Experiments were performed in an attempt to make thin n/sup +/ contacts on high-purity germanium by the solid phase/sup 1)/ epitaxial regrowth of arsenic doped amorphous germanium. After cleaning the crystal surface with argon sputtering and trying many combinations of layers, it was not found possible to induce recrystallization below 400/sup 0/C. However, it was found that simple thermally evaporated amorphous Ge made fairly good electron or hole blocking contacts. Excellent spectrometers have been made with amorphous Ge replacing the n/sup +/ contact. As presently produced, the amorphous Ge contact diodes show a large variation in high-voltage leakage current.

Analyses of experiments in the initial critical assemblies for the gas-cooled fast breeder reactor (GCFR) were conducted using the calculational methods at General Atomic (GA) for GCFR design. The assemblies, constructed on the ZPR-9 facility at Argonne National Laboratory, simulated features of the 300-MW(e) GCFR demonstration reactor. Studies relating to the safety of this reactor design and to the GCFR concept in general were concerned with (1) reactivity coefficients of fuel and poison materials to evaluate loading and control requirements, (2) the worth of helium coolant in a depressurization event, (3) the Doppler effect in uranium to determine power coefficients, and (4) the effect of hypothesized steam ingress into coolant channels as a potential for reactivity addition and altering core neutronic and control characteristics. Results are reported for GA analyses of such safety-related physics measurements in two basic assemblies, the 3150-liter phase I core with a coolant void fraction of 55% and the 1300-liter phase II core with a 45% void fraction.

A time-of-flight (TOF) atom-probe field-ion microscope (FIM) designed for the study of defects is described. This atom probe features: (1) a variable magnification internal-image-intensification system; (2) a liquid-helium goniometer stage; (3) a low-energy (less than or equal 3 keV) gas-ion gun for in-situ irradiations; (4) an ultra-high vacuum (approximately 3.10/sup -10/ torr) chamber; (5) a high vacuum (approximately 10/sup -6/ torr) specimen-exchange device; (6) a Chevron ion detector; and (7) an eight-channel digital timer with a +-10 nsec resolution for measuring the TOFs. The entire process of applying the evaporation pulse to the specimen, measuring the voltages, and analyzing the TOF data is controlled by a computer. With this system we can record and analyze 600 TOFmin. Results on unirradiated specimens of molybdenum, tungsten, W/25 at. % Re, Mo/1.0 at. % Ti, Mo/1.0 at. % Ti/0.08 at. % Zr and a special low swelling stainless steel alloy (LS1A) demonstrate the instrument's ability to quantitatively determine concentrations at the 5.10/sup -4/ at fr level and to determine their spatial distribution with a resolution of a few angstroms.

The present status of a development project to convert organic waste material to gasoline has been described. The method is based on the Fischer-Tropsch synthesis of straight-chain hydrocarbons from the pyrolysis gas with the subsequent reforming of these hydrocarbons to gasoline. The concept appears technically feasible. Implementation on a large scale is dependent on refinements in process performance and demonstrated operational reliability. If these objectives are achieved, the process economics could be attractive.

Calculations of damage energy and displacement cross sections using the recommendations of a 1972 IAEA Specialists' Meeting are reviewed. The sensitivity of the results to assumptions about electronic energy losses in cascade development and to different choices respecting the nuclear cross sections is indicated. For many metals, relative uncertainties and sensitivities in these areas are sufficiently small that adoption of standard displacement cross sections for neutron irradiations can be recommended.

An interesting dose dependance of the location of beam implanted tritium in titanium is studied by neutron time-of-flight spectroscopy. A concentration range of nearly 10/sup 16/ is achieved with a spatial resolution of 1.6 ..mu..m at depths of up to 12 ..mu..m. 6 figures.

Recent advances in positron cameras and positron ring detectors for transverse section reconstruction have created renewed interest in positron emitting radionuclides. This paper reports on: generator-produced /sup 82/Rb; cyclotron-produced /sup 62/Zn; and reactor-produced /sup 64/Cu. Investigation of the /sup 82/Sr (25 d)--/sup 82/Rb (75 s) generator determined the elution characteristics for Bio-Rex 70, a weakly acidic carboxylic cation exchanger, using 2% NaCl as the eluent. The yield of /sup 82/Rb and the breakthrough of /sup 82/Sr were determined for newly prepared columns and for long term elution conditions. Spallation-produced /sup 82/Sr was used to charge a compact /sup 82/Rb generator to obtain multi-millicurie amounts of /sup 82/Rb for myocardial imaging. Zinc accumulates in the islet cells of the pancreas and in the prostate. Zinc-62 was produced by protons on Cu foil and separated by column chromatography. Zinc-62 was administered as the amino acid chelates and as the ZnCl/sub 2/ to tumor and normal animals. Tissue distribution was determined for various times after intravenous injection. Pancreas-liver images of /sup 62/Zn-histidine uptake were obtained in animals with the gamma camera and the liver uptake of /sup 99m/Tc sulfur colloid was computer subtracted to image the pancreas alone. The positron camera imaged uptake …

In a nuclear reactor, tubes are pressurized from interior by coolant, while externally no pressure is applied on them. The pressure that causes any of the tubes to burst is random and has certain distribution. By using the presently available data from stress-strain experiment, mathematical procedure for finding the distribution form of the ultimate stress is made and is justified theoretically and empirically. The distribution function obtained is important in analyzing the problem of loss of coolant in the reactor.

Events at the Lawrence Radiation Laboratory at Berkeley to the end of 1940 are recalled. Radiation detection, discovery of new isotopes and elements, and accelerators are among the subjects included. 29 photographs. (RWR)

Computed transverse section emission tomography using /sup 99m/Tc with the Anger camera is compared to positron annihilation coincident detection using a ring of crystals and /sup 68/Ga. It is concluded that positron computed section imaging has a tenfold increase in sensitivity over multiple-view imaging with the gamma camera which gives multiple sections but requires camera or patient rotation.

The absorbed energy determined by the ion calorimeters was used as a basis for computations of the target behavior. Both neutron yield and x-ray spectra thus obtained were in agreement with the measured values within the precision of both calculations and experiments. Some results are described. (MOW)

It was found experimentally that high-purity Ge low-energy X-ray detectors have a relatively thick entrance window which renders them practically useless below approximately 2.3 keV. A simple X-ray fluorescence experiment establishes clearly that the window is physically in the Ge material itself. Experiments with detectors made from different Ge crystals, and with Schottky barrier contacts of different metals indicate that the effect is due to a basic property of the transport of electrons near a surface. Theoretical considerations and a Monte Carlo calculation show that the window is caused by the escape of warm electrons which are the end product of a photo event. The mean free path of the electrons becomes longer as they lose energy by optical phonon collisions and they can be trapped at the surface before they are picked up by the electric field.

Fast-wave heating at omega = n omega/sub ci/, n = 1 or 2, is well suited to heating intermediate-size tokamaks such as ATC and PLT, but for significantly larger machines, the frequency spectrum becomes thickly packed with these modes. Adequate mode selection could require elaborate antennas; otherwise, mode overlap may produce surface heating of the plasma due to strong near fields at the antennas. On the other hand, the large minor radius and high plasma density in next-generation tokamaks will accommodate fast-wave toroidal eigenmodes at much longer wavelengths and at frequencies which are well below all the cyclotron frequencies of ions of the fuel gas and of most impurities (carbon, oxygen, iron). Electron transit-time and Landau damping provide adequate absorption mechanisms, while the high intrinsic Q of the fast-wave modes will allow strong coupling to the plasma with minimal antenna structures. The low frequency range (1-2 MHz) is also advantageous for coupling together electronic modules to provide several hundred megawatts rf heating power. Also interesting to consider is excitation such that the Alfven resonance layer is halfway inside the plasma, weakly coupled to a m = 0 fast-wave propagating in the plasma core region.

An attempt to design and implement a computer system for control of and data collection from a set of laboratory experiments reveals that many of the experiments in the set require an extensive collection of parameters for their control. The operation of the experiments can be greatly simplified if a means can be found for storing these parameters between experiments and automatically accessing them as they are required. A subsystem for managing files of such experiment control parameters is discussed. 3 figures.

Simple, flat helical delay lines were developed for avalanche position determination along each anode wire, for unambiguous readout of multiparticle events in multiwire drift or proportional chambers. Lines of various propagation delay and dimensions were tested with x-rays and ..beta..-rays in several gas mixtures. Avalanche position resolutions of 0.2 mm and 0.6 mm FWHM, respectively, were obtained with a line 30 cm long in non electron-attaching gases.

Honeycomb structured lead ..gamma..-ray converters have been developed and coupled with Multiwire Proportional Chambers to produce a position-sensitive hybrid detector for spatial localization of MeV range ..gamma.. rays. Two such detectors operated in time coincidence mode function as a large-area large-solid-angle positron camera. The sensitivity of the camera system is measured to be 1600 counts/min-..mu..Ci, corresponding to a detection efficiency of 5.5 percent per detector. Images of phantoms and clinical objects are obtained by using the back-projection reconstruction method, and the results demonstrate the tomographic capability of such a positron camera system. A design analysis of the ..gamma.. converter is presented, the detection efficiencies of converters of various dimensions are measured, and the results agree quite well with calculation. Further improvements in converter efficiency can be expected with modifications in the converter designs based on the concepts of enhanced surface area and uniformity of electron extraction field. The new converters under consideration are made of small-diameter high-lead-content lead glass tubing made conductive by hydrogen reduction treatment.

High resolution computed transaxial radionuclide tomography has been performed on phantoms containing positron-emitting isotopes. The imaging system consisted of two opposing groups of eight NaI(Tl) crystals 8 mm x 30 mm x 50 mm deep and the phantoms were rotated to measure coincident events along 8960 projection integrals as they would be measured by a 280-crystal ring system now under construction. The spatial resolution in the reconstructed images is 7.5 mm FWHM at the center of the ring and approximately 11 mm FWHM at a radius of 10 cm. We present measurements of imaging and background rates under various operating conditions. Based on these measurements, the full 280-crystal system will image 10,000 events per sec with 400 ..mu..Ci in a section 1 cm thick and 20 cm in diameter. We show that 1.5 million events are sufficient to reliably image 3.5-mm hot spots with 14-mm center-to-center spacing and isolated 9-mm diameter cold spots in phantoms 15 to 20 cm in diameter.

Ionization chambers in which almost all of the energy released in electromagnetic showers is absorbed in liquid argon are considered. Electronic noise is determined as a function of the electrode configuration. It is shown that in a multiple-plate ionization chamber the optimum interelectrode gap is determined as one third of the product of the electron drift velocity and the event resolving time. The lower limit for electronic noise is determined only by the chamber volume, electron drift velocity, event resolving time and the unity-gain frequency of the field-effect transistor. This limit is approximately the same for ionization chambers with one or more large gaps where the electron drift time is much longer than the event resolving time.

Using copper (a fast diffusing, multivalent acceptor impurity in Ge) it was shown that hydrogen can form complexes with multivalent acceptors. Hydrogen is incorporated in the Ge single crystal during its growth from a melt in a H/sub 2/ atmosphere. By analogy with the interaction between lithium and multivalent acceptors two acceptor like complexes (Cu-H and Cu-H/sub 2/) were found. Using Photothermal Ionization Spectroscopy and Hall effect the following energy levels are assigned: Cu-H: E/sub V/ + 17.5 meV and E/sub V/ + 170 +- 20 meV and Cu-H/sub 2/: E/sub V/ + 17.0 meV. According to the model the Cu-H/sub 3/ complex is neutral. Consequences for the performance of large volume radiation detectors are discussed.

The neutral-beam energy required for adequate penetration of tokamak plasmas of high opacity can be reduced by a large factor if the beam is injected vertically into a region of large TF (toroidal-field) ripple. Energetic ions are trapped in local magnetic wells and drift vertically toward the midplane (z = 0). If the ripple is made very small on the opposite side of the midplane, drifting ions are detrapped and thermalized in the central plasma region. This paper discusses design considerations for establishing the required vertically asymmetric ripple. Examples are given of special TF-coil configurations, and of the use of auxiliary coil windings to create the prescribed ripple profiles.

Several methods for reducing impurity contamination in near-term tokamak reactors by modifying the first-wall surface with a low-Z or low-sputter material are examined. A review of the sputtering data and an assessment of the technological feasibility of various wall modification schemes are presented. The power performance of a near-term tokamak reactor is simulated for various first-wall surface materials, with and without a divertor, in order to evaluate the likely effect of plasma contamination associated with these surface materials.

A review is given of the principle results of the neoclassical theory of impurity transport in tokamaks, emphasizing those collisionality regimes of most practical interest. Some new results are given for the case where there are several different impurity species present at the same time, with both hydrogenic and impurity ions in the Pfirsch--Schlueter regime. The rate at which an impuritiy ion is transported into a plasma, and the radiation from it, are strongly dependent on the mean level of ionization (Z). An atomic physics code package, based on an ''average ion'' model is used to assess the validity of the ''coronal equilibrium'' assumption commonly made to determine (Z); coronal equilibrium is found to be a poor approximation for heavy metallic impurities in small present-day tokamaks, but its validity is much improved in larger devices, except perhaps in the edge region of the plasma. The computations are compared with the results obtained in an impurity injection experiment in the ATC tokamak. In practice, the most appropriate impurity transport model would be a combination of neoclassical transport and anomalous diffusion, with the magnitude of the anomalous diffusion coefficient chosen to give agreement with observed hydrogenic particle confinement times. Computations of oxygen …

The criteria for intense fast neutron generators for radiotherapy and fusion materials research purposes are examined. For generators producing near monoenergetic 14-MeV neutrons from the T(d,n) reaction or a broad spectrum of neutrons via deuteron stripping in a thick Be target, the demands upon accelerator and target technology are greater for the materials research application than for therapy use. The properties of sources presently available, under construction, or proposed for future construction are discussed.

The need, potential, and current status of the GRID programs are presented in a general way. Some examples of data from GRID files are used as illustrations. (MHR)