Biomedical subjects

J C Nunes

Publications and source records attributed to J C Nunes.

7 recordsLinked to original sources

PubMed2005

Evaluation of two personal dosemeters in polyenergetic mono- and multi-directional neutron fields.

The neutron dose-equivalent response of two commercially available electronic personal neutron dosemeters was studied in several laboratory-produced broad-spectrum neutron fields. Fluence-weighted mean energies ranged from 200 keV to 4 MeV; personal dose-equivalent rates ranged from 75 to 10 mSv h(-1); and angles of incidence were multidirectional, 0 degrees, 30 degrees and 60 degrees. Three of these fields have been shown previously to resemble ones found in CANDU (Canadian Deuterium Uranium is a registered trademark of the Atomic Energy of Canada Limited) power plant workplaces. Both dosemeters were found to perform reasonably well across the range of energy spectra and angles of incidence. One type of dosemeter displayed values of the personal dose equivalent that were, at worst, within a factor of approximately 2 of the reference values and, at best, within a few per cent of the reference values. The other type displayed values of the personal dose equivalent that were consistently within unity and 20% of the reference values. Although the radiological performance of one was found to be more accurate, this device was also found to be the less rugged of the two. Some of the data acquired in this work were compared with results previously published by others. There was consistency between these sets of data.

Humans↗

PubMed2003

Usefulness of laboratory neutron fields.

A moderator-type neutron survey meter, intended for radiation protection use at a nuclear power plant, was tested in five laboratory neutron fields, including neutron fields that resemble ones found in some reactor workplaces. Calibration constants (counts Sv(-1)) and responses (ratios of measured to reference values of ambient dose equivalent) were determined by measurement for each neutron field. Theoretical calibration constants were calculated for each field using a response function from the literature. These theoretical calibration constants were consistent with ones determined from measurement. Theoretical calibration constants were also calculated for several power-plant workplace neutron spectra. The range of calibration constants determined provided some insight into the amount of over-response and under-response that this particular survey meter would be likely to give when used in the intended workplace. Values for the calibration constant were suggested.

Calibration↗

PubMed2001

Characterisation of laboratory-produced CANDU-like workplace neutron fields.

Two neutron fields were produced in the Neutron Irradiation Facility (NIF) at the Chalk River Laboratories of the Atomic Energy of Canada Ltd. by directing (d,D) neutrons from a 150 kV neutron generator through a specially designed moderator assembly. Bonner sphere and proton recoil spectrometry systems were used to characterise these fields to determine whether they were CANDU-like*, i.e. whether they resembled neutron fields found in workplaces around pressurised heavy-water moderated power reactors such as CANDU reactors. Similarities were found between the distributions in energy of neutron fluence and ambient dose equivalent of the neutron fields produced in the NIF and those measured previously in power plants. In addition, there was agreement between theoretical (Monte Carlo) data and measured data, thereby validating continued use of Monte Carlo modelling for field characterisations in the NIF. The CANDU-like fields add to the repertoire of neutron fields available in the NIF and are expected to be useful for evaluating neutron dosemeters.

Clinical Laboratory Techniques↗

PubMed2000

Cytochrome P4501A1 polymorphisms in South American Indians.

A total of 131 individuals from five Brazilian Indian tribes were studied for two CYP1A1 gene polymorphisms. The presence of the *val allele at codon 462 varied from 54% in the Surui to 97% in the Xavante, while the presence of the MspI restriction site (*m2 allele) at position T6235C ranged from 72% in the Gavião to 95% in the Xavante. The haplotypes derived from these two sites showed a highly heterogeneous distribution among the five populations. The most common haplotype in South Amerindians was *val/*m2 (54% to 94%). This prevalence is the highest that has been observed in any world population.

Brazil↗

PubMed1997

Calibration of a portable tritium-in-air monitor for various radioactive gases.

A commercially available portable tritium-in-air monitor was calibrated for detecting the concentration of tritium-in-air, 14C-in-air, and various radioactive noble gases. Calibrations were performed both experimentally, using assayed quantities of the calibration gases, and theoretically, by simulating the monitor's response using Monte Carlo code. The experimental and theoretical calibrations agreed within +/- 10% for all gases tested with the exception of 41Ar-in-air where the agreement was approximately 20%. The results show that, although the monitor can be used to measure a wide range of radioactive gases, if more than one gas is present the monitor can not be used to accurately determine the concentration of, and hazard posed by, these gases. It is also shown that the monitor's ability to accurately assess tritium-in-air hazards would be seriously compromised by the presence of other radioactive gases.

Air Pollutants, Radioactive↗

PubMed1996

Neutron fields inside containment of a CANDU600-PHWR power plant.

Neutron fields in six locations inside containment of a CANDU600-PHWR power plant were characterized using Bonner-sphere spectrometry. Unfolded fluence spectra were used to predict and understand the behavior of a rem meter (a moderator-type dose equivalent survey instrument). The suitability of employing commonly-used sources such as 241Am-Be for calibrating the rem meter was investigated by calculational means. Results of these calculations suggest that employing a calibration field more representative of the power-plant fields would likely provide more accurate dose equivalents.

Neutrons↗

PubMedDate not supplied

[Hilbert transform-based modelling of EKG].

Recent developments in modeling methods on the non-linear and non-stationary data, such as electrocardiograms (ECG), have received large attention by the time-frequency analysts. The technique presented in this paper is based on parametrical modeling of the instantaneous module as well as instantaneous phase, estimated directly from each ECG beat. The estimation is adaptive since, the parameters related to a specific ECG beat are calculated from a given reference signal. In order to evaluate the performance of our technique, data recorded from the MIT-BIH arrhythmia database are used.

Algorithms↗