, and that the parameter values are uncertain. The parameter probability distributions used in the analysis were based on a combination of experimental results and expert judgement from several prominent European scientists. The assignment of the probability distributions describing the uncertainty in the values of the assigned fractions (ABB, Abb, AAI) of the tissue weighting factor proved difficult in practice due to lack of quantitative data. Because of this several distributions were considered. The results of the analysis give a mean value of w(lung) H(lung) per unit exposure to radon progeny in the home of 15 mSv per working level month (WLM) for a population. For a given radon gas concentration, the mean value of w(lung) H(lung) per unit exposure is 13 mSv per 200 Bq.m(-3).y of 222Rn. Parameters characterising the distributions of w(lung) H(lung) per unit exposure are given. If the ICRP weighting factors are fixed at their default values (ABB, Abb, AAI = 0.333, 0.333, 0.333; w(lung) = 0.12; and wr = 20) then on the basis of this uncertainty analysis it is extremely unlikely (P approximately 0.0007) that a value of Hw/Pp for exposure in the home is as low as 4 mSv per WLM, the value determined with the epidemiological approach. Even when the uncertainties in the ABB, Abb, AAI, values are included then this probability is predicted to be between 0.01 to 0.08 depending upon the distribution assumed for describing the uncertainties in the ABB, Abb, AAI, values. Thus, it is concluded that the uncertainties in the HRTM parameters considered in this study cannot totally account for the discrepancy between the dosimetric and epidemiological approaches.

Administration, Inhalation↗
PubMed2001

The outlook for the application of electronic dosemeters as legal dosimetry.

This study analyses new trends of a set of 12 electronic personal dosemeters in order to gain an overview of their main advantages and limitations. Physical characteristics and radiological, mechanical and environmental performance were tested according to IEC-61526 Standard requirements. The study highlights the different behaviour of the selected dosemeters. In particular, it is demonstrated that three of the tested devices fulfilled most of the established requirements, whereas another three of them presented important faults. The parameters that need more development are, in general, the response at low energy photon and beta radiation, and the dose rate alarm features. In some cases, mechanical problems as well as interference in the response due to external electromagnetic fields were also found. However, the results of the study foresee a promising future for the application of the newest personal electronic dosemeters as legal personal dosemeters and show the need for internationally agreed technical requirements within the European countries.

Consumer Product Safety↗
PubMed2001

Implementing new recommendations for calibrating personal dosemeters.

This paper analyses the differences between the calibration procedures for personal dosemeters recommended by ICRU 47 and ISO 4037-3. The tissue equivalence of the PMMA and the ISO water slab phantoms are analysed by means of the Penelope Monte Carlo code for monoenergetic and filtered X ray photon beams and compared with the results of two other independent codes. The influence of the calibration method is also verified experimentally, both on a thermoluminescence and an electronic personal dosemeter. Good consistency between both calibration procedures is shown provided that a correction factor for backscatter differences between the PMMA and the ICRU phantom is introduced. The Monte Carlo simulation is used to determine this correction to a greater accuracy.

Calibration↗
PubMed2001

Participation of the phosphoinositide metabolism in the hypersensitive response of Citrus limon against Alternaria alternata.

Lemon seedlings inoculated with Alternaria alternata develop a hypersensitive response (HR) that includes the induction of Phenylalanine ammonia-lyase (PAL, E. C. 4.3.1.5) and the synthesis of scoparone. The signal transduction pathway involved in the development of this response is unknown. We used several inhibitors of the Phosphoinositide (PI) animal system to study a possible role of Inositol-1,4,5-triphosphate (IP3) in the transduction of the fungal conidia signal in Citrus limon. The HR was only partially inhibited by EGTA, suggesting that not only external but internal calcium as well are necessary for a complete development of the HR. In this plant system, Alternaria alternata induced an early accumulation of the second messenger IP3. When lemon seedlings were watered long term with LiCl, an inhibitor of the phosphoinositide cycle, the IP3 production was reduced, and the LiCl-watered plants could neither induce PAL nor synthesize scoparone in response to fungal conidia. Furthermore, neomycin, a Phospholipase C (PLC, E. C. 3.1.4.3) inhibitor, also inhibited PAL induction and scoparone synthesis in response to A. alternata. These results suggest that IP3 could be involved in the signal transduction pathway for the development of the HR of Citrus limon against A. alternata.

Alternaria↗
PubMed2000

Dose conversion factor for radon concentration in indoor environments using a new equation for the F-fP correlation.

Since 1994 the radon studies group at the Institut de Tècniques Energètiques (INTE) of the Universitat Politècnica de Catalunya in Barcelona, Spain, has carried out a campaign of continuous measurements of the equilibrium factor (F) and the unattached fraction (f(p)) of radon decay products at four sites which are representative of different environmental characteristics on the Mediterranean littoral of Catalonia, Spain. It has been established that these parameters vary widely, F(0.03-0.87) and f(p) (0-0.72), from one site to another and with time, according to the characteristics of the site and climate. In spite of this variation, the F and f(p) parameters are log-normally or normally distributed. The measurements of F and f(p) show that f(p) is negatively correlated to F by a log-power equation, Ln(1/f(p))=1.90[Ln(1/F)](-0.68), which can be used in all the F range, instead of the commonly used power equation f(p)=aFb suggested by Stranden and Strand and other authors, which fits well for a reduced range of F. Power and log-power equations have been introduced into a simplified dosimetric model in order to estimate the effective dose per unit radon exposure as a function of F. From the log-power equation this value is quite constant and ranged from 9 nSv per Bq m(-3) h to 12 nSv per Bq m(-3) h when F is higher than 0.15. In the case of a lower F factor, a linear function that passes through 0 fits quite well. A value of 12 nSv per Bq m(-3) h is proposed for the Mediterranean littoral of Catalonia as the best estimation.

Air Pollutants, Radioactive↗
PubMed1998

Thermoluminescence dosimetry applied to in vivo dose measurements for total body irradiation techniques.

BACKGROUND AND PURPOSE: In total body irradiation (TBI) treatments in vivo dosimetry is recommended because it makes it possible to ensure the accuracy and quality control of dose delivery. The aim of this work is to set up an in vivo thermoluminescence dosimetry (TLD) system to measure the dose distribution during the TBI technique used prior to bone marrow transplant. Some technical problems due to the presence of lung shielding blocks are discussed. MATERIALS AND METHODS: Irradiations were performed in the Hospital de la Santa Creu i Sant Pau by means of a Varian Clinac-1800 linear accelerator with 18 MV X-ray beams. Different TLD calibration experiments were set up to optimize in vivo dose assessment and to analyze the influence on dose measurement of shielding blocks. An algorithm to estimate midplane doses from entrance and exit doses is proposed and the estimated dose in critical organs is compared to internal dose measurements performed in an Alderson anthropomorphic phantom. RESULTS: The predictions of the dose algorithm, even in heterogeneous zones of the body such as the lungs, are in good agreement with the experimental results obtained with and without shielding blocks. The differences between measured and predicted values are in all cases lower than 2%. CONCLUSIONS: The TLD system described in this work has been proven to be appropriate for in vivo dosimetry in TBI irradiations. The described calibration experiments point out the difficulty of calibrating an in vivo dosimetry system when lung shielding blocks are used.

Algorithms↗
PubMed1994

Estimation of peripheral dose from two linacs: Mevatron MX6700 and Mevatron KDS.

An empirical calculation method for high-energy beam peripheral dose estimation is described. The peripheral dose has been measured for a Siemens Mevatron MX6700 (6 MV) and a Siemens Mevatron KDS (6 and 18 MV) linear accelerators. The dose distribution is parameterized for each beam energy as a function of depth, distance from the edge of the field, and field size. A simple algorithm has been developed for dose calculation up to 100 cm from the field central axes. Predictions by this algorithm are compared with measurements in an Alderson phantom.

Particle Accelerators↗