Ion source for radioactive isotopes - IRIS ECR

Burke, J.T. ; Freedman, S.J. ; Lyneis, C.M. ; Wutte, D.

Lawrence Berkeley National Laboratory

关键词: Ion Sources;    Weak Interactions;    Cyclotrons;    Nitrogen;    Oxygen;   

DOI  :  10.2172/821748
RP-ID  :  LBNL--48317
RP-ID  :  AC03-76SF00098
RP-ID  :  821748

美国|英语

来源: UNT Digital Library

【 摘 要 】

A compact electron cyclotron resonance ion source for radioactive isotopes (IRIS ECR) has been developed for the {sup 14}O experiment at the 88-Inch Cyclotron. The {sup 14}O experiment is a joint effort between the Nuclear Science Division's Weak Interaction Group and the 88-Inch Cyclotron ECR ion source group. The initial goal of the experimentalists is to measure {sup 14}O half-life and the shape of the beta decay spectrum. The 70 second half-life of {sup 14}O requires producing the isotope on-line at the 88-Inch Cyclotron. The {sup 14}O is generated in the form of {sup 12}C{sup 14}O in a high temperature carbon aerogel target using a 20 MeV {sup 3}He{sup +} beam from the LBNL 88-Inch Cyclotron via the reaction {sup 12}C({sup 3}He,n){sup 14}O. The {sup 14}O atoms are then separated from the other radioactive isotopes produced in the target and then implanted into a thin foil. The implanted target serves to minimize the radiation background and maximize the signal in the beta spectrometer by concentrating the{sup 14}O into a 5mm diameter spot. An 8 meter long stainless steel transfer line connects the target chamber to the IRIS ECR through a turbo molecular pump. The gas coming from the turbo pump is fed into the ion source and ionized, extracted at energies of 20 to 30 keV and mass separated by an analyzing magnet. The ion source started operation in spring 1999 and achieved a beam intensity of 3 x 10{sup 5} {sup 14}O{sup +} ions/second. Extensive developments on the production target were made to increase extraction efficiency of the {sup 14}O. A liquid nitrogen trap was installed between the ECR and the turbo pump to minimize the gas load to the ion source. An improved support gas injection system was installed so that multiple support gases can be introduced. A bias disk is used to stabilize the plasma. A quartz liner in the plasma chamber is used to reduce the hold-up time for oxygen and increase the overall ionization efficiency. The extraction system was also modified to ensure reliable operation at 30 kV. In May 2000 IRIS produced a mass separated beam of {sup 14}O{sup 1+} ions at an average intensity of 2 x 10{sup 7} {sup 14}O{sup 1+} ions per second with a peak intensity of 3 x 10{sup 7} {sup 14}O{sup 1+} ions per second. This is the highest{sup 14}O intensity achieved at any radioactive beam facility to date. The physics program has begun with a measurement of the {sup 14}O lifetime in October 2001 and a test run for the CVC experiment during December 2001.