Index of content:
Volume 25, Issue 11, November 1954
25(1954); http://dx.doi.org/10.1063/1.1770937View Description Hide Description
25(1954); http://dx.doi.org/10.1063/1.1770938View Description Hide Description
A 0.6 μabeam of He++ions has been produced and accelerated to 7.6 Mev in an electrostatic generator. The He++ion source, contained in the high voltage electrode of the generator, consists of a second small 400 kv electrostatic generator driven by the upper belt pulley of the main machine. He+ions obtained from a low voltage arc type ion source in the dome of the small generator pass through a region of low pressure gas to become doubly ionized before entering the main accelerating tube of the large generator.
25(1954); http://dx.doi.org/10.1063/1.1770939View Description Hide Description
A cylindrical liquid scintillation counter, 75 cm in diameter and 75 cm high has been used for the detection of neutrons,gamma rays, and cosmic ray μ mesons. A delayed coincidence technique has been used to detect neutrons; the first pulse corresponding to a recoil proton or other associated event, the second pulse due to neutron capture in cadmium. The capture rate of neutrons in a solution containing toluene and cadmium has been calculated as a function of the cadmium to hydrogen ration by the Monte Carlo method and an experimental check performed. Detector design considerations and some possible uses are described.
25(1954); http://dx.doi.org/10.1063/1.1770940View Description Hide Description
The fraction of the charged particles traversing an absorber in a counter experiment which miss the last counter because of multiple Coulomb scattering in the absorber has been calculated for a general counter geometry. The results are presented in the form of graphs which give the fraction of surviving particles as a function of the counter geometry and the amount of multiple scattering in the absorber. It is shown that the effect of single scattering at large angles is very small.
25(1954); http://dx.doi.org/10.1063/1.1770942View Description Hide Description
A negative muon beam effectively free of pions and secondary particles has been obtained at the 102 Mev π− channel of the Chicago synchrocyclotron by placing a graphite filter 36.0 g/cm2 thick in the beam. The emerging muons were magnetically deflected from the main beam and their energy was shown to be about 50 Mev. A radiochemical method for determining the π−/μ− ratio in the range 10 to 0.01 was used to demonstrate the purity of the negative muon beam.
Although not directly tested, his method for producing a muon beam should work equally well with positive muons.
25(1954); http://dx.doi.org/10.1063/1.1770943View Description Hide Description
An improved electron current and energy regulator for mass spectrometerion sources is described. The improvements over previous regulator circuits consist of (a) a two kilocycle filament excitation supply which allows improved filament emission control and (b) a method of controlling the filament to shield voltage over a wide range of electron energies. Data on isotope ratio measurements are provided to show the increased stability over that of previous regulators.
25(1954); http://dx.doi.org/10.1063/1.1770944View Description Hide Description
The problems involved in the construction of a magnetic refrigerator operating below 1°K, using superconducting metallic links for the thermal valves and a paramagnetic salt as the working substance, are discussed. A cycle for the operation of the refrigerator is suggested and then examined for the optimum operating conditions with readily available laboratory facilities. Design equations are obtained and compared with our more recent experimental model. The constructional details of a completely automatic experimental model of the magnetic refrigerator using lead for the thermal valves, iron ammonium alum as the working substance, a helium bath at 1°K as the high‐temperature reservoir, a maximum magnetic field of 7000 gauss, a 2 minute cycle of operation, and capable of extracting 120 ergs/second from a reservoir at 0.3°K are presented in full. Temperatures as low as 0.2°K are obtained with this model. Improvements in this this design, its use either for the production of an isothermal reservoir or as a heat sink for adiabatic demagnetization work below 1°K, and the extension to a two‐engine refrigerator for the production of a reservoir at temperatures as low as 0.05°K are also discussed.
25(1954); http://dx.doi.org/10.1063/1.1770945View Description Hide Description
An interferometer of the amplitude‐splitting type has been constructed which operates with electron beams and produces a system of fringes in the viewing instrument. The appearance of the fringes may be varied at will by introducing changes in one of the (electron) optical paths. The instrument utilizes crystalline diffraction for beam splitting and recombining.
25(1954); http://dx.doi.org/10.1063/1.1770946View Description Hide Description
An elementary theory based on light optical analogues is presented. Calculations of fringe orientation are in good agreement with experimental values. The theory leads to a value, based on experimental data, of the coherence length of an electron in excess of 5800 wavelengths.
25(1954); http://dx.doi.org/10.1063/1.1770947View Description Hide Description
An improved type of transparent film sampling surface is presented for 25μ to 400μ diameter water droplets which contain halide ion concentrations greater than 0.5 percent by weight. A preliminary calibration of droplet size vs film spot size has been constructed. From the calibration data an experimental estimate is made of the chloride ion sensitivity per drop size on the film.
25(1954); http://dx.doi.org/10.1063/1.1770948View Description Hide Description
An Allen type electron multiplier has been studied to determine its feasibility as a quantitative detector of positive ions. Results are presented showing the gain or efficiency as a function of aging, pressure, dynode voltage, and input current. Also, the gain is presented for several positive ions (H+, H2 +, He+, N+, Ne+, N2 +, A+) in the energy range from 5 to 250 kev.
25(1954); http://dx.doi.org/10.1063/1.1770949View Description Hide Description
A method is described for obtaining quantitative pole figures for sheet material by the use of the reflection technique only. Seven different sections of the sample are used for obtaining the data for one quadrant of the pole figure which makes it possible to obtain adequate resolution of very close reflections. One section is prepared from a single piece of the sheet. The other six sections are made up of a number of small pieces of the sheet mounted in a jig in order to form a plane surface at an angle of 45° or 90° to the surface of the sheet. These jigs are mounted on a special table for the modified Schulz reflection specimen holder. Intensity data are obtained automatically for a number of different positions on the pole figure defined by φ and α. The method of plotting this intensity data is shown which results in quantitative pole figures with contour intensity lines.
25(1954); http://dx.doi.org/10.1063/1.1770950View Description Hide Description
The importance of determining the nucleus involved in a specific interaction within a nuclear research emulsion is discussed, and the technique used to embed thin filaments in these emulsions is described in detail. The usefulness of this method is illustrated by an experiment in which nylon, molybdenum, and tungsten wires were embedded in Ilford G5 emulsion, and the plates subsequently used to study neutron induced interactions. The uncertainties encountered and the corrections introduced in this method are analyzed.
25(1954); http://dx.doi.org/10.1063/1.1770951View Description Hide Description
Two energy‐sensitive gamma‐ray counters which have been used in experiments above 50 Mev are described. One counter uses a low Z scintillating liquid to measure the energy loss of an electron pair; the other uses high Z material to develop a shower which is sampled with scintillating plastic sheets. Curves of the experimental performance are included.
25(1954); http://dx.doi.org/10.1063/1.1770952View Description Hide Description
The Langmuir viscosityvacuum gauge has been modified to provide electrical recording of low‐pressure data. A particular advantage of this type of gauge is that, once calibrated, it may be used with any gas, including reactive or unstable compounds, or with gases having low condensation pressures.
The gauge utilizes the changing capacitance between a stationary electrode and an oscillating fiber, the rate of damping of which is a function of the composition and pressure of the ambient gas, to modulate the frequency of an oscillator. The output from the oscillator is demodulated in a discriminator circuit, amplified, and recorded. The pressure of the gas is then determined from the recorder trace. Alternatively, the signal may be used to actuate relays or servomechanisms. The fiber is set into oscillation by means of an electromagnet, so the entire operation of the device may be made automatic if desired.
- Letters to the Editor