Introduction We have developed a low-cost stopcock valve actuator for radiochemistry automation built using a stepper motor and an Arduino, an open-source single-board microcontroller. The con-troller hardware can be programmed to run by serial communication or via two 5–24 V digital lines for simple integration into any automation control system. This valve actuator allows for automated use of a single, disposable stopcock, providing a number of advantages over stopcock manifold systems available on many commercial radiochemistry rigs or over using solenoid valves. This actuator allows for the use a wide variety of stopcocks, ranging in size, shape and material, giving flexibility to be used in a large variety of applications. Material and Methods The actuated valve consists of two main parts, the actuator and the control electronics. The actuator consists of a stepper motor, an infrared ‘home position’ sensor, a stopcock backplate, and a coupler from the driveshaft to stopcock handle. The stepper motor is a NEMA-17 size that runs 200 steps/rotation with a 5mm drive shaft. The coupler is an interchangeable part, custom to each stopcock model, with each part drilled out to fit the motor drive shaft and milled out for a tight fit to the stopcock handle. The backplane consists of a plate offset from the motor body with 5 screws positioned to keep the stopcock body from rotating relative to the motor. A reflective optical sensor (Vishay TCRT1000) is used as a limit switch to determine a ‘home’ position for the stopcock. With a slight modification to most any stopcock in cutting off a tab that limits rotation, the handle can rotate 360°. This allows for opening all three ports to each other, which has been done to all stopcocks used with this actuator. The control electronics consist of an Arduino Uno board and a motor shield (add-on board), connecting to the actuator by an Ethernet cable. The motor shield functions to interface the low-power Arduino circuitry with a high power H-bridge motor driver circuit. The Arduino runs two sets of code, initialization and its loop. The initialization routine runs when power is first powered up, and then continues to run the loop. The initialization routine rotates the valve until the IR limit switch is activated, and rotates an-other 45° from position home, sealing off all ports on the stopcock. Following initialization, the Arduino enters its loop, which repeatedly compares its current position to its target posi-tion. When the target position and current posi-tion do not match, the stepper motor turns in the shortest direction towards its target position. The hardware can be interfaced by either serial communication or by two 5–24V digital signals defining positions 1–4. The wide range of allowed input signal voltages is realized by using an optocoupler that accepts 5–24 V inputs but outputs TTL signals compatible with the Arduino’s hardware. Results and Conclusion A photo of the implementation of the actuator is shown in FIGURE 1. It has overall dimensions of 3.5×1.75×2.5”, excluding a mounting bracket. Control electronics are housed in a compact box built for an Arduino, giving the control electron-ics a clean, professional look. Challenges in de-sign included determining a maximum motor speed where the motor would provide enough torque but yet move fast enough to be useful, finding that rotational speed of 6 seconds/full rotation is best.

Introduction The internal pressure experienced by a gas tar-get during irradiation is dependent on the beam energy deposited in the target, the beam cur-rent, and the thermal behaviour of the target. [1] The maximum beam energy deposited is a function of the cyclotron capabilities and the gas inventory within the target. The maximum beam current is limited by the pressure produced in the target and the ability of the target assembly to remain intact. This is also a function of the thermal behaviour of the target, which is difficult to predict a priori since it is dependent on such things as convection currents that occur during irradiation. We conducted bench tests with model gas targets with and without forced convection currents to observe the effect on thermal behaviour. Based on those results we constructed a prototype gas target, suitable for irradiation, with an internal fan assembly that is rotated via external magnets. Material and Methods Bench tests were conducted with cylindrical and conical target bodies of aluminum. A nickel-chromium heater wire was inserted into the gas volume through the normal beam entrance port (FIGURE 1) to heat the gas while water cooling was applied to the target body. The voltage and current of the heater coil was monitored along with the pressure inside the target and the water inlet and outlet temperature. In the case of tests with a driven fan blade either the voltage applied to the electric motor was monitored or the fan speed itself was recorded. By assuming the ideal gas law, the pressure gives the average bulk temperature and a global heat transfer coefficient can be calculated between the target gas and the cooling water. [2] A cylindrical target body was constructed that incorporated a fan blade driven by an external motor. This assembly used a simple o-ring seal on the rotating shaft. This seal was not robust enough for any tests under beam conditions. A prototype design suitable for in-beam operation employs a propeller mounted on a rotating disc housing two samarium cobalt magnets and spinning on two micro-bearings which are constructed to operate in high temperature environments. The micro-bearings are mounted on a pin projecting from a plate welded to the back of the gas target to allow assembly of the fan mechanism prior to attachment to the body (FIGURE 2).

Introduction Batch-style water targets used for F-18 production are known to operate under boiling conditions in the target irradiation chamber, but the distribution of vapor under steady-state conditions was previously unknown. Thermal performance of batch targets has been correlated to average void in the target [1], but the simplified assumptions of such models do not represent the true non-uniform boiling behavior. Visualization targets can be used to observe boiling inside of a target during operation [2–5]. Commercial BTI targets operate at 28–35 bar (400–500 psi) with heat inputs of 0.5 to 3 kW and fill volumes of 1 to 4 mL. Recently, a visualization target featuring two transparent viewing windows was used to observe boiling conditions for realistic operating beam power, target pressure, and fill volume [4]. The same methodology has been applied to three additional visualization targets to examine the effect of target geometry on observed boiling phenomena. Material and Methods The original visualization target featured an aluminum body with a 0.127 mm (0.005 inch) integral aluminum beam window and two viewing windows made of optically clear sapphire (Al2O3). It was operated on an IBA 18/9 cyclotron with 18 MeV protons at beam power up to 1.1 kW, for pressures of 5 to 21 bar (70 to 300 psi), and a fill volume of 2.5 mL. All of the new designs featured a wider chamber to allow for higher beam transmission and an increased chamber height, consistent with cur-rent trends in high power targets. One target featured a reduced chamber depth, and another had a ramp in the back of the chamber to reduce fill volume. Target pressure was limited to a maximum of 14 bar (200 psi) due to the larger diameter beam window. A video camera was used to record the boiling conditions observed for each target under several lighting conditions. During irradiation, the proton beam excites the water molecules, producing visible blue light emissions during de-excitation. These light emissions provide a good indication of beam distribution and penetration depth. A strong backlight can be used to produce clearer images of bubbles generated during boiling. Results and Conclusion Proton range and visible blue light emissions were recorded in dark ambient conditions. The width of the Bragg peak and natural circulation in the bulk fluid were visible with good ambient lighting. Size and distribution of vapor bubbles could be observed by using a strong backlight. The beam current was increased gradually to determine the thermal limit for each target for several fill volumes and pressures. Two thermal limits were observed which resulted in some beam penetration in the top region of the beam. For lower fill volumes, steam ac-cumulates in or around the helium overpressure bubble, causing the helium bubble to move into the upper region of the beam. For higher fill volumes, beam penetration occurs due to excessive voiding, when bubbles produced in the beam region cannot rise quickly enough out of the path of the beam.

Introduction The established methods for the production of 99Mo, based on fission in nuclear reactors, continue to present problems as a result of the plant’s aging and the significant investments needed for maintenance or for their renewal. Much research work is thus in progress on the study of alternative methods for the production of 99mTc in quantities and with the degree of purity required for the clinical use. Between them, the cyclotron production of 99mTc via the 100Mo(p,2n)99mTc reaction has turned out as the most attractive alternative. One critical aspect regarding the production of 99mTc with cyclotron is the need for a robust and reliable target production process. Several techniques have been indicated as extremely promising such has plasma spray and laser cladding; however these methods require specialized instrumentation and complex operations to be performed handling activated materials in order to recover irradiated Mo. In this work we report the development of the work done at the University of Bologna, as a part of a wider INFN project, as regards the methods of preparation of solid targets suitable for the production of 99mTc irradiating a target of 100Mo, employing a cyclotron for biomedical use, normally operated for the production of PET radionuclides. Material and Methods Irradiations were performed with a 16.5 MeV GE PETtrace cyclotron equipped with a solid target station previously developed by our group (1). In initial tests, a stack of 1–3 metallic foils, 100 μm thick, of natMo were irradiated with protons in the 15.9→9.8 MeV energy range. Foils were then dissolved in a HNO3-HCl solution and samples were analyzed with high resolution gamma-ray spectrometry (Canberra, including a HPGe detector with a 30% relative efficiency and a resolution of 1.8 keV at 1332 keV) using Genie2000 software; the measurement campaign lasted several weeks to take into account the different half-lives of the produced radionuclides. Results were extrapolated to a highly enriched 100Mo target and compared to Monte Carlo simulations previously performed with FLUKA and TALYS codes (2). In order to investigate a method of preparation of the target that would make easier the recovery of the enriched material and recycling for the preparation of a new target, it was subsequently studied the preparation of pellets of Molybdenum trioxide. MoO3 powder (Sigma Aldrich, 99.9% trace metals basis, particle size < 150 μm) was used to prepare pellets using a 10 ton press. Pellets obtained in this way were then sintered on a Platinum support using a CARBOLITE furnace under a controlled atmosphere; the temperature was ramped according to a controlled and reproducible temperature cycle. Sintered pellets were subjected to visual inspection, mechanical tests of resistance to loading and downloading in the cyclotron target station, thermal tests and then irradiated at increasing current. The irradiated targets were again visually inspected then weighed, dissolved and subjected to gamma-ray spectrometry analysis. Results and Conclusion The experimental saturation yield for 99mTc calculated on the basis of the gamma-ray analysis of irradiated metal foils, gave an extrapolated yield of 1.115 ± 0.015 GBq/μA for a 100 μm thick 100Mo enriched target, in accordance with the value of 1.107 ± 0.002 GBq/μA obtained in Monte Carlo simulations. On these bases, an irradiation of 3 h at 50 μA is expected to produce 16.3 ± 0.2 GBq of 99mTc; considering the use of an efficient purification system, a radionuclidic purity > 99.9 % 2 h after the EndOfBombardment and a specific activity comparable with the actual standards are expected as achievable. Experiments on sintering pellets are still on going at the time of writing this report; initial results showed that addition of proper aggregating materials allows for suitable pellets preparation. The sintering process allows to obtain pellets having sufficient mechanical strength to withstand loading and downloading operations. Initial irradiation tests with beam current up to 25 μA were performed successfully with no changes in mass and mechanical properties of the pellet. These encouraging results suggest that sintered pellets may be a relatively inexpensive and easy solution to prepare 100Mo targets for the cyclotron production of 99mTc. Further experimental tests at higher beam current will be performed in order to assess the maximum current achievable with no damage of the target. At the same time, a prototype automated module based on standard industrial components is in testing phase as regards performance in the separation and purification processes.

Introduction The worldwide use of PET has proven beyond dispute the importance for both routine diagnosis and physiological, oncological and pharmacological research. In many ways the present success of PET relies on the mature technology of PET compact medical cyclotrons. As long time developers of new targets, isotopes and com-pounds, we have been inclined to look for new block-buster applications, high power targets and sustainable ways of embracing the GMP and regional distribution, but recent pioneering development [1] around very small cyclotrons and “embedded synthesis and qc” has pointed out an old, but important nuclear physics lesson now halfway forgotten: that many PET isotopes can be made in high yields with proton energies far below 10 MeV [2]. This has opened a new interest in small cyclotrons and their targets. We have been testing the first GE Healthcare Prototype for a 7.8 MeV negative ion, internal ion source cyclotron with 3 production targets mounted on a short beamline. Here we present the first experimental yields of some of the important PET radionuclides. Materials and methods The prototype cyclotron (FIG. 1) has been in-stalled and tested without self-shield in designated experimental area in order to establish the neutron field around accelerator and targets in order to qualify design calculations for a future integrated shield. The cyclotron energy is fixed by the radial position of the extraction foil, while the azimuth determines which of the 3 targets are being irradiated. The beam energy at front of target foil was determined on several occasions: 7.8 ± 0.1 MeV by a 2 copper-foil sandwich method (adopted from [3]). The available beam inside the cyclotron at extractor position is > 50 μA, and 35 μA are easily and long term reliably extracted (> 90 %) on to any of the 3 target positions. The prototype is capable of delivering more than 40 μA to target, but target current was limited to 35 μA under present unshielded conditions. Results 18F We have tested the prototype gridded (> 80 % transmission) niobium body target with 10μm Havar foil using 95 % 18O water and 35 μA on target + grid with yields given in TABLE 1. The observed yields corrected for stopping in foil, grid loss and water enrichment are 75 % of theoretical. One Fastlab FDG run using 2 h irradiation yielded 16 GBq FDG EOS, confirming the “usual” 18F activity. Results 11C Using gridded target and a 10μm foil with 99% N2 + 1 % O2 at 10 bar followed by trapping into ascarite gave EOB activity as shown in TABLE 2. Results 13N We know that the 16O(p,alpha)13N cross section is a very steep function of energy around 7.8 MeV. In the hope of using the simple water target route to 13N NH3 we have measured the 13N yields (corrected for 18F contribution). It is still unclear if these yields can be improved to make useful single doses of ammonia. Results for other isotopes We have used solid targets to make 45Ti, 64Cu, 68Ga and 89Zr. The development of these solid targets is still in progress, but especially the 68Ga yield looks promising (3 GBq EOB after 1 h on natural Zn will give > 15 GBq on enriched 68Zn).

Introduction Measuring the beam profile on a medical cyclo-tron in real time can aid in improved tuning of the cyclotron and give important information for a smooth operation. Typically the beam profile is measured by an autoradiography technique or even by a scintillator that can be viewed in real time [1, 2]. Another method is to use collimators in front of the target to assess the beam center-ing [3]. All these methods have potential draw-backs including; an inability to monitor the beam in real time for the radiograph, exhibiting a non-linear correlation in signal response to the power deposited for a scintillator, and not providing a 2-dimensional profile of the complete beam for collimators. Our goal was to design a realtime, linear, 2-dimensional beam-profile monitor that is able to withstand the high power of a PET cyclotron. Material and Methods The beam-profile monitor (PM) is designed for the TR13, a 13MeV negative hydrogen-ion cyclotron at TRIUMF. The design follows the concept of a ‘harp’ monitor, widely used at TRIUMF for tuning proton and radioactive ion beams, and is installed on the extraction port without separation from the tank vacuum. The TR13 monitor is designed to withstand a 13 MeV proton beam with a beam current of up to 25 µA, has an active area of 10 by 10 mm and does not affect the 10-7 torr tank vacuum. The device consists of a water-cooled Faraday cup made out of aluminium for low activation and two orthogonal rows of eight tungsten electrodes each mounted on a water-cooled support frame. Electrodes are spaced 1 mm apart from each other, see FIG. 1. The electrodes are electrically isolated from each other and each has a current pickup soldered to it. The material and the shape of the electrodes are optimized to withstand the deposited power of the proton beam. A voltage of -90 V is applied to the electrodes to repel secondary electrons and prevent crosstalk between neighbouring electrodes. The electrode current is amplified using a custom current amplifier, and read by an ADC. From there, the current data is displayed on a PC. This allows one to observe changes of the beam profile in real time. The electronics are designed to read out all sixteen channels in parallel, or, if only a limited number of ADC channels are available, to cycle through the different channels. In our current setup all sixteen channels are read out simultaneously. Results and Conclusion The beam-profile monitor provides a real-time representation of the proton beam, see FIG. 2. The data can also be recorded and analyzed at a later time. The linearity of the monitor has been measured up to 30 µA of proton beam current [4]. With the use of the monitor, it was possible to increase the output of the ion source into the target by 50% in comparison to the standard tune.

Introduction Technetium-99m, the daughter of 99Mo is the most commonly used radioisotope in nuclear medicine [1–2]. Current global crisis of 99Mo supply, aging of nuclear reactors and staggering costs force the search for alternative sources of 99mTc. Radioisotope Centre POLATOM joined the IAEA Coordinated Research Project on “Accelerator-based Alternatives to Non-HEU Production of 99Mo/99mTc”. The planned outcome of this project is development of 99mTc production method using the reaction of 100Mo(p,2n)99mTc [3] in Polish cyclotron. This work presents the results concerning preparation of 100Mo target for irradiation with protons. Material and Methods The manufacturing of Mo target was performed using pressing of molybdenum powder into pellets and its sintering in hydrogen atmosphere at 1600 oC [4]. For this purpose a tantalum and stainless steel plates were used as support. Several pellets using molybdenum powder with particles size of 2 µm in diameter were pressed at different values of pressure. Results and Conclusion The optimized parameters of pressing molyb-denum pellets with various sizes are given in TABLE 1. It was found that the pellets did not adhere neither to the tantalum nor stainless steel plates but they conducted electricity very well. Pellets prepared with higher pressure were more mechanically resistant, however application, even the highest used pressure did not ensure its satisfactory stability. In order to improve mechanical strength, pressed Mo pellets were sintered in hydrogen atmosphere at temperature of 1600 °C. As a result of this process dimensions of Mo pellets decreased: diameter by 13 %, thickness by 12 %, weight by 1.5 %, volume by 34 % while density increased by 50 %. The changes of these parameters are associated with reduction of molybdenum oxide and removal of oxygen from intermetallic space. It was confirmed by photos of microscopic cross section of pellets before and after sintering. It was observed, that after sintering Mo pellets got a metallic form with very high hardness and mechanical strength.

Introduction When properly maintained, cyclotrons often remain in operation for 20 years and more. However, as the years pass the control systems in particular become challenging to support. The I/O cards and other hardware eventually become obsolete, making spare parts difficult or even impossible to find. And the knowledge and ability to reload and configure the software also gets lost as operating systems and media storage technology change. This obsolescence is true of the Siemens RDS-112 cyclotron, which is controlled using a 486 computer, connected to an external STD card rack containing up to 15 I/O cards. These I/O cards were last manufactured in the 1990’s, and the iRMX-based control programs malfunction on computers newer than a 486 processor. A control system upgrade for the RDS-112 cyclotron has been developed by PET Technical Consulting Inc. This commercially available control system reduces operator training time, requires less maintenance, and supports new targets and custom product processes. Material and Methods The availability of high channel count I/O cards, and the decision not to support the old CPCU synthesis units, means the entire STD card rack can be replaced with 5 National Instruments (NI) I/O cards. The replacement computer is an industrial grade rack mounted PC with RAID 1 mirrored pair hard drives in front panel access quick swap bays. Two NI PCI-6509 Digital I/O cards connect directly to the RDS electronics, channel assignments are mapped using software configuration. Three NI PCI-6229 Multifunction I/O cards connect to the RDS electronics through a cable breakout interface plate, the terminal blocks are wired as needed to map the channels. The new control software was created using National Instruments LabVIEW. The new control sequences have a core based on the original RDS-112 FORTRAN control programs. Then hundreds of improvements were made to simplify operation, increase flexibility, minimize user involvement and mistakes, and clearly display key parameters and fault conditions. System control has been combined into a comprehensive Graphical User Interface, with controls and indicators grouped together onto subsystem pages. Commands that once needed to be typed-in have been replaced with a clickable control for each function. Bar graphs display target and slit currents. Status is obvious with red faults against normally green indicators. Audio alarms cue the operator for process interaction, warn if target current or pressure drifts from setpoint, or if faults occur with power supplies, vacuum, or water cooling. Improvements in sequences and beam algorithms have reduced the time to achieve full beam on dual targets from 10 minutes down to 3 minutes. Results and Conclusion This new control system has been installed on (5) five RDS-112 cyclotrons used for commercial isotope distribution. The total combined operation time of these systems after receiving the upgrade is now over 17 years, during this time the control system operation has been nearly problem free. UPDATE: The Siemens RDS-111 cyclotron is controlled by a VME computer that is now end-of-life. The VM30 and VM42 CPU boards and many of the I/O modules are no longer manu-factured. PET Technical Consulting is developing a control system replacement for the RDS-111 cyclotron with expected completion in 2014.

Introduction It is shown that a very simple model reproduces the pressure versus beam current characteristics of elongated single-cavity boiling water targets for 18F production surprisingly well. By fitting the model calculations to measured data, values for a single free parameter, namely an overall heat-transfer coefficient, have been extracted for several IBA Nirta H218O targets. IBA recently released details on their new Nirta targets that have a conical shape, which constitutes an improvement over the original Nirta targets that have a cylindrical shape [1,2]. These shapes are shown schematically in FIGURE 1. A study by Alvord et al. [3] pointed out that elevated pressures and temperatures in excess of the saturation conditions may exist in a water target during bombardment. However, as long as the rate of condensation matches the rate of vaporization, the bulk of the system should remain at saturation conditions. Superheated regions are therefore likely to form but also likely to disappear rapidly, typically on the scale of a few milliseconds. Even though the boiling process is generally quite complex, enhanced by radiation-induced nucleation, the presence of fast mixing mechanisms in the water volume justifies some simplifications to be made. Materials and Methods The simplified model assumes that the bulk of the target water has a constant temperature, which is the same as the inner wall temperature of the cavity, Tw. A second simplification is to neglect the temperature difference across the target chamber wall, which is only justified if the wall is thin. The boiling is not explicitly taken into consideration, including the rather complex boiling behaviour at the Havar window, except to acknowledge that it is the main mixing mechanism. Large temperature gradients can briefly exist in the water medium but they also rapidly disappear. A further assumption is that a single, overall convective heat-transfer coefficient can be applied, which is constant over the entire water-cooled surface. As the wall thickness is neglected, the heat-transfer surface is assumed to be the inner surface of the cavity, excluding the surface of the Havar window. One can then write down an energy balance between the beam heating and the convection cooling (Newton’s law of cooling), where Ib is the beam intensity, ΔE is the energy windows of the target (taken as 18 MeV), h is the convective heat-transfer coefficient, A is the inner cavity surface through which the heat has to be transferred from the target-water volume to the cooling water, and T0 is the cooling-water temperature. The saturated vapour pressure of water versus temperature is a characteristic curve, given by the steam tables [4]. Assuming the bulk of the system at saturation conditions, one gets from (1) and (2). The function f is represented by a polynomial. The only unknown in Equation (3) is the overall convective heat-transfer coefficient h. Our approach was to adjust h until a good fit with a set of measured data was obtained. It also has to be mentioned that subtle differences in the physical properties between 18O-water and natural water have been neglected. All in all, quite a few assumptions and simplifications are made in deriving Equation (3) and the system is, admittedly, much more complex. Nevertheless, the results obtained by applying Equation (3) are rather interesting. Results and Conclusion Measured data and corresponding calculations are shown in FIGURE 2 for three different conical targets and one cylindrical target. The extracted convective heat-transfer coefficients are pre-sented in TABLE 1 for the four cavities. As can be seen in FIGURE 2, while there are some differences between the data and calculated curves, especially towards lower beam currents, the overall agreement is remarkably good. It is possible that the better agreement towards higher beam intensities is related to more ebullient boiling and more rapid mixing, i.e. closer to the conditions that the model assumes. The values obtained for the overall convective heat-transfer coefficient are also remarkably similar. This tells us that, by and large, all the cavities perform in a similar way and the performance in terms of maximum operational beam current depends largely on the available surface to effectively remove the heat from. The values of h increase marginally if a smaller value is adopted for the cooling water. Note that the choice of T0 = 30 ᵒC used to obtain the results in TABLE 1 is typical for the room temperature closed-loop cooling system used at iThemba LABS, once it has stabilized under operational conditions. A study by Buckley [5] on a quite different target design reports a value of h = 0.49 W cm−2 ᵒC−1, which is reassuringly similar. That study describes a cylindrical target cavity with a volume of 0.9 cm3, 8 mm deep, cooled with 25 ᵒC water from the back, operated with a 15 MeV proton beam with an intensity of 30 µA. The Nb Nirta targets are typically filled with 18O-water to about 60% of the cavity volume (see refs. [1,2] for the recommended values). The elongated shape, in combination with the ebullient properties of the boiling water, prevents burn-through. All the targets deliver the expected saturation yield. The targets are self-regulating ─ no external gas pressure is required. While the thermosyphon targets seemingly take advantage of a superior concept, we are now questioning whether this is really so in practice? It is not clear to us that the much more complex thermosyphon targets deliver any operational and/or performance advantages compared to the simple elegance of these elongated, single-cavity boiling target designs.

Cyclotron production of 99mTc through the 100Mo(p,2n)99mTc reaction1 is being actively investigated as an alternative to reactor-based approaches. A challenge facing cyclotron pro-duction of clinical-quality 99mTc is that proton bombardment of Mo targets results in production of a number of additional Tc and non-Tc isotopes through various reaction channels.2,3 While non-Tc products can be chemically re-moved, other Tc radioisotopes cannot and will therefore degrade radionuclidic purity and contribute to patient radiation dose.5 The radionuclidic purity of cyclotron-produced 99mTc depends on the nuclear cross section governing each reaction channel, the proton current and energy distribution, duration of bombardment, target thickness and isotopic composition. Although conditions that minimize dose from radioactive Tc impurities have been identified,5 cyclotron performance and thus irradiation conditions may randomly fluctuate between and/or during production runs. Fluctuations of certain parameters, for example the total number of bombarding protons, are expected to have little influence on radionuclidic purity, whereas fluctuations in beam energy, target thickness and isotopic composition may dramatically affect the relative amounts of 93gTc, 94gTc, 95gTc, and 96gTc impurities. It is critical to quantify relationships between potential fluctuations and the reproducibility and consistency of the radionuclidic purity of cyclotron-produced 99mTc to guide development and optimization of target preparation, irradiation, and processing techniques. The purpose of this work is to present a mathematical formalism for quantifying the relation-ship between random fluctuations in Mo target thickness and variability of proton-induced nuclear reaction rates for enriched Mo targets. In this study, we use 96gTc as an example of impurity which can potentially contribute to increased patient dose for patients injected with cyclotron-produced 99mTc.4 Herein, we apply the developed formalism to both the 96Mo(p,n)96gTc and the 100Mo(p,2n)99mTc reaction channels, however, the same approach can be applied to any reaction channel of interest.