摘要:

A liquid helium scintillation counter has been constructed and used in analyzing the spin polarization of neutrons in the range of energy near 20 Mev. Details of construction and operation of the device are described. The glass scintillation flask contains 8 moles of helium, and is supplied by a reservoir which provides 7 hours continuous operation under experimental conditions. The pulse‐height spread for a source of natural alpha particles is approximately 25%. It is found that the attenuation of the helium scintillation light in the liquid is not appreciable at a distance of 10 cm, while the wavelength is observed to be less than 1600 A. Consequently, use of a fluorescent material as a wave shifter within the helium flask is required. The intensity of the wave shifted helium light compares favorably with that from CsI(Tl). The helium counter is used in coincidence operation with a plastic scintillator neutron detector. Under these circumstances, the width of a gated helium recoil pulse‐height distribution is generally less than 30%. The geometry and electronics for a typical neutron polarization experiment are described.

ISSN:0034-6748    

DOI:10.1063/1.1717200

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

This paper describes a mechanical method of producing polished spheres constant in radius to about one microinch. Spheres have been made to this accuracy in anisotropic materials such as yttrium iron garnet and also in steel, sapphire, quartz, and ceramic. The method has not been fully exploited; it may yield even further improved surfaces and also be found suitable for softer materials. The principle may also have application for finishing concave and convex mirror and lens surfaces of small radius. The instrument is also suited for the rapid production of spheres to a lesser degree of accuracy.

ISSN:0034-6748    

DOI:10.1063/1.1717201

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A pulsed X‐band electron paramagnetic resonance spectrometer suitable for observing spin echoes in the sub‐microsecond time domain has been designed and operated. Cryogenic apparatus makes possible measurements in the 300−1.6°K temperature range. System design considerations are discussed and circuit schematics are presented. Results of measurements of the spin‐lattice relaxation timeT1and the spin‐spin relaxation timeT2are reported for several paramagnetic substances. Application of such instrumentation to information storage is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1717202

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A scintillation detector with an area of 4 m2and a transistorized amplifier with a logarithmic height‐to‐time converter are described. The detector employs tapered sheets of plastic scintillator and a single 16‐in. photomultiplier mounted in a pyramidal can, coated inside with a commercial 90% reflecting white paint. The response is uniform to within 5% over the entire sensitive surface. A traversal by one relativistic charged particle (energy loss ∼10 Mev) generates approximately 20 photoelectrons in the photomultiplier. The amplifier and converter yield a rectangular pulse whose duration is accurately proportional to the logarithm of the input pulse amplitude over a range of four decades. The gain is constant to 1 db from 10 to 45°C, and the equivalent noise input is 200 &mgr;v.

ISSN:0034-6748    

DOI:10.1063/1.1717203

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

An instrument is described which has the property of accurately measuring the magnitude of magnetic field to 0.05 &mgr;gauss at the center of a set of Helmholtz coils while simultaneously reducing by a factor of 600 stray fluctuations of the field caused by drift in the earth's magnetic field, power supply anomalies, and external magnetic noise generated by the motion of magnetic material. The device utilizes an optically pumped metastable helium magnetometer which senses the total magnetic field. The output signal of the magnetometer is used to control the current in the Helmholtz coils. The new features of this device are (a) its ability to discern and hence control magnetic field variations at the microgauss level and (b) its scalar character enabling the field control to be accomplished with a single set of coils

ISSN:0034-6748    

DOI:10.1063/1.1717204

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A feedback system is described for canceling magnetic fields resulting from alternating currents. The design features of an operational amplifier are offered. In addition the nature of the phase shift contributed by mutual inductance elements in the feedback path is discussed. Magnetic fields with a flux density of one milligauss can be reduced by about two orders of magnitude with the system.

ISSN:0034-6748    

DOI:10.1063/1.1717205

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A shaft is supported by means of a laminated rotor which is magnetically suspended inside a four pole laminated stator. The diameter of the rotor is 1¾ in. and the radial clearance is 0.002 in. The position of the shaft is sensed with the aid of four quadrant electrodes which surround the shaft with a small radial clearance. Each electrode provides part of the tuning capacity of an rf tuned circuit which is tuned to one side of its resonance peak with respect to an rf generator. The rf signal is detected and amplified to provide the control current in the corresponding winding on the stator. The bearing was found to run smoothly up to 23 000 rpm. With further development, a reliable and useful bearing should result. The use of electromagnetic bearings would appear to be justified in special applications where conventional bearings cannot be employed. They would appear to be useful at cryogenic temperatures, in vacuums, and in applications where contamination with lubricants must be avoided. Since there is no wear the life should be indefinite.

ISSN:0034-6748    

DOI:10.1063/1.1717206

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Avalanche transistor circuits offer several features which are desirable in fast counting systems; simplicity, versatility, fast response, and large charge gain. This paper describes the evolution of avalanche circuits which retain the desirable features but which do not suffer from the two defects of the basic avalanche circuit: low duty cycle, and a pulse propagation delay which is dependent upon input. Several transistor types which are suitable for fast avalanche circuits are compared and comments are made about the application of these transistors. Described also are several useful circuits which may be constructed with avalanche transistor techniques.

ISSN:0034-6748    

DOI:10.1063/1.1717207

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A high‐speed valve has been designed for opening a deLaval nozzle in times less than 10−3sec.

ISSN:0034-6748    

DOI:10.1063/1.1717208

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The long dead time and cathode erosion of the Rosenblum corona‐spark counter for heavily ionizing radiations have been overcome by forming only the streamer stage of the spark by the addition of a few percent of some diatomic gas to nitrogen‐contaminated argon in corona detectors of coaxial wire‐cylinder geometry. The amplitude of the streamer pulse at the anode wire is large (>10 v) and distinctly greater than background, with a risetime of about 1 &mgr;sec. The recovery of the anode potential is made rapid (typically 5 &mgr;sec) by a simple RC anode circuit. Efficiencies for streamer formation of 7.5% for U234&agr; particles, 1.5% for (n, B10) &agr;'s and 5% for (n, U235) fission fragments have been obtained in coated counters.

ISSN:0034-6748    

DOI:10.1063/1.1717209

出版商:AIP    

年代:1961

数据来源: AIP