Quantification of pure beta spectra in mixed beta gamma fields as part of eye lens dosimetry at CANDU power plants.

To address the issue of eye lens dosimetry in nuclear industry, we initiated the project to quantify the beta and gamma-ray source term in CANDU power plants and to convert this source term into dosimetric quantities of interest, such as eye lens dose and personal dose equivalents Hp(10), Hp(0.07). This way, the eye lens dose can be compared with dosimetric operational quantities to evaluate whether independent dosimetry is required for eye lens protection, or present dosimetry is adequate.

CHARACTERIZATION OF A LANTHANUM BROMIDE DETECTOR FOR EYE LENS DOSIMETRY AT THE CANDU NUCLEAR POWER PLANTS BASED ON DIRECT MEASUREMENTS OF THE GAMMA-RAY SPECTRA.

Gamma-ray spectra were measured using a LaBr$_{3}$(Ce) spectrometer during the outage periods, aiming at quantifying the gamma source term of radiation workers' exposure, at the CANDU nuclear power reactors, for the purposes of eye lens dosimetry. The spectra were measured inside the boiler rooms, of the Bruce Power and Ontario Power Generation (OPG) CANDU nuclear power plants, where workers are exposed to relatively high dose rates radiation fields during the maintenance work. Prior to measurements at the CANDU reactors, the pulse shaping parameters of the gamma spectrometer were optimised for high rates gamma fields, up to an input rates of 120 kcps, in order to accomplish a high output rate with a reasonable energy resolution. In parallel, the response of the LaBr$_{3}$(Ce) detector was characterized by experiments and Monte Carlo simulations. The gamma spectra measured at the CANDU reactors were reported in terms of the gamma-ray fluence rate spectrum. In all measured data, $^{60}$Co and $^{95}$Nb were main contributors of the gamma fields. The measured spectra have been used to calculate the dosimetric quantities of interest: personal dose equivalents H$_{p}$(10) and H$_{p}$(0.07) and eye lens absorbed dose.

[Risk factors for cerebrovascular stroke in a cohort of hypertensive patients]. / Factores de risco de acidente vascular cerebral numa coorte de hipertensos.

OBJECTIVES: To identify stroke risk factors in hypertensive patients and the probability of stroke in relation to those risk factors and follow-up. STUDY DESIGN: A cohort study (patients with high blood pressure). MATERIAL AND METHODS: 707 hypertensive patients were studied (Hypertension Register) in what concerns stroke incidence until 1992 (n = 126), considering one case per individual. The following variables were analysed: age, sex, body mass index (Quetelet), systolic and diastolic blood pressure, heart rate, types of hypertension (JNC-IV), left ventricular hypertrophy, changes in ST segment and T wave (Minnesota Code), fundi, angina pectoris, heart failure, central nervous (neurological) disturbances, antihypertensive treatment, smoking, serum potassium, serum sodium, blood urea, creatinine, uric acid, blood sugar, diabetes and cholesterol, in the initial record. Individually, in relation to the control of hypertension, the subjects were classified according to the casual recording of normal blood pressure, the absence of drug treatment, diastolic pressure > 114 mmHg and, at the end of 1992, according to survival, causes of death and follow-up. Stroke risk factors have been identified by multivariate analysis (Cox regression model). The survival probability (without stroke) was defined by Kaplan-Meier method. RESULTS: It was possible to maintain the epidemiological surveillance, from 1975 to 1992, of 598 cases. From those, 109 hypertensive patients were victims of at least one episode of non transient cerebral ischaemia, during their follow-up of 10.5 years. From the characteristics studied, only five were identified at risk factors. The adjusted relative risks and confidence intervals (95% CI) were the following: age: 1.08 (1.06-1.10); diastolic pressure > 114 mmHg: 1.96 (1.32-2.91); neurological disturbances 4.64 (2.99-7.2); diabetes: 2.57 (1.62-4.05) and left ventricular hypertrophy: 1.34 (1.13-1.58). CONCLUSIONS: As far as stroke is concerned: a) Age, diabetes, a casual measurement of diastolic blood pressure > 114 mmHg and left ventricular hypertrophy (electrocardiogram) were the risk factors identified; b) Prevention should include blood pressure and diabetes control, although this disease has shown more risk than a casual measurement of severe hypertension; c) Its occurrence, in this model, has only partly been explained, therefore it has become necessary to deepen the study of the risk profile.