L. Cabrera

Long term and equilibrium factor indoor radon measurements

This paper presents the annual radon gas concentrations obtained during the 1994–1995 monitoring campaign using passive electret system (type E-PERM). Radon levels were measured in 154 single family dwellings, in normal occupancy conditions (open house condition) in the metropolitan zone of Mexico City. At the same time radon monitoring was performed outdoors. The results show the general log-normal distribution of integrated indoor radon concentration with an annual indoor mean of 3.8 pCi·l−1. The seasonal variations show the minimum mean values in the summer season which are 39% lower than that in autumn. Equilibrium factors (F) were measured in 12 typical houses both in autumn and winter using a continuous working level monitor for short-lived radon decay products and H-chamber loaded with a short term electret (HST, E-PERM) for radon gas. The obtained total mean equilibrium factors are:F=0.41±0.17 andF=0.29±0.04 for indoor and outdoor, respectively. A quality program was also improved.

Urinary selenium excretion in patients with cervical uterine cancer.

In this work, we report on a relationship between urinary selenium and the development of cervical uterine cancer. A simple chemical method was developed to concentrate trace amounts of selenium from relatively large urine samples by use of small activated carbon filters. When these filters are irradiated with thermal neutrons, selenium can be determined either by 77mSe (t1/2=17.5 s) or 75Se (t1/2=120 d). In this article, we report the results for 82 urine samples from women with cervical uterine cancer in several stages of development and from healthy controls. These results show a statistically significant increase of selenium excretion in cancer patients as compared to controls. Urinary selenium excretion is highest for patients in the intermediate stages of the disease.

Gamma radiation and radon levels in Mexico City dwellings

Gamma exposure rate and radon levels were measured in 75 single-family dwellings in Mexico City in order to correlate them with local environment. Radon monitoring was performed both indoors and outdoors using a continuous working level monitor for short-lived radon decay products; the gamma exposure rate was measured using CaSO4: Dy+PTFE. The results obtained show a log-normal distribution. The mean indoor radon concentration is lower than 45 Bq/m3 and the mean indoor gamma exposure rate was 11.29 μR/h.

Determination of pollutants in dwellings by neutron activation analysis and X-ray fluorescence

Metallic pollutants were measured in dwellings in Mexico City by instrumental neutron activation analysis (INAA) and X-ray fluorescence techniques. Monitoring was performed in the west side of the city and in the winter season. In general the average concentration of contaminants collected, when compared with the average concentrations reported in a previous paper, have increased with time and in the particular case of lead and mercury some samples are above the indicative WHO maximum levels.

Activation analysis of selenium in cancer research

The method described in a previous work to separate trace amounts of selenium in organic samples without using a carrier, based on the adsorption on active carbon filters of the complex formed with ammonium pyrrolidindithiocarbamate (APDC) at pH 1.5–2, has been applied to urine samples from 15 females patients suffering from cervical uterine cancer. With this type of sample the method reaches a maximum sensitivity (few ppb) with a good statistical variation (±12%). Since the highest concentration of selenium in human tissues is found in the kidney, and the elimination of this element is mainly by the urine, the method seems to be a powerful tool in the research about the human metabolism of selenium. This paper shows a possible relation of selenium concentration in human urine and the evolution time of cervical uterine cancer, in spite of limits imposed by the statistical error plus the inhomogeneity of the sample.

Use of activated carbon as pre-separation agent in NAA of selenium, cobalt and iodine

The position of pre-irradiation separations in neutron activation analysis is shortly discussed. Special attention is given to separations for purification and/or concentration of analyte elements, either complexed or uncomplexed, via sorption on activated carbon. It was shown for a number of trace elements that the blank value introduced due to the use of activated carbon is small or mostly even negligible. The NAA determination via pre-separations based on activated carbon is highlighted for selenium, cobalt and iodine.

Concentration of iodine traces in solution by filtering through activated carbon

The retention of iodine traces (ppb) was investigated in small activated carbon filters (50 mg) from solution at a yielding rate exclusively determined by pH. Retention is approximately 100% at pH values of 4–6, while no retention of iodine traces occurs after filtering them through an activated carbon filter from very acidic and basic solutions (pH values of 1 and 11, respectively) with 0% yielding rate. Since activated carbon is a very pure material, this procedure may be an alternative method of the activation analysis of iodine traces in foodstuffs, because the half-life of 128I, formed by (n,g) reaction, is only 25 minutes. It does not allow either the sample to be placed readily in solution or the radioisotope to be separated after irradiation with the purpose of attaining maximal accuracy and sensitivity in this type of analysis.

Metallic pollutants in Mexico Valley

Pollution has reached critical levels in the Metropolitan Zone of Mexico Valley. Concerned about, the Faculty of Chemistry has been performing environmental studies since 1995. This work presents the distribution and evolution of metallic pollutants in the Metropolitan zone of Mexico Valley. Samples consisted in aerosol filters (classified as total solid particles and respirable particles) as well as dry fallout. Samples were collected in several areas of the Mexico Valley, in different seasons along successive years. Metallic elements were determined by Instrumental Neutron Activation Analysis (INAA), X-ray fluorescence, and others techniques. Simultaneously, total solid particles (TSP) and respirable particles (RP) were determined by gravimetry. Elemental analysis of samples and matrix correlation allow us to establish some contaminant sources as well as relationship between concentration and relevant parameters.

INAA of Aerosol Samples in Mexico City

Total solid particles (TSP), respirable particles (RP) PM10 and 17 metallic pollutants were measured in dwellings in the Metropolitan Zone of Mexico Valley (MZMV) by gravimetry and instrumental neutron activation analysis (INAA). Monitoring was performed in Northeast, Center, Southeast and Southwest Zones in the winter and spring seasons. In general, the average concentration of contaminants (derived from industrial activities) that we have determined have increased with time. TSP and RP PM10 are often above the US and Mexican norms.

Separation of63Ni traces from low and medium level radioactive wastes produced during the operation of nuclear power reactors

The classification of low and medium level radioactive wastes produced regularly by nuclear power plants is becoming ever more important in Mexico, after a few years of running the first of two units, 600 MeV each, in Laguna Verde nuclear power plant. This paper describes a method to separate and detect traces of the weak β-emitter63Ni, which is one of the activation products used to classify low and medium level radioactive wastes originating from the operation of nuclear power plants.