We report on the construction and operation of a monoenergetie slow positron beam apparatus in ultra-high vacuum. These slow positrons are used as a probe to study surfaces and defects below sub-surfaces. Positrons from a22Nasource are thermalized by a venetian-type vane consisting of well annealed tungsten foils with a thickness of 25.4 μm. The converter is floating at 100 V higher than extraction grid, which gives a small amount of energy to the positrons along the beam axis. A source chamber and a specimen chamber are placed at a distance of 4 m apart in order to reduce back ground radiation. A gate valve is installed between them in order to keep ultra-high vacuum conditions while changing specimens. Slow positrons from the converter are guided by nine separated magnetic coils of 100 G with a diameter of 700 mm. Acceleration of slow positrons is performed by applying a high voltage between 0.1-50 kV desired to the source chamber. An acceleration stage containing five lenses which are stueked with 200 MΩ resisters are installed in a linear part of the beam line. Characteristics of the apparatus are described and the measurements of the Doppler broadening profile of the positron annihilation radiation as a function of incident positron energy are shown.
The performance of a 160 keV slant hole collimator (160 keV SH) was compared with that of a 140 keV high resolution collimator (140 keV HR) for SPECT imaging of the head using99mTc.The minimum radius of revolution was reduced from about 23 cm to 13 cm using 160 keV SH. Relative sensitivity of the 160 keV SH was 108% of that of the 140 keV HR. Compared with SPECT using 140 keV HR, 160 keV SH SPECT yielded approximately a 15% increase in resolution. The 160 keV SH SPECT images of phantom were superior in resolution and contrast to that of 140 keV HR SPECT. We concluded that high quality SPECT images of the head can be obtained from rotating gamma cameras equipped with slant hole collimators.
The efficacy of assay procedure for estimation of serum alpha fetoprotein (AFP) was examined on“Amerwell AFP”immunoradiometric assay (IRMA) using monoclonal AFP antibody. The condition of incubation was most satisfactory for 2 hours at 37°C. Coefficients of variance for intraassay and interassay were 5.1-10.0% and 8.4-9.9% respectively. Dilution test gave satisfactory results. The binding capacity of microplatewell tagged monoclonal AFP antibody with AFP antigen was satisfactory for assay reactions. This method showed a good correlation to the AFP RIA bead (Dinabot Co.) method. The normal range (reference value) was within the level of 5.0 IU/ml due to Hoffmann's method in the examination of 860 subjects. Estimation of AFP with“Amerwell AFP”IRMA kit was a feasible routine method of clinical application for tumor marker.