Gian Luca Poli

Nonobservation of {sup 12}C cluster decay of {sup 114}Ba

By means of the on-line mass separator at Gesellschaft f{umlt u}r Schwerionenforschung, Darmstadt, we produced {sup 114}Ba through the {sup 51}Ni({sup 58}Ni,2n) reaction, separated it as a {sup 114}Ba{sup 19}F{sup +} beam, and implanted it into a stopper foil positioned in the center of an array of track detectors, which were used to search for {sup 12}C radioactivity of {sup 114}Ba. A total number of (5.4{plus_minus}1.7){times}10{sup 4} {sup 114}Ba atoms were implanted. No {sup 12}C event was found after a total exposure time of 116 h, corresponding to a {sup 58}Ni beam dose of 1.3{times}10{sup 17}. The resulting upper limit of 3.4{times}10{sup {minus}5} (84{percent} C.L.) for the branching ratio for {sup 12}C decay of {sup 114}Ba is considerably lower than the limits obtained in previous experiments, which represents an inconsistency at levels of more than 90{percent}. A semiempirical estimate of 19.3 MeV for the upper limit of the Q value for {sup 12}C decay of {sup 114}Ba is derived. {copyright} {ital 1997} {ital The American Physical Society}

Multi-centre evaluation of accuracy and reproducibility of planar and SPECT image quantification: An IAEA phantom study.

Accurate quantitation of activity provides the basis for internal dosimetry of targeted radionuclide therapies. This study investigated quantitative imaging capabilities at sites with a variety of experience and equipment and assessed levels of errors in activity quantitation in Single-Photon Emission Computed Tomography (SPECT) and planar imaging. Participants from 9 countries took part in a comparison in which planar, SPECT and SPECT with X ray computed tomography (SPECT-CT) imaging were used to quantify activities of four epoxy-filled cylinders containing 133Ba, which was chosen as a surrogate for 131I. The sources, with nominal volumes of 2, 4, 6 and 23mL, were calibrated for 133Ba activity by the National Institute of Standards and Technology, but the activity was initially unknown to the participants. Imaging was performed in a cylindrical phantom filled with water. Two trials were carried out in which the participants first estimated the activities using their local standard protocols, and then repeated the measurements using a standardized acquisition and analysis protocol. Finally, processing of the imaging data from the second trial was repeated by a single centre using a fixed protocol. In the first trial, the activities were underestimated by about 15% with planar imaging. SPECT with Changs first order attenuation correction (Chang-AC) and SPECT-CT overestimated the activity by about 10%. The second trial showed moderate improvements in accuracy and variability. Planar imaging was subject to methodological errors, e.g., in the use of a transmission scan for attenuation correction. The use of Chang-AC was subject to variability from the definition of phantom contours. The project demonstrated the need for training and standardized protocols to achieve good levels of quantitative accuracy and precision in a multicentre setting. Absolute quantification of simple objects with no background was possible with the strictest protocol to about 6% with planar imaging and SPECT (with Chang-AC) and within 2% for SPECT-CT.