Iodine Gas Detection System Using Color Sensor

Iodine can exist in the form of radioactive and non-radioactive states. Radioactive Iodine-131 (I-131) has been utilized in nuclear facilities. Due to its ability to be absorbed by the thyroid gland, I-131 is used for therapy in thyroid cancer cases. Contrary to the benefit, Iodine is a volatile material that becomes a health problem if humans inhale more than a certain dose under a certain period. Thus, to prevent overexposure to Iodine, all Iodine-related facilities must equip their facilities with Iodine detection systems. The most common radioactive detection system uses an expensive Na(Tl), and HPGe detector. So, this study will build a low-cost iodine detection system by means of a low-cost color-based sensor utilizing the color property of the Iodine gasses. This finding showed that the color sensor will detect the Iodine gas leaks in the air in a range of 0 - 100 ppm, resulting in a pink-dark purple color. This finding showed that the sensor could detect low concentrations of Iodine gas in particular areas very well. Since the good resolution of this detection system, it will be promising to be applied in a real-time iodine gasses detection system.


Introduction
Iodine (Z=53) is a non-metallic chemical element in the halogen group of the periodic table.Under normal conditions, iodine is a black, shiny, crystalline solid.When heated, iodine sublimes to form a purple vapor [1].Iodine exists in radioactive and non-radioactive isotopes.The only non-radioactive isotope is I-127.Other common radioactive isotopes like I-129 and I-131 impacting environmental release, are formed in nuclear reactors from gaseous fission products that form within fuel rods as they fission [2].As a product of nuclear fission, I-131 can change directly from a solid to a dark purple gas which can be inhaled, or absorbed through the skin [3].Iodine has both good and detrimental impacts on human health.Iodine is required by the thyroid gland to make thyroid hormones [4].Unnecessarily high levels of nonradioactive and radioactive iodine can damage the thyroid, and result in burns to the eyes and skin.If iodine were released into the environment, individuals may consume it through food or drink, or breathe it in [3].
The history of research and usage of radioisotope Iodine-131 (I-131) with a half-life of 8.04 days in nuclear medicine has begun since its discovery in 1938 [5].This isotope has a unique property easily absorbed by the thyroid gland, so it is usually used for thyroid cancer therapy [6].Besides its benefit, I-131 gasses can threaten human health when inhaled within a specific dose under a certain period.Using the guideline for using Iodine for medical purposes, oral Lethal Dose 50 for humans is approximately the same as breathing 126-190 ppm for 30 minutes [7].
The National Research Council defined an RDA for iodine of 150 micrograms per day (150 g/day), with extra allowances of 25 g/day during pregnancy and 50 g/day during breastfeeding.These dietary intake amounts are adequate to meet the body's metabolic requirements.For I-131, the Nuclear Regulatory Commission (NRC) has set a limit of 2x10-8 microcurie per milliliter (Ci/mL) in workplace air.The EPA has set an average annual drinking water limit for I-131 of 3 pCi/L, ensuring that the public dose does not exceed 4 millirems [4].
To prevent the overexposure of the usage of iodine, any facilities including hospitals and research facilities that use iodine or radioiodine, need to monitor the presence of iodine to prevent any leak probability of iodine.In the nuclear industry, gaseous iodine is the most abundant form.Monitoring of radioactive iodine may be conducted by both continuous real-time monitoring or sequential sampling and trapped in a charcoal filter or zeolites [8], the trapped iodine is measured by gamma spectrometer, and the most common method is measured by single channel analyzer, NaI (Tl) or multichannel analyzer High Purity Germanium (HPGe) [8].Those detectors have a very good resolution to obtain the radioactive data of any radioisotopes, but in contrast, have a relatively high cost for installment and maintenance of the system.Moreover, the use of charcoal filters in nuclear facilities might have caused a radioactive leakage if installed improperly [9].Thus, the filters must be replaced and counted by the channel analyzer regularly.Therefore, the detection of iodine becomes time-consuming.
Due to the aforementioned problems, this study aims to propose an alternative real-time detection system for iodine gasses.The volatile properties of Iodine make it possible to detect the presence of iodine in the form of iodine gasses, having a pink-purple color.The pink-purple gasses are detected by means of a low-cost color sensor in a closed system.The detection system uses the color sensor that uses the physics principle of the scattering of electromagnetic waves.This study will use three different wavelengths of light such as red, green, and blue (RGB).The scattering principle of electromagnetic waves states that a colored substance for example red colored will reflect the wavelength of red light and absorb the wavelength of the other colored light [10].Using this principle will lead us to obtain RGB values of the substance, for this case could be used to estimate the iodine gas concentration.

Materials and Methods
The iodine gas is produced by the sublimation process of the iodine solid on the hotplate.The producing gasses are then detected by the low-cost color-based sensor, resulting in a particular red, green, and blue (RGB) in the particular experimental system.

Block Detector Module
The color sensor model TCS3200 was employed to constitute a block detector module.The sensor will emit RGB light to a colored system.The emitted RGB light will be absorbed depending on the color of the system using the principle of electromagnetic wave scattering.Then the wavelength that did not absorb by the system, will be reflected and will be measured by the photodiode on the TCS3200 module then will be processed to become a digital signal based on the current on the photodiode as illustrated in Figure 2.This research set each RGB value range to 0-255.

Processing Module
NodeMCU Dev Kit/board consists of an ESP8266 wifi-enabled chip.The ESP8266 is a low-cost Wi-Fi chip developed by Espressif Systems with TCP/IP protocol.NodeMCU uses an on-module flashbased SPIFFS (Serial Peripheral Interface Flash File System) file system.NodeMCU is implemented in C and is layered on the Espressif NON-OS SDK.The firmware was initially developed as a companion project to the popular ESP8266-based NodeMCU development modules, but the project is now community-supported, and the firmware can now be run on any ESP module.In this project, NodeMCU is used as a microcontroller for the sensor and to transfer data from the sensor to other NodeMCU boards using ESP NOW Protocol.After that after host board receives data from the client board and data can show in another device.

Light Isolation System
The light isolation system was used to prevent noise that will occur from the light outside the TCS3200 module.The isolation system simply used cardboard to cover our measurement system.Besides the noise from outside, the system should make sure that the most of RGB light is only absorbed by the iodine gas, and other light that did not absorb will be reflected back to the TCS3200 module.So that the inside of cardboard covered by the white paper that has properties to reflect light, the detail is shown in figure 3.

Sublimation of Iodine
Potassium Iodide (KI) was weighed in 4 grams, solubilized in 3 mL distilled water, and mixed by stirring.The resulting white solution is added by 3 mL concentrated Hydrochloric acid (HCl), producing the yellowish suspension.Then, 20 mL of Hydrogen Peroxide (H2O2) 3% was added drop by drop to the yellowish suspension, resulting in a mixture of brownish liquid with solid black iodine on the bottom of the mixture.The iodine is then filtered and weighed for the sublimation process.The obtained iodine was weighed in 1 gram then put in Erlenmeyer glass, heated on the hotplate, and put inside the closed box to prevent unwanted interference from the environment.
The concentration of iodine gas concentration was determined by calculating the difference between the initial solid iodine mass (  ) and the remaining iodine mass (  ) after sublimation in the Erlenmeyer glass as shown in the following equation, () −    ()  () × 1000. (1)

Detection of Iodine Gas
The utilized low-cost color sensor is TCS3200.The resulting color of iodine gasses was detected for a certain period of 23 minutes with 2-minute intervals using the low-cost color-based sensor as shown in Figure 4.The RGB values for each period were recorded, and the loss of mass for each period was also collected to determine the concentration of iodine gas.The Iodine gas produced from Iodine sublimation will reflect light at a specific wavelength to TCS3200, then will proceed to become RGB value using the simple processing unit Nodemcu esp 8266.This procedure aims to gather information about the sensitivity and resolution of our detector module.The sensitivity of the detector system can be measured using linear regression of the curve of the measurement data.One of the crucial parameters was the limit of detection (LOD) defined as the information of the lowest quantity that can be observed with a sufficient degree of confidence.Th LOD can be calculated using the following equation [12],

Sublimation of Iodine
In this study, the iodine was freshly prepared for each experiment from KI in acid conditions following the chemical reaction 1.The resulting solid iodine is used to produce the iodine gas through the sublimation process as shown in the chemical reaction 2 [13].Iodine could directly transition into a gaseous state and bypass the liquid phase.When solid iodine is heated, it sublimes and a bright purple vapor is formed [14].

Detection of Iodine
Using the methods explained in Section 2, this research had the response of the sensor due to Iodine gas concentration in ppm, which can be seen in Figure 5. From Figure 5, this research had 7 points of measurement where each point had 4 data taking.The dot marks in the plot mean the mean of the data while the bar in each dot means the error for each point measurement.
It was crystal clear that the RGB value of TCS3200 in general had an increased trend compared to Iodine gas concentration, especially below 120 ppm of Iodine concentration gas.The red, green, and blue lines present the regression from the RGB value from TCS3200.Since Iodine gas looks like a purple-pink gas, the value of R and B will increase as the rise of Iodine concentration gas.The detector system had good sensitivity to detect even small amounts of Iodine gases in the system, for this case 40 ppm of Iodine gas concentration.The concern of our detection system is about detector performance on high-concentration Iodine gas which had fluctuating RGB values, which will be the limitation of this detection system.Our aim is to make Iodine gas leak detection, which we need to detect Iodine gas below LDL doses of Iodine gas for humans at 120 ppm, this detection system had a good resolution at that region of Iodine gas concentrations.From the statistical method, the focus will be on the 0-100 ppm concentration region due to the detector system limitation.For this region, the standard deviation for each RGB value was calculated as 2.425 for the red value, 3.385 for the green value, and 2.873 for the blue.The small standard deviation of RGB value means that our system had good accuracy to present RGB value due to Iodine gas concentration.The sensitivity value can be shown from the slope of the linear regression of the curve.Based on Figure 6, linear regression can be calculated for each RGB value with the y-axis as the color value and the x-axis as the Iodine concentration.The regression for Red-line y = 0.6817x + 39.747, Green-line y = 0.8979x + 14.328 and Blue-line y = 0.7762x + 7.2171.Values for the determination coefficient ( 2 ) for each RGB regression were obtained as 0.8045, 0.8273, and 0.8104.Since the Green value had the highest  2 , the Green line was chosen to determine the sensitivity of the detector system.The LOD calculated using equation (2) was 12.44 ppm/L.This result can be considered that our detector system has good sensitivity for our aim to make Iodine gas leak detection.

Conclusion
The resulting iodine gas concentration in a range of 0 -200 ppm could be detected by the low-cost colorbased sensor.Since our detection system has a good resolution and sensitivity on low concentrations of Iodine gases, in this case, range of 0 -100 ppm, this detection system will be a good system for the early detection of Iodine gas leaks in facilities that use Iodine in their production.The utilization of low-cost color-based sensors is promising to be applied in a real-time iodine gasses detection system.However, further experiments should be conducted on several detection systems that will communicate with each other using wireless methods, which can provide us with the Iodine gas concentration distribution in a certain area and the output will be provided in a web-based system using ThingSpeak.

Figure 3 .
Figure 3. Design of Light Isolation System

Figure 4 .
Figure 4. Schematic of our procedure of this research

Figure 5 .
Figure 5. Graph of RGB value compared with the Iodine gas concentration

Figure 6 .
Figure 6.Graph of the regression of RGB value to Iodine gas concentration (0-100ppm region).