Identification and Separation of Radioactive Isotope Beams by the BigRIPS Separator at the RIKEN RI Beam Factory

摘要

We have developed a method for achieving excellent resolving power inin-flight particle identification of radioactive isotope (RI) beams at theBigRIPS fragment separator at the RIKEN Nishina Center RI Beam Factory (RIBF).In the BigRIPS separator, RI beams are identified by their atomic number Z andmass-to-charge ratio A/Q which are deduced from the measurements of time offlight (TOF), magnetic rigidity (Brho) and energy loss (delta-E), and deliveredas tagged RI beams to a variety of experiments including secondary reactionmeasurements. High A/Q resolution is an essential requirement for this scheme,because the charge state Q of RI beams has to be identified at RIBF energiessuch as 200-300 MeV/nucleon. By precisely determining the Brho and TOF values,we have achieved relative A/Q resolution as good as 0.034% (root-mean-squarevalue). The achieved A/Q resolution is high enough to clearly identify thecharge state Q in the Z versus A/Q particle identification plot, wherefully-stripped and hydrogen-like peaks are very closely located. The preciseBrho determination is achieved by refined particle trajectory reconstruction,while a slew correction is performed to precisely determine the TOF value.Furthermore background events are thoroughly removed to improve reliability ofthe particle identification. In the present paper we present the details of theparticle identification scheme in the BigRIPS separator. The isotope separationin the BigRIPS separator is also briefly introduced.