Diamond-Like Carbon Coatings for Rhenium Wire and Foils
- PDF / 1,870,324 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 23 Downloads / 155 Views
endovascular brachytherapy with stents of shorter half-lives than 32p (TI/2 of 14 days) might be beneficial.13 One class of beta-emitting isotopes with shorter half-lives are the rhenium isotopes "'Re and 88' Re864(T 1/2 of 90.6 and 17 hours, respectively)' 4 . One limitation of rhenium stents, however, is the tendency to slowly oxidize and then release radioactive rhenium in the form of the highly water soluble perrhenate anion ReO 4_ (released activity). Released activity can be reduced by coating the stents with a thin, radiation hard material. DLC is one such coating with potentially good biocompatibility, good adhesion, and radiation hardness' 5 . As shown below, coating radioactive rhenium with DLC is effective in reducing the released activity. Experimental Methods Carbon films were grown from a methane/argon mixture by plasma enhanced chemical vapor deposition. An inductively coupled RF plasma system was used to deposit the films; the
design of this RF plasma system was proposed and first tested by Hopwood and co-workers. 6,7 The dual RF inductively coupled plasma (ICP) provides high ion densities and uniform deposition over large areas. The substrates to be coated are placed on top of the substrate electrode, which is mounted within the vacuum chamber parallel to the planar coil electrode. The bias voltage, which is provided by the substrate electrode, is varied to control the ion bombardment energy. The substrate electrode temperature is normally maintained at 25°C. Films were deposited on rhenium foils, wires, and coils, and on glass microscope slides. Multiple foils were coated at each set of conditions. The foils were used for measuring released activity. The wires and coils were used to assess the film adhesion and the ability to deposit films onto complex shapes. Films were deposited onto glass substrates for identification and characterization by FTIR spectroscopy. Deposition conditions were varied to determine the main effects on the resulting free release of radioactive rhenium. The deposition pressure was varied between 20 and 55 milliTorr, the induction power was varied between 0 and 100 watts, and the bias voltage was varied between 400 and 500 volts. The source gas was kept constant at a methane to argon ratio of 9:1. Following deposition of the DLC film, the rhenium foils were made radioactive using a nuclear reactor. The foils were first cleaned by immersing in 95% and 100% ethanol and acetone. The foils were then neutron-activated at a neutron flux of 5x102 n/cm2 sec-1 for 5 to 30 minutes to yield between 0.4 and 2.6 MBq 186Re and 2.5 and 15.1 MBq 188Re. The neutron activation was carried out at Ohio State University in Columbus, Ohio. The radioactive foils were then incubated in 3 ml of 0.9% saline at 370 C for up to 1 month. The released activity, or the amount of radioactive rhenium which escaped from the rhenium sample into the liquid (supernatant), was measured together with the activity of the foil at each time point. The released activity was then divided by the total activity (super
Data Loading...
