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7. The HRIBF Low energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS)
(K. Rykaczewski, Spokesperson)

A new experimental end-station dedicated to decay spectroscopy studies, Low-energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS), is presently under construction at the HRIBF. The construction of LeRIBSS is a joint effort between ORNL and HRIBF users interested in nuclear structure studies performed using decay spectroscopy methods. The construction is supported by the UNIRIB Consortium, with the Louisiana State University being the largest external contributor. The total cost, which includes the ORNL and LSU investments, is about $250k .

LeRIBSS is located behind the RIB injector magnet, at the bottom of the HRIBF Tandem accelerator, see Fig.7-1. It consists of a beam steerer and a focussing quadrupole, a universal detector support called CARDS, and a new moving fast tape collector. The space left behind the CARDS array in the initial configuration, see Fig.7-1, will allow us to accommodate the Multi-Turn Time-of-Flight (MTOF) mass spectrometer when it is ready for operation. CARDS can support several detectors, including Ge (clover, X-ray and gamma-X) gamma-counters, a fast timing BaF2 array as well as high resolution electron detectors and β-counters. A proposed high-efficiency β-delayed neutron detector will also fit into the CARDS ring at LeRIBSS.

Figure 7-1: Schematic drawing of LeRIBSS in the RIB injection hall. The low energy radioactive beam, after being separated by the high resolution injector magnet, will be transmitted straight to the LeRIBSS tape collector.

LeRIBSS is strategically positioned at the HRIBF location, where the best quality and intensity Radioactive Ion Beams (RIBs) are available. In particular, it profits from the high-resolution injector magnet, which was designed to have a mass resolution ΔM/M better than 10-4 . The transmission and mass resolution will be verified and optimized online during the commissioning of LeRIBSS. It is important to note that the experiments at LeRIBSS can be performed with negative as well as positively charged ions since transmission through the charge exchange cell is not required. Initial attempts to transmit low-energy 40-keV positive ions through the high-resolution injector magnet with reversed magnetic field direction were successful.

The LeRIBSS setup will also profit from the completion of the IRIS2 project (and hopefully from the newly proposed electron driver). The radioactive beams produced at the High Power Target Laboratory will be merged with the existing RIB delivery system in front of the high resolution injector magnet. This means that at LeRIBSS we can perform experiments with the mass separated radioactive ions produced at both RIB platforms. Ion energies of about 200 keV should be large enough to provide an implantation timing signal from the Microchannel Plate detector equipped with a 10 μg/cm2 carbon foil and improve the signal/background ratio using the implantation-decay time correlations.

The time scale of completing of the construction work of the LeRIBSS ion optics is funding dependent. We hope to be ready for first experiments in CY 2007.

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