Ion implantation in nanodiamonds: Size effect and energy dependence

Nanoparticles are ubiquitous in nature and are increasingly important for technology. They are subject to bombardment by ionizing radiation in a diverse range of environments. In particular, nanodiamonds represent a variety of nanoparticles of significant fundamental and applied interest. Here we present a combined experimental and computational study of the behaviour of nanodiamonds under irradiation by xenon ions. Unexpectedly, we observed a pronounced size effect on the radiation resistance of the nanodiamonds: particles larger than 8 nm behave similarly to macroscopic diamond (i.e. characterized by high radiation resistance) whereas smaller particles can be completely destroyed by a single impact from an ion in a defined energy range. This latter observation is explained by extreme heating of the nanodiamonds by the penetrating ion. The obtained results are not limited to nanodiamonds, making them of interest for several fields, putting constraints on processes for the controlled modification of nanodiamonds, on the survival of dust in astrophysical environments, and on the behaviour of actinides released from nuclear waste into the environment

Legislative Documents

Also, variously referred to as: House bills; House documents; House legislative documents; legislative documents; General Court documents

Operational measurements of 18F and 81Rb activities during transport

Introduction Activity measurement of the produced radionuclide prior its transport to further processing in the clean rooms indicates proper irradiation settings and target functioning. It is particularly true for shortlived radionuclides. Precise online activity measurement of the radionuclides transported from the target to the hot cells in a liquid phase was highly desirable in order to estimate compliance with the required value. In this paper, we present simple operational systems for activity measurement of the irradiated enriched (18O) water for 18F labelled PET radiopharmaceuticals and 81Rb aqueous solution for manufacturing radionuclide generator 81Rb/81mKr. Material and Methods Irradiated aqueous solution (2.5 ml of enriched water with 18F up to 200 GBq) is transported via capillary to a synthesis module. Due to spreading out the liquid product on measuring vial walls, measured activity may vary up to 12 %. In order to avoid this variability, we have introduced simple system based on the measurement of several loops of the transporting capillary. The product is then evenly distributed around GM tube positioned in the loops’ centre. Typical GM tube response is displayed on FIG. 1. The data are recorded and processed online. Maximum mean value of 20 consecutive values is calculated. The GM tube response was calibrated by precise activity measurement of the same product in a calibrated ionizing chamber (Atomlab). Calibration covers full range of the produced 18F activities. Radionuclide 81Rb for the 81Rb/81mKr generator is produced via proton irradiation of pressurized enriched 82Kr gas. The product deposited on the target walls is washed out by water and transported to a container in a hot cell for filtration before transfer to a clean lab. The solution activity in the container (7–25 GBq) is measured with a GM tube in constant geometry. Typical response of the GM tube to the measured activity of 81Rb is displayed on FIG. 2. For activity determination, the mean value of 200 consecutive readouts starting from the 120th readout following maximum is used. The calibration for the whole range of the produced activities was performed via precise measurement of the cumulative 81Rb activity concentration by standard γ-spectrometry using HPGe detector. Results and Conclusion A simple operational system for online activity measurement of 18F and 81Rb in aqueous solutions using GM tube was designed, calibrated and implemented. Long term statistics show that the measured activities do not differ from the values obtained on calibrated ionizing chamber (18F) or γ-spectrometer (81Rb) for more than ± 2.5 %. The method seems to be cheap and rapid for reliable estimate of the produced activities online

New gas target system for 83Rb production

Introduction Short-lived isomer 83mKr (T½ = 1.83 h) is an ideal calibration source in several low-energy experiments like or KATRIN (determining the neutrino rest mass, monitoring high voltage stability and investigation of the main spectrometer properties) or XENON (detection of the dark matter). The isomer 83mKr is formed by decay of 83Rb (T½ = 86.2 d) that can be produced predominantly via the reaction 84Kr(p,2n)83Rb by irradiation of natKr (57 % abundance of 84Kr). The design and construction of the new gas target for effective production of radionuclide 83Rb as well as target processing will be shortly described. Material and Methods For the target design, we selected the following criteria: minimizing activation of target components; efficient cooling system allowing higher beam currents; easy handling; high life-time of the target chamber (low impact of the irradiation and radionuclide separation process on the target chamber surface and 83Rb recovery). The target consists of three parts: 1. Water cooled aluminium (alloy EN 6082) mechanical interface for easy connection of the target to the beam line. It also serves as a beam collimator (diameter 9 mm). 2. Holder of He-cooled foils (vacuum separation foil – Havar 0.025 mm, target body window – Ti 0.1 mm). 3. Aluminium (alloy EN 6082) water cooled target body with 150mm long cone-shaped target chamber of the volume 27.1 ml. Internal surface of the chamber is nickel-coated. The target filled with natural Kr of purity 0.9999 and absolute pressure 13 bar was irradiated on the external beam of the isochronous cyclotron U-120M of the NPI AS CR. The proton beam energy was set so that it is decreased after deg-radation in the separation foils to 25.6 MeV. Beam energy loss in the natural Kr gas filling is 9.6 MeV. The target was tested up to 25 µA beam current. After irradiation, the target is left for a week to let the short-lived activation products to decay. Then, 83Rb is washed out from the target walls by two portions of freshly prepared de-ionized water, target is rinsed by high-purity ethanol and dried. The two portions of 83Rb aqueous solution are then connected and activity and radionuclidic purity of the product is determined via γ-spectrometry (HPGe detector). Large-distance sample-detector measurements of the target prior and after the separation are used in order to determine recovery of 83Rb. Results and Conclusion The new gas target for routine production of 83Rb was successfully designed, tested and im-plemented for regular 83Rb production. Six-hour irradiation with 15 µA proton beam resulted repeatedly in ca 300 MBq of 83Rb (EOB). Besides 83Rb, we identified in the separated product also 84Rb (T½ = 32.82 d) at levels ca 31 % of the 83Rb activity (EOB) and 86Rb (T½ = 18.631 d) at levels ca 8 % of the 83Rb activity (EOB). Both radionuclidic impurities do not disturb the use of 83Rb, since none of them emanates any radioactive krypton isotope. Moreover, their relative content decreases in time. Rubidium isotopes are recovered from the target almost quantitatively (98–99 %)

Structural re-arrangement and peroxidase activation of cytochrome c by anionic analogues of vitamin E, tocopherol succinate and tocopherol phosphate

Background: An anionic phospholipid, cardiolipin, converts cytochrome c into a peroxidase. Results: Anionic tocopherol derivatives, tocopherol succinate and tocopherol phosphate, similarly to cardiolipin, unfold cytpchrome c and stimulate its peroxidase activity. Conclusion: Peroxidase activation of cytochrome c by tocopherol analogues is one of their pharmacological mechanisms. Significance: Peroxidase activation of cytochrome c may induce apoptosis and contribute to anti-cancer properties of α-tocopherol succinate