Abstract
Low energy gamma emitters with short physical half lives are useful as scanning agents, because a larger amount of radioactivity can be applied to a patient without raising radiation dose to a possible hazard, and the shielding effectiveness for gamma rays will increase. A good quality scintigram, having less background can not be always obtained in organ scintigraphy. The reason being is that low energy gamma rays produce a larger amount of the scattered rays than those of the medium energies over 200 keV.
For the measurements of scattered rays, eight nuclides energies ranging from 30 to 412 keV, as thyroid and liver-phantoms, were prepared. The fraction of scattered rays in a photo peak was determined by the ratio of the area of the “scattered region” to that of the photo peak, which is found in the window of±10%.
The fraction of scattered rays was higher in 197Hg and lower in 203Hg. In 131I, however, the fraction was a little higher than 203Hg, because of the gamma rays penetration of the collimator septa.
The best energy of the gamma rays used in scanning was found in 250 keV from the view point of the shielding effectiveness and the incidence of the scattered rays.
