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RA1. RIB Development
(D. Stracener)

The last few months of 2009 were a busy period at the On-Line Test Facility (OLTF). Efforts included twelve on-line tests to i) measure yields from a variety of uranium carbide targets, ii) measure yields from an ion source that is specifically designed to provide Sr beams with greater purity, and iii) provide 120Ag to the CARDS array that was installed on a beamline after the OLTF separator. Specifics of the ion source projects were detailed in the last HRIBF Newsletter. Uranium carbide targets that were recently tested include UC targets produced at ORNL and several higher-density targets that were produced using a hot-press technique. The ORNL-produced UC targets are made by mixing graphite with a uranyl nitrate solution, which is then heated to make uranium dicarbide. This material is ground to a very fine powder (less then 3 micron diameter) and mixed with synthetic graphite powder before a pellet is formed using a cold-press technique. The resultant UC targets are quite uniform with an average density of 2.2 g/cm3. While these targets have been used for RIB production at the HRIBF since 2006, this is the first extensive survey of fission fragment yields. The other UC targets that were tested had densities up to 5.2 g/cm3 and are being studied in collaboration with Will Talbert. The release from these targets has been shown to be reasonably fast and the yields are comparable to yields from other UC target geometries that have been tested at the OLTF. In addition, the OLTF provided beams of 3He and 4He at 40 keV, which were implanted in thin aluminum foils. These successful tests were made in collaboration with Ray Kozub and his student, Jonathan Wheeler, from Tennessee Tech. The 3He targets, to be irradiated with radioactive beams, will be used to study (3He,d) reaction cross sections that are important in the rp process of nucleosynthesis.

During this period, we also completed another series of off-line tests with the HRIBF laser ion source in collaboration with Klaus Wendt and Tina Gottwald from Mainz University, along with Jens Lassen and Ruohong Li from TRIUMF. This year's campaign planned to investigate ionization schemes for three elements (Sb, Te, Sr) that had not previously been ionized at HRIBF and to make an efficiency measurement for Ga. Laser ionization of Sr was successful and several Rydberg states in Sr were observed. To the best of our knowledge, this is the first time resonant ionization schemes for Sr were demonstrated in a LIS with Ti:Sapphire lasers. On the other hand, we did not successfully produce laser-ionized beams of Sb and Te. We have several possible explanations (low laser power, misalignment, inaccurate ionization schemes), which will be investigated in the coming months. The measured efficiency for Ga was only 10%, which is quite low when compared to the 60% efficiency that was previously measured at Mainz and we are also investigating the cause for this discrepancy. These tests were carried out using the complete HRIBF laser system which includes a Nd:YAG pump laser and three tunable Ti:Sapphire lasers.


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