Self-triggering spark chambers are very useful for measuring radionuclide distribution, though they have some undesirable aspects such as non-uniformity of sensitivity and instability of operation. For overcoming these difficulties a hybrid chamber was developed and it was tried to lower the sparking voltage by increasing the number of initial electrons which trigger a spark. The chamber has four plane parallel electrodes in flowing gas, a mixture of argon and ethyl alcohol. The first and the second electrodes compose a spark chamber (SC), the second and the third a proportional chamber (PC), and finally the third and the fourth an ionization chamber (IC) . The second and the third electrodes are gauzes for electrons to go through. Auger electrons or X-rays from55Fe deposited on the fourth electrode ionize the gas in the IC locally. Then electrons produced drift toward the third electrode and some of them pass through it. In the PC these electrons create an electron avalanche. A part of the electrons in the avalanche, multiplied greatly, pass through the second electrode and trigger a spark in the SC. Non-uniformity of sensitivity becomes destructive for high intensity of incident particles and instability of operation becomes so in the reverse case. For a source of relatively high activity (-0.025μCi) sparking voltage, starting voltage of sparks, was decreased with increase of applied voltage on the PC and then the condition of good images was determined. For a source of very low activity, nearly back groud, the dependency of sparking rate on the operational voltage of the SC was examined and it was found that the plateau characteristics were improved and better stability was obtained with increase of applied voltage on the PC. It was assumed that non-uniformity was due to the slight difference of the gap distance in the sensitive area and that it would be improved by increasing over-voltage, difference between operational voltage and sparking voltage. And also it was assumed that instability was based on the refiring of sparks due to the imperfect quenching and that it would be improved by decreasing total charges in a spark. Decreasing the sparking voltage by increasing initial electrons good uniformity of sensitivity was obtained without, refiring even at relatively high over-voltage. Good images were obtained for β emitters and the usefulness was proved for radiochromatography.
In a previous paper a hybrid chamber was proposed to improve non-uniformity of sensitivity and instability of operation of normal self-triggering spark chambers. It was composed of an ionization chamber (IC), a proportional chamber (PC) and a spark chamber (SC) . The method of the improvements was based on the decrease of the sparking voltage, the starting voltage of sparks, by increasing the number of initial electrons which trigger a spark. In this paper two subjects about the performance of the chamber are described. One is the dependency of the sparking voltage on the number of initial electrons at the cathode of the SC. Another is the property of the sparks in the PC induced by the sparks in the SC. To begin with, gas multiplication factor of electrons in the PC and transmission coefficient of electrons through the gauze, the electrode between the IC and the PC, were determined experimentally. Then the relation between sparking voltage Va and average number of initial electrons N was examined. As the result, it was found that Va was decreased with increase of N, more than 20% at N=106. The dependency of Va on N was roughly understood from the model of streamer formation. When the electric field strength in the PC was increased to increase the number of initial electrons and exceeded the critical value (-5kV/cm) sparks were induced in the PC by the sparks in the SC. As the occurrence of induced sparks was not desirable for the improvement of the instability of the operation the properties were examined. The delay time of the induced spark appeared after the spark in the SC was nearly 0.1-1μsec and depended on the field strength in the PC not depending on that in the SC. The occurrence of the induced sparks are considered as the following. The positive ions produced by a spark in the SC pass through the gauze electrode and form space charge field in the PC. By increasing the field strength near the anode of the PC a streamer will be formed and a spark induced.
Eight trace elements (Co, Cu, Zn, As, Cd, Sn, Sb and Hg) in powered milk have been determined simultaneously by neutron activation analysis with chemical group separation. The irradiated samples were digested with a mixture of HNO3and H2O2in a reflux system and subjected to the group separation. Then γ-rays from the radioactive products were measured with a Ge (Li) detector coupled with a 4096 channel pulse height analyzer. The powdered milk samples investigated have been found not to contain heavy metal elements over the warning levels. This method has been shown to be useful for simultaneous determination of heavy metals in biological materials.
Seeds of rice c.v. Norin-8 and two radiation induced dwarf mutants MGS-46 and -96 were used to investigate the effects of gamma- and 14 Me V neutron-radiations in different culture systems. Seedling growth of irradiated seeds in soil, and in two types of synthetic media, modified White's (M-W) or modified Eriksson's (M-E), as well as the callus growth on 2.4-D supplemented media were measured as an index of radiation damage. Comparing the seedling height about two types of media, the M-E promoted the plant growth than the M-W in irradiated as well as non-irradiated lots of the three strains studied. The callus growth on M-E surpassed by more 10 times that obtained on the M-W in all the lots. The M-E medium seem to be appropriate for both the seedling and callus growth of rice.
Distribution patterns of14C-labeled oxolinic acid, a new synthetic antimicrobial agent, were studied in mice, rats, hen quails and eels by means of whole body autora-diography. In mice14C-oxolinic acid administered orally in a dose of 20 mg/kg was absorbed to a considerable extent from the intestinal tract and distributed in almost all tissue. At 30 to 60 minutes after the administration, highest concentrations of radioactivity were observed in the liver, kidney, myocardium, bone and brown fat, while radioactivities were moderate in the blood, skeltal muscle, adrenal gland and pituitary gland, and lowest in the central nervous system and testis. The concentration in the fetus at 60 minutes after the administration was about equal to that of the placenta, and then it gradually decreased with a lapse of time. In the tissues of the fetus high concentrations of radioactivity were found especially in the bone. The radioactivity was almost completely eliminated from mice body within 48 hours after the administration. In rats the distribution pattern was also very similar to that in mice. But the uptake of radioactivity into brown fat was considerably less than that in mice. In hen quails, the distribution pattern resembled those in mice and rats. It was of note that the compound was localized in the melanin containing tissues in the eye, skin and hair follicles, but it was only slightly incorporated into the maturing follicles of the ovary. In eels, the absorption and elimination of the compound seem to be very slow.
Distribution studies in Wistar male rats were performed with 6β- [3H] methyl-19-norcholest-5 (10) -en-3β-ol (NCL-3H) and [1α, 2α (n) -3H] cholesterol (CL-3H) . The up-takes of NCL-3H by adrenal at 3 and 7 days were respectively four and eight times greater than those of CL-3H. The ratio of adrenal gland to liver concentration at 7 days was 251 for NCL-3H while that for CL-3H was 4. Thus, NCL-3H showed a higher adrenal uptake as compared to CL-3H. The above fact shows that NCL-3H has the basic structural feature exhibiting high affinity for the adrenal.
A semiconductor scanner equiped with a coaxial type lithium drifted germanium detector was constructed. The detector is 46 mm in diameter and 32 mm high, and has effective volume of 51cm3. Lead-shielded germanium detector is coupled with its cooling system to a NaI scintillation detector head which is originally installed as a rectilinear scanner. Its high energy resolution allowed to produce better scan images with good contrast by lessening the scattered component of gamma rays, and to clearly discriminate two photopeaks closedly neighbored in the double tracer studies such as tumor visualization with67Ga and75Se-selenomethionine, or thyroid scan with99mTc and123I Its major disadvantage is the low sensitivity relative to that of NaI crystal and is necessarily being refrigerated all the time by liquid nitrogen.
Ruthenium-103 was used in scintigraphy of 37 patients with various types of malignant tumors. Malignant tumors were delineated as strongly positive in 54% of cases and slightly positive in 27% of cases. Head and neck tumors were identified as strongyl positive in 10 out of 13 cases (77%) and as slightly positive in 3 out of 13 cases (23%) . Primary lung cancer was strongly positive in 6 out of 8 cases (75%) . Two cases of hepatoma were not identified by ruthenium nuclides or by67Ga-citrate. Two case with inflammatory lesions showed a positive scan by ruthenium nuclides. The ruthenium radionuclides are, therefore, probably not suitable for differentiating carcinoma from inflammatory states. In four lung cancer patients, the uptake ratio of the tumor activety-to-normal symmetrical area activity was between 1.35-2.45 and did not undergo changes at 22 to 27 days after administration of103Ru.