Isotope Counting Research Articles

Measurement of tissue 3-β-hydroxy sterols by tritiated digitonin

1. 1. A method for the determination of cholesterol using radioactive digitonin is reported. 2. 2. The sensitivity of this technique is comparable to other microtechniques. 3. 3. The specificity of radioglycoside analysis is comparable with ferric chloride colorimetric measurement as determined in tissues obtained from the human, monkey, rabbit, and rat. 4. 4. Specific activity measurements of dog tissue C 14-cholesterol have been made by double isotope counting and the values obtained by H 3-digitonin and ferric chloride compared favorably in the tissues studied, with the exception of the adrenal gland.

Electronic design of an absolute counting system for Mn 56

To permit accurate counting of weakly activated solutions of Mn 56SO 4 drawn from an integrating neutron detector of the “manganese bath” type, a two-stage counting facility has been developed. Two liter aqueous solutions are counted directly in a gamma-gamma coincidence arrangement which features relatively high efficiency and long-term stability. An electronic delay, mixing, splitting, and repeating technique is used to allow full utilization of radiation detected in both NaI(Tl) crystals while only two single channel analyzers are required. This system is calibrated on an absolute scale through another unit which counts small aliquots of a strongly activated sample mixed with liquid scintillator in a 4 π beta-gamma coincidence mode. Signals from two high-gain, low-noise photomultiplier tubes viewing the same scintillation cell are put into coincidence to reduce thermionic photocathode noise below background level for room-temperature operation. Automatic punched-card readout with subsequent computer analysis of data is available. Otherwise incompatible requirements of convenience, stability, efficiency and accuracy are satisfied by using this two-stage process of direct counting backed up by calibration. The gamma-gamma counter, with twice the efficiency of ordinary gamma-gamma coincidence systems, has demonstrated better than 2 3% stability over months of operation. Comparisons with standard sources and with a 4 π- beta proportional counter indicate better than 1% accuracy for the beta-gamma setup. Single channel efficiencies for Mn 56 are 4% at 1.9 c/s background and 9% at 1.5 c/s background; coincidence efficiency is 0.2%. While intended primarily for precision detection of Mn 56, the system is readily adaptable to other radio- isotope counting requirements.

Radioisotope (l131) studies of placental location and circulation

A modified isotope method, requiring lower levels of radioactivity, for localization of the placenta is presented and its application in 66 patients described. A dose of 3.0 mu C of radioiodinated human serum albumin was injected into the antecubital vein, and after 10 min a collimated scintillation detector connected to a count rate meter was used to count radioactivity in a reference position over the precordium and in 21 positions around the uterus. Administration of iodine as Lugol's solution, prior to and after the radioisotope study, reduces the thyroid exposure markedly so that the total-body irradiation to both mother and fetus is significantly less than that from one or two diagnostic x-ray exposures of the abdomen. Although earlier methods employ 10.0 mu C of I/sup 131/ and more recent reports maintain that 5.0 mu C is a min dose, satisfactory results were obtained with 3.0 VC of I/sup 131/-labeled albumin. Various abdominal scanning patterns are illustrated for anomalous placental locations and obstetric problems. Fetal death in some instances was associated with elevated isotope counts which were consistent with placental localization. In cases of intrauterine death, there were differences in the maternal placental circulation which varied with the duration of themore » retention of the dead fetus. In several cases there was an early period of marked reduction of maternal placental blood flow followed by a return of this circulation to its previous level or even to a higher level. Thus, there is a possibility that after fetal death there is an early phase of shutdown of the major maternal placental circulation and that during this phase, isotope studies fail to localize the placenta. (BBB)« less

A plastic phosphor well counter for sample volumes up to 400 ml.

A scintillation counter using a plastic phosphor well is described in which the count rate is satisfactorily independent of a sample volume for 10—410 ml. Its efficiency and sensitivity are some 25 and 2 to 4 times greater, respectively, than for a counter using 32 small G.M. tubes. The use of the counter with 59Fe, 131I, and 51Cr, is discussed with particular reference to both urine and faecal samples and whole-body counting of small animals. It is not suitable at present for double isotope counting.

Detection of Leukocyte Antibodies by Means of I131-Labelled, Purified Anti-Human-Globulin Antibody. Problems of Nonspecific Adsorption of Globulin by Leukocytes

Abstract Initial studies of a quantitative method for detecting sensitization of white blood cells by antileukocyte antibodies are presented. The method entails isolating I131-labelled, anti—human-globulin antibody (prepared in rabbits) by adsorption and elution from insoluble antigen, globulinazobenzylcellulose. The degree of adsorption of the labelled antibody by presumably sensitized as opposed to nonsensitized leukocytes is measured by radioactive isotope counting technics. The vexing problem of nonspecific adsorption of human or rabbit globulin by leukocytes is considered, and procedures for partially circumventing this problem are set forth. Seligmann's solution with normal rabbit serum added to a final concentration of 10 per cent appeared to be the most effective washing fluid in most instances for removing nonspecifically adsorbed globulins from leukocytes. The use of purified anti—human-globulin antibody, as opposed to whole Coombs serum, also very favorably affected the ratio between immunologically specific adsorption and nonspecific adsorption. Results of the over-all I131 method as applied to selected positive and negative human sera are detailed.

The Solubility of Tantalum and Cobalt in Sodium by Activation Analysis

The solubilities of tantalum and cobalt were determined by equilibrating sodium in tantalum and cobalt vessels at three temperatures. The sodium was irradiated in the Materials Testing Reactor. The solubility values were determined from a separation and counting of active isotopes in the sodium metal. Tantalum solubility ranged from 0.032 to 2.9 parts per million from 325 to 525 deg C. The range on cobalt was from 0.28 to 0.1 part per million from 365 to 525 deg C. (auth)

Precision Cailbration of Large 4 Pi Scintillation Crystals for Routine Gamma Counting

By use of new techniques in isotope calibration, and scintillation spectrometry, a large well-type scintillation crystal counter has been calibrated very accurately. This now readily available counting system can be used routinely for mixed isotope analysis, for absolute counting of isotopes, and for decay scheme analysis. Accurate absolute counting of electron-capture isotopes is a further possible application. (auth)