Biomedical subjects

L V E Caldas

Publications and source records attributed to L V E Caldas.

7 recordsLinked to original sources

PubMed2006

Use of composites of topaz-glass as TSEE and TL dosemeters.

The properties of the thermally stimulated exoelectron emission (TSEE) and thermoluminescent (TL) emission of topaz-glass composites were studied with the aim of using them as solid-state dosemeters. The TSEE response was studied as a function of radiation energy and as a function of absorbed dose. Topaz-glass composites presented a linear TL and TSEE response to dose within a range of 0.01-1 Gy. The topaz-glass composites presented higher TSEE peaks than topaz-Teflon pellets. In the dosimetry of radiotherapic fields normally the responses of the topaz-glass dosemeters are comparable to topaz-Teflon pellets. The results confirmed that these new dosemeters can be useful in monitoring the quality of the radiation sources. This dose mapping technique is particularly useful in investigating dose distribution throughout a planned target volume.

Computer Simulation↗

PubMed2003

A special ionisation chamber for quality control of diagnostic and mammography X ray equipment.

A quality control program for X ray equipment used for conventional radiography and mammography requires the constancy check of the beam qualities in terms of the half-value layers. In this work, a special double-faced parallel-plate ionisation chamber was developed with inner electrodes of different materials, in a tandem system. Its application will be in quality control programs of diagnostic and mammography X ray equipment for confirmation of half-value layers previously determined by the conventional method. Moreover, the chamber also may be utilised for measurements of air kerma values (and air kerma rates) in X radiation fields used for conventional radiography and mammography. The chamber was studied in relation to the characteristics of saturation, ion collection efficiency, polarity effects, leakage current, and short-term stability. The energy dependence in response of each of the two faces of the chamber was determined over the conventional radiography and mammography X ray ranges (unattenuated beams). The different energy response of the two faces of the chamber allowed the formation of a tandem system useful for the constancy check of beam qualities.

Equipment Design↗

PubMed2002

Performance of pellets and composites of natural colourless topaz as radiation dosemeters.

The aim of the present work is to investigate the possibility of using the properties of the thermoluminescent emission (TL) of Brazilian natural topaz for dosimetric applications. Topaz is an aluminium fluorsilicate with general composition of Al2(SiO4)(F,OH)2 found with relative abundance in Brazil and in other parts of the world. Topaz from Santo Antonio do Jacinto, Minas Gerais. Brazil, was used in this work, in the form of pellets of topaz mixed with Teflon and composites made with topaz embedded in a glass matrix. The TL sensitivity was tested between 10(-4) and 10(4) Gy. The TL peak intensity increases with the dose before saturation, which occurs around 2 kGy. The peak intensity showed a strong dependence with radiation energy. The effect of visible light and the behaviour of the TL signals after successive irradiation-reading-annealing cycles are presented and discussed.

Aluminum Silicates↗

PubMed2002

Dosimetric characterisation of Brazilian natural stones using the thermally stimulated exoelectron emission technique.

A thermally stimulated exoelectron emission (TSEE) measuring system developed and constructed at IPEN was used to verify the feasibility of the use of Brazilian natural semi-precious stones, such as jasper. amethyst, agate (blue and rose) and quartz (rose and white) for gamma and X radiation detection. Its counting system consists of a 2pi windowless gas-flow proportional counter, and the heating system is formed by a temperature programmer that provides linear heating of the samples. The samples were tested in gamma and in X radiation beams and evaluated in relation to their main dosimetric characteristics, as TSEE glow curves, calibration curves and energy dependence. The TSEE results are compared with those of thermoluminescence. The results obtained show the usefulness of Brazilian natural stones as dosimetric materials, using the thermoluminescence and thermally stimulated exoelectron emission techniques.

Brazil↗

PubMed2002

Influence of thermal treatments on the response decay of glass radiation detectors.

Commercial transparent glass has received attention in relation to its use as a gamma radiation detector. This kind of material presents a strong post-irradiation thermal decay at room temperature, which is a problem for high dose dosimetry purposes. This effect may be avoided by taking measurements always at the same time after irradiation of the glass samples. However, in this work effort has been given to this material characteristic, submitting the glass samples to different thermal treatments. The best results were obtained with a post-irradiation treatment at 130 degrees C during 10 min. This procedure seems to destroy the unstable entities responsible for the initial strong decay of the sample response, showing acceptable stability as a function of room temperature storage time.

Gamma Rays↗

PubMed2002

Commercial glass for high doses using different dosimetric techniques.

Glass samples were tested for use in high-dose dosimetry in radiation processing. The main dosimetric characteristics were determined: lower detection threshold, reproducibility, response to gamma radiation of 60Co and thermal decay at room temperature, with the use of a densitometer, spectrophotometer and thermoluminescence reader. The results show that this kind of material could be useful for dosimetry in several applications of ionising radiation, taking into account its thermal fading.

Calibration↗

PubMed2002

Calibration of kVp meters used in quality control tests in diagnostic radiology by spectrometry.

A non-invasive calibration methodology of quality control instruments for diagnostic radiology was established and applied to different kinds of commercial kVp meters. The method uses the measurement of the spectrum endpoint as a reference. The results showed a variation of 10% between the responses of the instruments calibrated and the spectrometric system, a fact that demonstrates the need for instrument calibration.

Calibration↗