摘要:

A spectrophotometer, equipped with photomultiplier tubes, is described for the wavelength range 2500–7000A. The apparatus is intended for the determination of light absorption in microscopic objects and is especially useful for studies of biological material. The guiding principle of the construction is that the object in the course of the measurement should have a fixed position. Some applications concerning studies of small parts of cellulose and wood fibers are given. The weight of the examined samples has been between 10−10−10−12g.

ISSN:0034-6748    

DOI:10.1063/1.1745818

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The potentiometer embodies the principle of the normal fluxmeter method of measuring hysteresis loss but, while retaining the accuracy, enables the measurement to be made in a fraction of a minute. The potentiometer incorporates a number of tappings which are connected to individual contact studs so that by rotating a contact arm the current supplied to a magnetizing circuit can be varied in a cyclical manner between two limiting values. There are intermediate positions of the arm which correspond to intermediate values of current and these values differ by fixed amounts from one cycle of magnetization to the next. The contact arm also forms part of a stud switch so that a search coil can be disconnected from a fluxmeter over the part in each cycle over which the current changes between the intermediate and one of the limiting values. In this way a complete rotation of the arm is made to take a specimen through twelve cycles of magnetization and since the intermediate current values are evenly distributed over a complete cycle the fluxmeter registers a deflection which can be related to the hysteresis loss.

ISSN:0034-6748    

DOI:10.1063/1.1745819

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

An instrument for measurement of the low frequency magnetic properties of thin layers is described. The difference signal from two opposed pick‐up coils, one of which contains the sample, is amplified, integrated, and amplified again to cause the vertical deflection of a cathode‐ray oscillograph to be proportional to the intensity of magnetization of the specimen. A signal is applied to the horizontal deflecting plates of the oscillograph to cause it to represent the applied magnetizing field in the region of the pick‐up coils. A large reduction in low frequency noise in the difference signal preamplifier is accomplished by use of a circuit similar to electrometer tube circuits. Noise introduced through integration of sharp peaked signals is reduced by use of first and third harmonic components in the magnetizing field current. A signal equal to noise is produced by a flux change of 75×10−6maxwell.

ISSN:0034-6748    

DOI:10.1063/1.1745820

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The trajectories of an electron with zero canonical angular momentum(p[open phi]−(erA[open phi]/c)=0)have been computed with third‐order accuracy for a 1/(1+x2) axial field shape. By suitably matching the above solutions with a set of similar solutions obtained by shifting the origin, it is possible to obtain the complete zero canonical angular momentum trajectories corresponding to the double lens problem in which the axial field shape approximates rather closely one that is physically realizable. The numerical computations illustrate several typical trajectories. Design considerations are given to illustrate the utility and limitations of the theory.

ISSN:0034-6748    

DOI:10.1063/1.1745821

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A micro‐electrophoresis apparatus based on interferometry is described. The interferometer consists of a modified Jamin arrangement, using only one plate while the other is replaced by a reflecting cell at right angles to the beam, thereby doubling the sensitivity. A cell filling requires 0.4 ml of solution. No thermostat is provided. Details of the optical and electrical equipment are given. The apparatus may also be used for diffusion experiments.

ISSN:0034-6748    

DOI:10.1063/1.1745822

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Air absorption in the conventional x‐ray fluorescence analysis equipment limits detection to elements heavier than calcium. To avoid absorption of the longer‐wavelength x‐rays from lighter elements, a vacuum system, or one filled with H2or He, is required. A vacuum apparatus has been developed for the analysis of elements from magnesium to titanium. It contains the x‐ray tube for exciting fluorescence; a specimen holder for six specimens; a collimator to limit the fluorescent radiation to a parallel beam; and a single‐crystal, Geiger counter spectrometer to analyze the radiation. A pressurized, double‐film, nitrocellulose window is used for the Geiger counter because the usual mica windows are opaque to radiation from elements lighter than sulfur. For calcium K&agr;, the increase in intensity resulting from evacuating the chamber is 100‐fold, with far greater increases for the lighter elements. Alkali halides and gypsum were tested as analyzing crystals. An application of the equipment to the measurement of sulphur in oil indicates that 0.5 percent sulfur can be detected with ±0.03 percent accuracy in 5 to 10 minutes.

ISSN:0034-6748    

DOI:10.1063/1.1745823

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The main purpose of this paper is to describe an apparatus for measuring the intensity of the focused electron beam as it passes through the final viewing chamber of the RCA electron microscope Model EMU. A portion of the electron rays serving to form the final image is collected by a metal probe; these electrons are passed to ground through a high resistor. The voltage developed across this dropping resistor is measured; it represents the intensity of the focused electron beam. Uses as an exposure meter in micrography and for metering the current density incident on the specimen are described.

ISSN:0034-6748    

DOI:10.1063/1.1745824

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Construction and filling procedures are described for neutron proportional counters filled to 101‐cm Hg of enriched BF3+20‐cm Hg of A.Examples are given of the plateau and bias curves obtained for different values of the gas multiplication. Characteristics taken at different times after filling are practically identical, which indicates that no deterioration occurs.The effect of the electron affinity of the BF3is discussed, and it is shown how the counter parameters affect the survival probability of the electrons, hence the quality of the pulse size distribution.It has been verified experimentally that negative ions produced by electron attachment are present in the counter gas.

ISSN:0034-6748    

DOI:10.1063/1.1745825

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A simple circuit for obtaining nuclear magnetic resonance absorption signals has been developed. Conventional modulation of the magnetic field is replaced by frequency modulation of the oscillator, a method which is technically convenient for the accurate measurement of magnetic fields in the range of 1000 to 18,000 gauss. The principles of operation and construction techniques are described in order that the user may readily duplicate results.

ISSN:0034-6748    

DOI:10.1063/1.1745826

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A gamma‐ray counter for liquid or solid samples is described. It uses an RCA 5819 phototube at room temperature with a thallium activated sodium iodide crystal in the shape of an annular ring. The gamma‐ray counting efficiencies of this counter for 2‐milliliter samples of Fe59, Co60, and I131are about equal to the beta‐particle counting efficiency of a mica‐window G‐M counter when counting thin samples. When the counter is heavily shielded, the background is about 160 counts per minute. The phototube operating voltage is not critical since over a wide range of operating voltage the counting efficiency and background count change only slightly. A directional gamma‐ray counter is also described.

ISSN:0034-6748    

DOI:10.1063/1.1745827

出版商:AIP    

年代:1951

数据来源: AIP