M. A. Van Dilla

Cell Microfluorometry: A Method for Rapid Fluorescence Measurement

A high-speed flow system for quantitative determination of fluoresence of cells containing fluorochrome has been developed. Feulgen-DNA distributions in populations of tissue culture cells and human leukocytes havebeen measured at a rate of 104 to 105 cells per minute and compare well with results of other independent methods.

Cell Sizing: A Light Scattering Photometer for Rapid Volume Determination

Theory predicts that small angle light scattering by spherical particles of 5 to 20 μ diam is nearly proportional to volume and insensitive to particle refractive index. A flow system photometer with helium‐neon laser light source measures the scattering between 0.5 and 2.0° from individual particles at 104 to 105/min. Volume distributions of mammalian cells and plastic microspheres agree with other independent determinations.

DNA Constancy in Heteroploidy and the Stem Line Theory of Tumors

Cellular DNA was measured by high-speed flow microfluorometry in mammalian diploid and heteroploid cell populations stained by the fluorescent Feulgen procedure. Heteroploid cells with elevated modal chromosome number showed the expected increase in modal DNA content. However, the variability of DNA content was the same in diploid and heteroploid cell populations despite the large variability of chromosome number in the latter populations. This suggests that heteroploidy may include defects in the chromosomal condensation and kinetochore development systems.

On the radioactivity of stone meteorites

Abstract The γ-ray spectra of 37 samples of 25 chondrites, 3 carbonaceous chondrites, and 9 achondrites have been investigated using a large NaI(Tl) scintillation spectrometer. An extensive set of measurements are presented here. Long lived K 40 and Al 26 were the predominant radioactivities detected; more unusual γ-ray emitters detected were 308-day Mn 54 , 2.6-year Na 22 , and probably a mixture of Sc 46 and Co 56+58 (half-lives approximately 80 days). These nuclides were detected in relatively recent falls (the youngest, the Harleton, Texas, chondrite was measured 21 days after fall). Furthermore, thorium was detected and measured in 5 of the 9 achondrites. The average potassium content in chondrites was found to be 0.081 per cent, in excellent agreement with Edwards and Urey. Chondritic potassium concentrations vary ±10 per cent from this average value. The average Al 26 concentration in stone meteorites was 245 ± 42 disintegrations/min/kg (silicon and aluminum). The variation from the mean of both potassium and Al 26 concentrations is real, not analytical.

Volume Distribution and Separation of Normal Human Leucocytes.

Summary Leucocytes from normal adults have been studied by electronic sizing and separating methods. The volume distribution was found to be bimodal. Three cell groups of small volume dispersion were isolated and subsequently identified by hematological methods. The smaller-volume leucocyte peak was found to contain small lymphocytes and little else. The large-volume peak contained granulocytes in its central portion and mono-cytes in its large-volume tail. Using these methods, the relative abundance of a specific type of leucocyte can be greatly increased. These methods may also be applied to other cell suspensions.

Spectrometric measurement of natural and cosmic-ray induced radioactivity in meteorites

Abstract A nondestructive method of analysis of meteorites for natural and cosmic-ray induced radioactivity using low-level γ-ray spectrometry of kilogram samples is reported. Results so far obtained are essentially qualitative but appear to be in agreement with previous chemical measurements of K and Al 26 in chondrites and achondrites. Cobalt 60 was detected in the Ussuri (Sikhote-Alin) siderite (fell 1947) but not in old falls such as Odessa and Canyon Diablo. The rate of production of some interesting cosmic-ray induced activities is discussed.

Lunar Composition by Scintillation Spectroscopy

Information on the composition of the moon and its past history is being sought through measurements of the spectrum of the gamma rays emerging from the lunar surface. The detector is a 3 × 3 in. CsI-plastic scintillator phoswich feeding a 32-channel analyzer weighing 5 pounds. Energy range is to 3 Mev; in-flight calibration is provided by a small Co-57 and Hg-203 source fixed to the detector. Energy resolution is 12 ± 2 per cent at 0.66 Mev. The spectrometer, and indeed the entire spacecraft, is biologically sterile. The spectrometer aboard Ranger 3 (launched January 26, 1962; missed the moon by about 20,000 miles) transmitted back spectra currently being studied; Rangers 4 and 5 are repeats scheduled for later in 1962.

Zinc-65 and Zirconium-95 in Food.

Zinc-65 has been found in small amounts in muscle and liver samples obtained from cattle raised in Nevada, and also in commercial hamburger and beef liver from the southwestern area. Zirconium-95 and niobium-95 were found in the liver samples but not in the muscle or hamburger. A trace of zinc-65 was detected in milk buLt none in people.

Zinc-65 in Cyclotron Workers

Small but persistent body burdens of zinc-65 have been found in cyclotron workers. This radionuclide and others are produced by nuclear reactions with the construction materials of the cyclotron. Only zinc-65 has gained entry into the body, but in amounts of less than 1 percent of the maximum permissible amount.

Low-Level Gamma Ray Detection in Humans

The problem of measuring gamma activity at the natural levels, particularly in people and foodstuffs, is an extremely important one because of the necessity of monitoring both fallout from nuclear weapons tests and the disposal of reactor wastes. This problem will also be encountered because of the necessity for minimizing radiation in clinical and industrial tracer applications. Two principal techniques have been developed for this purpose which are applicable to in vivo studies: the NaI crystal spectrometer in a special, low-activity shield, and the large 4π liquid scintillation counter. Both have sensitivities which permit the detection of gamma activity in the human body at levels a factor of 10 to 100 below the natural K-40 concentration. The choice between the two systems depends largely on the particular application, since they are comparable in terms of ultimate sensitivity and cost. The liquid scintillator is the method of choice used for routine studies involving large numbers of samples in which the identity of the activity is known. This is the case, for example, in studies of the gamma activity of people and foodstuffs due to fallout because of the large discrimination factors in biological systems against elements not closely resembling nutritional essentials. Natural K-40 and Cs-137 are normally the only gamma activities present, and the energy resolution of the liquid scintillator permits their simultaneous determination. Because of the constancy and predictability of the K-40 level, additional hard gamma activity (e.g.