Development of Corrugated CVD Diamond Stripper Foils. ROBERT POTTER (Brigham Young university Idaho Rexburg, ID 83440) ROBERT SHAW (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Investigations of the growth and production process of micro and nano-crystalline diamond films have been conducted for use as stripper foils in the Spallation Neutron Source (SNS). Due to the expected ion beam power of the SNS currently under construction in the U.S.A., conventional carbon stripper foils are estimated to fail in approximately 10 hours. Chemical vapor deposition (CVD) diamond films have been grown and tested in a simulated SNS environment and were found to have a beam life of over 130 hours. Semiconductor-grade <100> silicon wafers are sonicated in diamond powder slurry to promote uniform nucleation during growth. Microcrystalline diamond film growth is accomplished using a 1500-watt microwave CVD system with a plasma composition of 1-2% methane, 98-99% hydrogen, at 50 Torr pressure and running at 1300 watts for micro size crystals. Adding argon to the plasma gas produces nano crystalline diamond. Typically 1-2% methane, 8-9% hydrogen and 90% argon at 900 to 1000 watts and 130 Torr pressure is used. These films were then analyzed using SEM and Raman Spectroscopy to determine continuity, uniformity, and substance. One requirement due to the Linac beam physics is that the diamond stripper foil be free standing, i.e. only supported on one side by silicon. This has led to the development of corrugations in the substrate, using conventional photolithography techniques, that allows a structured diamond film to be grown to increase stiffness and to combat the inherent stress related to the mismatched thermal expansion occurring during the growth process. New photolithography mask patterns are being considered in order to better resist the multidimensional stresses. Another development currently under investigation is a different method to dissolve the silicon substrate without the use of protective Teflon tape, which is difficult to apply and remove without damaging the film. These methods include applying silicon nitride and using KOH etchant instead of HF, or sputtering on a protective metal film. As it has been demonstrated that micro and nano diamond films are robust enough to withstand the purposed SNS beam strength, finalized manufacturing process details are currently being established.

Effect of Thiourea Anion Receptors on Cesium Extraction. CAROL PHAM (University of Hawaii at Manoa Honolulu, HI 96822) LAETITIA DELMAU (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Bis(t-octylbenzo-crown-6)calix[4]arene (BOBCalixC6) is a cation receptor with high selectivity for cesium in solvent extraction. When used as co-extractants with BOBCalixC6, anion receptors such as thioureas (RR'N-C(S)-NR'R) may hydrogen bond with counterions of cesium, facilitating the transfer of anions into the organic phase and thus increasing the extraction efficiency. To determine the extent to which a thiourea compound improves cesium extraction as well as the stoichiometry of the process and the importance of the anion's identity, it is necessary to perform a quantitative investigation of the extraction. Previous experiments using chloroform as the organic phase diluent produced complex systems containing apparently both dissociated and ion-paired species. In this project, nitrobenzene was used in place of chloroform to ensure a fully dissociated system, which is expected to follow a simpler model. During the survey portion of the experiment, extractions were performed using three thioureas and the following anions: bicarbonate, bromide, carbonate, chloride, chromate, hydroxide, iodide, nitrate, oxalate, perchlorate, and sulfate. Using radiotracers, the amount of cesium present in the aqueous and organic phases after extraction was determined. Plots relating the distribution ratio to the anion's energy of partition ( G_p) revealed each thiourea's selectivity towards certain anions. The survey showed that using BOBCalixC6 and an anion receptor together produced a synergistic effect in the extraction of most of the salts tested, especially cesium bicarbonate, but an antagonistic behavior in some cesium perchlorate experiments. From survey data, G_p for bicarbonate was determined to be 40.1 kJ/mol. After performing experiments varying the concentrations of salt and thiourea, the SXLSQI program was used to model cesium bromide extraction with one of the anion receptors and obtain thermodynamic data. The model allowed calculation of the equilibrium constants K for complexation of cesium with BOBCalixC6 (logK = 8.55) and of bromide with the thiourea (logK = 3.12). The value for cesium-BOBCalixC6 complexation is in good agreement with the calculation results derived from a different set of experiments carried out in the group. This investigation of anion recognition is part of a larger study of the fundamental principles underlying the properties of new cation and anion receptors.

Lead Doped Scintillators for Gamma Radiation Detection Synthesized by Room Temperature Sol-Gel Processing. DUSTIN TRAVAGLINI (University of Florida Gainesville, FL 32611) BANU KESANLI (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

With a growing focus on homeland security, efforts have been made to improve present radiation detectors. Room-temperature sol-gel synthesis is an effective way to create solid scintillator. The challenge is to create a sol-gel material that is transparent, durable, and crack-free while also containing a radiation absorber and a suitable fluorescence sensitizer. A lead salt, in this case lead acetate, liquid organic scintillators such as a 2,5-diphenyloxazole/1,4-bis-2-(5-phenyloxazolyl)-benzene (PPO/POPOP) mixture and Ultima Gold™, and various siloxane precursors were used in an effort to create a transparent scintillating material for gamma detection. The solid scintillators were then characterized by Energy Dispersive X-ray (EDX) spectroscopy and a photoluminescence study. The EDX shows that the lead is incorporated into the sol-gel matrix of the samples. The photoluminescence study shows that the sol-gels have an emission wavelength in the blue region (425nm) when excited at a wavelength of 385nm. Lead has been doped in the sol-gels up to 6.1 weight percent while still maintaining optical transparency. When a gamma source becomes available, the scintillators will be tested for their detection quality.

Synthesis of Ionic Liquids for Green Chemistry Applications. MIAO YU (University of Florida Gainesville, FL 32611) HUIMIN LUO (Oak Ridge National Laboratory, Oak Ridge, TN, 37831)

Ionic liquids are essentially organic salts, which are liquid at low temperatures, have negligible vapor pressure, are highly thermally stable, and are non-flammable. These properties and their excellent solvation capabilities for many compounds (organic and inorganic) make ionic liquids particularly attractive for replacing volatile organic solvents and reducing the release of toxic vapors into environments. In this project, methylimidazolium -based ionic liquids with different anions and different alkyl groups were synthesized and their thermal stability measured using thermogravimetric analysis (TGA) to determine the effect of alkyl chain length of the imidazolium ring and the size of the anions on thermal stability. The anions included tetrafluoroborate (BF₄^-), hexafluorophosphate (PF₆^-), bis(perfluoroethylsylfonyl)imide (BETI^-), and bis(trifluoromethylsulfonyl)imide (NTf₂^-), among others. The basic synthesis procedure involves a metathesis reaction. Typically, metal salts containing the corresponding anions (e.g. LiBETI and LiNTf₂) and organic salts containing the alkyl and imidazolium groups (e.g. C₄mimBr) were mixed. The resulting ionic liquid was extracted using CH₂Cl₂ and subsequently washed with de-ionized water to remove remaining metal ions (Li or Na) from the reaction mixtures. Using the data from TGA runs, the T_onset temperature, at which the decomposition was initiated, was calculated for each ionic liquid. The value of T_onset for each run was compared to determine the effect of alkyl groups and anion structures on the stabilities of ionic liquids. For the C₆ chain, the T_onset temperatures for the BETI^-, NTf₂^-, BF₄^-, and PF₆^- are, respectively, 405, 425, 415, and 365 C. In general, larger anions and longer chains of alkyl groups increase the stability of the ionic liquid.