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The potassium-argon age of the Siknote Alin iron raeteorite was determined. The value is 1.7 plus or minus 0.2 x 10/sup 9/ years. Previous lead data suggest an age of 4.6 x 10/sup 9/ years. The date of solidification may be the sum of these two ages. (auth)

Developments in Project Rover are reviewed. History, considerations in reactor design, materials problems, and reactor construction and test are discussed. (M.C.G.)

Sequential autoradiographed sections through the shoot apical meristem of Arabidopsis thaliana treated for six hours with a solution of H/sup 3/- thymidine in combination with 0.1% Tween 20 and dilute mineral solution reveal a differential pattern of labeling, indicative of differential rates of DNA synthesis. This pattern corresponds to the histological zonation of the apex and reveals a sub-apical block of cells in which the amount of incorporation is significantly lower than in the adjacent flank cells. (auth)

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The design and operation of a beam current integrntor are described, and the theory of operation is discussed. The instrument has two channels. The console channel is designed to measure the accumulation of charge received by a target during a period of a day no matter what the range used in the experimenter's chaanel. An analysis indicated that this unit will measure the accumulation of charge by a target to an accuracy of 0.1215% assuming that the constant error due to shorting the integrating capacitor is accounted for. The instrument is ranged to haadle from 0.5 to 500 mu a of beam current. (M.C.G.)

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>Reference information and guidance on procedures and basic assumptions related to reactor siting are presented which can be used to calculate distance requirements consistent with current siting practices. A single method of competing distances and exposure for a general class of reactors is giveo. (J.R.D)

A Monte Carlo calculation to determine the pulse-height response of NaI(Tl) scintillation counters to gamma rays is described. Comparisons of several calculations with experiments using 3-in.-dia by 3-in.-high crystals for source energies from 0.32 to 7.48 Mev are presented and show good agreement at large pulse heights. At small pulse heights the calculations underestimated the experimental data and indicated that background radiation can contribute significantly to the experimental results. An extensive series of calculations are reported for a 3-in.-dia by 3-in.high crystal using monoenergetic, point isotropic sources placed on the crystal axis l0 cm from one end. The source energy ranged from 0.l to 6.0 Mev in this series of calculations. (auth)

A review is presented of calorimetric measurements of the heats of combustion and other reactions. The precision of the measurements is discussed, and possible sources of error in combustion calorimetry are considered. Measurement of the heats of formation of the oxides and other compounds is also discussed. Recent developments in calorimetry are described briefly, including the rotating bomb calorimeter, use of gases other than oxygen, fluorine bomb calorimetry, and combustion bomb with window. Tables are presented of the heats of reactions measured by oxygen bomb calorimetry, nitrogen bomb calorimetry, and fluorine bomb calorimetry. (D.L.C.)

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An analytical study was made of turbulent heat transfer in a vertical circular tube under the conditions of combined forced and free convection with uniform heat flux at the wall.

An experimental study designed to provide a basis for estimating protection against fallout radiation was made on two types of structures at the Nevada Test Site. The two buildings studied were a lightly constructed building with a basement, and an underground group shelter. An idealized fallout radiation field was simulated by the use of a sealed radioactive Co/sup 60/ source that was pumped at a uniform speed through a long length of flexible tubing evenly distributed over the area of interest. Radiation levels at selected points inside the structures were measured with sensitive ionization- chamber detectors. These measurements were compared with measurements taken under actual fallout conditions at an earlier time and were also compared with the theoretical calculations. Protection factors from fallout data and mobile radiological measurements (MRMU) at the basement structure compared roughly within a factor of 2. This was good, considering the limitations of the two sets of data and other factors affecting the differences. Comparisons between protection factors from fallout data and MRMU data at the underground group shelter were excellent. MRMU data and theoretical calculations also compared satisfactorily. (auth)

The essential components of the program for the control of tritium hazards at Savannah River include radiological engineering, training of operating personnel in techniques of protection, protective clothing, control of surface and air contamination, bioassay, and environmental monitoring. Rapid change of air in process areas and the continuous measurement of tritium in air are two important facets of the protection program. Workers in a tritium atmosphere wear inexpensive, polyvinyl suits which are supplied with air ana envelop the entire body. Permissible working time limits are established with the help of a nomograph that reflects the tritium concentration in air and the protective value of air masks or plastic suits. Employees submit urine specimens after jobs involving tritium exposure. These specimens are immediately assayed by means of liquid scintillation counting. Grease, oil, and other hydrocarbons retain tritium. Surface contamination is detected qualitatively by use of smears and gas flow proportional counters. Ventilation air from process areas is released to the environs through tall stacks. The stack air is continuously monitored. At the perimeter of the plant and 25 miles away, air is sampled to determine the effect of tritium released through the stacks. The Savannah River, streams on the plant, and …

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Critical studies were performed with a metallic, fast reactor core designed to snvestigate the effects of replacing highly absorbing U/sup 238/ diluent with high-scattering, lowabsorbing sodium diluent. The fuel was 15.7 wt% enriched U/sup 235/ and the core contained 18.2 vol% sodium and 12.68 vol% stainless steel. The experimental program was designed to measure the effect of the material replacement on spectral indices, which consisted of the standard fission ratios, foil irradiations, and a large number of central reactivity coefficients. Other measurements included the Rossi- alpha , radial fission traverses, and edge reactivity worths of a few samples. (auth)

Nuclear rocket development problems have resulted primarily from the stringent operational requirements of designing a reactor with optimized parameters of core temperature, rapid start-up capability, ability to withstand extreme temperature gradients, and minimum weight. Disasterous consequences resulting from the entrance of appreciable amounts of liquid hydrogen in the reactor core during start up was feared. Efforts to program the start-up such as to increase the reactor power simuitaneously with the flow rate to prevent two- phase hydrogen from entering the reactor core were attempted. The heat input into the propellant was adjusted as it progressed sequentially through the various portions of the reactor such that the hydrogen entering the reactor core remained well above its critical temperature (33 deg K) during the period that the core inlet pressure was c the critical pressure of hydrogen (12.9 atm). A set of hydrodynamic and heat transfer equations were developed using the transport properties and heat transfer data for fluid hydrogen to produce the necessary start-up program for the reactor. Tests prove that it is possible to start up a reactor on liquid hydrogen. (H.G.G.)

Trees in a natural pitch pine-oak forest have been exposed to varying amounts of low-level chronic gamma radiation for several years. Responses range from lethality to minute morphological changes, depending upon dose rate and species. The cumulative effects of low-level chronic gamma radiation on male and female flowers. pollen production. pollen germination and development of seedlings from seeds of irridiated mother trees are described. (C.H.)

A research program to determine the extent to which Zr and Zircaloy-2 exhibits delayed fnilure (static fatigue) as caused by absorbed H/sub 2/ and applied stress is outlined. Dynamic tensile tests were carried out on Zr and Zircaloy-2 without and wlth 200 ppm H/sub 2/. Preliminary results of a delayed failure investigation suggest that Zr containing 200 ppm H/sub 2/ is relatively insensitive to delayed ailure at room temperature up to 900 hr. (D.L.C.)

A pressurized water loop constructed in the Oak Ridge Research Reactor for use in the Maritime Reactor Program is described. irradiation testing of pressure vessel materinl specimens and several sets of fuel pins for the NS Savannah'' Nuclear Merchant Ship Reactor, NMSR, was completed. Operating conditions for the fuel tests nominally were 500 deg F and 1750 psig. The loop has capability for operation at 650 deg F, 2500 psig, with a maximum water flow rate of 80 gpm, and heat removal in excess of 150 kw. Design features include convenient access for insertion and removal of test specimens, efficient use of equipmert cubicle space, and reliable operation. The loop is entirely constructed of 300-series stainless steel. A bypass purification and sampling system affords continuous waterchemistry control, and provision was made for attachment of special equipment for chemistry studies. Fuel and material test specimens are irradiated in the space provided by two tubes, 1.5 in. ID by 24 in. long, in positions A-1 and A-2 of the ORR core. The maximum unperturbed thermalneutron flux is approximately 7.5 x 10/sup 13 neutrons/cm/sup 2/. sec and the peak gamma heat about 5 w/g with the ORR operating at 30 Mw. (auth)