Article pubs.acs.org/IECR
Selective Area Chemical-Deposition Process: An Innovative and Facile Route to Prepare 147Pm Sources for Dust Monitors Manoj Kumar,† Rakesh Shukla,‡ Shyamala S. Gandhi,† J. Udhayakumar,† A.K. Tyagi,‡ and Ashutosh Dash*,† †
Radiopharmaceuticals Division, ‡Chemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai-400 085, India ABSTRACT: The potential utility of selective area chemical-deposition technique in the preparation of 147Pm source for the measurement of particulate emission in air was demonstrated. The process consists of electrodeposition of Ni on a precisely defined surface area of a copper wire followed by deposition of 147Pm activity from an aqueous solution. The influences of various experimental parameters such as pH of the aqueous solution, deposition time and reaction volume were systematically investigated for the optimum deposition of 147Pm. To prevent leaching of 147Pm from the source, we subsequently sheathed the radioactive area with a thin layer of polystyrene. The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM) analyses. The quality of the prepared sources in compliance with regulatory norms were evaluated to ensure their safety during application and found to be satisfactory.
■
INTRODUCTION Rapid industrialization, urbanization, and development of transport network have added impetus to economic development but at the same time has resulted emission of airborne particulate matter in to the atmosphere.1 The ubiquitous presence of particulate matter in air can imperil not only to human health but also to plant life.2,3 They also play a role in the green house effect and global warming because of their contribution to cloud formation.4 While the prevention of particulate matter emission is a major road block in the economic development of a nation, control technologies to clean air and monitor particulate matter represent an effective and efficient proposition in managing particulate matter emission tribulations. In light of the perceived hazards of particulate matter in the atmosphere, the regulatory driving force for air pollution control in the United States is the Clean Air Act. Other countries around the world have similar legislation and national policies aimed at protecting air quality. In view of this, measurement of fine particulate matter concentration seems not only an interesting prospect, but may be viewed as a necessary one. A wide variety of techniques such as photoextinction, gravimetric, pressure measuring, and radiometric techniques have been used for the continuous measurement of static dust concentration for compliance with the particulate emission standard. A dust monitor based on radiometric technique is an important tool for the continuous measurement of particulates from the atmospheric aerosol. Such a device collects suspended particles on its filter and measures the weight of those particles by the β-ray absorption attenuation technique. Early use of beta gauge was confined to aerosol monitoring near sources such as in or near smokestacks and in coal mines.5,6 Later, with improved sensitivity, it was used for monitoring ambient aerosol concentration.3−12 As a further development, a number of commercial beta gauge instruments are now available for © 2012 American Chemical Society
continuous or semicontinuous aerosol mass monitoring. Effective use of this technique necessitates an external radioactive source containing low energy pure β-emitting radioisotope able of providing a steady beta radiation flux. In order to avoid the decay correction over the duration of measurement and to reduce the frequency of source replacement, the half-life of the radioisotope used should be sufficiently long. In this context, 147Pm, a pure β-emitter (Eβmax = 0.225 MeV) with a half-life of 2.6 years seemed an attractive radionuclide as it satisfies these requirements and at the same time offer the convenience for measurement of particulates in the 1−10 mg/cm2 range. The radioactive source for this purpose consists of a long cylindrical copper wire of 1.5 mm (ϕ) × 9 mm (l) that contain small amounts of 147Pm, on a small surface area of the tip [1.5 mm (ϕ) × 1.5 mm (l)]. The need to realize deposition of predicted quantity of 147Pm only on a geometrically well-defined area of a substrate with adherence to regulatory requirement of the radioactive source prompted us to search for a viable technique. Over the past few years, several need-based strategies have been developed in our laboratory for the preparation of a variety radioactive sources13−19 for a wide range of applications. To tap the potential of anodized porous surface of alumina, we have earlier reported the preparation of 147Pm source of similar category for their utility in the beta-backscatter thickness gauge applications.18,19 Although effective, one of the major drawbacks of this method is the requirement of longer deposition time to impregnate required amount of 147Pm activity on the anodized area because of slow kinetics of adsorption. The recent resurgence of interest on this category of radioactive source for dust monitors prompted our interest to search for an Received: Revised: Accepted: Published: 11147
April 13, 2012 August 8, 2012 August 9, 2012 August 9, 2012 dx.doi.org/10.1021/ie3009692 | Ind. Eng. Chem. Res. 2012, 51, 11147−11156
Industrial & Engineering Chemistry Research
Article
polythene scintillation vials (Meridian, Epsom, UK). AGFA film grade-G-7 was used for autoradiography. Optical density measurements were carried out using OPTEL Transmission densitometer model 125. 3E NDT, LLC, Pasadena,California, USA. Preparation of the Substrate. The copper wire used in this work was of high purity metal (99.99%). Platinum wire of dimension 10 mm(l) × 1.5 mm (ϕ) was used as anode. Prior to electrodeposition, the surface of the copper wire was polished with emery paper to a rough finish, washed in an ultrasonic bath containing acetone, rinsed with deionized water and then air-dried. Selective area Electrodeposition of Ni. The schematic diagram illustrating the electrochemical set up used for the deposition nickel on a selective area of a copper wire is shown in Figure 1. The copper wire was placed vertically, with just the
alternative technique to mitigate this drawback. Among several alternative techniques available, the chemical deposition technique on a metallic substrate20−23 seems to be the promising pathway because of technical simplicity, rapidity, and ability to create homogeneous deposits. Moreover, they require simple equipment and the amount of deposit can be easily tailored by varying bath composition and reaction conditions. Despite the remarkable potential of chemical deposition technique, this method has seldom been exploited for the preparation of radioactive sources. To realize the potential of chemical deposition technique in the relatively unexplored field of radioactive sources preparation, here we evaluated the aptness of this method to prepare 147Pm source. In this context, the reported chemical deposition of cerium on electrodeposited nickel substrate from aqueous solution by Huang et al.24 deem worthy of consideration owing to the similar chemical properties of Ce and Pm. Such a theme was simplified in our work and directed toward the selective area deposition of 147Pm on a metallic substrate. To assess the suitability of Pm in lieu of Ce, further studies are essential. In view of this, a thorough investigation of experimental parameters was considered worthwhile investigating to arrive at the optimum conditions for the preparation of 147Pm sources of desirable quality. It is also essential to characterize the deposit to assess their adherence to the substrate as well as distribution. In this communication, we described the overall process concept, experimental procedure to prepare 147Pm source, characterization of the deposit and quality control of 147Pm source to meet regulatory compliance. The present investigation is the first example exploiting selective area chemicaldeposition technique to prepare radioactive sources.
■
EXPERIMENTAL SECTION Materials. 147Pm as promethium(III) chloride of specific activity ∼18.5−25.9 GBq (500−700 Ci/g) was procured from M/s Tritec, Switzerland. Reagents such as boric acid, nickel sulfate, sulphuric acid, ammonium hydroxide, and water were of spectroscopic grade and procured from BDH (India). Polystyrene granules used for coating was of analytical grade and procured from BDH (India), Mumbai. Copper and platinum wires of high purity with material testing certificates, were procured from M/s Hindustan Platinum Ltd., Mumbai, India. The electrolytic solutions were prepared from ultrapure water (Millipore Milli Q system). Electrodeposition of nickel was carried out using a 1−28 V, 0−2.5A regulated power supply of Aplab Limited (model L1282), India. Beta Radiation Survey Meter (PRM131A) of PLA Electro Appliance Pvt Ltd., India was used to measure the radiation dose on the surface of the source. X-ray diffraction measurements were carried using monochromatized Cu−Kα radiation on a Philips X-ray diffractometer, Model PW 1927. Microstructures were recorded using Tescan VEGA MV2300T/40 Electron Microscope. The chemical composition was obtained by energy dispersive X-ray (EDX) analysis (Oxford, Model INCA E350). Atomic force microscope (AFM) measurements were performed using NT-MDT solver model instrument with 50 μm scanner head and silicon nitride tip in contact mode. Liquid scintillation measurements were performed using a low level liquid scintillation counter (Model: Tricarb 2100TR, Packard Instrument Co., USA) with Aquasafe 300 Plus scintillation cocktails obtained from M/ s Zinsser Analytic GmbH, Frankfurt, Germany and 22 mL
Figure 1. Schematic diagram of the selective area nickel electrodeposition setup.
tip up to a distance of 1.5 mm immersed into the electrolyte. Electrodeposition of Ni on the targeted area of the copper wire was carried out galvanostatically using modified Watt type bath following the reported procedure.11 After electrodeposition, the wires were washed thoroughly with double distilled water and ethanol, and then dried in a current of dry air to a constant weight. These were stored in sealed vials until use. Optimization of 147Pm Deposition Parameters. The effect of reaction volume on 147Pm deposition was investigated by varying the volume of the feed from 50 to 200 μL at pH 6 for 5 min. The effect of pH on the deposition of 147Pm was studied by varying the pH of the 147Pm feed from 1 to 6, keeping the volume of the feed 50 μL and time duration of 5 min. Further, the effect of time on the sorption of 147Pm on the Ni electrodeposited Cu wires was studied by varying the sorption time from 1 to 10 min at pH 6 by keeping the volume of the feed 50 μL. Fresh aliquots of 147Pm at concentration of 3.7 KBq in 50 μL were used for each experiment. The activities of the solution before and after deposition were measured following liquid scintillation counting (LSC). 11148
dx.doi.org/10.1021/ie3009692 | Ind. Eng. Chem. Res. 2012, 51, 11147−11156
Industrial & Engineering Chemistry Research
Figure 2. Autoradiography gadget to determine distribution of
Article
147
Pm activity. (a) Gadget, (b)
Ai − Af × 100 Ai
Pm source.
Source Preparation. Selected area [1.5 mm(ϕ) × 1.5 mm(l)] of copper wires were electrodeposited with Ni following the described procedure. Each Ni electrodeposited copper wires were immediately put in safe-lock micro test tubes. The pH of the feed solution was maintained at 4−6 with the addition of 1 M NaOH. About 50 μL of the 147Pm feed containing 9.25 MBq (250 μCi) was pipetted out and added separately to the individual reaction tubes and kept for 5 min. The 147Pm deposited wires were taken out with the help of a forceps and dried under an infrared lamp. The sample was heated in a small portable tubular resistance furnace at a temperature of 250 °C in air. The heating rate was 20 °C/min, and the dwelling time at 250 °C was 30 min. The active area of the sources was coated with polystyrene by the dip-pull method. The polymer attached to the active surface of the matrix and coalesces into a continuous protective film. The solution left inside the tube after removal of the Ni electrodeposited copper wire was transferred and its activity content was measured by liquid scintillation counting (LSC).The amount of 147Pm deposited was estimated as the difference in activity of the solution before and after deposition, as measured by liquid scintillation counting (LSC). Quality Control of the Sources. Measurement of Activity of the Source. Activity measurement of the source was carried out in two stages for activity confirmation. In the first step, the total activity strength was assayed by liquid scintillation counting (LSC) by drawing suitable aliquots of feed solution before and after the chemical deposition. The amount of 147Pm deposited on the matrix was calculated to assess the activity deposited on the substrate. Accurate assaying of the activity on the sources was carried out using an ion chamber calibrated with standard 147Pm sources. Removable Activity. The radioactive source should be free from loose contamination under normal condition of use. To
The percentage of 147Pm deposition (%) was calculated using the following expression relationship %deposition =
147
(1)
Where Ai and Af are the initial and final radioactivity of 147Pm, respectively. All equilibration experiments were carried out in triplicate. Polymer Coating of the Radioactive Zone. The 147Pm deposited end of the rod immersed into a solution of polystyrene in benzene (175 mg/mL), for 3 min and pull out. The polymer coated samples were placed onto a wire mesh trays located in a frame on an elevated platform until the excess of the uncoated polystyrene reagent drained out.19 XRD, SEM, EDS, and AFM Analysis. The quality of the copper, Ni electrodeposited and chemical deposited surfaces were examined by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Energy Dispersive X-ray (EDS) analysis of a dummy source prepared in an identical manner as of the active source. Since there is no stable isotope of 147Pm in nature, Sm was used as the surrogate isotope in simulated experiments, owing to their very similar chemical properties.19 EDS microanalysis technique was used to identify the elemental constituents of the electrodeposited samples. Atomic force microscopy (AFM) technique was used to analyze surface roughness. The influence of Sm contents in the absorbing solution on the surface morphology of Sm deposited film was considered worthwhile investigating to ensure homogeneous deposition of Sm or 147Pm on the electrodeposited Ni surface. Several deposition experiments were performed by using different concentration of absorbing solution (100, 200, 300, 400 μg/ mL) and the morphology of the Sm deposited surfaces were examined by SEM and EDS analyses. 11149
dx.doi.org/10.1021/ie3009692 | Ind. Eng. Chem. Res. 2012, 51, 11147−11156
Industrial & Engineering Chemistry Research
Article
ascertain the integrity of the radioactive deposit, swipe test was performed by swiping the radioactive area using alcohol immersed cotton wool and the radioactive content of the swipe was checked in a G.M. Counter. Leachability. The leachability of the 147Pm source was tested following the technique prescribed by regulatory authorities.25,26 In this procedure, each source was placed in beaker containing100 mL water at room temperature for 48 h, at the end of which the sources were removed with the help of a tweezer. The water was concentrated to 0.1 mL by heating and radioactivity content was measured in a liquid scintillation counter. Uniformity of Activity Distribution. The distribution of 147 Pm activity was examined by autoradiography following the reported procedure.27 The photograph of the autoradiography gadget is shown in Figure 2. Radiological Safety. In view of radioactive nature of 147Pm, safe and appropriate radioactive procedures were adopted during the whole preparation process. Since 147Pm is a pure β− emitter of low energy particles (Eβmax = 0.225 MeV), it is easily shielded by a few micrometers of glass and amenable for handling in a fume hood. Radioactive experiment was carried out in a fume hood with proper protective clothing to avoid radioactive contamination. Each step of the source preparation methodology were planned and executed carefully to contain radioactive contamination. Radiation monitoring of personnel was accomplished with TLD dosimeters worn while working. The ALARA principle was observed with regard to the radiation exposure of the operating staff.
Figure 3. Effect of pH of the feed solution on the chemical deposition of 147Pm.
be optimized. In order to study the effect of contact time on the deposition of 147Pm, deposition experiments were carried out at various time interval and the result is depicted in Figure 4. It is
■
RESULTS In order to achieve the objective of depositing147Pm within a geometrically well-designated area of a substrate utilizing chemical deposition technique, our attention was focused toward electrodeposition of Ni onto the target area to render chemical deposition of 147Pm. Owing to the no carrier-added (nca) nature, the concentration of 147Pm used for this purpose was extremely low and the effect of various experimental parameters such as pH of the chemical bath, time of deposition and reaction volume was hence considered worthwhile investigating to arrive at the optimum deposition conditions. Effect of pH of the Chemical Bath. The dependence of the percentage deposition of 147Pm on the pH is presented in Figure 3. From the results, it can be inferred that, within the range of pH range investigated, optimum deposition of 147Pm could be achieved when the pH was kept at 4 and thereafter further increase of pH results in marginal decrease of the deposited activity. The deposition studies of 147Pm were not pursued beyond pH of 6 as 147Pm would precipitate in alkaline solutions. It has widely been assumed that Pm deposition proceeds along the electrochemical mechanism at the Ni surface. The difference between the redox potential of the metals, ΔE, is the driving force for deposition. It can be seen that with increase in pH, the potential shifts cathodically and the deposition of Pm increases and reaches a limiting value at pH 4. The marginal decrease of deposition rate beyond pH 4 may be attributed to the formation of self-catalytic activity center in the bath, resulting in the decrease of the virtual deposition rate on the Ni deposited substrate. Effect of Contact Time. The reaction time required to achieve near quantitative deposition of 147Pm on the electrodeposited surface is another crucial parameter, which needs to
Figure 4. Effect of contact time on the chemical deposition of
147
Pm.
evident that the deposition of 147Pm on the electrodeposited surface increased with increasing contact time and remains constant after 5 min of contact. This is a typical behavior of a chemical deposition process that is controlled both by the reaction kinetics and by mass transport. As is known, deposition of Pm at the electrodeposited Ni surface takes place by ion diffusion. As the contact time increases more and more Pm ions gradually overcome the energy barrier for cathodic reaction (polarization resistance), diffuses onto the surface leading to the increase of the deposition rate. The maximum of deposition rate maybe result from the completion of Pm ions diffusion. Effect of Reaction Volume. The reaction volume of the chemical bath is another parameter which needs to be optimized. The dependence of the 147Pm deposition efficiency on the reaction volume is shown in Figure 5. Ignoring some fluctuation, the percentage deposition of 147Pm activity on the 11150
dx.doi.org/10.1021/ie3009692 | Ind. Eng. Chem. Res. 2012, 51, 11147−11156
Industrial & Engineering Chemistry Research
Article
copper metal when compared with the standard PCPDF data (Card no- 04−0836). Figure 6b showed peaks of Ni metal (card no- 04−0850) for the electrodeposited sample. However, we observed the presence of the copper also [Figure 6b] even after the deposition of the nickel, possibly due to the very small thickness of the deposited Ni layers. Figure 6c represents the XRD pattern of the chemical deposited surface. However, the XRD data did not show any peaks other than that of Cu substrate and Ni. Therefore, at this stage it is difficult to unequivocally characterize the nature of adsorbed Sm. There can be several possibilities namely (i) the Sm layer is amorphous, (ii) it is too thin to be seen by XRD, (iii) Sm deposition has not taken place. Therefore, this situation necessitates employing other techniques such as SEM and EDS, which will be described subsequently. Scanning Electron Microscopy (SEM) Analysis. The SEM micrographs of the copper substrate and electrodeposited Ni samples are shown in Figure 7. It can be clearly seen that the Figure 5. Effect of reaction volume on the chemical deposition of 147 Pm.
substrate up to 50 μL volume was nearly quantitative, but after 50 μL decreases sharply and finally at 200 μL volume the retention was only 33%. Hence, a reaction volume of 50 μL was used in subsequent experiments. With peculiar electronic structure and unique behavior of rare earth, 147Pm will adsorb preferentially at the Ni deposited surface of the substrate. The adsorbed 147Pm tends to give away electrons and part of 147Pm becomes cationic due to the low electronegativity, which change the interface structure of the surface. With the increase of the reaction volume of bath, i.e., the decrease in the concentration of 147Pm ions in bath, diffusion and deposition of the 147Pm3+ ions are hindered, and thus lead to the decrease in deposition. The most favorable values of experimental parameters as described in the source preparation method were chosen for the preparation of the radioactive source. X-ray Diffraction Studies. Figure 6 depicts the XRD pattern of the substrate, after Ni electrodeposition and after chemical deposition of Sm. Figure 6a showed all the peaks of
Figure 7. SEM micrograph of (a) copper substrate, (b) electrodeposited Ni surface, (c) chemical deposited Sm sample.
Figure 6. XRD pattern of (a) copper substrate, (b) electrodeposited Ni sample, and (c) chemical deposited Sm sample.
electrodeposited sample (Figure 7b) showed uniform deposition with small granular crystals of Ni metal on the surface of the Cu substrate indicating good adhesion with the copper backing. The SEM micrograph further indicated that the surface is very rough and flaky, which promotes the chemical deposition of Sm or Pm. The chemical deposited sample (Figure 7c) showed various distinct areas, which could be due to Sm in agglomerated form. In a separate experimental run, the influence of Sm contents in the absorbing solution on the surface morphology of Sm deposited film has been examined within the concentration range of 100−400 μg/mL. The surface morphology was studied by SEM analyses and Sm contents of the deposited film were carried out by EDS analyses. Figure 8 shows the SEM images of Sm deposited surface at different magnification obtained from using different concentrations of absorbing solution (100, 200, 300, 400 μg/mL). Several SEM images of the Sm deposited surface generated are shown in Figure 8. Figure 8 100a, 100b,100c, depicts the SEM images obtained from using absorbing solution concentrations of 100 μg/mL.. Similarly, Figure 8 200a, 200b, 200c were for 200 μg/mL, Figure 8 300a, 11151
dx.doi.org/10.1021/ie3009692 | Ind. Eng. Chem. Res. 2012, 51, 11147−11156
Industrial & Engineering Chemistry Research
Article
content on the deposited layer increases. On the basis of EDS elemental mapping of Sm at different position of deposited surface, homogeneity of deposition can be ascertained. The results of the EDS elemental mapping obtained with 100, 200, and 400 μg/mL of absorbing solution revealed a nonuniformity of Sm deposition at the surface. On the other hand when the concentration of the absorbing solution was maintained at 300 μg/mL, near uniform deposition of Sm was observed at the surface. From the above, it is inferred that in order to obtain a homogeneous deposition of Sm or Pm on the Ni electrodeposited surface, the concentration of the feed need to be maintained at 300 μg/mL. The concentration of the absorbing solution plays a major role when large surface area target is to be prepared. For our type of application, owing to the extremely small surface area [1.5 mm (ϕ) × 1.5 mm (l)] of the substrate, the concentration of the absorbing solution is not a major direct concern. For the envisaged application, it is important to deposit predicted quantity of 147Pm to obtain required β− output and fairly consistent deposition so as to attain uniform β− radiation flux in all directions. The method adopted here could result in achieving these aims. Atomic Force Microscopy (AFM) Analysis. To evaluate the influence of the surface properties of the Ni deposited surface on the chemical deposition of Pm, we carried out atomic force microscopy (AFM) analysis. Atomic force microscopy (AFM) images of the electrodeposited Ni and Sm adsorbed is shown in images a and b in Figure 10 . The scanning area of AFM was 10 μm × 10 μm. The AFM images indicate that the Ni electrodeposited film surface as shown in Figure 10a is homogeneous and rough with mean square roughness (rms) value of ∼93 nm ± 0.2 nm. AFM image of Sm adsorbed on the substrate as depicted in Figure 10b demonstrated the rms value of ∼187 nm ± 0.2 nm. Further, it is found that the surface morphology is more uneven than that of Ni electrodeposited. Thus from AFM images it can be concluded that after the adsorption of Sm on the surface of the electrodeposited Ni, the roughness of the film increased. Preparation of 147Pm Sources. After the systematic optimization of key experimental parameters and following the procedure, several 147Pm sources were prepared with an aim to obtain ∼9.25 MBq (250 μCi) of 147Pm activity in each source. Because of the high reactivity of electrodeposited Ni surface with oxygen and water vapor, freshly electrodeposited surface was used for chemical deposition of 147Pm. The activity of the final source was measured in an ion chamber calibrated with standard 147Pm sources. The results show acceptable batch-tobatch reproducibility in terms of activity content. Having successfully completed the source preparation strategy, a thorough assessment of the quality of 147Pm deposit in compliance with Atomic Energy Regulatory Board (AERB) of India, was found essential to ensure their safety during use and thus pursued. Quality Control of the Sources. Evaluation of Distribution of 147Pm. In order to ascertain the spatial distribution of 147Pm on the matrix, autoradiography examination of the active samples was carried out following the reported method.27 The image of the exposed radiographic film is shown in Figure 11. The optical densities (O.D.) of radiographic film after different times of exposure at various directions were measured and were 1.14 ± 0.02 for 10 min and 1.6 ± 0.08 for 20 min exposure. Results of autoradiography
Figure 8. SEM micrograph of chemical deposited Sm samples at different concentration of Sm feed concentration (a) 500× magnification, (b) 1K× magnification, (c) 3K× magnification.
300b, 300c were for 300 μg/mL, and Figure 8 400a, 400b, 400c were for 400 μg/mL. As can be seen, the four series of photomicrographs yield interesting differences. Therefore, the concentration of the Sm solution has determinative effects on the morphologies of the deposited surface. When the concentration of the absorbing solution were 100 and 200 μg/mL, agglomerated particles of irregular shapes and sizes were found to be randomly distributed over the surface of the substrate (Figure 8 100a, 100b,100c and Figure 8 200a, 200b, 200c). On the other hand, by increasing the concentration of the absorbing solution to 300 μg/mL, the microstructure, characterized by SEM, shows the development of dense film with smooth surface (Figure 8 300a, 300b, 300c). On further increasing the concentration to 400 μg/mL, the deposit show the presence of intergrown aggregate crystals of heterogeneous size, distributed irregularly on the surface of the substrate (Figure 8 400a, 400b, 400c). EDS Characterization. Figure 9a depicts the EDS spectrum of the electrodeposited Ni on the Cu substrate. It shows peaks pertaining to Ni only which indicates complete coverage of Cu substrate by Ni. The deposited surface is free from any other chemical impurities. Figure 9b clearly shows the presence of chemically deposited Sm and oxygen sample. EDS spectra of chemical deposited surface as seen from Figure 9b indicated the coverage of Ni surface with deposited Sm. From the EDS data, it appears that the deposited Sm is in the form of samarium oxide. Table 1 depicts the effect of concentration of Sm on the Sm contents of the deposited surface obtained from EDS measurements. The results in Table 1 indicate that increasing the concentration of the absorbing solution from 100 to 300 μg/mL has only marginal effect. On further increasing the concentration of the absorbing solution to 400 μg/mL, Sm 11152
dx.doi.org/10.1021/ie3009692 | Ind. Eng. Chem. Res. 2012, 51, 11147−11156
Industrial & Engineering Chemistry Research
Article
Figure 9. EDS spectra of (a) electrodeposited Ni surface, (b) chemical deposited Sm surface.
local level would promote the use of dust monitors based on radiometric technique.
Table 1. Effect of Concentration of Sm in the feed Solution on the Sm Contents of the Deposited Surface Obtained from EDS Measurements S.No
feed concentration of Sm (μg/mL)
concentration of Sm deposition at the surface (wt %)
1 2 3 4
100.00 200.00 300.00 400.00
3.87 4.02 4.06 8.14
■
DISCUSSION The current work is an attempt to explore the effectiveness of selective area wet chemical deposition approach to prepare 147 Pm sources for their utility in beta gauge to measure particulate matter in the atmosphere. The concept of a beta gauge is to determine the mass collected on a filter by measuring the relative change in the β-particle intensity passing through the filter when clean and then loaded with the collected particle mass. It represents a preferred approach in continuous monitoring programs. The selection of beta emitting radioisotope plays an important role in the sustainable operation of such device. The beta spectrum of the radionuclide should match the range of mass thickness to be measured. If the electrons in the spectrum have a maximum range which is less than the thickness to be measured, very few electrons will penetrate the sample and the attenuation relationship (I = Ioe−μx) would not be established. Similarly, if the electrons are extremely energetic relative to any losses in a thin sample, then little or no effect will be observed and a sensitive measurement of mass is not possible. The common pure β- emitting radioisotope isotopes used in beta gauges are 14C (T1/2= 5732 y, Emax = 156 keV) and 147 Pm (T1/2 = 2:62 y, Emax = 225 keV). Either of these isotopes seems to be an effective radionuclide for the measurement of an aerosol sample, which is generally a thin specimen in the 1 −10
examination revealed that the distribution of 147Pm on the matrix was near uniform. Leachability and Removable Activity Studies. The sources were subjected to quality control test to ensure that there is no danger of activity leakage and the results obtained are depicted in Table 2. Leaching studies conducted on 5 randomly selected sources reveals that ∼0.006 ± 0.002% of the original activity only leached out, which complies with the specifications (
