A two-dimensional positron annihilation angular correlation apparatus based on 256 bismuth germanate scintillation detectors for solid state research has been developed. The apparatus is distinguished by the use of the bismuth germanate crystals as a scintillator and two position detectors assembled of individual scintillation detectors. In many respects, bismuth germanate crystal (Bi4Ge3O12: BGO) is one of the best materials available for compact individual detectors of positron annihilation gamma rays (511keV) . Though BGO crystals as detector materials have some disadvantages, expensive, small light yield (21% as much as NaI), small crystal grown, they possess excellent properties, high stopping power (density: 7.13g/cm3), high photopeak to Compton ratio (effective atomic number: 74), nonhygroscopic, lack of cleavage. Owing to those attractive properties, we selected BGO crystal as scintillation material of the individual detectors. Each position detector developed is one type of large multicounters, and consists of the assembly of 128 BGO individual detectors and a crossed-slits collimator. The multicounter as a position detector has manifested distinguished properties as compared with the others (anger camera, multiwire-proportional chamber) . Especially, resolving time is very short (17 ns) because that each individual detector is independently operated, and position resolution is definitely decided by the use of the crossed-slits collimator. Each BGO individual detector is constructed of a BGO crystal with the size of 10×10×20 mm3and a photomultiplier tube with the diameter of a half inch (Hamamatsu R 647-01) . The crossed-slits collimator consists of double layers of two sets of long-slits, one is a set of 12 vertical long-slits and another 12 horizontal long-slits. Both sets of the long-slits have the open width of 6 mm, the length of 182 mm and the depth of 100 mm. The following is the specifications of the apparatus; the angular resolution was 0.75 mrad by 0.75 mrad over the angular field of 22.57×22.57 mrad2, the active-area to the dead-area ratio of the position detector was 0. 19, and the efficiency for counting coincidence events was about 50 cps/GBq. In order to examine the performance of our apparatus, we applied the apparatus to measurements of two dimensional positron-electron momentum space density distributions integrated in fixed directions (‹100›, ‹110›) of niobium and we could recognize many hollows in the momentum space density distributions corresponding to the holes at the Γ point and twelve N points in the Brillouin zone.
Hepatobiliary clearance of99mTc-EHIDA was investigated in cases with altered thyroid function by deconvolution method. The results indicated that mean hepatic transit time of all control subjects revealed less than 10 minutes. On the other hand, mean hepatic transit time of cases with altered thyroid function revealed prolonged more than 13 minutes. Cases especially showing an elevated serum concentration of TSH compared with normal range (4.6 μU/ml) had a tendency of a high incidence of markedly prolonged mean hepatic transit time. These results suggest that thyroid hormone may inf uence on the hepatic metabolism of hepatobiliary radiopharmaceuticals. This phenomenon also could partly explain the cause of liver dysfunction seen in subjects with altered states.
To determine the concentrations of elements of atomic number higher than about 60, the KX-ray fluorescence technique employing a 3.7 GBq137Cs gamma-ray source with a pure germanium semiconductor detector is examined. Due to the fairly high energy of the KX-rays this technique is capable of determining the element concentration in a considerably large sample volume with little effects of matrix elements and vessel wall. A narrow gammaray beam and large scattering angle geometry is chosen to discriminate between the KX-rays and the scattered radiations in the measurement. A 300 second measurement allows a relative precision of less than 3% for samples of aqueous solution, mixing powder and alloy containing more than 1-3 wt% high atomic number elements such as W, Pb or U.
The adsorption of67Ga to the inner surface of stainless steel, polyethylene and silicone tubings was studied. The three tubings remarkably adsorbed67Ga in order of stainless steel, silicone and polyethylene tubing. Sodium citrate inhibited the adsorption of67Ga in a dosedependent manner. These phenomena were also observed in blood sampling via the catheter inserted into the external jugular vein. These results show that constant concentration of sodium citrate is necessary for the in vitro study of67Ga in order to prevent the adsorption to the surface of experimental materials.