Jesse W. M. DuMond

A Determination of the Wave Forms and Laws of Propagation and Dissipation of Ballistic Shock Waves

Experiments to ascertain the wave forms and laws of propagation and dissipation of ballistic shock waves to large distances (80 yards) from the bullet trajectory are described. Calibers 0.30, 0.50, 20 mm, and 40 mm were studied. In every case an N‐shaped wave profile was observed consisting of a sudden rise in pressure, the “head discontinuity,” followed by an approximately linear decline to a pressure about equally far below atmospheric and then a second sudden return, the “tail discontinuity,” to atmospheric pressure. The peak amplitudes of this disturbance are found to diminish about as the inverse 3/4 power of the miss‐distance (perpendicular distance from the trajectory) while the period T′ (measured between the discontinuous fronts) increases about as the 1/4 power of the miss‐distance for calibers 0.30, 0.50, and 20 mm. For 40‐mm shells the amplitude decays a little faster, about as the inverse 0.9 power of miss‐distance over the range studied. A theory taking account of the dissipation of the N‐wave energy into heat is developed to explain the observed behavior. A method of measuring absolute N‐wave amplitudes by observing the rate of change of period T′ with propagation is described. The theory leads to an absolute relationship at large distances between distance, amplitude, and period in which no arbitrary constants appear.

A High Resolving Power, Curved‐Crystal Focusing Spectrometer for Short Wave‐Length X‐Rays and Gamma‐Rays

Description is given of a transmission‐type, curved‐crystal focusing spectrometer for short wave‐length x‐rays, and gamma‐rays having a dispersion of 1.186 x.u. per mm at short wave‐lengths. The spectrometer utilizes the (310) planes of quartz in a crystalline plate of dimensions 80×70×1.0 mm curved cylindrically to a radius of two meters. High luminosity is obtained since the useful aperture in the crystal holder has an area of 10 cm2 and subtends 0.00025 stereradians at the focus. It also affords high resolution since by photographic tests with x‐rays the curved plate has been shown to focus a specified x‐ray wave‐length to within 0.06 mm of the same position on the focal circle for all parts of its useful aperture and over the entire operating wave‐length range. The geometry of the mechanism permits absolute measurements with a precision screw of the sine of the Bragg angle on both sides of the reflecting planes, affording a wave‐length range which includes at longest wave‐lengths the K‐spectrum of silver and goes down to zero wave‐lengths. For short wave‐length gamma‐rays the source is placed at the focus. A multiple‐slit collimator of tapering die‐cast lead partitions spaced apart with tapering separators, is used at short wave‐lengths to transmit the monochromatic diffracted beam and absorb the directly transmitted and scattered heterogeneous beam. The present collimator limits the spectrum that can be studied to a shortest wave‐length of 7. x.u. corresponding to 1.75 Mev. The intensity of the diffracted beam is to be measured with a special multi‐cellular G. M. counting tube of high efficiency, provided with a number of thin lead partitions through which the beam passes successively. In photographic spectra made with this instrument the tungsten and also the silverKβ_1β_3 doublet is completely and clearly resolved. Reproductions of such photographic x‐ray spectra are shown in which the line breadths have substantially the natural breadth. Fluorescence spectra of silver have been made in 10‐minute exposures. A companion paper gives the all‐important precision technique of generating the curved cylindrical stainless steel clamping blocks for the crystal.

THE MULTIPLE CRYSTAL X‐RAY SPECTROGRAPH

The need for improvements in scattered x‐ray spectroscopic technique along the lines of increased intensity and contrast is discussed and a new instrument composed of fifty small units, each a Seeman Spectrograph in itself cooperating to form a single spectrogram, is described in detail. The technique of adjusting the instrument is also described.

Submicroscopic Structure Determination by Long Wavelength X‐Ray Diffraction

This paper reviews the theory of low angle x‐ray diffraction as applied in the long wavelength region for the determination of particle sizes and shapes and other structural features in the submicroscopic size range and emphasizes the advantages to be gained by employing the longer x‐ray wavelengths (8 to 25 A). It also is intended to serve as an introduction to a description of an entirely new instrumental technique developed for this long wavelength range utilizing a diffraction apparatus consisting of a special gas‐filled x‐ray tube and a total reflection camera in which the primary radiation is simultaneously monochromatized and made to converge to a point focus. The sample for study is placed in the converging part of the primary beam and the diffraction patterns are formed around the point focus on a photographic film.

Conditions for Optimum Luminosity and Energy Resolution in an Axial β‐Ray Spectrometer with Homogeneous Magnetic Field

In a β‐ray spectrometer with axial homogeneous magnetic field, it is shown that optimum energy resolution and luminosity are obtained when the trajectories make an angle close to 45° with the field and that an annular resolving slit should be provided at a determined radial and axial location relative to the source. The combined effect of three independent sources of instrumental energy line width is analyzed for the optimum condition. Formulas are given for the optimum dimensions, the energy resolution and the luminosity.

New Point-Focusing Monochromator

A method is described here for cutting and bending a single crystal for a point-focusing monochromator which does not produce a nondevelopable surface.

Status of knowledge of the fundamental constants of physics and chemistry as of January 1959

Abstract If at a given epoch one wishes a consistent system of values of the fundamental constants of physics and chemistry, that is to say a system consistent with all the accepted laws interrelating these quantities and as consistent as possible with all the reliable precision data then available, it is emphasized in this paper that one cannot treat the problem in a piecemeal way, one constant at a time, but one is forced to adopt a unified approach involving a complete analysis and synthesis of all the data simultaneously. The least-squares adjustment of 1955 by Cohen, DuMond, Layton, and Rollett is briefly reviewed as an example. A wealth of new data has been accumulated since the 1955 adjustment and a list of 26 examples of such new determinations, either completed or in process, is presented, described, and discussed. When the results of certain of these redeterminations, now well advanced, have become definitely available it is felt that a new least-squares adjustment will be in order. The desirability of such periodic reassessments as well as their unavoidable shortcomings are discussed. A graphic record of past performance shows that the “best values” so obtained tend satisfactorily to stabilize within ever narrower error ranges which at each epoch are satisfactorily close to (usually in fact inside ) the error ranges of prior adjustments.

Superiority of a Knudsen Type Vacuum Gauge for Large Metal Systems with Organic Vapor Pumps; Its Design and Operation

The McLeod, Pirani, Knudsen and ionization gauges have been studied as to their suitability in the operation of large metal vacuum systems with organic vapor pumps now coming into extensive use in modern physics. Advantages and disadvantages of each type based on our experience are critically discussed. The superiority of a gauge on the Knudsen principle for this work is stressed and we present a new design and a simpler mode of operation of such a gauge together with a full discussion of its construction, calibration and characteristics.

An iron-free magnetic beta-ray spectrometer of high luminosity, resolving power, and precision for the study of decay schemes of the heavy isotopes☆

Abstract A complete detailed description of the purposes, theory, design, and techniques of operation of this high-precision, high-resolution, automatically recording instrument is presented. Some representative results are shown and figures of merit are obtained and displayed on Persico-Geoffrion charts for comparison with other instruments. A few examples of its performance are shown and a complete list of references to all nuclear decay schemes so far studied with the instrument is given. The present design represents the cumulative result of numerous modifications and improvements over five years of practical working experience since it was first put into operation.

A Point Focusing X-Ray Monochromator for the Study of Low Angle Diffraction

A point focusing x‐ray monochromator was designed and constructed for low angle scattering studies. The anastigmatic point focus is achieved by means of two cylindrically bent quartz crystals whose focal circles are mutually perpendicular. The beam, emanating from the copper target of an x‐ray tube, is reflected in succession, first from the crystal defining the horizontal focal circle, and second from the crystal defining the vertical focal circle following which it comes to a monochromatic point focus of wavelength 1.537A (CuKα_1). The sample to be studied is placed between the second crystal and the point focus, and the scattered beam is detected by means of a photographic film placed at the point focus, at right angles to the undeviated beam, the latter being suppressed by means of an absorber, or allowed to pass through a hole in the film. Mathematical analysis, in which a ray was traced through the two‐crystal system, revealed correctly the shape and size of the point focus, and the possibility of reducing the latter in size by stopping down the beam emerging from the target.