Contains reports on three research projects

Redi, O.

Stroke, H. H.

Tomlinson, W. J., III

Walter, W. T.

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IV. NUCLEAR MAGNETIC RESONANCE AND HYPERFINE STRUCTUREProf. F. Bitter R. Arndt H. C. PraddaudeProf. J. S. Waugh J. C. Chapman 0. RediDr. L. C. Bradley III J. K. Flicker C. J. Schuler, Jr.Dr. H. H. Stroke T. Fohl W. W. SmithDr. W. T. Walter W. D. Halverson W. J. Tomlinson IIIDr. J. F. Waymouth E. R. Hegblom C. G. WadeJ. D. MacomberA. SPINS, MOMENTS, AND ISOTOPE SHIFTS IN NEUTRON-DEFICIENTMERCURY ISOTOPESA thesis with this title has been submitted by W. J. Tomlinson III to the Departmentof Physics, Massachusetts Institute of Technology, July 18, 1963, in partial fulfillmentof the requirements for the degree of Doctor of Philosophy.W. J. Tomlinson III, H. H. StrokeB. SPIN AND NUCLEAR MOMENTS OF Hg 2 0 3Optical spectroscopic measurements were made of the splittings in a magnetic field203 3 21of one Hg hyperfine-structure component in the 2537 A (6s 6p 3P 1 -6s 1S o) Hg linein absorption. From these measurements a spin assignment was made, and a set ofmutually dependent values of the magnetic dipole and electric quadrupole hfs interactionconstants A and B was determined. 1 Additional data needed to determine the values203of A and B was obtained from measurements of Hg hyperfine structure in 2537 A,3 3 o3 24047 A, (6s7s S - o) and 4358 A ( S1- P 1 ) Hg emission lines. The high-resolutionspectra were obtained with the use of a 10-in. plane diffraction grating (M. I. T. No. 97)mounted in a 36-ft focal-length mirror monochromator.In earlier hfs investigations of other radioactive mercury isotopes, transmutationreactions were used to produce Hg isotopes of sufficiently high isotopic purity and quan-tity (=1013 atoms) for spectroscopic work with electrodeless lamps. Only pile-producedHg 2 0 3 (ratio of Hg 2 0 3 to natural mercury z3 X 10-4) was available for this experiment,since adequate quantities were not obtainable by transmutation reactions. Generally itis not possible to measure weak hfs lines in the presence of strong ones if the ratio ofintensities is in excess of 100:1 (because the stronger line produces a diffraction patternthat has an intensity approximately 1/100 of the line in the region of extent of the hyper-fine structure); hence this Hg 2 0 3 could not be used for a study of emission spectra.203Pile-produced Hg , however, was adequate for measurements in the absorption spec-trum in which this difficulty is not incurred. Some emission-spectrum measurementswere made possible through the use of Hg 2 0 3 enriched electromagnetically at the ArgonneNational Laboratory, in which the ratios of Hg 2 0 3 to the other mercury isotopes presentranged from =1/10 to =1. Sufficient mercury was obtained to fill successfully two elec-trodeless lamps with approximately 1014 atoms. The presence of other Hg isotopes inQPR No. 71(IV. NUCLEAR MAGNETIC RESONANCE)these lamps made the measurement of all the Hg 2 0 3 hfs components impossible, becauseof overlap with stable Hg components.198For the absorption measurements, a pressure-broadened Hg lamp was used as thesource for the continuum background. The absorption cell, 10 cm long and 14 mm indiameter, was placed in a magnetic field and heated to =100 0 C. This was found to be the203optimum temperature for producing sufficient Hg absorption without producing anexcessive width of the natural Hg absorption. The cell contained approximately 5 X 1014203Hg atoms.A spectrum of the 2537 A line was obtained in emission. It revealed only one new-1hfs component, removed approximately 0.5 cm-1 from the stable Hg hyperfine-structure203spectrum. In view of the high intensity of this component, if the hfs of Hg is resolved,any other components must be overlapped by the natural mercury hfs. Because of this203fortuitous position of the isolated Hg component with respect to the stable mercury,it was apparent that the magnetic-field splitting of the observed line could be studied in203an absorption spectrum experiment by using unenriched Hg 2 0 3 The absorption line wasobserved, first, at zero field, and then magnetic-field splitting measurements were madeat 17 values of the field between 2250 and 10, 200 gauss. Also, five observations weremade in the low magnetic-field region, 0-2250 gauss, where the components were notFig. IV-1.-3/2 -1/2-0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7RELATIVE TERM VALUE (cm- I )Magnetic-field dependence of the P I , F = 3/2 level of Hg03 drawn for-1 -1A = 0.165 cm , B = -0.010 cm . The experimental points are indicated.Error limits for individual points are approximately ±0. 005 cm-1Error limits for individual points are approximately ±0. 005 cmQPR No. 71(IV. NUCLEAR MAGNETIC RESONANCE)resolved. The splitting as a function of the magnetic field is shown in Fig. IV-1.From the observed splittings it is concluded that with only four MF components, the203observed Hg hfs component originates from an F = 3/2 level, where F = I + J,with I the nuclear spin, and J the electronic angular momentum (J=1). The spin assign-ments I = 1/2 and I = 3/2 are definitely excluded, since the qualitative behavior of theirF = 3/2 levels as a function of the magnetic field is completely different. For example,for I = 1/2, F = 3/2 (and in fact for any F = I + 1 level) there are two straight lines withslope togJ (with 4o = Bohr magneton, and gj = electronic g-factor) for outer components,and for I = 3/2, F = 3/2, the highest energy component would always have the same signof slope and would not display the change of sign observed at ~3000 gauss (Fig. IV-1).The possibility that more components exist in the magnetic-field pattern than weredetected, because of (a) an intensity that is too low, or (b) overlapping of several com-ponents, was investigated and eliminated on the basis of the observable intensities, thelinewidths of the components, and the positions of the other hfs components. We con-cluded therefore that the only consistent spin assignment is I = 5/2.Our results for the magnetic dipole and electric quadrupole hfs interaction constantsA and B are:-lA = 0.165±0.004 cm--1B = -0.010±0.015 cm-The magnetic dipole moment obtained from the known ratio of 4 (Hg 0 1) toA (Hg20 1) isi = 0.833 0.020 nm.O. Redi, H. H. StrokeReferences1. The computations were carried out on the IBM 7090 computer at the ComputationCenter, M. I. T., by using the program "Hyperfine 3" supplied by D. H. Zurlinden, AtomicResearch on Radioactive Atoms - Hyperfine 3, Lawrence Radiation Laboratory, Univer-sity of California, Berkeley, August 1, 1960.C. MAGNETIC SCANNING OF MERCURY 193Two unsuccessful attempts have been made to optically pump Hg 19 3 (6 hour) anddetermine its nuclear magnetic moment. A number of scanning curves, however, havebeen obtained (see Fig. IV-2) which show the hyperfine structure in the 3P 1 level of sev-eral mercury isotopes. These curves were obtained by varying the magnetic field inwhich an Hg 2 0 2 lamp is placed and comparing the 2537 A light scattered at 90" by radio-active mercury vapor in a quartz cell with the 2537 A output of the lamp. The scanningcurves can be compared with the spectroscopic measurements of Tomlinson. 1 Thevertical lines below the curve indicate the location and approximate intensity expectedaccording to Tomlinson. A comparison between the scanning peaks and the spectralQPR No. 71(IV. NUCLEAR MAGNETIC RESONANCE)193 a196 194193 b MERCURY 192,193,194,192 193B 193 196192 193B 193 c1195*a I I I MERCURY 195195A 99A20a204 195b 195 B 195c1 99A,201a,2041202 1200 1198 ,199B,201c NATURAL MERCURY (198-202,204)201b0 1000 2000 3000 4000 5000 6000 7000SCANNING FIELD AT THE POSITION OF THE MERCURY 202 LAMP (AMPERES THROUGH THE BITTER SOLENOID)Fig. IV-2. Magnetic-scanning curve of Hg 1 9 3lines is also made in tabular form below. The agreement is good193isotopes present except Hgfor all of the mercuryComponent193 * a201b198196194192193 *b193B195 * c193 * cScanning Peak740 amp1260 amp1950 amp2560 amp3320 amp397047405420ampampampInterval-289 ± 10 mK-170 ± 10 mK0 mK148 ± 10 mK332 ± 10 mK490677842473165187196-202195*C-193 * c19 3B-195*cmKmKmK10 mK14 mK22 mKSpectral Line-294 mK-160 ± 4 mK-137 ± 4 mK0 mK147 ± 7 mK304 ±326442 ±665 ±821 ±47415622320 mKmK10 mK5 mK6 mKmKmKmKQPR No. 71193 A202 i2.22.32.5(IV. NUCLEAR MAGNETIC RESONANCE)As far as the structure of the scanning curve is concerned, the zero-field peak, forthe most part, is due to the large change in lamp intensity when a field is applied. Thesmall wiggles above 6000 amps were not reproducible and should be neglected. Thepeaks at 1260 amps and 3970 amps, however, were observed in every one of the fivescanning curves taken and, therefore, are presumably real. The 1260-amp peak isprobably due to a small trace of natural mercury contaminant, while the 3970-amp peakis probably the Hg 1 9 3 B (that is, F = 3/2) component.Except for Hg 1 9 3 , the agreement between the scanning and spectroscopic resultsis good. Only the last peak (193 * c ) falls outside of the combined error limits. Thisresult may be due to a small error in the ampere-to-gauss calibration of the magnet,or to a small departure from linearity at high fields.The significance of these magnetic-scanning results is, first, that they confirm the192 193* 194 195* 1962537 A results of Tomlinson for Hg 9 , Hg 9 3 , Hg 9 , Hg 9 5 , and Hg 9 6 , and, second,they suggest that the Hg 1 9 3 B component is displaced farther from the Hg196 componentthan the spectroscopic results indicate. If the scanning data are correct, then both the193isotope shift and the staggering parameter y of Hg would fall into line with the results1 9 3  196of the other mercury isotopes. The isotope shift of Hg relative to Hg would be213 ± 26 mK, instead of 165 ± 20 mK, and thus place it within the error limits of theHg 1 9 3 * isotope shift (231 ± 6 mK). The staggering parameter y would be 1.16 ± 0.39instead of 1.77 ± 0.43. A y of 1.0 is within the error limits of this value, and thus theTomlinson-Stroke explanation2 of the odd-even staggering effect in isotope shift would193hold for Hg , as well as for the other odd mercury isotopes. Notice that it would nolonger be necessary to consider a possible nuclear spin of 3/2 for Hg 9 3 to reduce yto 1.0.W. T. Walter, H. H. StrokeReferences1. W. J. Tomlinson III, Spins, Moments, and Isotope Shifts in Neutron DeficientMercury Isotopes, Ph.D. Thesis, Department of Physics, M.I. T., 1963.2. W. J. Tomlinson III and H. H. Stroke, Phys. Rev. Letters 8, 436 (1962).QPR No. 71

Nuclear Magnetic Resonance and Hyperfine Structure

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Nuclear Magnetic Resonance and Hyperfine Structure

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