Estación RN50

Bienvenidos al sitio Web de la Estación RN50 del Sistema Internacional de Vigilancia (IMS) de la Organización del Tratado de Prohibición Completa de Ensayos Nucleares, situada en la Ciudad de Panamá. Específicamente, en el Campus Central de la Universidad de Panamá.

Bienvenidos al sitio Web de la Estación RN50 del Sistema Internacional de Vigilancia (IMS) de la Organización del Tratado de Prohibición Completa de Ensayos Nucleares, situada en la Ciudad de Panamá. Específicamente, en el Campus Central de la Universidad de Panamá.

Bienvenidos al sitio Web de la Estación RN50 del Sistema Internacional de Vigilancia (IMS) de la Organización del Tratado de Prohibición Completa de Ensayos Nucleares, situada en la Ciudad de Panamá. Específicamente, en el Campus Central de la Universidad de Panamá.

Bienvenidos al sitio Web de la Estación RN50 del Sistema Internacional de Vigilancia (IMS) de la Organización del Tratado de Prohibición Completa de Ensayos Nucleares, situada en la Ciudad de Panamá. Específicamente, en el Campus Central de la Universidad de Panamá.

Bienvenidos al sitio Web de la Estación RN50 del Sistema Internacional de Vigilancia (IMS) de la Organización del Tratado de Prohibición Completa de Ensayos Nucleares, situada en la Ciudad de Panamá. Específicamente, en el Campus Central de la Universidad de Panamá.

Bienvenidos al sitio Web de la Estación RN50 del Sistema Internacional de Vigilancia (IMS) de la Organización del Tratado de Prohibición Completa de Ensayos Nucleares, situada en la Ciudad de Panamá. Específicamente, en el Campus Central de la Universidad de Panamá.

Articulo 3

Be-7, K-40 and Pb-210 as atmospheric tracers in Panama City.

 

Omayra Pérez C.
Universidad de Panamá, Estación RN50

 

Bernardo Fernández G.
Universidad de Panamá, Estación RN50

 

 

Abstract — The “radionuclide stations” of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) were originally designated for detecting nuclear tests.  However, the network has a scientific and environmental interest for civil applications beyond the original aim. So, in this paper, the Be-7, Pb-210 and K-40 detection as climatic and meteorological parameters, in Panama City, give us valuable information for modeling the transport of air pollutants.   These parameters can be correlated with the spread of a radioactive cloud, near the RN50 station site.  It is suggested that the Be-7 is a more global indicator parameters and both, Pb-210 and K-40 are more local indicators of the RN50 effectiveness of radionuclide monitoring.

 

Keywords — CTBTO, atmospheric tracers, Be-7, K-40, Pb-210.

  

I. INTRODUCTION

 

World peace is essential for the mankind survival. So the immediate elimination of mass destruction weapons is required. One of such weapon is the nuclear bombs. Both, production and dismantlement of nuclear bomb arsenals required on-site inspections. These sites inspections affect the sovereignty of countries. So it came to a tacit agreement between countries, to start the process towards peace, monitoring the nuclear test. The radioactivity coming from nuclear test pollutes the environment. For example, due, to these nuclear tests, the Cs-137 content in the atmosphere substantially increased, also the tritium in the water, etc. The Comprehensive Nuclear Test-Ban Treaty (CTBT) was opened for signature and ratification by countries, on the United Nations headquarters, in 1996, after becoming aware that over 2000 nuclear tests not only threaten world peace but endangered the environment.

 

Among the provisions of the treaty and in order to verify the compliance, the regime established 337 stations in a international monitoring system (IMS), 80 of which for monitoring radioactivity in airborne (with relevant radionuclides coming from nuclear tests), 40 monitoring stations of radioactive gases products (primarily radioactive xenon) of nuclear explosions and also the establishment of 16 laboratories for the detection of very low radioactivity, as support for the monitoring radionuclides stations.

 

The treaty assigned two radionuclide stations to Panama (noble gas PAX50 and airborne particles PAP50), one of relevant radioactive gases and the other of airborne particles. Within the treaty verification regime the IMS have civilian applications supporting the regional environmental monitoring. This data are obtained by the IMS with high quality equipment and reliability. For example, the IMS network gave reliable information from the nuclear Fukushima event [1]. At the time, the treaty organization (CTBTO) could give information to those responsible for Fukushima. The data, detected few kilometres from the accident, on the JP38 station of the IMS network, were very useful to adopt radiation protection measures. On the other hand, the data of the stations gave information to simulate the spread of a radioactive cloud and provided useful information for countries around the globe, on the scope of the event. Particularly, the characteristics of the cloud that spread into two climatic layers met, between cero and 0.5 km and between 2 and 5 km from soil. The pollution measurements propagated by the cloud, in different stations, was useful as a test of the capability of the network in case of an event not just a product of a nuclear test, but as a result of a radioactive accident (incident). The data products of the network will be better interpreted in the study of the local, regional and global radioactive incident, if we know the correlation between the climatology and local weather within the propagation of the cloud, in different network sites.

 

The distribution of Na-24 of radioactive particles in aerosols detection was studied by Matthews [2], as a possible natural airborne tracer, assessing the effectiveness of radionuclide monitoring. In this work the latitude and the altitude (sea level and 18 km altitude) was taken into account in order to evaluate the efficiency of different stations. In this study, covering a period exceeding five years, Na-24 detection was found over 3 000 times in all seasons with an average value of 12 μBq/m3.

Fig. 1. Variation with latitude, Na-24 and the dose of cosmic origin [2].

 

According to the data, the 10 stations having the highest detection frequency as a function of latitude (figure 1, by Matthews [2]) and a high correlation (reverse or direct) with the season are reported in table 1. This table list the stations shown by Matthews [2].

 

Table 1.

Station

Latitude

Site

PAP 50

8.9° N

Panamá

FJP 26

18.0° S

Fiji

USP 72

28.3° N

Florida, USA

GBP 68

37.0° S

Tristan da Cunha

NZP 47

35.1° S

New Zealand

NZP 46

44.0° S

Chatham Island

RUP 60

53.1° N

Petropavlovsk, Russian Fed.

USP 71

55.2° N

Dubna, Russian Fed.

RUP 61

56.7° N

Alaska, USA

 

Matthews concludes that the coupling movement of air masses for detection is better in some seasons than in others of the same latitude and in some latitudes than others, below 5 km altitude. 

 

The above results suggest that the PAP50 (airborne particles) station, in the latitude 0-10º, is the most effective monitoring station of the IMS for detecting radionuclide tracers produced in the atmosphere below 5 km.  We make the same suggestion studying K-40 (primordial) coming from the sea and erosion of rocks and Pb-210 of terrestrial origin (primordial).

 

To the present times, our aim is study Be-7, K-40 and Pb-210, as atmospheric tracers, in PAP50 station.   The climates and weather events are non-deterministic, so this study can contribute as an indicator of climatic and meteorological parameters needed in software simulations of spread of  radioactive clouds in case of radiation incidents.

 

 

II. The beryllium 7 as tracer

 

The Earth has an atmospheric gaseous layer divided into regions, according to some parameters that depend on the altitude. These include the stratosphere and troposphere. These, in turn, are divided into sub regions, according to characteristics that directly affect humans, such as having a weather layer. This layer is generally limited by a barrier such as a change in slope in the variation of temperature with height.

 

Most authors refer to the atmospheric weather when they are studying in the medium term, implying a time scale of decades. Moreover the meteorology deals with the behaviour at smaller time scales. There are variables that significantly influence the physical and chemical characteristics of the atmosphere, for example, the cosmic rays.

 

The cosmic rays, received at the atmosphere, depend on the geographical latitude, on the inhomogeneity of the magnetic field, as we know, deflects charged particles. The magnitude of the magnetic field can go up to 70 % of the total at the poles up to 7 % in the Ecuador. It may also depend on the seasons and on the day-night cycle [3].

 

For many authors [4], cosmic rays primarily affect the lower stratosphere (66 %) and upper troposphere (33 %). The same, when colliding with particles in the atmosphere, produced cosmogony elements such as Be-7 and Na-24, which are natural radioactive isotopes (isotopes, formed from cosmic rays, that have generated more atmospheric studies are C-14, Be-7, Na-22, Na-24 and tritium). Therefore, the formation rate is greater in the layer located between the troposphere and the stratosphere). Its mechanisms of decay can be complicated. Some radioactive elements are indicators of interchange of air masses between the stratosphere and troposphere. Its production and decay is variable, then the concentration in the soil is also variable [5]. Be-7, for example, near the earth surface, varies by an order of magnitude between the tropical and sub-polar latitudes.

 

The natural formation mechanism of Be-7 in the atmosphere is by spallation, and occurs when the highly energetic protons and neutrons of cosmic rays collide against air light nuclei such as carbon (Z = 6), nitrogen (Z = 7) and oxygen (Z = 8). Because of its short half-life and habits to adhere to very fine particles in air, beryllium-7 has been widely used as a tracer for atmospheric studies, both climate and weather. In the decay scheme of Be-7, it can be seen that the half-life is 53.22 days and is a gamma emitter in 477.62 keV. Another tracer used, Na-24, has a shorter half-life, of 14.96 hours and emits gamma radiation at 1.37 MeV. The Be-10 has a much larger half-life (over a million years and it is a beta emitter).

 

When the half-lives are short, these elements can be used as tracers of the evolution of air masses and to determine the deposition of fine particles on the surface of the Earth.

 

Similarly, the concentration of the short half-life, isotopes in the troposphere, is sensitive to vertical Eddy diffusion coefficients. Note that in the low and very high latitudes, there is less concentration of Be-7 and the deposition on the surface, is therefore smaller. Because the microscopic processes responsible for the air mixture is very complex (the complex phenomena are in the field of deterministic chaos) to describe atmospheric mixing in detail, model builders, generally treat the system as an Eddy diffusion macroscopic process.

 

For short-term predictability, an approximation is enough for the desired effect [6]. An important factor, for example, is the coefficient of vertical diffusion of Eddy K. This ratio is in the range of 5x104 and 3x106 cm2 s-1, but for altitudes below 4 or 5 km, the sensitivity of Na-24 concentration decreases with Eddy diffusion coefficient. That leads us to the conclusion that the Na-24 is also produced in the lower atmosphere [7].

 

The radioisotopes concentrations in air are dependent on production and decay time. On the other hand it also depend on the exchange of air masses between the stratosphere and troposphere and dry and wet deposits of aerosols (removal in the troposphere can be given by the rainfall activity). There are three main factors influencing the exchange of air masses: gravity, pressure gradients and Coriolis inertia. The vertical distribution of the particles is influenced by the balance between gravity and the pressure gradient. In the horizontal direction, Coriolis pressure gradient play an important role in generating the geostrophic flows. At low altitudes this flow is modified by friction between air masses and topography (mountains, buildings, etc.). Leppanen et al. [8] found a dependence on the production of Be-7 with the geography, and a seal from the local weather pattern and appears, though not so clearly, separation between production and transport of beryllium.

 

As a result of the Chernobyl accident, the particle size distribution of Cs-137 and I-131 was studied [9] and a median aerodynamic diameter on 0.4 μm was found that is similar to Be-7. The speed dry deposition over land 1x10-5 m.s-1 is similar to Beryllium and Cesium and 3x10-4 m.s-1 for I-131. The results of this studies lead to the conclusion that neither the temperature of the earth’s surface, or atmospheric turbulence had observable influence on the deposition. Its origin is rather due to water condensation in the air which increases the size of the aerosol. Be-7 adheres to aerosols of diameters between 0.3-0.6 μm (fine particles) and whose residence time in the atmosphere is on average, 20 days [10]. Be-7, a natural tracer into the atmosphere, allows knowing the long term variations in the deposition of aerosols whose grain size and dynamics are 0.4 micrometers. This allows knowing the dynamics of deposition of aerosols that are similar such as Cs-137 and I-131. This result is interesting for solving environmental and radiation protection problems.

 

III. Materials and methods

 

3M Filters fully studied [11] are replaced daily in a Senya airborne particle pump, that has a nominal flow 1 000 m3 per hour and is properly calibrated. With an average flow 980 m3/h, after about 24 hours, 23 000 cubic meters of PM10 are collected. There is a weather station manufactured by Vaisala on the site where the pump is located. This station monitors temperature, humidity, rain precipitation, wind speed and direction.

 

The filters have an efficiency of almost 100 % for particles whose diameter is equal or greater than 0.4 μm. It is over 85 % for those between 0.15 and 0.4 μm [11]. The retention of fine particles was verified by scanning electron microscopy. Studying superparamagnetism by Transmission Mössbauer Spectroscopy on the sample confirms that the nanoparticles are collected [12].

 

Once the filter is collected, it is transported to a laboratory located about 300 m away from the particle pump site. On the laboratory it is compressed (Karl Kolb press from Scientific Technical Supplies) to 100 kN, into a mold that allows transform it to cylindrical pads of 50.0 mm in diameter and 5.0 mm thick, in order to ensure the reproducibility of the sample geometry. The daily samples are packaged in a plastic holder, studied and made to ensure reproducibility with very low radiation background (Alron Plastics Pil, Australia). Traceability is ensured with a barcode label.

 

The laboratory is controlled in temperature and humidity by sensors that measure parameters in real time. Radon levels are also measured daily. The compressed filters are left in a decay chamber for 24 hours in order to avoid interference of non-relevant very short half-life nuclides with the radioactive nuclides relevant to the treaty. A Canberra Germanium hyper-pure detector GC5020 is used, with a cylindrical crystal, 65 mm in diameter, 67 mm long and on 5 mm away from the window, with a factory efficiency of 56 % (relative to NaI) and a nominal resolution concerning the standard peak 1 332 keV (Co-60) of 1.93 eV (in the laboratory we measure a monthly average 1.9 eV). The daily quality control (QC) is made with a source pattern NPL (81020X). The spectra are collected in a multichannel analyser with 8 192 channels (Canberra DSA- 1000) with an energy up to 2 800 keV. The calibration curve in energy and in efficiency is shown in Figures 2 and 3 respectively.

 

Fig. 2. Detector´s energy calibration.

 

Fig. 3. Detector´s  efficiency calibration.

 

The system is cooled with an electric cryostat model Cryo-Press 5 from Canberra. To avoid interruptions due to power outages or variations in the electrical, the system has a UPS (true-on-line) coupled to an auxiliary generator. To control the spectrometer and accessories, and analyses the spectra the Genie 2000 software is coupled to a library and to special CTBTO subroutine. Electronic filters are used to prevent the resolution degrade due to the piezoelectric effects (vibration). The routine is made in compliance with the protocol to avoid cross contamination.

 

The coupled geometry between detector and sample-holder is insured with a Teflon mold (studied radioactive background) so that the sample always fit the same position on the detector. The system is shielded with Canberra Model 747. With this system it is got excellent MDC.

 

For external quality control measurements, samples are regularly sent to one of the 16 laboratories in the external network (IMS) that allows international comparisons to make corrections. The inter-comparison with these specialized and certificates laboratories, allows stations the necessary corrections to maintain quality of the measurements.

 

IV. Location and meteorological site characterization

 

The PAP50 station is located in Panama City, at the University of Panama. The referenced coordinates are: latitude 8º 59´ 00.9´´ N (8.984º N), longitude 79º 31´59.1´´ W (79.533º W) and a height (at the particle pump) of 90 m above sea level.

 

In Figure 4, it is show the mean rainfall in Panama City (10 years). This chart indicates the existence of two seasons. The rainy season from mid-April to mid-December with peaks in May and October, and a mini summer called “veranillo de San Juan” between the two. The dry season runs from January to April.

Fig. 4. Rainfall in Panama City.

 

Figure 5 shows irradiation (insolation) measured in PAP50 station (values taken every day) and plotted for a year.  We observe two large regions of accumulation points (darkest parts) corresponding to clear days (dry season) and overcast days (rainy season).

 

Fig. 5.  Daily radiation on PAP50 station.

For most of the rainy season, the inter-tropical convergence ensures good coupling between layers of the atmosphere. Due to this convergence that has vertical movement of air, allowing the Be-7 formed in the upper middle atmosphere goes to PAP50 station and it is detected. In the dry season vertical movement of air is demonstrated by regular radiosonde deliveries on weather balloons.

 

Summarizing site`s characteristics, PAP50 is located in a place with a humid tropical climate, average annual rainfall of 120 cm with maximum of 27 cm/h, with prevailing winds in the direction 350º, continuous about 2,5 m/s, even vertical gusts, temperature max/min 33 ºC/23 ºC, near large bodies of water (at the edge of the Pacific Ocean and 80 km from the Atlantic Ocean), small hills, two seasons: dry and rainy, average irradiation 13 j/m2, is located in the inter-tropical convergence north and relatively good coupling between high, middle and lower atmosphere.

 Fig. 6.  Airborne particles pollution in Panamá City.

 

We note fluctuations in the annual average of suspended particulates. However, outside the fluctuation in annual mean value, a systematic increase appears that begins in the 2010 (associated with the substantial increase on construction activity) and continues to rise significantly which is confirmed so far in 2013.  This increase in PM10 pollution is reinforced by the construction of urban subway and improvements in the road system of the city of Panama generating traffic gridlock, then increase the pollution emitted by cars.  This increase in pollution (particles suspended in the air) coming primarily from the movement of cars as seen in the curve for weekday, during the dry season and no other sources of increased.  The Be-7 has short life, so normally should not increase its content per m3 in airborne particles collected by the increase in vehicular traffic.

 

V. Results and conclusions.

 

A. Tracer Be-7.

 

It was studied, daily, Be-7 from April of year 2005 to October 2013.

Figure 7 is a graph of the week (average of seven days) for eight years, of measurement of Be-7 with the hyper-pure Ge-detector. It is observed a wave with amplitude modulated by an envelope wave. That indicates that there are two waves with very close frequencies. This phenomenon is not observed in the graphs in the literature for measuring beryllium elsewhere. This behaviour is possibly due to the double peak showing the solar emission in its eleven-year cycle. In daily curve (Figure 8) a chaotic phenomenon of fluctuation intense is observed (similar to the Brownian motion curve).

 

 

Fig.7. Be-7 weekly average (eight years) in PAP50.

 

In the following graphs (figure 8 and 9) it is showing the average daily variation and then, by month, measured along eight years. The behaviour is in agreement with the local climate change, including even the "Veranillo de San Juan". In the graph of Figure 8, it is noted the linear increase, the linear lowering, and then almost constant slope.

 

 

Fig. 8.  Average daily Be-7 variation with strong fluctuations of a meteorological phenomenon.

 

Fig. 9.  Average monthly variation of Be-7.

 

Linear growth means that with the increase of rain, the washing of the beryllium particles, increase too. Due to their size, composition, or habits, particles are sensitive to the continuous washing. In the dry season, Be-7 content increases linearly with the lack of rain.

 

 

In the graph of figure 9, the monthly averages variation are observed with the calendar month, indicator of the dependence phenomenon associated with the inter-tropical convergence. There are two relative minima associated to the "Veranillo de San Juan". There are two relative maxima. It is a very pronounced dry season, and a small one, in the "Veranillo de San Juan". It can be said then, that beryllium is a good indicator of phenomena that influence climate and weather.

 

B. Tracer K-40

 

Potassium-40 is a radioisotope with half-life of 1.277 x 109 years and gamma energy on 1 460.75 keV. It decays in two ways, in Ar-40 and in Ba-40. It is found in rocks and sediments as well as on marine ionic compounds. Their presence in airborne particles must come from the sea or from the dust at the ground. They reach the particle pump due to winds. The potassium content in the particles suspended in the air was analysed by optical emission spectroscopy inductively coupled plasma (ICP - OES) [12]. The concentration captured in PAP50 indicates that is a bit high when compared to other cities like Coimbra, Azusa, Edison and Anaheim. This is caused because of the proximity of the seas to Panama City (located at the edge of the Pacific Ocean and 80 km away from the Atlantic Ocean). Figure 10 shows that in the first 90 days of the year, the average rises linearly, after lower and remains constant until the end of September and then decreases slightly and remained constant until it is restarted again what happens in dry period. It should be noted that the growth or decline is less pronounced than for the Be-7.

 

Fig. 10.   Average daily K-40 of the eight years studied.

 

Detection of K-40 is sensitive to local phenomena such as wind and rain. In the dry season, the dust rising and stays in the air and increases as the days pass. With the arrival of the rains, airborne particles with K-40 remain constant. In October, with the dramatic increase in rainfall, the proportion of particles in the air drops (rain washed the larger particles), then the concentration remains constant. The K-40 is not sensitive to the influence of other climatic factors, or environmental pollution due to increased vehicular traffic or construction.

 

C. Tracer Pb-210

 

The Pb-210 is a natural radioisotope in the fossil chain of uranium-238 (4n +2), also called radium´s chain element. It is an alpha, beta and gamma emitter, with half-lives 22.3 years. The gamma peak is found in 46.52 keV. In the atmosphere, Pb-210 is associated with sprays of 0.05 and 2.0 microns, i.e. with fine particles. According to studies conducted by different authors, the flow of Pb-210 depends on the region in question and it is related to local precipitation. It is appears in aerosols by wind and cycle through radon.

 

Fig. 11.  Measured daily Pb-210, en PAP50.

 

 

The graph of Figure 11 is observed daily, with strong seasonal fluctuations that appear due to the chaotic nature of weather phenomenon. In Figure 12 the completely linear dependence of Pb-210 with day of the year is observed. We remark linear increase in the dry season and the linear decrease in the rainy season.

 

 Fig. 12.  Content daily average Pb-210, depending on the day of the year.

 

The amount of Pb-210 increases linearly in dry season and decreases linearly in rainy season. In either case, neither the K-40, nor Pb-210 are is related to the phenomenon of solar activity because the formation of the K-40 and Pb-210 is not related with cosmic rays. They are essential or fossil elements.

 

D. Conclusions

 

There have been three natural radioactive tracers of atmospheric phenomena (weather and climate), Be-7, K-40 and Pb-210. Matthews [8] had studied the Na-24 in the case of PAP50 (and other stations of the IMS) and noted that it is an efficient station for latitudes in the range 0-10° in case of radioactive detection of phenomena that propagate in the atmosphere below the barrier which is about 5 km.

Addition of Na-24, each radioisotope studied in this article (Be-7, K-40 and Pb-210) provides information regarding the behaviour of the station PAP50. The Be-7 gives information about the behaviour of cosmic rays (solar and galactic) influencing the atmospheric behaviour. The detection in PAP50 is under the inter-tropical convergence phenomenon that strongly modulates the climate and weather. It also depends on the insolation. Be-7 provides information on the vertical movement’s then link the detection in the station with the spread in upper layers. The K-40 give information about marine and terrestrial winds, then it is dependent on local phenomena. The Pb-210 depends on winds over land, but very little environmental pollution by particles.

 

In this regard, during the Fukushima event, which took place in March 2011, corresponding to the dry season in Panama, measurements yielded the following values for these parameters (see figure 13, 14 y 15).

 

 

Fig.  13.  Detection of Be-7, March 2011, during the Fukushima event, in PAP50 station.

 

The Pb-210 was below average (Figure 14) and as this radioelement is indicative of the propagation near surface; we can say that there were few winds. This coincides with the rainfall. That is showing little rain and less washing the I-131. This phenomenon is very similar to the K-40 (Figure 15) that was also below the historical average.

 

Fig.  14.  Values of Pb-210 in the event of Fukushima.

 

Fig.  15. Values of K-40 during the Fukushima event.

 

In PAP50, detections of I-131, Cs-137, Cs-134 appeared for the first time on March 23, 2011 and on April 10, of Xe. The spread of the cloud was not following winds of 11 km altitude, as it would be in the opposite direction. The wind direction indicated by the meteorological earth stations was 350º. Winds were not of local origin, as indicated by the low values of K-40 and Pb-210.

 

One can conclude, although very short way, that PAP50 and PAX50 stations have proved successful in detecting radionuclides at low latitudes between 0-10º. This allows, with the IMS network of the CTBT, that in addition to the main goal to monitor nuclear tests, the station can also supports environmental monitoring system in the region (Central America and the Caribbean). In addition to monitoring the climate and the weather behaviour, and their radioactive tracers, the network allow to know the climate changes that are taking place, and would provide, in case of emergency, supporting criteria for making decisions on reliable parameters to be used in the simulation of the propagation of a radioactive cloud of local, regional or global origin. The civil authorities and early warning support systems can take decisions with this information to avoid affecting population. In this way they can fulfil the basic principles of radiation protection, “justification, dose limitation, optimization of protection”.

 

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References

 

[1] K. Haupt, T. Mützelburg, “Global radiation monitoring in the wake of the Fukushima disaster,” in CTBTO Spectrum, issue 16, May 2011, pp. 18-19.
[2] M. Matthews. “The effectiveness of radionuclide monitoring: assessed with a natural airborne tracer (Published Conference Proceedings style),” in Comprehensive Nuclear-Test-Ban Treaty: Science and Technology Conference, Vienna, Austria, 2011, pp. 68.
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[7] W. Roedel, “Cosmic-ray-produced sodium 24 and other nuclides in the lower atmosphere,” in Journal of Geophysical Research, Published online September 2012.
[8] A. –P. Leppänen, I. G. Usoskin, A. Aldahan, E. Echer, H. Evangelista, S. Klemola, G.A. Kovaltsov, K. Mursula, G. Possnert, “Cosmogenic 7Be in air a complex mixture of production and transport,” in Journal of Atmospheric and Solar-Terrestrial Physics, 72 (2010), pp. 1036-1043.
[9] J. Roed, “Dry deposition on smooth and rough urban surfaces", the post- Chernobyl workshop, 1987 Brussels, 3-5, NKA/AKTU-245 (87)1.
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[11] V. Tuomas, M. Mikael, “Testing of different types of flat filtering media for IMS radionuclide stations”, Contract 02/1/20/025 Testing Services, STUK-Radiation and Nuclear Safety Authority, 2000, Research and Environmental Surveillance, Airborne Radioactivity, Finland.
[12] O. Pérez, B. Fernandez, J. Jaen, B. Mojica, “The RN50 station of the International Monitoring System (IMS) as a reference station to the airborne particles pollution in Panama City (Published Conference Proceedings style),” in Comprehensive Nuclear-Test-Ban Treaty: Science and Technology Conference, Vienna, Austria, 2011, pp. 35.
[13] B. Fernández, O. Pérez, M. Acosta. “Informe de factibilidad de la Instalación de la Estación PAP50, “On site survey radionuclide station RN50 at Panamá City. Panamá, July 1999. Universidad de Panamá.

 
Acknowledgements
Thanks to operators for the daily work to have the data.

 

Funding sources
To the PTS of the CTBTO and to the University of Panama for the support of this work.

 

Author Contributions
Conceived and designed the experiments: O.P.C., B.F.G. Analysed the data: O.P.C., B.F.G. Wrote the first draft of the manuscript: O.P.C. Contributed to the writing of the manuscript: B.F.G. Agree with manuscript results and conclusions: O.P.C., B.F.G. Jointly developed the structure and arguments for the paper: O.P.C., B.F.G. Made critical revisions and approved final version: O.P.C., B.F.G. All authors reviewed and approved of the final manuscript.