Conceptual Design of the Argonne 6-GeV Synchrotron Light Source
The Argonne National Laboratory Synchrotron Light Source Storage Ring is designed to have a natural emittance of 6.5 × 10-9 m for circulating 6-GeV positrons. Thirty of the 32 long straight sections, each 6.5-m long, will be available for synchrotron light insertion devices. A circulating positron current of 300 mA can be injected in about 8 min. from a booster synchrotron operating with a repetition time of 1.2 sec. The booster synchrotron will contain two different rf systems. The lower frequency system (38.97 MHz) will accept positrons from a 360-MeV linac and will accelerate them to 2.25 GeV. The higher frequency system (350.76 MHz) will accelerate the positrons to 6 GeV. The positrons will be produced from a 300-MeV electron beam on a tungsten target. A conceptual layout is shown in Fig. 1. Related papers on the Argonne Synchrotron Light Source may be found in references 1-3.
An Inexpensive Positron Converter of High Reliability and High Yield
A new positron converter of the simplest construction is described, consisting of a multiple fixed tungsten target and a very small helical positron lens, both inside a small vacuum chamber. By utilizing the good vacuum insulating properties the lens may be pulsed with 6000 A at an operating voltage of 10 kV without insulating material, except for the vacuum feed throughs, for which the extremely radiation-resistant aluminiumoxide ceramic is used. The lens construction out of a copper pipe allows direct water cooling and gives sufficient mechanical strength without further reinforcement. The system has been in operation for 3 years and gives a positron conversion ratio I+/I- of 0.8 % as a routine value for an e--energy of 300 MeV, where the positron energy spread is within ± 1.5 MeV. Compared to a dc-lens saving factors of about 500 in weight, 50 in power consumption and 100 in cost have been achieved.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%