摘要:

Techniques are described for chemical purification and measurement of radiocarbon at natural levels (10−12curie/g or less). The chemical cycle has the following steps: (1) conversion of the starting material to carbon dioxide, by combustion or hydrolysis, (2) precipitation as calcium carbonate, followed by evolution of the purified carbon dioxide, (3) reduction to elementary carbon with magnesium turnings, and (4) extraction with hydrochloric acid and water to remove magnesium and magnesium oxide. The over‐all yield is about 85 percent, based on the carbon in the original sample.The counting is done in a screen‐wall counter, twenty‐four inches long, with an eight‐inch effective counting length. The sample (about 8.5 g) is mounted uniformly in an ``infinitely thick'' layer, on a split cylinder which can be shifted from ``sample'' to ``background'' position by sliding from end to end of the counter. An argon‐ethylene filling is used. The background of the counter (about 400 cpm, unshielded) is reduced to 4.5 cpm by the use of an eight‐inch thick iron shield and eleven anti‐coincidence counters, eighteen inches long. The calibration of the counter on an absolute basis is described. Its efficiency for a 20 mg/cm2layer of carbon, over a 400 cm2area, is 5.46±0.03 percent.

ISSN:0034-6748    

DOI:10.1063/1.1745896

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A simple exposure meter has been developed which measures directly the beam current reaching the fluorescent viewing screen of the electron microscope. By its use, the characteristic curve of a Kodak lantern slide plate has been plotted at constant intensity of electron beam. The value of beam intensity given by the exposure meter is confirmed by direct counts of electron tracks in the developed emulsion.

ISSN:0034-6748    

DOI:10.1063/1.1745897

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Physiological applications and technical limitations of the RCA 5734 mechano‐electronic transducer tube are discussed. A variable protecting mount adapts this tube to full‐scale ranges of force from 5 g to 2.5 kg or more with a 5 volt swing on all ranges. Fundamental resonance frequency varies linearly with the range, from 40 to 300 cps. Amplitude distortion is small and restricted to small deflections. Frequency and phase distortion depend on the driving tissue but are small for myographic phenomena whose highest harmonic is generally around 15 cps. Adaptation of the 5734 tube to ballistocardiography (1&mgr; to 10&mgr; swing) is also shown.

ISSN:0034-6748    

DOI:10.1063/1.1745898

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

It is widely recognized that the zero stability of dc amplifiers for measuring currents in the micro‐micro‐ampere region can be enhanced by the application of negative feed‐back. The promised advantages are often not fulfilled, however; and a design approach which emphasizes the economic exchange of amplifier gain for these benefits is outlined. In portable battery‐operated ionization chamber instruments, which are the main concern of this paper, it is not easy to achieve the loop gain needed for optimum performance; and a subsidiary reflexing scheme is adopted to overcome the limitation.In conclusion a practical instrument incorporating this improved circuit receives brief discussion and performance figures are given.

ISSN:0034-6748    

DOI:10.1063/1.1745899

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A magnetically compensated buoyancy balance is described. This instrument provides precise and continuous indications of gas and vapor densities falling in the range of 0 to 4 g/l. Measurements can be made at temperatures that are freely variable up to 220°C; mildly corrosive vapors can be handled; and the data are automatically corrected for adsorption effects. The long term reproducibility of the readings is 0.001 g/l.Magnetic compensation is attained by adjusting the current in an external electromagnet until this magnet's interaction with a small permanent magnet sealed in the balance beam restores the beam to a standard null position. The virtually linear relationship between this ``restoring'' current and the ambient vapor density is established by calibration with a standard substance. High constancy of calibration has been achieved through the use of a special beam suspension which, though extremely friction free, is unaffected by repeated and relatively severe mechanical and thermal shocks.

ISSN:0034-6748    

DOI:10.1063/1.1745900

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

Two calorimeters for the determination of the heat capacity of solid materials and heats of fusion are described. Typical data for potassium nitrate and for a solution of nicotinic acid in sulfuric acid are presented.

ISSN:0034-6748    

DOI:10.1063/1.1745901

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A continuous flow, tube viscosimeter is described which permits determination of viscosities and gel strengths of abrasive thixotropic fluids at temperatures up to 250°F. Provision is made for the introduction of treating chemicals into the closed system, while under pressure, without interrupting fluid flow. The new instrument employs a special rubber tube pump which maintains constant flow under various pressures and is unaffected by abrasive materials. Flow characteristics of the pump are discussed, and tube and Stormer viscosimeter data are compared.

ISSN:0034-6748    

DOI:10.1063/1.1745902

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A new phase‐sensitive detector circuit has been developed having unusually high balance stability. Its inherently fixed balance should make it useful in the many types of servo circuits which utilize phase detected error signals. It has been found to be particularly useful in nuclear resonance measuring circuits.

ISSN:0034-6748    

DOI:10.1063/1.1745903

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

The construction of a device known as a ``peaking strip'' and its use in the measurement of static and dynamic magnetic fields to an accuracy of approximately ±0.02 gauss is described. Fields up to several hundred gauss are easily measured using air‐cooled back bias coils. Using water‐cooled back bias coils, the range is extended to the kilogauss region.

ISSN:0034-6748    

DOI:10.1063/1.1745904

出版商:AIP    

年代:1951

数据来源: AIP

摘要:

A combination cloud chamber and ionization chamber in which the gas (argon at 51 lb in.−2saturated with iso‐amyl alcohol) is common to both chambers is described. The ion chamber, a 3¾in. diameter brass cylinder 8 in. in length open at both ends and having a116−in. central wire, is mounted coaxially with the cloud chamber, which has a useful rectangular volume 10 in.×10 in.×8 in. A burst occurring in the ion chamber generates a pulse which is used to trigger the expansion mechanism. Rapid reduction of the cylinder voltage from −1800 volts to ground, after electron collection is over, prohibits any appreciable motion of positive ions and thus permits observation of the tracks of the burst producing particles. In preliminary tests at sea level, cosmic ray bursts from cascade showers and from stars occurring in the wall (up to 10 prongs) and in the gas (up to 5 prongs) of the ion chamber have been observed.

ISSN:0034-6748    

DOI:10.1063/1.1745905

出版商:AIP    

年代:1951

数据来源: AIP