The third group includes the positron-emitting isotopes C-11, N-13, O-15, and F-18, all of which are cyclotron produced. The very short half-lives of the first three limit their use to a facility at or near the cyclotron site. While it is possible to transport F-18 compounds, great dedication must be made to the transportation arrangements. Included in this group are also the gamma emitters Co-57, Ga-67, In-111, I-123, and Tl-201. Also cyclotron-produced, they all have reasonably long half-lives and are easily transported across the country.
Of particular interest in this group is Tl-201. The majority of photons collected by the camera for image formation are the low energy Hg-201 X-rays since the % abundance of the 135 and 167 keV gamma rays is so low. Co-57 is used for flood field, dose calibrator standards, spot markers, and other sealed sources.
A cyclotron is a source of hi-energy protons, deuterons, and other particles. Various reactions takes place, e.g., (d,n), (p,pn), (p,5n), (p,a). Net effect: change in A number and/or Z number. A different element is usually formed.
Example: 14N (d,n) 15O
Cyclotron yield is dependent upon:
Principle of operation: a beam of charged particles is produced by accelerating ions around a widening circle using magnetic field for control and electric current for acceleration. Various separation techniques are available to separate product from target. Requirement: chemical forms of target and product must be different to effect separation.
|Stephen Karesh, PhD.||
Last Updated: August 14, 1996