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American Journal of Public Health Research
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Clinical and Histological Features in Wegener Granulomatosis
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Anne Lanham, Lillian Mwanri

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Measurement of Radon 222 Concentrations in the Basements of the New Engineering Building from the Pontificia Universidad Católica del Perú

Rojas Jhonny, Bertín Perez, Patrizia Pereyra*, María Elena Lopez, Luis Vilcapoma

Sección Física, Pontificia Universidad Católica del Perú, Lima-Perú

Abstract: Historical data of 222 Radon concentrations were collected in the building of Engineering PUCP recently built with eleven levels (eight on grades and three basements). The measurements were made in the three basement levels of the building. The first results of the history of 222 Radon concentrations in the basements of this building used as a parking lot are shown. The monitoring started the first week it was opened to the public. As nuclear track detectors we use the polymer cellulose nitrate (LR115 - Type 2). Changes in the concentration of 222 Radon registered, are linked into account aspects such as the use of exhaust extractors, increase in the number of vehicles, construction time and seasonal parameters. The results show adequate levels of 222 Radon concentration in all basements, the highest value is 97, 41 Bq/ m³ at the deepest level, the third.

Keywords: radon, new building, basements, LR-115-Type 2

Citation: Rojas Jhonny, Bertín Perez, Patrizia Pereyra, María Elena Lopez, Luis Vilcapoma, Measurement of Radon 222 Concentrations in the Basements of the New Engineering Building from the Pontificia Universidad Católica del Perú. International Journal of Physics, 4 (3). 55-58. January 2016. doi:10.12691/ijp-4-3-2

1. Introduction

The Pontifical Catholic University from Peru (PUCP), in the context of preparations to celebrate its first centenary has recently completed the construction of a classroom building of eleven levels (eight floors and three basements) within its university campus. Taking advantage of this new construction, it is intended to obtain historical data regarding the evolution of 222 Radon concentrations in the recent building taking into account environmental and other factors that affect it, the measurements have been made in the three basements levels of the building.

Nearly all naturally occurring radioisotopes belong to one of three radioactive series in the soil, thorium, actinium and uranium [1]. Radon isotopes, belonging to these radioactive series, are colorless and odorless. 222 Rn is the most stable isotopes of radon with an average half-life of 3.826 days, which is universally known as radon or radon gas; part of the uranium series radioactive and is an immediate relative of 226 Ra, with an average half-life of 1602 years; radon thus formed by the decay of radium in the soil and rocks entering homes, buildings, basements, tunnels, mines and accumulates particularly in enclosed areas [2].

Radon is the most important source of naturally occurring radiation and the largest contributor to the dose of ionizing radiation received by living organisms. This is mainly due to exposure to radon and its decay products in the air in confined areas; radon is the second leading cause of lung cancer in the general population after the tobacco; epidemiological studies have shown the relationship between exposure to indoor radon and lung cancer. The World Health Organization (WHO), showed the health effects due to exposure in homes (1979) [3], through a European work group in the study of indoor air quality. Later, radon was classified as a human carcinogen by the IARC (International Agency for Research on Cancer) in 1988, the specialized agency in cancer research of the WHO [3]; also, several studies conducted by the ICRP (International Commission on Radiation Protection) show cancer risk associated with exposure to radon and its decay products [4]. Finding a direct relationship of increased lung cancer, in 2005, two studies showed definitive evidence between residential radon exposure and lung cancer [5,6].

According to the above, several organizations in Europe and the United States have made recommendations and have established limits on the concentration of radon in interiors. In USA the maximum recommended limit is 4 pCi/l (150 Bq/m³). In England, the limit is 200 Bq/m³ (5.4 pCi/l). The European community recommends not exceeding 400 Bq/m³ in existing housing and 200 Bq/m³ in new buildings in accordance with the recommendations given by the Environment Committee of the European Community on February 21st, 1990. The Environmental Protection Agency (EPA) recommends that if levels exceed 200 pCi/l (7400 Bq/m³) actions should be taken to reduce levels within several weeks. For levels between 740 and 7400 Bq/m³ a reduction below 4 pCi/l should be achieved within several months. For levels between 4 and 20 pCi/l these should be reduced below 150 Bq/m3 over a period of several years. And in the case of levels below 150 Bq/m³, although this level of exposure is of lower risk, reduction of such low levels is sometimes difficult to achieve [7].

So, measuring the concentration of radon and its decay products becomes important because they affect health. For this purpose, different measuring methods are used; including nuclear tracks solid state detectors. The use of this type of detector is justified by the fact that a heavy charged particle causes a great ionization as it passes through a medium. An alpha particle ionizes molecules that are close to its path. The primary ionization process creates a chemically unstable area near the path of the particle that contains free radicals; this area is known as a latent track [8]. The material containing the latent track is exposed to a chemical solution, which becomes more intense (the etch rate is higher) in the latent track area; the solutions commonly used are NaOH or KOH. The effect caused by this chemical attack is that it etches the tracks on the detector’s surface, and it can be observed that the etch rate in the damaged area will be higher. Thus the particle tracks are etched or formed, and can be seen under a microscope or by use of the spark counting method or some other method such like image processing.

Using a suitable calibration factor, which depends on several parameters such as the shape of the container where the detector was calibrated, energy of the alpha particles related with the radioisotope, the parameters of the etching and counting process, etc. They are determined in a laboratory under controlled environmental conditions. The following relation is used [12]:

[picture] | (1)

Where ρ is the density of tracks in (tr.cm⁻²), k the calibration factor (tr. cm⁻² /t Bq.m⁻³), C the concentration in (Bq.m⁻³) and t is the exposure time (in days).

2. Experimental Procedures

The effect of the tracks left by the particles occurs in many materials such as cellulose nitrate particles or different polycarbonates, these materials, are also used to detect radon. This track forming effect is only seen in dielectric materials; in semiconductors by recombination processes the latent tracks are unstable and disappear [9].

The most common commercial detectors used for this purpose are the CR39 and the LR115; these detectors have certain differences, the first and most important is the active layer´s thickness, which is 12 microns for LR115 type II and 0.5 mm for CR39, also the tracks formed in them are different, in the case of LR115 they are little holes. The LR115 is based on nitro cellulose while the CR39 is based on polycarbonates, due to these characteristics there are differences in their parameters, which are compared in [10].

Concentration on a specific location based on the solid state detector is derived from the density of tracks observed in the SSNTD.

This work has been focused on determining the concentration levels of 222 Radon in the basements of a new building at the PUCP (Figure 1), opened in mid-2014. A few days after opened, the places were selected to measurement radon 222; each of places had to be checked to make a survey representative the concentration of radon 222 so every week students and professor were reviewed the experimental procedure because of in previous measurements (other places) the detectors were lost and the data could not be retrieved.

Figure 1. (a) New engineering building of the PUCP (b) Panoramic view of the basements

For this purpose, the LR115 detector with the above-mentioned characteristics was used. As the construction of the new building had just ended, the PUCP's Nuclear Tracks research group decided to monitor the concentration of Radon 222 in this new building, particularly in the basement where staff work 8 hours a day with the relevant labor turnover. For measurements, critical places such as corners were selected as these are placed far away enough from the existing exhaust fans. Places near the exhaust fans were also considered.

2.1. Materials

The materials used were: LR115 - type 2 detectors, etching 2.5 N NaOH thermostatic baths, and an optical microscope including a computer interface. (Figure 2). Each of these materials were used the better way so the LR115 – type 2 due to is very sensitive are stored as manufacturer recommends so these detectors have a very low background, the thermostatic baths are controlled by a thermocouple type k through temperature controller also distilled water was used to stop the etching this to neutralize the NaOH then the optical microscope were used for displaying the tracks are white holes, this holes are counted and related to the radon concentration. Also we used radon monitor to measurement radon concentration outside of the basement.

Figure 2. Equipment used for counting nuclear tracks associated to 222 Radon concentrations

2.2. Experimental Setup

The LR115 detectors were placed in the three basements of the new building of Engineering PUCP. Ten detectors are installed in every basement; four pairs in each corner and a couple stood on the stairs, all were placed at a height of approximately 1.5 m above the floor. In total thirty detectors were placed at all three levels like show in the Table 1.

Exposure time of the detectors was thirty days each period, this was repeated five times (periods 1 to 5), after that, the detectors were etched under the above mentioned conditions and recording time of 90 minutes. Subsequently the respective counting was made using a microscope; during the counting five fields of the detector were taken, since track distribution is random, with 10X magnification with a 3mm radius field approximately. Equation 1 was used to quantify Radon concentration with calibration factors of 20,41Bq m⁻³ corresponding to 100 tracks per cm² [11], both recording and counting were brought to standard conditions in the experimental physics laboratory of the PUCP.

Table 1. Positions of 222 Radon detectors in the basement of the PUCP Engineering building, where P1 is the first basement, P2 the second basement and P3 the third basement

3. Results

This report presents the measurements of 222 Radon in the basement of the new building of Engineering PUCP, made during the winter and spring of 2014 (southern hemisphere), for five consecutive periods, from August to December, every thirty days on average. The value of this study lies in the fact of verifying whether there is compliance with the standards of radon indoor concentration. Natural radon levels are determined for the first time in such workplaces in the PUCP, thus helping the relevant authorities to establish an appropriate healthy working environment. The results are shown in the following tables 2, 3, 4 and figures 3, 4, 5. Also there are measurements which were done outside of the basements near of the new building through digital radon monitor Canary® to compare outdoor and indoor radon concentration.

Table 2. Results of monitoring 222 Radon in the first basement of the PUCP Engineering Building

Figure 3. Histogram of the results of Radon 222 measurements in the first basement of the PUCP Engineering building, indicating the concentration in Bqm⁻³ for each period

Table 3. Results of monitoring 222 Radon in the second basement of the PUCP Engineering Building

Figure 4. Results of Radon 222 monitoring in the second basement

Table 4. Results of Radon 222 measurements in the third basement of the PUCP Engineering building

Figure 5. Results of Radon 222 monitoring in the third basement

Table 5. Results of monitoring 222 Radon in outside of the basements of the PUCP Engineering Building

4. Conclusions

This work has enabled taking measurements in a newly constructed building with different materials among which cement predominates and the particularity of walls kept unpainted and large basements with relatively poor ventilation. The results of the measurements in the basements show the presence of Radon 222 in such environments Table 2, Table 3 and Table 4. However, the levels found in different measurement periods in each of the places measured, are below the maximum allowable levels recommended by different organization like EPA and European community mentioned above. It is noteworthy that the highest measurement was found in the deepest basement, the third. The concentration level found was 97.59 Bq/m³, Table 4. It could be related with the deepness and also less ventilation factors. In all the cases, however, the results indicate that for the moment no corrective action is necessary. Also measurements outside of the basements in Table 5 are shown encountering low values of radon concentration than inside of basements, so we can conclude that there is a major presence of radon in closed places than open spaces. It is planned to check in the future the possible presence of Radon 222 in other environments of the building and continue monitoring the basements where staff remains 24 hours a day in labor turnover periods.

References

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[2]   | World Health Organization, “SELECTED POLLUTANTS”, 2010.
[3]   | World Health Organization, “WHO HANDBOOK ON INDOOR RADON”, 2009.
[4]   | ICRP, 1987. Lung Cancer Risk from Exposures to Radon Daughters. ICRP Publication 50.
[5]   | S Darby, D Hill, A Auvinen, J M Barros-Dios, H Baysson, F Bochicchio, et al., “A Radon in Homes and Risk of Lung Cancer: Collaborative Analysis of Individual Data from 13 European Case-control Studies”, British Medical Journal, 2005 January 29, 330 (7485): 223.
[6]   | D Krewski, JH Lubin, JM Zeilinski, M Alavanja, VS Catalan, RW Field, et al.,”A Residential Radon and Risk of Lung Cancer: A Combined Analysis of 7 North American Case-control Studies”., Epidemiology, 2005 March; 16 (2):137-45.
[7]   | “Radon Risk If You've Never Smoked”, http://www.epa.gov/radon/healthrisks.html. 1999-2001.
[8]   | Espinosa, G., “Trazas Nucleares en Sólidos”, UNAM. México, 1994.
[9]   | R.L. Fleischer, P.B. Price, R.M. Walker, Nuclear Tracks in Solids, University of California Press, Berkley, 1975.
[10]   | D. Nikezic 1, K.N. Yu., “Proﬁles and parameters of tracks in the LR115 detector irradiated with alpha particles”, Nuclear Instruments and Methods in Physics Research B 196 (2002) 105-112.
[11]   | Pereyra P., “Aplicación de la técnica de huellas nucleares en dosimetría de partículas alfa”, Tesis de bachiller de la Pontificia Universidad Católica del Perú., 1991.
[12]   | KP Eappen and YS Mayya Calibration factors for lr-115 (type-ii) based radon thoron discrimination dosimeter. Radiation Measurements, 38(1):5-17, 2004.