Direct Pickup Research Articles

Search for Photodeuterium from Copper

Copper foil samples were irradiated with bremsstrahlung of 24-, 30-, and 40-Mev peak energy, and production of deuterium by the ( gamma ,d) reaction investigated. After irradiation, gas released from the samples was introduced into an omegatron mass spectrometer and the ion currents HHD/sup +/ and HH/sup +/ measured. The sensitivity of the detection was sufficient to use the amount of deuterium in natural hydrogen as calibration. No HHD/sup +/ was observed after irradiation at 24 and 30 Mev and the ratio of deuterium to hydrogen in the irradiated samples was estimated to be less than 0.0016 and 0.00014, respectively. At 40 Mev the ratio was measured to be approximately 0.0009. The ratio of deuterium to hydrogen expected on an evaporation theory was calculated for several level density formulas. The predicted values are much greater than the observed deuterium to hydrogen ratio. It is concluded that deuterons are not evaporated from copper at these photon energies. The direct photointeraction pickup process of Madsen and Henley is estimated to predict a ratio of deuterium to hydrogen of 0.0012 at 40 Mev and 0.0003 at 30 Mev for relatively high residual nucleus excitations. Such predictions seem consistent with the experimental results. (auth)

Performance of Multistage Image Amplifying Tubes; Astronomical Applications; and Proposed Use with Fabry-Perot Etalons for Stellar Spectroscopy.

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Performance of Multistage Image Amplifying Tubes; Astronomical Applications; and Proposed Use with Fabry-Perot Etalons for Stellar Spectroscopy. Dunham, T., Jr. Abstract and Weekly, B., Nature 185, 370, 1960) offer advantages for photometry at low flux levels: (1) high- speed recording; (2) background electrons are focused at the output, thereby reducing the number per resolution band to approximately 10-~ of the contribution encountered with photomultipliers; and (3) scintillations, corresponding to individual photoelectrons, are bright enough to permit recording a considerable fraction on moving film. Information storage is greater on moving film and scintillations in individual spectral resolution bands can be counted, so that the tubes can be used as multi- channel pulse counters [Dunham, T., Jr., J. Opt. Soc. Am. 50, 1129(A), 19601. The factor of merit of an image tube for spectrophotometry may be expressed as G2r2/N, where G is the over-all light gain, r the linear resolution, and N the background. For direct stellar photometry, an image tube offers the possibility of recording flux from a number of star images (and sky) simultaneously, using fiber light guides to transfer images to a linear array on the photocathode, so that scintillations can be recorded and counted on moving film. Speed, resolution, and background have been investigated, using test spectra and coude' spectra with Baum's microprojector (Baum, W. A., Advances in Electronics and Electron. Phys. 16, 391, 1962). The percentage of incident photons that can be recorded on film has been determined by using a low-intensity scattering source of approximately monochromatic light. For high-resolution spectroscopy, the use of an image tube and moving film, with a scanning FabryPerot etalon (Jacquinot, P., and Dufour, C., J. Reck., Cent. Nat. Rech. Sci. 2, 19,1948) and rotating grating, appears to offer an efficient system that permits pulse counting of many fringes simultaneously. For space spectroscopy, direct electrical pickup at the output, on narrow conducting strips corresponding to the fringes, and connected to individual pulsecounting circuits, would have advantages. The experimental part of this study was carried out at Imperial College, thanks to the kindness of Dr. J. D. McGee. Publication: The Astronomical Journal Pub Date: June 1962 DOI: 10.1086/108872 Bibcode: 1962AJ.....67R.575D full text sources ADS |

Excitation Functions for Lithium-6 Induced Reactions on Aluminum-27

Excitation functions for a number of Li/sup 6/-induced reactions on A1/ sup 27/ were studied using stacked foil techniques and the Li/sup 6/ ion beam from the Yale Heavy Ion Accelerator. Excitation functions corresponding to radioactive residual nuclei P/sup 32/, P/sup 30/,Si/sup 31/,Al/sup 29/,Al/sup 28/ ,Mg/sup 27/,Na s/sup 4/ and Na/sup 22/ were measured in the Li/sup 6/ range from 1 to 63.3 Mev. The data strongly suggest that the P/sup 32/, P/sup 30/, and Si/sup 30/ result from compound sy stem processes and the Na/sup 22/ and Na/sup 24/ from a predominant direct knochout process. In the cases of Al/sup 28/ and Al/sup 28/ both compound system and direct pickup reaction amplitudes contribute to the reaction yield. (auth)

Deuteron Production by Nucleons Bombarding Atomic Nuclei

Deuteron production by nucleon bombardment is discussed in detail. According to the general theory of nuclear reactions developed by Ui, the transition matrix is written as the sum of two elements, which corresponds to the compound and the noncompound nuclear processes. In the processes proceeding through the compound nucleus, the indirect pickup process, in which a neutron emerging tom the compound nucleus picks up any proton, gives a larger yield than the deuteron evaporation in the usual sense. The average kinetic energy of deuterons thus produced is about three times larger than that in the Maxwellian type. In the direct pickup process of low energy (p,d) reaction, the Coulomb effect is found to play an important role and the remarkable backward maximum in the angular distribution of the reaction product is predicted. Direct pickup process at moderate and high energies is calculated by the Born approximation, assuming the Gaussian momentum distribution for the tail of the wave function of the nucleon to be picked up. The forward peak in the angular distribution for sharp energy deuteron groups corresponding to the ground state and the low-lying levels is interpreted in terms of the direct process taking place in the external regionmore » of the target nucleus. In the limiting case of the weak coupling, which is an approprinte approach to the high energy reaction, the calculation is performed using the Chew-Goldberger's procedure on the basis of the non- degenerate Fermi gas model, sand the total cross section is found to obey approximately 1/v law. Further the production cross section of is deuterons is evaluated in the same way, and is found to give a contribution comparable to the production of deuterons in the ground state. (auth)« less

An Impulse Interference Blanker for Communications Receivers

The necessity for adequate and reliable communications for military operations has always existed. Today, with the trend toward everincreasing specializations of military forces and the continued growth of complex systems of radar, fighter control, etc. , this requirement has become more urgent. Since items of communication apparatus are often in close physical proximity to facilitate coordination, the equipment has almost invariably been subjected to detrimental effects from mutual interference. When communications receivers are placed close to radars, impulse interference may occur, which is at times severe enough to cause complete loss of intelligibility. Such interference may be introduced into a receiver through various channels: a. Shock excitation of the tuned circuits of the receiver by the large modulatorgenerated d-c pulses. b. Direct pick-up of the radiated r-f radar pulses. c. Feed-back through common power supplies. d. Non-linear detection of the r-f pulse. As a remedial measure, the ground communications equipment has often been located as far as one-half mile from the radar sites. Such physical separation naturally increases the problems of remoting, maintenance, real estate procurement, additional buildings, heating, etc. Where airborne equipment is involved, such remoting possibilities obviously cannot be plausibly considered. Therefore, as the most effective method of reducing the effects of pulse interference to a minimum or negligible value, the impulse interference blanker for communications receivers was developed. Study and investigation by engineers of the Interference Analysis and Control Section of the General Engineering Laboratory, RADC, has shown that (a) above is the most common type of interference. However, the impulse interference blanker as developed will eliminate impulse interference no matter how it is introduced into the receiver. The blanker facilitates close-in operation of communications receivers with high-power pulsed equipments of present and projected design. It is so synchronized with the interfering pulse that it generates a blanking gate which is applied to the local oscillator of the affected receiver. Such a measure greatly attenuates the interfering impulse.

The performance of television receiver installations in the presence of interference

The television receiving installation is susceptible to interference by three processes which can broadly be classified as follows:(a) Pick-up of interference by the aerial system,(b) Direct pick-up by the receiver circuits, and(c) Mains-borne interference introduced by connection to supply.Measurements are described which give the relative significance of these processes under typical operating conditions. The data provided on modern commercial receivers lead to the conclusion that the performance standards of the average receiver are satisfactory and that large strides to achieve immunity from interference do not involve radical development of receiver design.

Absolute Measurement of Small Vibration Amplitudes

This paper describes an acoustic method for the absolute measurement of small vibration amplitudes and which, as a by-product, results in a method of calibrating vibration pick-ups. Vibrations generated by an electrodynamic device are transmitted to a piston arranged to vibrate within a cavity. The diaphragm of a condenser microphone is coupled directly to the cavity, and the pressure change in the cavity resulting from the motion of the piston is detected by the microphone and transformed into an electrical output. One side of a parallel plate condenser is rigidly attached to the piston, forming a direct electrostatic pick-up. Transformation into electrical energy is accomplished in both cases by a low noise-level electronic circuit after Van Zelst, which provides a sensitive coupling device and eliminates the danger of stray fields. The output of the microphone circuit as a function of sound pressure is found independently by a reciprocity calibration, while the amplitude of motion of the piston is computed from the observed sound pressure. With the electrostatic device used as a pick-up, the method can be used to measure the absolute amplitude of vibration of other structures without loading them. Preliminary measurements of the order of magnitude of 10−9-cm displacement have been made. The frequency range of the instrument as presently constructed is 20 to 6000 cycles per second but could be readily extended.

A Triple-Quartz-Plate Supersonic Generating and Receiving System

This treatise is an exposition of the measurement of high frequency sound by means of an originally designed and constructed apparatus, together with results obtained and the interpretation thereof. The apparatus consists of a high precision, supersonic, sending and receiving system of a triple-quartz-plate type. Two of the piezo-quartz plates used act as supersonic transducers to transform electromagnetic energy into gas pressure waves and to retransform them. The third plate, of the same frequency, controls the oscillations of an external vacuum tube circuit, the output of which drives and controls the frequency of the first transducer plate in the gas chamber, within extremely narrow limits. An original interference method is used to eliminate troublesome standing waves along the supersonic path. The signal, amplified for observation, is the vector sum of the electromagnetic wave impressed on the receiver by the retransformed energy and a controlled direct pick-up through the capacity coupling of the high voltage leads to the gas chamber. The amplifier consists of two stages of radiofrequency amplification and a peak tube voltmeter. By this means absorption constant values are obtained to three significant figures. Velocity measurements may be made to include four significant figures.

Some experiments on the screening of radio receiving apparatus

The chief object of the investigation was to obtain quantitative information on the effect of screens, of which the dimensions are small compared with the wave-length of the waves they are intended to screen. Some preliminary experiments are described, in the first of which the screening effect of a totally closed iron tank was investigated by an operator inside it with a frame coil receiver; and in the second an investigation was made on the effect of screening a square frame receiving coil by totally enclosing each of its four sides in a metallic envelope. A description is then given of the method employed in subsequent experiments of measuring the effect of screens based upon the employment of two receiving coils connected in opposition. This is followed by an account of measurements made by this method on some specially constructed screens of straight wires, open and closed loops, and wire-netting, etc. These measurements demonstrate the important part played by closed circuits in screening the magnetic field of radio waves, and show that an effective screen may be constructed of wire-netting. In this connection a description is given of the screening of the interior of a hut with this material to protect direction-finding apparatus within it from ?direct pick-up.? Further experiments, in which the effect of screens on the electric field of the waves is measured, are then described. Three types of screen investigated were shown to reduce substantially the electric field without affecting the magnetic field, while, later in the paper, it is shown that a fourth type will screen the magnetic field but not the electric field. A cage of the former type is then described which is now in practical use as a means of eliminating ?antenna? effect from a single-coil direction-finder contained within it. A discussion of the experiments follows, some explanation of the various effects being given, and conclusions are drawn as to the general principles of screening and as to the essential points to be attended to in the design of efficient screens for various purposes.