There are numerous tools available to detect and measure environmental lung carcinogen radon gas [1] [2] [3] . Those are in general classified into active and passive techniques respectively for short and long-terms assessment.

We have to decide according to what we aim to do which technique to use on the basis of the feasibility and cost of the measurement as well as the accuracy and the applicability of the technique.

The risk of lung cancer from radon is related to the long-term exposure of people, so it is important that estimates of radon levels in homes and workplaces should be as close as possible to the long-term average [4] . For this reason, it is generally advised that short-term measurement should not be used as the basis of advice on whether or not a building has a radon problem. And this is why long-term measurement using passive methods should be appropriate. But continuous active measurements can be helpful in identifying the cause of the radon problem.

Among the different passive techniques, the Solids State Nuclear Tracks Detectors (SSNTD) and particularly the LR 115 detector, are the most widely used to do integrated measurements necessary for epidemiological studies [5] [6] [7] . We must therefore count the number of etched alpha tracks from radon on samples of this detector. Among the main instruments commonly used for this work, we have the optical microscope and the spark counter. Several authors used either one of these devices or the other separately for radon alpha tracks counting [8] [9] . But, our main concern in this study was to use both apparatuses alternatively to count tracks on a given sample. That allowed to compare the tracks densities obtained and also the corresponding radon concentrations. Thus, calibration process was performed to determine factors for the reading of LR 115 type 2 detector with both devices since those were needed to convert etched alpha track densities into radon concentrations [10] [11] . In addition, the saturation phenomenon for tracks counting on LR 115 samples by means of the spark counter, which could distort the results given by this apparatus, was carried out.

The results obtained are reported in Tables 1-4 below.

Table 1 shows that tracks density read by the microscope is very much higher than the value given by the counter for each etched sample of LR 115 type 2. That agrees well with results we found in the literature [19] . In fact, with the microscope, all the visible etched tracks are read, even the smallest. But, for the counter, only tracks with a certain etching level to allow the voltage pulse to be produced are counted.

The average calibration factors found are in Table 2 [20] . We notice that their relative uncertainties are between 45% and 47%. That is due to the uncertainty on the concentration of radon into the barrel during the calibration process [(1.99 ± 0.93) kBq/m³] which also gives a relative uncertainty of about 47%. This concentration which derives from the radon source used during this process was obtained in particular conditions we have to explain. We said previously that the radon source was a radium-226 solution contained in a polyethylene capsule.

Unfortunately, when we were doing the calibration, we noticed that an important part of water in the capsule vaporized. And the consequence was that the diffusion process through the polyethylene was not done properly. So, we were even obliged a few days after the beginning of the process to inject again radon from the source into the barrel. We can observe that on the graph of Figure 2. Finally, the LR 115 type 2 samples were exposed to radon into the barrel for 10 days instead of 15 days as we initially wanted to do. The values of calibration factors obtained were used for calculation of radon concentrations applying the Formula (1). And due to errors propagation, the concentrations of radon also have relative uncertainties between 45% and 47%. But the different results are acceptable first because in this domain of radon metrology, relative uncertainties vary a lot and also because these results allow to maximize the radiological risk.

Table 3 shows the different values of radon concentration obtained. Using these values, a statistic correlation particularly the linear correlation between radon concentrations obtained by means of the microscope and those given by the counter was studied.

Two regression lines were drawn on the graph of Figure 3 representing radon concentration obtained with the microscope as a function of radon concentration obtained with the counter and vice versa. These lines are intersecting, close to each other and almost merged. The linear correlation coefficient r is equal to 0.95.

All these mathematical characteristics regarding the two regression lines show a very good correlation between the two variables i.e. the results of radon concentration given by the microscope and those given by the spark counter. It is therefore reasonable to use the optical microscope as well as the spark counter for measurements of environmental radon concentrations and also for the monitoring of the radiological risk of this gas.

Table 4 gives alpha track densities read on LR 115 samples and the corresponding irradiation times. These results allowed to draw the graph of Figure 4.

On this figure, we observe that track density increases with the irradiation time up to almost 11,000 tr/cm² and remains approximately constant beyond this value. 11,000 tr/cm² can reasonably be interpreted as the maximum value of track density that can be read by the spark counter. Beyond this value, we have the saturation phenomenon which distorts the results when it occurs. But it doesn’t matter since this maximum track density is never reached as far as our environmental radon measurement is concerned. Therefore, the use of the spark counter is free for such a survey.

The investigations carried out in the present work show that care should be taken to the different steps in the handling of the optical microscope and the spark counter for the determination of radon concentrations in order to obtain good results.

Otherwise, the densities of etched tracks from radon alpha particles on each sample of LR 115 type 2 detector counted by the optical microscope are always very much higher than those counted by the spark counter. But, taking into account the respective calibration factors of the two devices for the reading of the detector, corrections were made. Therefore, both apparatuses give radon concentrations with a very good linear correlation coefficient of 0.95. Moreover, the saturation phenomenon regarding the reading of LR 115 detector by means of the spark counter which can distort the results, occurs beyond 11,000 tr/cm² i.e. a density never reached as far as our environmental radon measurement is concerned. Thus, we can use the optical microscope as well as the spark counter to determine environmental radon concentrations as we did in Côte d’Ivoire. And in case of large scales measurements, the results obtained can be used for epidemiological studies related to the radiological risk of this gas.

The authors would like to thank the International Atomic Energy Agency (IAEA) which financed this work in the frame of a Technical Cooperation among Developing Countries (TCDC) through an AFRA/RAF 0038 project entitled radon gas monitoring in Cote d’Ivoire. For their precious help, particular thanks to Dr Z. L. Mokrani and Dr M. Aitziane from the Department of Dosimetry and Ionizing Radiations located at the Nuclear Research Centre/Nuclear Energy Commission of Algiers (Centre de Recherche Nucléaire/Commissariat à l’Energie Atomique d’Alger (CRNA/COMENA) where this study has been carried out.

The authors declare no conflicts of interest regarding the publication of this paper.

Agba, D.S.I., Kezo, P. and Konaté, I. (2023) Comparative Alpha Tracks Counting Using an Optical Microscope and a Spark Counter. Detection, 10, 7-18. https://doi.org/10.4236/detection.2023.102002