摘要:

The limitations of alpha counters using air in the proportional amplification region were investigated with a view toward a better design that would provide improved performance and reliability. A new detector is described which incorporates a shielded guard‐ring insulator assembly that provides freedom from insulator failure at high humidities. It is believed that spurious pulses also arise from the effect of humidity on the conductivity of foreign particles adhering to the anode wires. Reducing the relative humidity (rh) by the use of a small heater which maintains the detector 20°F above room temperature prevents this type of failure and provides reliable operation at 98% rh. The associated amplifier and discriminator were designed to detect the slow components of the ionization pulses associated with the transit time of negative oxygen ions. The resulting efficiency is 39% of the total disintegrations, with a plateau of over 150 volts having a slope of less than 4% per 100 volts.

ISSN:0034-6748    

DOI:10.1063/1.1715207

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Apparatus and procedures for conversion of sample carbon to carbon dioxide, quantitative hydrogenation of carbon dioxide to methane, and radiocarbon assay of the methane are described. Two sizes of counters are used. At the operating pressure of two atmospheres, the larger size contains 0.85 g of carbon and the smaller 0.22 g. If the sample and background are both counted for 24 hours in a 0.85‐g counter, a sample 34 000 years old (26 000 years old in the 0.22‐g counter) gives a C14count equal to twice its standard statistical error. If desired, this method can readily be adapted to larger samples with a consequent increase in the maximum measurable age.

ISSN:0034-6748    

DOI:10.1063/1.1715208

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A divergent beam of monoenergetic charged particles can be refocused by a homogeneous magnetic field whose sharply defined boundaries are straight lines or circles. The transverse aberration of order &agr;3at the image point is evaluated and a general third‐order focusing condition is given. Design equations for third‐order instruments are obtained and the results presented graphically. Many third‐order focusing designs follow, both symmetrical and asymmetrical.

ISSN:0034-6748    

DOI:10.1063/1.1715209

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A dc amplifier that uses the condenser‐charging principle of electron counting has been constructed and used for the measurement of stars as faint as magnitude 20.8 with the 82‐inch and 100‐inch telescope. The device is simple (15 tubes), will measure stars of any brightness permitted by the photomultiplier, and has a simple automatic recording feature using a Brown recording meter.

ISSN:0034-6748    

DOI:10.1063/1.1715210

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Weak hyperfine satellites have been observed with very large signal‐to‐noise ratios when microwave power at frequencies corresponding to these satellites is introduced into a ``maser'' which is oscillating at the frequency of the main inversion line of NH3. The satellite transitions are accompanied by a reduction of the amplitude of oscillation at the main‐line frequency. A composite oscilloscope trace showing the structure of the weakest of the four quadrupole satellites associated with the 3–3 inversion line of N14H3is presented.

ISSN:0034-6748    

DOI:10.1063/1.1715211

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A new type of ion gun is described which greatly improves the resolution of a nonmagnetic time‐of‐flight mass spectrometer. The focusing action of this gun is discussed and analyzed mathematically. The validity of the analysis and the practicability of the gun are demonstrated by the spectra obtained. The spectrometer is capable of measuring the relative abundance of adjacent masses well beyond 100 amu.

ISSN:0034-6748    

DOI:10.1063/1.1715212

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Scattering of the electron beam by the residual gas in the vacuum chamber is calculated for the 1 Bev strong focusing Cornell Mesotron. It is shown that the elastic scattering by the nucleus and the inelastic scattering by the atomic electrons are the only important contributions to the loss due to the presence of gas. These two effects are calculated in detail. Radiation and space charge effects are not discussed. Because of the small scattering angles involved the details of the screening by the atomic electrons must be taken into account accurately. Multiple scattering is shown to be of little importance because of the damping of the beam oscillations as the energy increases. The calculations are carried out for two different injection conditions and little difference is found between them as far as the loss due to the scattering itself is concerned. The numerical results for the Cornell Mesotron show that about half of the beam gets lost at a vacuum of 5×10−6mm Hg. The scattering losses will depend on the field lattice of the synchrotron.

ISSN:0034-6748    

DOI:10.1063/1.1715213

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A fast neutron coincidence spectrometer utilizing stilbene scintillators is described. The principle of the spectrometer is based upon the pulse‐height analysis of the recoil protons resulting from a 45 degree scattering of the incident neutron beam. This is achieved by requiring the scattered neutron to be recorded in a secondary ring of ten stilbene scintillators. With delays corresponding to a fixed time of flight, a coincidence between the primary and secondary crystals gates the primary pulse. At 4 Mev the efficiency is of the order of 10−4per incident neutron, and the pulse‐height distribution has a width at half‐maximum of 17%. The corresponding energy width is 10%. The time‐of‐flight characteristic is used to reject gamma rays. Limitations caused by accidentals and pulse‐height resolution are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1715214

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A description is given of a three‐terminal cell for dielectric measurements on polymeric materials over a wide temperature range. Use is made of a lightly spring‐loaded, floating electrode to maintain good electrical contact with the specimen when it expands or contracts thermally. A differential‐capacitor, built into the movable electrode, is used with a simple detector circuit to indicate the position of the electrode with respect to its micrometer‐driven carriage. Simultaneous measurements can be made of cell capacitance and electrode separation. The latter can be determined with a precision of better than 10−4inch. Provision is made to confine the specimen when it softens at temperatures above its glass‐transition temperature. The cell has been operated successfully at frequencies between 20 cps and 1 Mc and at temperatures between 20 and 200°C.

ISSN:0034-6748    

DOI:10.1063/1.1715215

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A device is described which converts a train of electrical impulses into a succession of hyperbolic wave forms of amplitude proportional to the interval between successive impulses. These wave forms when applied to an oscilloscope furnish a display capable of showing rapid changes in the frequency of an electrical signal. Unlike conventional counting‐rate meters response to sudden changes in frequency is immediate so that averaging over several cycles is not required. The instrument as constructed operates in the lower audio‐frequency range and is being used in the study of the electrical discharge of single fibers of the optic nerve.

ISSN:0034-6748    

DOI:10.1063/1.1715216

出版商:AIP    

年代:1955

数据来源: AIP