Contains reports on three research projects

Bitter, F.

Brossel, J.

Plotkin, H. H.

Sagalyn, P. L.

Wimett, T. F.

DSpace@MIT

VII. MAGNET LABORATORY RESEARCHProf. F. BitterN. I. Adams IIIT. F. WimettA. NUCLEAR MAGNETIC RESONANCES1. The New Barrel-Type ElectromagnetThe installation is now complete.teristics of the new electromagnet forJ. BrosselP. L. SagalynThe graphs in Fig. VII-1 summarize the charac-a power input up to 20 kw.i II i4Z1/ X/ ao-0 i,,FIELD IN KILOGAUSS4 5 6 7 8, /. .e I I -, ' 9II INCH DIAMETER POLE FACESI I/ I/ I I / I I 10/ v /I /r / 23,0 10 20 30 40 50 60 70 80 90 I00CURRENT THROUGH EACH OF 1060 TURNS IN AMPERES0 0.2 0405 10 2 3 4 5 6 8 10 12 14 16 18POWER IN KILOWATTSGraphs showing fields obtainable with the new magnet.F. Bitter2. Deuteron-Proton Moment RatioThe deuteron resonance has been observed at a thousand gauss in the Helmholtzcoils, using a fairly large sample of heavy water with added paramagnetic ions. Thesignal-to-noise ratio through the "lock-in" amplifier was of the order of fifteen-to-one,which was somewhat lower than expected. Work is therefore in progress to improve-31-Fig. VII-1I 1 _I II '(VII. MAGNET LABORATORY RESEARCH)this ratio which, it is believed, is not limited by the low-noise electrical circuits usedbut perhaps by excess paramagnetic ions. This signal-to-noise ratio may prove to bethe limiting factor in this low-field measurement.Radio frequency equipment is being revised and new circuits are being constructedby means of which both proton and deuteron driving frequencies will be generated fromharmonics of a low-frequency, crystal-controlled oscillator. This simplifies the prob-lem of determining the ratio of the two resonance frequencies and at the same time main-tains the ratio of the driving frequencies practically fixed once they are adjusted. Thelatter is very important in a precision measurement as it allows for circuit adjustments,such as those affecting shapes, without constant rechecking of the frequency ratio.T. F. WimettB. DOUBLE RESONANCE EXPERIMENTS1. Effects in MercuryThe line shape of the resonance lines has been computed under varied conditions forthe mercury atoms, Hg 199 and Hg 201, and even isotopes.The cases concerned area. No magnetic orientation in the ground state (case of a very shortrelaxation time, or of a constant supply of atoms entering the spacewhere optical excitation takes place).1) The line shape has been obtained for resonances within aZeeman pattern for each of the hfs levels of each isotopefor T or <r+ optical excitation, Tr and o detection, for allpossible values of the r-f field.2) The intensity at resonance has been obtained for resonancesbetween hfs levels of the odd isotopes for Tr and o-+ opticalexcitation and detection, for large values of the r-f field.The intensities obtained in that case are small.b. Magnetic orientation in the ground state.1) The intensities at resonance have been calculated in all theabove cases for large values of the r-f field.2) The line shape has been obtained for very small values of ther-f field in the case of Tr excitation.The above calculations assume broad line excitation and do not take into account theeffect of collisions on the degree of polarization of the excited state (conditions easilymet with in practice). The effect of magnetic orientation in the ground state is mostpronounced with o+ excitation, where whole patterns disappear and where some lines areconsiderably enhanced. F. Bitter, J. Brossel-32-(VII. MAGNET LABORATORY RESEARCH)2. Effects in the AlkalisComputations were carried out to determine the feasibility of measuring the nuclearelectric quadrupole moments of the alkalis by the double resonance method. (This in-volves measuring the hyperfine separations of the P3/2 level with sufficient accuracy todetect deviations from the interval rule. ) Calculations were made of optical line inten-sities, radio-frequency line widths, and estimates were made of the deviations from theinterval rule to be expected. The conclusion was reached that sodium and cesium werethe two most favorable elements on which to begin research. Sodium will be close tothe limit of resolution but cesium appears to be well within it.A proton resonance circuit has been constructed which will enable us to check thefield of our solenoid in the vicinity of 80 gauss. P. L. SagalynC. MAGNETIC PROPERTIES OF SOLIDSThe Rare EarthsPrevious experimental results as well as theoretical considerations lead one toexpect that some of the rare earth elements may have very interesting and useful mag-netic properties at low temperatures. A program is being initiated to investigate therare earth metals at liquid helium temperatures. The Curie points of those that becomeferromagnetic and their saturation magnetization are to be measured. A small sensitiveelectrodynamic balance has been built for the measurement of magnetic susceptibilitiesof very small samples by the Faraday method, and initial calibration curves have beenobtained.Preliminary investigations are to be carried out with one of the existing magnets inthe M. I. T. Magnet Laboratory. For final measurements, Helmholtz coils capable ofproducing 30, 000 gauss with independently controlled gradient coils are to be used.This magnet is being constructed under the supervision of Prof. A. R. Kaufmann.F. Bitter, H. H. Plotkin-33-

Magnet Laboratory Research

http://dspace.mit.edu/bitstream/1721.1/50895/1/RLE_QPR_019_VII.pdf

Magnet Laboratory Research

Abstract

Similar works

Full text

Available Versions

DSpace@MIT