摘要:

The operation of a heat switch is described in which the conducting substance is liquid He II and in which the nonconducting state is achieved by displacing the He II with a poor conductor, e.g., Teflon. The switch is well suited for use in the first stage of a magnetic refrigerator operating with a bath temperature near 1°K. At this temperature it performs better than a lead superconducting switch.

ISSN:0034-6748    

DOI:10.1063/1.1717119

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Artificial pitch‐bonded graphite is known to exhibit an extremely large variation of heat conductivity with temperature. It is both rigid and strong, and below 1°K its heat conductivity is exceptionally small. For these reasons we have found it to be an ideal support material for use within the adiabatic enclosure of a cryostat operated below 1°K. Furthermore, above liquid nitrogen temperature graphite is an excellent heat conductor, and when used in parallel with a lead heat switch, it proves unnecessary to admit exchange gas during the precool period. The graphite exhibits a strong pumping action for helium gas at low temperatures.

ISSN:0034-6748    

DOI:10.1063/1.1717120

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The resolution of CsI(Tl) for Po210alpha particles has been measured as a function of crystal thickness. The best resolution of a ½‐in. diam cylindrical crystal was obtained for a thickness of 0.38 mm, and the effect of thickness on the resolution is discussed. Based on the proposed model, a conical crystal was designed, which yielded a line width of 1.8% for Po210alpha particles with a selected photomultiplier tube.

ISSN:0034-6748    

DOI:10.1063/1.1717121

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A transistor marginal oscillator circuit for nuclear magnetic resonance measurements is described. The circuit is self‐contained, simple, nonmicrophonic, and noncritical and has been used in a variety of measurements in both research and instructional laboratories. The sensitivity of the device is approximately one‐half that of a Pound‐Knight‐Watkins system.

ISSN:0034-6748    

DOI:10.1063/1.1717122

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The design of a modified cathode follower circuit which possesses an extremely linear response and a voltage gain of essentially unity is presented. Analysis of the circuit shows that, in principle, the harmonic distortion may be made arbitrarily small, and at the same time the voltage gain may be made arbitrarily close to unity. The modification is applied to a White cathode follower where the increase in linearity and gain is accompanied by a decrease in the output impedance. A practical modified White follower having a measured intermodulation distortion of 2×10−5%, a calculated voltage gain of (1−10−6), and a calculated output impedance of 2×10−3ohms is given.

ISSN:0034-6748    

DOI:10.1063/1.1717123

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A six‐meter radius bent‐crystal spectrograph for the precision measurement of nuclear gamma‐ray wavelengths has been designed, constructed, and placed into operation at the Massachusetts Institute of Technology. This instrument is particularly well suited for directly measuring neutron capture gamma rays produced by samples placed in the through port of the MIT research reactor. The spectrograph is designed to measure wavelengths of gamma rays in the energy region from 0.1 to 4.0 Mev with an estimated precision that varies from about 0.01% at 0.1 Mev to 0.3% at 4 Mev. Photographic methods are used to record the gamma‐ray lines on the focal circle. A bent crystal is used to diffract and focus the gamma rays. Line width and efficiency data have been obtained for the (310), (003), and (006) planes of quartz. The efficiency of the instrument is quite low. In order to record a line at 2.0 Mev an exposure time of about 6000 curie hours is required.

ISSN:0034-6748    

DOI:10.1063/1.1717124

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A pressure gauge is described that can be encased in a small‐bore plastic cathether. The small size permits insertion directly into the heart. The unit uses a two‐section piezoresistive element, operated as a cantilever. The sensitivity of the gauge is 0.16 mv/v/psi, and the frequency response is flat from 0 to 400 cps.

ISSN:0034-6748    

DOI:10.1063/1.1717125

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Diffusion and sputtering techniques are described for applying low resistance, highly transparent, antireflecting, electrical contacts to CdS. The diffusion process entails heating CdS for several minutes in the presence of indium vapor. The resulting crystal surface resistance has been adjusted to range as low as 12 ohms/square without any observable crystal discoloration. The sputtering process employs an 82–18% indium‐tin alloy that is placed onto the crystal surface using oxygen as the sputtering atmosphere. The resulting film is Sn‐doped In2O3, measuring 100–150 ohms/square, and showing 80–100% transmittance from 4600 to 20 000 A.

ISSN:0034-6748    

DOI:10.1063/1.1717126

出版商:AIP    

年代:1960

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1717128

出版商:AIP    

年代:1960

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1717130

出版商:AIP    

年代:1960

数据来源: AIP