Activity induced in different rare earth materials using heavy ion oxygen beam; thin layer activation analysis

Abstract

Activities have been measured in spectroscopically pure rare earth materials viz; Terbium, Thulium and Tantalum, based on the remnant radioactivity induced in the material, when bombarded by ¹⁶O beam in the energy range from 70 MeV to 110 MeV. The cross sections of a number of isotopes populated through various reaction channels have been measured by the stacked foil activation technique. To measure the activity, yields of the radioactive isotopic products ^172,171,170Ta, ^171,170Hf, ^{171,170, 169}Lu, ^182,181Ir, ^182,181Os, ¹⁸¹Re, ^194,193,192Tl, ^{193, 192}Hg, and ^192,191,190Au have been determined using the measured cross-sections and subsequently used to measure the activity in these materials which has been found up to 8–16 μm.

Introduction

Recent advancement in science and technology has led to a positive shift towards establishment and growth of industries such as heavy engineering, conventional and/or nuclear power plants, manufacturing & processing industries. It is well known that these industries are substantially influenced by surface phenomenon such as wear, corrosion and erosion of materials [1], [2], [3], [4]. The functioning of the conventional power plants at elevated temperatures for increased efficiency and demand is often coupled with challenges such as degradation of structural materials subjected to extreme temperature and pressure operating conditions [2], [3], [4]. Electric power industry and plants have been reported an estimated loss of around 150 million US$ in a year in terms of efficiency, forced outages and repair costs due to solid particle erosion [5]. Installation of offshore wind plants due to climate change has gained importance over a couple of years. The materials used in monopile foundation and its components are subjected to varying wind currents leading to surface degradation and wear. Determination of reliable wear measurement methods for such fluctuating conditions in offshore wind plants is an emerging challenge [6]. The pipelines in the nuclear power plants are often subjected to accelerated flow corrosion and thinning of welds at heat affected zones leading to failure of systems [7]. Various conventional non-destructive methods and techniques are available but with limitations to measure the surface defects occuring in various industries like; aerospace, manufacturing, process industries, military and defence, nuclear industry etc. [8]. Some of the commonly adopted methods are visual inspection, microscopy, radiography, dye penetrant, ultrasonic, magnetic particle testing, eddy current for metals, acoustic emission testing etc [9]. In case of visual inspection and microscopy only macroscopic and small surface flaws can be detected. Radiography and dye penetrant testing are not suitable for porous materials. For utlrasonic testing material subjected under test necessarily needs to be good conductor of sound. Magnetic particle testing is applicable to its best only with ferromagnetic materials. Eddy current is limited only for metals and acoustic emission involves cost implications for testing of a component [9]. In of the studies it was concluded that gravimetric method for determination of surface degradation could yield accurate results but is very time consuming [10]. New developments and sustainable solutions in medical field such as artificial joints replacement are gaining siginificant importance. In one of the recent studies, wear evaluation of artificial joints subjected to more than several million cycles [11]. Assessment of non-contacting optical methods was carried out and sucessfully developed technique for measurement of wear up to 0.0001 mg in ceramics [12]. Studies employing gravimetric analysis for measurement of wear in knee implants subjected to as many as 3 million cycles [13]. A very high sensitive and reliable tool technique is required to investigate the near surface phenomenon.

For a couple of years, Thin Layer Activation (TLA) using charged particles has been preferred over conventional surface phenomena measurement methods due to many advantages [14], [15], [16], [17]. With the help of TLA, surface degradation of multiple components can be measured in a single go without influencing the operating conditions of system. It is also economically more feasible with increased level of sensitivity and reduced amount of radioactivity leading to easy handling of samples. The precision of TLA ranges from several hundred micrometers to few tens of nanometers [15], [16], [17] With the availability of cutting edge research in the accelerator technology, it is now possible to activate the desired surface of the material with the help of light and/or heavy charged particles such as proton, deuterons, alpha particles, oxygen beams. etc[18], [19], [20]. Since the charge particles quickly loose their kinetic energy as a consequence of intense interaction with the target atoms in a very thin layer, it is known as thin layer activation. TLA mechanism can be achieved either by activity loss measurement or collected activity measurement [18], [19], [20]. Activity has been measured using heavy ions up to 110 MeV in a Cu target for determination of surface wear induced in a very thin layer (up to nanometers)[21]. Studies conducted in titanium alloys using TLA with different beams viz; (nitrogen, carbon and light ions) lead to conclusion that wear measurement by TLA are more precise than conventional gravimetric analysis in titanium and chromium alloys [22]. TLA was employed for measurement of wear induced in piston ring and cylinder of automobile [23]. Wear analysis employing TLA with the help of light ions (proton, deuteron and alpha particles) in molybdenum was carried out, which is used as alloying elements in steel to increase corrosion resistance [24]. In of the studies, TLA was employed to study pseudoelasticity effect on nicket-titanium alloys used for orthodontic applications [25]. In one of the investigation conducted, it was concluded that platinum and platinum alloys can be activated in a very thin layer with most suitable radio-isotopes being ¹⁹⁷Au & ¹⁹⁶Au [26]. Recent studies conducted in neobium alloys could be employed in TLA by measuring cross sections as niobium alloys are commonly used in industries like nuclear and medicine [27]. In one of the studies conducted, calibration curves were deduced indicating amount residual activity induced in Rhodium & Rhodium alloys [28]. For investigation of wear and erosion specimens containing tungsten it was concluded that ¹⁸³Re and ¹⁸⁴Re are the most suitable ones by employing TLA [29]. see Table 1, Table 2, Table 3.

In the present work, we have used the TLA method to study the surface wear activation in different rare earth materials of interest. Tantalum and Terbium have been classified as rare earth materials of significant importance due to their wide range of applications and mechanical properties [30]. Terbium, Thulium & Tantalum have wide range of applications in electronics, medicine and heavy engineering works [30], [31], [32], [33]. ${\mathit{Tb}}^{3+}$state is very significant in number of applications. Terbium being classified as one of the rare earth materials of significance has wide range of applications. It is being used predominantly in electronics industries, smart appliances due to its luminescence property. ${\mathit{Tb}}^{3+}$ ions can be used to check for the presence of microbes. Terbium chloride is applied to the test area, which is then illuminated with UV light. Within minutes, any live endospores present will glow green. Terbium in the form alloying element with iron is very useful in magneto-optics for recording data. Terbium coupled with neodynium and dysprosium is capable of producing magnets which are widely used in electric motors of hybrid engines and wind turbines functioning at elevated temperatures. Terbium is also used as a dopant for materials in solid-state devices and optical fibers [31]. ${\mathit{Tm}}^{3+}$ ions emit a strong blue luminescence when excited. Thulium is used to dope yttrium aluminum garnets (YAG) used in lasers. Thulium is also used in alloys with other rare earth metals [32]. Tantalum is highly corrosion resistant due to the formation of an oxide film. It is an excellent conductor of heat and electricity. The metal has a melting point exceeded only by tungsten and rhenium. Ta is used in the electronics industry for capacitors and high power resistors. It is also used to make alloys to increase strength, ductility and corrosion resistance. The metal is used in dental and surgical instruments and implants, as it causes no immune response [33]. Tantalum and tantalum alloys could be the futuristic potential materials used for space nuclear mission due to their excellent stability and mechanical properties at elevated temperatures [34]. Tantalum, Terbium and Thulium belong to rare earth materials which can play a very pivotal role in areas of nations security, development and economy. Tantalum has been listed as one of the most critical material for India’s manufacturing sector by 2030 in a study conducted by think-tank council on Energy, Environment and Water. Tantalum could also be a potential substitute for emerging uses in new mining and nano technology [30].