摘要:

A mounting of metallic resistivity specimens is described which allows low temperature electron irradiation within the vacuum system of the particle accelerator. The heat generated in the specimens during irradiation is transferred to the specimen holder via solderable sapphire plates which provide a good thermal contact and also the electrical insulation required. The temperature distribution in the specimens is calculated for general parameters. The maximum specimen temperature can be monitored continuously during the irradiation. Good agreement is found between calculated and measured maximum temperature.

ISSN:0034-6748    

DOI:10.1063/1.1684281

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A dynamic bomb calorimeter of a novel type has been developed for the purpose of thermochemical investigations of organometallic and inorganic compounds using the most advanced methods. The calorimeter combines the operating principles of the two existing types of calorimeters (liquid and massive) and enables to combine the advantages and to eliminate disadvantages of the two types. In addition, it is best suited to the requirements of calorimetric theory.

ISSN:0034-6748    

DOI:10.1063/1.1684282

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

This paper describes the design of a precision, programmable impulse generator capable of producing repetitive impulse trains of accurately defined parameters, selectable over a wide range. The generator was conceived for the specific purpose of gating the audio modulation of the applied magnetic field in an HA 100 Varian NMR spectrometer. The basic circuit is much more general, however, and may be used for the generation of a wide variety of impulse trains. The present configuration is capable of producing repetitive trains of one &pgr; pulse followed by several equidistant 2&pgr; pulses. The width of these pulses, their number, their separation, and the repetition rate of the sequence are independently selectable. The selections may be made manually or by remote control from an on‐line digital computer. All times are increments of a basic clock period, derived in our case from the 16.7 MHz crystal oscillator of the spectrometer. Construction is modular and TTL integrated circuits are used throughout for simplicity.

ISSN:0034-6748    

DOI:10.1063/1.1684283

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

We describe a liquid helium temperature regulator of unusually simple design, operation, and construction utilizing miniature solid state operational amplifiers. The combination of a unique saturating amplifier and an analog multiplier type of cross‐correlation phase detection circuit eliminates fast risetime signals and switching transients, enabling the regulator to be used in a low noise shielded environment. The circuit is of the conventional ac Wheatstone bridge type using a carbon resistance thermometer for the sensing element and providing a proportional heater feedback of >1 W to the bath. The balanced input circuitry has been optimized for thermometer resistances between 500 &OHgr; and 5 k&OHgr;, and the regulator is capable of detecting a temperature change of 30 &mgr;K at a thermometer power dissipation of <3×10−11W. Regulation of a superfluid4He bath to better than ±4 &mgr;K for periods greater than 30 min has been achieved at a thermometer power of <5×10−9W, with a response time of 0.1 sec. Owing to the high gain and broad bandwidth of this regulator, it is adaptable to a wide variety of other situations, such as a sample mounted on a copper block outside the bath, without encountering the usual problems of excessive power dissipation, instability, and thermal oscillations.

ISSN:0034-6748    

DOI:10.1063/1.1684284

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The wall shift of the atomic hydrogen maser has been determined by a series of 18 measurements on a variety of storage bulbs coated with FEP Teflon. The result is −24.3 mHz for a 15.25 cm (6 in.) bulb at 30°C. This is about 25% smaller than the previous values. It is most likely that a change in the properties of the Teflon caused the difference, which is far larger than possible measurement errors. The systematic correction due to the entrance stem has been estimated using several independent models. The fractional variation of the wall shift with temperature has been measured in the range 27 to 56°C and found to be (−11.4±0.4)×10−3/deg at 35°C. It is suggested that care be taken in applying the value of the wall shift found by one laboratory to bulbs prepared by different techniques or with different samples of Teflon.

ISSN:0034-6748    

DOI:10.1063/1.1684286

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The production of a polarized3He+ion beam by Stern‐Gerlach splitting of a neutral atomic3He beam requires slow moving atoms because of the small nuclear magnetic moment. A miniature supersonic nozzle cooled to liquid helium temperatures has been used to produce intense slow beams of both3He and4He. Their measured intensities are 1×1018and 0.7×1018atoms/sr. sec, respectively, with corresponding most probable velocities of 310 and 270 m/sec and velocity full widths at half‐maximum of typically 50 m/sec.

ISSN:0034-6748    

DOI:10.1063/1.1684287

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A description is given for the correct assembly and operation of the variety of components of a zonal ultracentrifugation system, useful for several kinds of zonal particle separations. Simple, reproducible means are provided for the storing, volume measurement, and output control of the gradient, sample, and overlay solutions. These fluids do not come in contact with lubricated parts. The liquid flux along the lines is free from pressure pulses or local areas of turbulence. The various solutions are kept cold without installation of the whole setup in a temperature controlled environment. The system of connections is designed to be smooth and compact, with a minimum of dead spaces. The type and size of the necessary tubing connectors, stopcocks, etc. was chosen as to preserve lamellar flux of gradient solutions and to insure permanent tightness. The proposed system can be easily disassembled for the purpose of cleaning and a large number of experiments did not affect its hermeticity. All parts in contact with solutions are autoclavable for sterilization.

ISSN:0034-6748    

DOI:10.1063/1.1684288

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

For the investigation of the interaction between traveling magnetic fields and plasma it is necessary to excite long wave trains with high amplitudes on transmission lines. A special feedback circuit is described which permits generation of these wave trains with a relatively economical power supply. Field amplitudes of 2 kG at 1 MHz can be excited for pulse times of several milliseconds, using a 5 MW pulsed transmitter by reinjecting the output energy of the line at the input. The transient phenomena which depend upon the line losses and on a special method of self‐excitation of the transmitter are calculated.

ISSN:0034-6748    

DOI:10.1063/1.1684289

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

An electron gun is described which will provide a current of 0.16 &mgr;A at 2 eV, in a beam of convergence half‐angle 0.03 rad, 2.5 mm in diameter at the space charge limited waist. At electron energies above 12 eV, the beam current is 2.7 &mgr;A and independent of energy.

ISSN:0034-6748    

DOI:10.1063/1.1684290

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Two methods for the measurement of the drift velocity of ions in liquids are described in detail. Both the dc voltage applied across the drift length, and the time or delays involved in the methods can be measured with an accuracy better than 0.1%. Moreover the time of flight is deduced with good accuracy from an extrapolation of a linear plot of the ionic current as a function of time. As a result, drift velocity or mobility measurements with an accuracy of 1% or better can be made. Drift velocities from 0.1 up to 3000 cm/sec, in electric fields up to 25 000 V/cm, can be measured.

ISSN:0034-6748    

DOI:10.1063/1.1684229

出版商:AIP    

年代:1970

数据来源: AIP