摘要:

We describe a method for measuring heat capacity of small specimens in the 1.5–10 K range by means of thermal relaxation over that range. Our methods of calibration and analysis make use of the simple properties of the thermal link between specimen and its surroundings, and offer several advantages. The cryostat has been used in magnetic fields of up to 4.5 T, and simple relationships for the magnetoresistance of heat links and thermometer have been determined. Measurement of the heat capacity of a 90 mg copper sample shows that the method is accurate to 1%.

ISSN:0034-6748    

DOI:10.1063/1.1136237

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

The steering of ion beamlets by aperture displacement is studied analytically and numerically for the case of triode extractors with large acceleration‐deceleration ratios. Here the acceleration‐deceleration ratio &egr; is defined by &egr;≡Va/Vb, whereVaandVbare the potentials applied to the second and third grids of the extractor, relative to the beam forming grid at zero potential. Both slit and round apertures are examined. When the second‐order effects of space charge and potential sag in the extractor are included in the analysis, good agreement with numerical simulations is obtained.

ISSN:0034-6748    

DOI:10.1063/1.1136238

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A fast valve which can inject gas pulses with durations from 25 to 400 &mgr;s into a vacuum system is described. Quantities up to 5 Torr l can be injected. A pressure rise time of ∼0.5 Torr/&mgr;s has been determined at the valve opening. A fast opening time is achieved by having a magnetically accelerated ring collide with a disk which is used as a vacuum seal. Gas pulse parameters have been measured with a fast ionization gauge.

ISSN:0034-6748    

DOI:10.1063/1.1136239

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Relative changes of inductance &Dgr;L/Lof a single layer coil surrounding a thin electrically conducting disk which can rotate about an axis perpendicular to the coil axis are studied experimentally as a means of measuring angular displacements. &Dgr;L/Lis found to be a strong function of disk diameter and is weakly dependent on the ratio of disk thickness to electromagnetic skin depth when this ratio is of the order unity. Values of &Dgr;L/Las a function of disk diameter are given for lead, brass and copper. Detection sensitivities using a resonant tank circuit or an astatic transformer are given in terms of &Dgr;L/Land it is shown that sensitivities of the order of 10−3to 10−4deg are practical. Application of this system to the Rayleigh disk and cryogenic environments are emphasized and an expression for the magnetic torque due to detection currents is given.

ISSN:0034-6748    

DOI:10.1063/1.1136240

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A microcomputer-based data acquisition and stabilization system is presented for piezoelectrically scanned plane-parallel Fabry-Perot interferometers which typically required some form of active stabilization system for long-term operation. The microcomputer takes the place of the programable ramp generator, multichannel analyzer, and stabilizer. The control algorithm developed here is workable against strong fluctuations of reference peak. Brillouin scattering spectrum from fused quartz is included to demonstrate the operation of the system.

ISSN:0034-6748    

DOI:10.1063/1.4755945

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Giemsa stain shows an intense and durable cathodoluminescence (CL) when studied at 20–30 kV with a quartz transmission light pipe–photomultiplier system in a scanning electron microscope. Clear CL images of Giemsa‐stained chromatin, nuclei, and chromosomes were recorded at low electron does (approximately 10−5–10−4C/cm2). Careful and control experiments have suggested that true cathodoluminescence of Giemsa has been recorded. The CL emission of Giemsa is attributable to one of its ingredients, eosin‐y, whose bromine molecules apparently act as radiation scavengers.

ISSN:0034-6748    

DOI:10.1063/1.1136241

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

A quadrature interferometer designed to measure radial electron density profiles in a long (3 m) small bore (2.8 cm) plasma tube, and described previously in this journal, has been further developed to have ten simultaneously operating channels. Achieving multichannel operation was essential to the accurate measurement of radial electron density profiles and required the design, fabrication, and implementation of two closely matched optical polished quartz tube sections. The first polished cylinder forms the cross tube scene beam window and is used as a sleeve to join ceramic tube sections that comprise the bulk of the 3‐m plasma tube. The second matched cylindrical section is placed in the interferometer reference beam to compensate for the strong negative lens affects of the cylindrical scene beam window. Design criteria for the cylindrical tube sections is discussed, the plasma tube assembly technique is given, and typical ten channel data is presented for a laser heated 3‐m‐long theta‐pinch.

ISSN:0034-6748    

DOI:10.1063/1.1136242

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

X‐ray collimators using grid patterns which are random offer several significant advantages over collimators using periodic grids. In particular, random array grid collimators (RAGC’s) eliminate the requirement that there be very closely spaced grids if a wide field of obscuration outside the central peak is desired. The RAGC should be less susceptible to systematic off‐axis leaks, and the RAGC has a better high energy response than a periodic grid collimator. The random array technique can also be used to produce converging or diverging collimators. A general theory is presented which predicts the angular response of a RAGC. It is shown that pure random arrays have two problems: there are strong wings in the response function and the patterns are not self‐supporting. Restrictions on the randomness of the pattern are suggested which eliminate these problems but at the price of putting an upper limit on the available throughput. However, even in the worst case, the upper limit for a two‐dimensional collimator is as high as 23%. In other cases, throughputs the order of 40% are possible with two‐dimensional collimators and of 50% with one‐dimensional collimators. These techniques can provide 10 arc second two‐dimensional collimators with a large collecting area. Suggestions are presented for easing the fabrication effort of the grids.

ISSN:0034-6748    

DOI:10.1063/1.1136243

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Theoretical expressions are derived for the signal‐to‐noise ratios in magnetic resonance experiments for the lock‐in and multiple‐scan direct detection schemes. Effects of noise character, post‐spectrometer filters, and modulation frequency are included in the analysis. The theoretical results are found to be in good agreement with experiment for the specific case of nuclear acoustic resonance in a metal single crystal.

ISSN:0034-6748    

DOI:10.1063/1.1136244

出版商:AIP    

年代:1980

数据来源: AIP

摘要:

Specimens are placed in sealed chambers to which scintillation cells are attached and radon concentrations,R, are measured in the air of the chambers at intervals thereafter by inserting the cells into scintillation counters. The Rn emanation rate is calculated from the rate at whichRincreases, or from the maximumRreached. Uncertainties are estimated to be 10%–25%, detection limits 10−19Ci cm−2s−1or 5×10−19Ci g−1s−1. Effects of disequlibrium in the Rn decay chain, or the diffusion rate of Rn, and of Rn leakage are considered. Powdering a rock usually has little effect on its emanation rate per gram.

ISSN:0034-6748    

DOI:10.1063/1.1136245

出版商:AIP    

年代:1980

数据来源: AIP