The desired neutron spectrum for the High Flux Beam Reactor under construction at BNL requires use of U-Al fuel elements with more then 30 wt% U235 in the meat. The operating cycle of this reactor requires a minimum burn-up of 20%, and preferably 40% of the uranium in the element.

One of the major, as well as first, decisions which must be taken on a large chamber is to decide on the direction of the magnetic field, i.e., vertical or horizontal. Either alternative has advantages and disadvantages ad it is the intention of this note to discuss these features.

Speed limits of decimal counting schemes based on binary-to-decimal conversion are considered. A simple "1-2-4-8" decimal logic is described, which is inherently as fast as the basic bistable. A decade for counting in 100-200 Mc/sec range, based on this logic and the tunnel diode-transistor bistable, is presented.

Mammalian bone marrow contains a considerable number of small lymphoid cells (small lymphocytes and small lymphocyte-like cells). The total number of these cells (50,000 to 500,000 per mm3) depends on species, age and other factors. The origin, function and fate of these cells remain obscure in many respects. In particular, it has not been shown beyond doubt, if and to what extent small lymphoid cells enter the bone marrow via the blood stream or if their origin is in part or entirely within the bone marrow. In addition it has not been clearly shown whether or not these cells may function as multipotential hemopoietic stem cells. Results obtained from experiments with irradiated parabiotic animals and animals given regional fractioned doses of X-irradiation, and transplantation of leukocytes from peripheral blood into lethally irradiated recipients afford indirect evidence that peripheral blood of mice and rats may contain stem cells capable of DNA synthesis and division.

The blue-green algae, classed as primitive monerans, represent the lowest level of organization known to possess a higher plant type of photosynthesis. The role in photosynthesis of the phycocyanin in these organisms is particularly interesting from the point of view of ultrastructural biochemistry. It has been shown repeatedly that despite the primacy normally assigned to chlorophyll, the light absorbed by phycocyanin is used more efficiently for photosynthesis (equated with photosynthetic oxygen evolution). This property is all the more intriguing since Hill activity is very labile in these organisms; the loss being correlated with the release of phycocyanin. Then too, it has been observed that fluorescence at about 685 mμ, attributed to chlorophyll, is proportionately greater for wavelengths absorbed by phycocyanin. French and Young attributed the differential to inactive absorption by carotenoids in the "Soret" region of chlorophyll, but Duysens concluded that the magnitude of the difference observed by him was too great to be explained by screening. Duysens proposed the existence of two pools of chlorophyll of about equal size; one containing fluorescent, photosynthetically active chlorophyll in proximity to phycocyanin, the other nonfluorescent, photosynthetically inactive and remote from phycocyanin.

The vacuum system for the bubble chamber must evacuate rapidly a volume of approximately 500 cubic feet and eliminate the outgassing of a surface area of approximately 50,000 square inches. The backstreaming of oil from the diffusion pump must be kept to an absolute minimum to prevent oil films forming on the window. The vacuum system must also provide the protection against liquid nitrogen and hydrogen/leaks to prevent pressure buildup.