Littérature scientifique sur le sujet « Boiling water targets, cyclotron »

In the present work the patterns of relationship of photonic radiation dose rate from Cyclone 18/9HC water cooling system were studied at production of positron-emitting nuclides. Reaction (n, p) was shown to be the main source of activation nuclides in cyclotron cooling water at 18F production, resulting in formation of 16N (T1/2 = 7 s) from 16О. In water targets with high accumulated dose, when beam partially irradiates a target body, proton-induced reactions: 16О(p, α)11С and 18О(p, n)18F take place. Fluoride 18F–, carbonate 11СО32– and hydrocarbonate Н11СО3– anions, formed in proton-induced activation reactions, efficiently precipitate on anion-exchanging resin during water circulation resulting in circuit purification from the named radionuclides. Activation of cooling water does not occur at irradiation of gas targets. Projected annual dose for cyclotron operator from cooling water activation is less than 1 % of annual dose limit for personnel from technogeneous radioactive sources. In order to minimize operator`s accumulated doses it is recommended to decrease the duration of personnel activities at the distance less than 1 meter from heat exchanger during 18F production. At operation of water targets with absorbed dose higher than 2500 μA·h it is desirable to conduct the preventive maintenance of water cooling system not earlier than in half an hour after the end of irradiation and with mandatory dosimetry control. To decrease the activation of impurities it is essential to use only deionized water in cooling circuit. In case of its specific conductivity increase due to corrosion the coolant should be replaced promptly.

A simple model, for the estimation of changes in the nuclear fuel element cladding temperature as well as the conditions of the formation of the onset of nucleate boiling, is proposed. The results of this estimation are sufficient to assess the effect of the transient with the peak of the reactor's power on the device's safety, without the need for time-consuming thermal calculations. The basic parameters determined using the proposed model are the maximum wall temperature of the device in a hot spot, the time constant of the wall temperature change, and the course of changes in the onset of nucleate boiling ratio in time. The model may be used for investigating the thermal behavior of thin heat-generating and water-cooled elements (such as fuel elements or uranium irradiation targets) during rapid power rise. The results of the temperature estimation with the proposed model were tested considering the hot spot in the MR-6 type nuclear fuel. The SN code with coupled kinetics and thermal-hydraulics, developed in the MARIA reactor was used to validate the results. The maximum cladding temperature, the thermal time constant and the onset of nucleate boiling ratio parameter simulated by the SN code and the proposed scheme appeared to be very consistent.

Microspheres comparable with yeast cells in size were obtained by the glutaraldehyde crosslinking of polyvinyl alcohol (PVA), whose 25 g/l water solution containing magnetite particles was dispersed in the isooctane/Span 85/Tween 85 medium. yeast cell walls were partially hydrolysed by sonication in formic acid near the boiling point. The microspheres were made targets for phagocytosis by the addition of yeast lysate to the crosslinkable PVA solution and a subsequent treatment of the freshly crosslinked microspheres with diluted yeast lysate. The microspheres were also made fluorescent when the emulsification medium saturated with fluorescent 2-aminopyrimidine derivatives was used. A protocol for phagocytosis assay using the thus modified microspheres was developed.

The therapeutic efficacy of a herbal mixture, being multi-target, multi-function and multi-pathway, is the niche of traditional Chinese medicine (TCM). Systems biology can dissect the network of signaling mechanisms in a complex biological system. In preparing TCM decoctions, the boiling of herbs together in water is a common practice; however, the rationale of this specific preparation has not been fully revealed. An approach of mass-spectrometry-based multi-omics was employed to examine the profiles of the cellular pathways, so as to understand the pharmacological efficacy of Danggui Buxue Tang (DBT), a Chinese herbal mixture containing Astragali Radix and Angelicae Sinensis Radix, in cultured rat osteoblasts and mesenchymal stem cells. The results, generated from omics analyses, were compared from DBT-treated osteoblasts to those of treating the herbal extract by simple mixing of extracts from Astragali Radix and Angelicae Sinensis Radix, i.e., herbal mixture without boiling together. The signaling pathways responsible for energy metabolism and amino acid metabolism showed distinct activation, as triggered by DBT, in contrast to simple mixing of two herbal extracts. The result supports that boiling the herbs together is designed to maximize the osteoblastic function of DBT, such as in energy and lipid metabolism. This harmony of TCM formulation, by having interactive functions of two herbs during preparation, is being illustrated. The systems biology approach provides new and essential insights into the synergy of herbal preparation. Well-defined multiple targets and multiple pathways in different levels of omics are the key to modernizing TCM.

This paper presents results from eight field studies in Asia and Africa on the emissions performance of 16 stove/fuel combinations measured during normal cooking events in homes. Characterizing real-world emissions performance is important for understanding the climate and health implications of technologies being promoted as alternatives to displace baseline cooking stoves and fuels. Almost all of the stove interventions were measured to have substantial reductions in PM2.5 and CO emissions compared to their respective baseline technologies (reductions of 24–87% and 25–80%, for PM2.5 and CO emission rates, respectively), though comparison with performance guidance from the World Health Organization (WHO) and the International Organization for Standardization (ISO) suggests that further improvement for biomass stoves would help realize more health benefits. The emissions of LPG stoves were generally below the WHO interim PM2.5 emissions target (1.75 mg/min) though it was not clear how close they were to the most aspirational ISO (0.2 mg/min) or WHO (0.23 mg/min) targets as our limit of detection was 1.1 mg/min. Elemental and organic carbon emission factors and elemental-to-total carbon ratios (medians ranging from 0.11 to 0.42) were in line with previously reported field-based estimates for similar stove/fuel combinations. Two of the better performing forced draft stoves used with pellets—the Oorja (median ET/TC = 0.12) and Eco-Chula (median ET/TC = 0.42)—were at opposite ends of the range, indicating that important differences in combustion conditions can arise even between similar stove/fuel combinations. Field-based tests of stove performance also provide important feedback for laboratory test protocols. Comparison of these results to previously published water boiling test data from the laboratory reinforce the trend that stove performance is generally better during controlled laboratory conditions, with modified combustion efficiency (MCE) being consistently lower in the field for respective stove/fuel categories. New testing approaches, which operate stoves through a broader range of conditions, indicate potential for better MCE agreement than previous versions of water boiling tests. This improved agreement suggests that stove performance estimates from a new ISO laboratory testing protocol, including testing stoves across low, medium, and high firepower, may provide more representative estimates of real-world performance than previously used tests. More representative results from standardized laboratory testing should help push stove designs toward better real-world performance as well as provide a better indication of how the tested technologies will perform for the user.

The huge interest in the health-related properties of foods to improve health has brought about the development of sensitive analytical methods for the characterization of natural products with functional ingredients. Greek olive leaves and drupes constitute a valuable source of biophenols with functional properties. A novel ultra-high-performance liquid chromatography–quadrupole time of flight tandem mass spectrometry (UHPLC-QTOF-MS) analytical method was developed to identify biophenols through target and suspect screening in Greek olive leaves and drupes of the varieties: Koroneiki, Throumbolia, Konservolia, Koutsourelia, Kalamon, Petrolia, Amigdalolia, Megaritiki, Mastoeidis, Agouromanakolia, Agrilia, Adramitiani and Kolovi. The method’s performance was evaluated using the target compounds: oleuropein, tyrosol and hydroxytyrosol. The analytes demonstrated satisfactory recovery efficiency for both leaves (85.9–90.5%) and drupes (89.7–92.5%). Limits of detection (LODs) were relatively low over the range 0.038 (oleuropein)–0.046 (hydroxytyrosol) and 0.037 (oleuropein)–0.048 (hydroxytyrosol) for leaves and drupes, respectively For leaves, the precision limit ranged between 4.7% and 5.8% for intra-day and between 5.8% and 6.5% for inter-day experiments, and for drupes, it ranged between 3.8% and 5.2% for intra-day and between 5.1 and 6.2% for inter-day experiments, establishing the good precision of the method. The regression coefficient (r2) was above 0.99 in all cases. Furthermore, the preparation of herbal tea from olive leaves is suggested after investigating the optimum infusion time of dried leaves in boiling water. Overall, 10 target and 36 suspect compounds were determined in leaves, while seven targets and thirty-three suspects were identified in drupes, respectively.

AbstractA new approach to spectroscopy of laser induced proton beams using radiochromic film (RCF) is presented. This approach allows primary standards of absorbed dose-to-water as used in radiotherapy to be transferred to the calibration of GafChromic HD-810 and EBT in a 29 MeV proton beam from the Birmingham cyclotron. These films were then irradiated in a common stack configuration using the TARANIS Nd:Glass multi-terawatt laser at Queens University Belfast, which can accelerate protons to 10–12 MeV, and a depth-dose curve was measured from a collimated beam. Previous work characterizing the relative effectiveness (RE) of GafChromic film as a function of energy was implemented into Monte Carlo depth-dose curves using FLUKA. A Bragg peak (BP) “library” for proton energies 0–15 MeV was generated, both with and without the RE function. These depth-response curves were iteratively summed in a FORTRAN routine to solve for the measured RCF depth-dose using a simple direct search algorithm. By comparing resultant spectra with both BP libraries, it was found that the effect of including the RE function accounted for an increase in the total number of protons by about 50%. To account for the energy loss due to a 20 µm aluminum filter in front of the film stack, FLUKA was used to create a matrix containing the energy loss transformations for each individual energy bin. Multiplication by the pseudo-inverse of this matrix resulted in “up-shifting” protons to higher energies. Applying this correction to two laser shots gave further increases in the total number of protons, N of 31% and 56%. Failure to consider the relative response of RCF to lower proton energies and neglecting energy losses in a stack filter foil can potentially lead to significant underestimates of the total number of protons in RCF spectroscopy of the low energy protons produced by laser ablation of thin targets.

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.

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 Liquid targets using top-of-foil loading concept have been succesfully employed for routine high current production of 18F and 13N at Cyclotope (Houston,TX), over the past ten years1,2. These targets are typically filled with 3.5 ml of water, then pressurized with helium gas at 22 bar and bombarded with 18MeV protons (70–100 µA). Average calculated saturation yield for produc-tion of 18F is ~7.8 GBq/µA (210 mCi/µA) using in-house recycled [18O]-water at approximately 93% enrichment. Reduction of beam power per unit of area is one of the advantages of a tilted entrance-foil geo-metry. Implementation of this target geometry on the ACSI TR19 cyclotron 25degrees upwards irradiation port results in an almost horizontal target entrance foil. A 6ml total cavity volume target allows variable liquid fill volumes of 1.2–4.5 ml for beam current operation from 30–120 µA, resulting in a very efficient use of the costly 18O-water. In a near horizontal installation as in the mayority of cyclotrons, the fill volume flexibility is drastically reduced, having a minimum fill volume of 3.3 ml. At the requirement of Laboratorios Bacon, Cyc-lotope modified the target design with a front mounted collimator compatible with the IBA Cyclone 18/9 cyclotron. A second requirement was to reduce the minimum fill volume for horizontally mounted targets to 2.5 ml or less, while maintaining saturation yield performance. To preserve compatibility with existing IBA targets, the target hardware was modified to operate in self-pressurization mode. This paper presents the results obtained with high and low volume Niobium target inserts (6ml and 4 ml) mounted near horizontally on the IBA Cyclone 18/9 cyclotron and operated in self-pressurization mode. We present pressure/current characteristics, target performance (saturation yield, produced activities, maintenance frequency, FDG yields, etc.). Material and Methods The following targets manufactured by Cyclotope were tested and routinely used for production at Laboratorios Bacon: 1-High Volume Target CY2 model (“American Standard”), 6ml Niobium cavity. 2-Low Volume Target, CY3a model (“Traful”), 4ml Niobium cavity. 3- Low volume Target, CY3b model (“Ferrum”), 4.1ml Niobium cavity. Results and Conclusion The advantages of self-pressurization mode (Laboratorios Bacon setup) are: - Using the vapor pressure as a performance parameter - heat removal by boiling/condensation cycle starts at lower temperature (beam cur-rent) . While, the advantages of the pre-pressurized targets (Cyclotope setup) are: - reduced pressure fluctuations - performance is basically unaffected by plumbing dead volume - flexibility to locate instrumentation farther away from radiation fields - less dependence on fill volume - potential target leaks can be detected before starting an irradiation No significant differences were found in target performance when operated in either pressu-rization mode. The self-pressurizing setup seems to require a sligthly lower fill volume (approxi-mately 5%). The maximum beam current was limited by the foil rupture pressure (~ 40 bar). Safe maximum operating pressure was determined as 30 bar. No foil rupture was experienced during nine months of daily irradiation of these targets in self-pressurizing mode at Laboratorios Bacon. The irradiation parameters and target performance for the different targets are shown in Tables 1 and 2 below. The low volume Traful and Ferrum targets have the best saturation activity vs. fill volume, A(sat)/V, relation. Both targets produce 310 ± 31GBq (8.4 ± 0.8 Ci) of high quali-ty fluoride (F-18) in two hours of irradiation at 70 µA. The low volume targets have a low operation pressure (20bar @ 70µA) when compared to the IBA (NIRTA XL) targets. The typical saturation activity for the low volume targets was 592 ± 59 GBq (16 ± 1.6 Ci) of F-18 at 70 µA, 8.5 GBq/µA (228 mCi/µA) using 2.7ml enriched O-18 water (98 % +). The maintenance interval (> 10 mA.h) is very conveniente to reduce personnel radiation dose. No reduction in FDG yields was observed during that operation interval. In contrast, operation of the high volume targets in pre-presurization mode at the Cyclotope facility results in a higher maximum beam current limit (135 µA) for the same operating pressure (25 bar). Nevertheless, more O-18 water will be required to irradiate at this high current (4.5 ml vs. 3.0 ml). In self-pressurizing mode, a higher filling volume will reduce the expansion volume and, in consequence, the maximum beam current.

NOx pollution from Diesel engines causes over 10 000 premature deaths annually and the trend is increasing. In order to decrease this growing global problem, exhaust after-treatment systems for Diesel engines have to be improved. The most common SCR systems in the market place inject an aqueous Urea solution, DEF that evaporates prior the catalytic surface of the SCR-catalyst. Due to a catalytic reaction within the catalyst, NOx is converted nominally into Nitrogen and Water. Currently, the evaporative process is enhanced by aggressive mixer plates and long flow paths; these, negatively, create extra exhaust back pressure and cool the exhaust gases decreasing engine and catalyst efficiency. To achieve future emission legislation targets SCR efficiency has to be improved especially under low catalyst temperature conditions, plus Ammonia slip has to be avoided as it is now legislated against. Swedish Biomimetic’s novel μMist® platform technology, inspired by the Bombardier Beetle, injects a hot, effervescent, finely atomised, highly dispersed spray plume of DEF into the exhaust stream. This is achieved by raising the temperature of the DEF, in a closed volume, above its saturated vapour pressure. The DEF is then rapidly released creating effervescent atomisation. This study investigates a back to back study of the evaporating and mixing behaviour of the μMist® injector and a class leading DEF injector. The test conditions are with and without a mixer plate and the use of two different flow path designs. Spray distribution across the face of the catalyst is assessed by measuring NOx conversion whilst Ammonia slip is also measured post catalyst. This report describes how the novel μMist® injector significantly increases NOx conversion and catalyst surface usage whilst considerably reducing Ammonia slip.

A Probabilistic Safety Assessment (PSA) was provided as an integral part of the safety case for the United Kingdom Advanced Boiling Water Reactor (UK ABWR) Generic Design Assessment (GDA). The main objectives of PSA for GDA is to provide a demonstration of the compliance, for a single unit UK ABWR, with numerical risk targets defined in the UK Safety Assessment Principles (SAP) and to support the “As Low As Reasonably Practicable” (ALARP) assessment. This content of this paper includes: • An overview of the UK ABWR PSA • Identification of the PSA scope • PSA model development to compare with numerical risk targets and inform design and operational features • Illustration of PSA results, e.g., Core Damage Frequency (CDF), Large Release Frequency (LRF) and Large Early Release Frequency (LERF) • Peer reviews • Use of PSA in ALARP assessment