Identification of TENORM in Zirconium Oxychloride with Gamma Spectrometry

Gamma spectrometer used to determine the type and activity of gamma emitting radionuclides, such as the measurement of TENORM (Th-232, U-238, Ra-26 dan K-40) in the zirconium oxychloride or environmental radioactivity. This research was carried out to know each the TENORM on the zirconium oxychloride (ZrOCl2.8H2O) which accommodation of environment data the radioactivity in draft job safety about the workers. Zirconium oxychloride is a result of chloride acid leaching process from sodium zirconate, containing uranium and thorium, so that it has the potential for contamination and increase the radiation exposure. The instrument used for counting by HPGe detector and the spectrum were analyzed further using software Genie 2000. Mean measured activity concentrations (radioactivity) of U-238, Th232, Ra-226 and K-40 respectively were 13.43±0.876 Bq/kg, 12.040±1.483 Bq/kg, 11.400±0.582 Bq/kg dan 32.940±3.270 Bq/kg.


Introduction
Industries whose basic activities are processing activities and services of raw materials derived from the earth with a large scale crossed with the peak of natural radionuclide during the process, various natural radionuclides contained in the earth's skin rocks will be mobilized so as to form a by-product of radioactivebased materials [1,2]. Naturally zirconium sand mining material that has a brownish white color, non magnetic, non conductor, and contains NORM (Naturally Occurring Radioactive Material). This sand is very cheap and easy for which everywhere is the mining material that is on the surface. This material is processed further will add selling value and also have a very strategic role in various industries. In the nuclear industry, this material when combined with other metals (Zircalloy) then this alloy will be able to be done as a fuel cladding of nuclear reactors and many become large corrosion-resistant materials [3]. In the nuclear industry, this material can be processed into zirconia or in advanced ceramic materials due to its high strength and very high melting point (2700°C) [6,7].
In Indonesia, zircon mineral sources in addition to obtained from Bangka, can also be obtained from Kalimantan. Zircon minerals will have bright prospects as the main source of zirconia if the material can be processed appropriately. Zircon sand when processed into zircon oxytoc chloride (ZrOCl2.8H2O) and continued into zirconia, allowing each stage of the process will produce products containing TENORM. The existence of TENORM can be known by detecting the content of uranium, thorium, radium and radon and its decay [2,3].
A previously research of identification TENORM in zircon sand processing at a Typical Chinese Enterprise was carried out in 2019 by Shoulong [3]. In China, the composition of monazite in zircon sand is rich in radionuclides, such as uranium, thorium and radium. This makes radiation a safety issue in the production of zirconium products. The monazite in zircon sand can be separated by the physical method because of its weak magnetic characteristic. However, the naturally-occurring radioactive materials in zircon sand are transferred and enriched with the chemical separation process, and discharged into the environment in the form of wastewater or solid waste. Therefore, the radiation issues mainly occur in the zirconium oxychloride production process, resulting in a potential radiation health hazard to workers in zirconium oxychloride production enterprises [3,4].
A research of assesment of the radiological impacts of zircon sand processing in the North-Eastern part of Italy have been conducted in 2005 using gamma spectrometry. Activity concentrations of radionuclides found in materials associated with this industrial process are presented as well as the results of the assessment of the annual effective doses to the workers and the members of the public [5].
Stages of the process in the zircon sand processing unit to obtain or produce zirconium oxychloride that is zircon sand melted with caustic soda, the melting results are leached with water that will produce residues. Residues of water leaching are dried and then leached with hydrochloric acid with a certain comparison to take the element zircon, filtrate obtained to produce zirconium oxychloride octahydrate (ZrOCl2 8H2O) [2]. At this stage of the process is suspected to contain radionuclide which is often called TENORM (Technologically Enhanced Naturally Occurring Radioactive Material) [2]. Therefore, certainty is needed at which stage should be inserted TENORM processing treatment so as not to be taken in the product and pollute the environment. In this case, tenorm identification is carried out in the process of zircon sand into zirconium oxychloride octahydrate, especially radionuclides U-238, Th-232, Ra-226 and K-40. Radiation exposure mainly occurs in the production process of zirconium oxychloride, resulting in potential radiation health hazards for workers in the production company zirconium oxychloride [2].
Radionuclide in TENORM is derived from primordial radionuclide decay from the decay of U-228, Th-232, and K-40. TENORM problems should get serious attention, because it can pollute and poison the environment and interfere with public health. Coordination of handling NORM and TENORM in Indonesia is an activity involving government agencies (BATAN, BAPETEN, DEPKES, BAPEDAL, related departments), NGO, and scientists / academics.
This study was conducted with the aim of knowing the concentration of activities on TENORM in zirconium oxychloride octahydrate (ZrOCl2 8H2O) results of HCl leaching process against sodium zirconate (Na2ZrO3 8H2O) from zircon sand melt that accommodates radioactivity environment data in the framework of occupational safety for employees. TENORM radioactivity results, especially radionuclide U-238, Th-232, Ra-226 and K-40, can provide information for workers involved in zircon sand purification peroses, so it is expected that the work / employees carefully in acting to start a job, or follow existing work procedures.
The ingredients used in this study are: zircon oxychloride (ZrOCl2 8H2O) result of HCl leaching process against sodium zirconate (Na2ZrO3 8H2O) from zircon sand melt, Standard Reference Material (SRM) IAEA 315 Radionuclides in marine sediment as detector efficiency controller, and EU-152 as determination of energy calibration and efficiency

Sample Preparation
The solids sample of zirconium oxychloride is sifted with a sieve of 100 mesh then homogenized. 70g samples of zirconium oxychloride (ZrOCl2 8H2O) put in polyethylene vials, closed tightly, and stored in a certain place at room temperature for approximately 30 days to achieve radionuclide equilibrium. The sample is ready to be identified tenorm content using gamma spectrometry technique.

Sample Measurement
The sample is placed on a gamma spectrometer detector with an counting time of 86400 seconds, the measurement is done with 4 (four) repetitions. After that, the calculation of the results of the enumeration is carried out. To determine the content of radionuclide use the equation (1).

Determination of Uncertainty
When estimating measurement uncertainty, all important components of uncertainty in an existing situation must be taken into account using the appropriate analytical methods [12,13]. Sources of cause for uncertainty include, (but do not need to be limited to) the standards of reference and reference materials used, the methods and equipment used, environmental conditions, the nature and condition of the goods tested or calibrated, and the operator.
Estimates each component of uncertainty so that it is equivalent to a standard deviation according to the fault factor. Factors to be aware of the stages of sample preparation, calibration, probability of radionuclide, detector efficiency, sample counting.

Result and Discussion
Identification of natural radionuclides (TENORM) of  transmitters contained in samples for qualitative and quantitative analysis using equations (1). In Table 1 the tenorm quantity identified by gamma spectrometry method is Ra-226, Pb-214, Bi-214, Ac-228, Pb-212, Bi-212, Tl-208 and K-40. The radionuclide has different concentrations of activity although the difference is not inconspicuous with 4 (four) times the measurement and the standard deviation (SD) which is then used for estimated uncertainty. The measurement of TENORM radioactivity contained in zirconium oxychloride in Table 1 determines the concentration of radioactivity activity or radioactivity U-238, Th-232 and Ra-266. This is because U-238 and Ra-266 are measured based on the average radionuclide radioactivity of Pb-214 and Bi-214 while Th-238 is measured based on radionuclide Pb-212 and Ac-228 [10,11,14].
Radionuclide Ra-226 can be determined in 2 (two) ways, namely at the peak of characteristic energy of 186.2 keV with probabilities of 3.28%, but can be interfered with the presence of radionuclide U-235 with characteristic energy of 185.7 keV [16], the concentration of Ra-226 activity is 11.67 Bq/kg presented in Table 1. While the second way to determine radionuclide Ra-266 through the estimated concentration of average activity of two peak photons from Pb-214 (at characteristic energy 295.2 and 351.9 keV) and three peak photons from Bi-214 (at characteristic energy 609.3; 1120.3 and 1764.5 keV) [10,13,14] and obtained a concentration of Ra-266 activity of 11.40 Bq/kg presented in Table 2. The results of radionuclide measurement Ra-266 in the first way or the second way have an insignificant difference.
Radionuclide U-238 can be measured directly at characteristic energy of 48.0 keV with a probability of 0.075 % [15]. This cannot be done because it is adjacent to the 46.5 keV energy of radionuclide Pb-210 with a higher probability of 4.0%. In Table 2    To see the comparison of the results of radionuclide activity concentration contained in zirconium oxychloride oxidation namely radionuclide U-238, Th-232, Ra-226 from the calculation of concentration value of decay activity and Ra-226 in individual characteristic energy (186.2 keV) and K-40 activity, then made histogram comparison such as Figure 2. Visible concentration of activity almost evenly except K-40, while the lowest concentration of activity is radionuclide Ra-266. Identify uncertainties Drafting a model of the work step and estimating each component of uncertainty, then combining the standard uncertainty components to create the combined default uncertainty. The value of uncertainty obtained is expanded to provide an interval where the quality measured is estimated to be located and at a certain level of trust.
The uncertainty component of weighing derived from the calibration of scales, resolution, repeatability has been done previous research [13], where the influence of weighing uncertainty on the enumeration has a value of 0.79877 mg.
From Table 2 the result of activity concentration of U-238 is 13.43 Bq/kg with the calculation statistic has a standard deviation value (SD) = 0.4377 Bq/kg with a repetition of 4 times the enumeration. Correction derived from nuclear constants is the probability of U-238 derived from the child (Pb-214 and Bi-214) which is 32.645% [6], taken 5% assuming normal data distribution then the default uncertainty radionuclide U-238 is 0.008161% presented in Table 3. From the calculation results using radionuclide Eu-152 and SRM IAEA-315 detector efficiency of 4.182% with standard deviation (SD) = 0.1976% and the standard uncertainty of detector efficiency is = 0.0988%.
There are 4 (four) components that affect uncertainty in the analysis of U-238, this can be seen in Table 3  The combined uncertainty (I) of the sample with a coverage factor (k=2) is expanded to k*3.2606 = 6.5212 %. In Table 2 the concentration of radionuclide aktvitas U-238 was 13.43 Bq/kg, with uncertainty expanded by 6.5212 % equal to 0.876 Bq/kg. This indicates the concentration of radionuclide activity U-238 in zircon oxytoxyl chloride value is located between 13.43±0.876 Bq/kg. With the same step, the uncertainty for radionuclides Th-232, Ra-266 and K-40 in zircon chloride value can be known, this is presented in Table 5. Concentration of radionuclide activity, Th-232 = 12.040 Bq/kg has an uncertainty value of ±1.483 Bq/kg, Ra-226 = 11.400 Bq/kg has uncertainty value of ± 0.582 Bq/kg, and K-40 = 32.940 Bq/kg has uncertainty value of ±3.270 Bq/kg.  Uranium (U-238) and thorium (Th-232) are undesirable filthy elements in the processed zircon sand into zirconia, so it is expected that U-238 and Th-232 in the process results no longer exist or with a small concentration value. The radioactivity values of U-238 and Th-232 in zirconium oxychloride when converted to heavy concentrations are shown in Table 6. Table 6 shows the conversion from Bq/kg to ppm or mg/kg, to U-238: 1 ppm = 25 Bq/kg and Th-232: 1 ppm = 8 Bq/kg [16,17]. The International Atomic Energy Agency (IAEA) through technical document 390 provides a conversion factor of potassium-40 radionuclides (K-40): 1 ppm = 131 Bq/kg [18]. The result of conversion of radiactivity into weight concentration can be seen in Table 6, where U-238 = 13.43±0.876 Bq/kg equivalent to 0.54±0.02 mg/kg, Th-232 = 12.040±1.483 Bq/kg equivalent to 1.51±.01 mg/kg, and K-40 = 32.94 ±1.63 Bq/kg to 0.25±0.02 mg/kg.