In conjunction with low temperature experiments on nuclear alignment and nuclear specific heat, a spectrometer has been developed in order to investigate the hyperfine structure of compounds with suitably large quadrupole coupling by the technique of Nuclear Quadrupole Resonance. The auxiliary equipment which was built in addition to an externally quenched superregenerative oscillator provided for frequency modulation and oscilloscopic display as well as Zeeman modulation and chart recorder display. The superregenerative oscillator has a frequency range of 150 - 600 Mc./sec., which is the range required for investigation of the compounds concerned; the spectrometer has reproduced satisfactorily test signals over the range 164.5 to 332.4 Mc./sec. The test signals were obtained from the known quadrupole resonances of I¹²⁷ and Br⁷⁹ in Snl₄, I₂, SbBr₃ and Ba(BrO₃)₂. Using the spectrometer, a search was made for resonances in a number of substances which were of interest for the nuclear alignment programme, and in which no resonances had yet been reported. In particular, we were able to make a careful investigation of the magnesium salt of para-iodo benzene sulphonate since we knew from theoretical investigations the approximate frequency at which the I¹²⁷ resonance occurs. A possible explanation is given for the failure to detect any such resonance. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Modifications have been made to a semi-circular focussing spectrometer to facilitate its operation and to improve its performance. Geiger counters filled with the saturated vapour of heptane kept in an ice bath are used to detect the beta-particles. The windows of the counters are made of zapon films about 10 micrograms/cm² in thickness. The sources are mounted on similar films and have a total thickness less than 100 micrograms/cm². The combination of thin source and thin windows permits the measurement of beta-particle energies down to 2 Kev. An examination of the beta-spectrum of Eu¹⁵²⁻⁴ has been carried out. It consists of 7 peaks corresponding to the energies 8.0, 15.0, 26.4, 33.2, 38.3, 73.1 and 74.8 Kev. The two upper peaks are assigned as K conversion lines for gamma-rays of 121.5 and 123.2 Kev. The 33.2 and 38.3 Kev lines are assigned as L and M Auger electrons in Sm. The 8.0 Kev line is assigned as an M Auger electron in Sm. The 15.0 Kev peak is assigned tentatively as an M conversion line corresponding to a gamma-ray of 16 Kev. The 26.4 Kev line is tentatively assigned as either a K conversion line corresponding to a gamma-ray of 73 Kev or an L conversion line corresponding to a gamma-ray of 34 Kev. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The sensitivity, resolution, and efficiency of a time-of-flight neutron spectrometer developed in this laboratory (Neilson and James, 1955) have been improved by the use of a liquid scintillator neutron detector and improved electronic techniques. By observation of the D(d,n)He³ reaction, the neutron detection efficiency of the liquid scintillator for neutrons in the energy range 2 to 3.5 mev has been shown to follow the curve ε = 0.146 + 0.45 / E[subscript n] + 0.82 where E[subscript n] is the neutron energy in mev. Investigation of the Be⁹(d,n γ)B¹⁰ reaction has shown that the γ-radiation from the 0.72, 2.15, and 3.58 mev levels in B¹⁰ is isotropic to within 5% in the reaction plane while that from the 1.74 mev level is isotropic to within 15%. Further, the radiation from the 0.72, 1.74, and 3.58 mev levels is isotropic to within the same precision about the respective recoil axes, while the angular distribution from the 2.15 mev level is 1 + (0.07 ± 0.05) sin²θ , where θ is measured from the normal to the reaction plane. Since energy selection of the γ radiation was not performed, it is not known which of the three transitions listed by Ajzenberg and Lauritsen (1955) is responsible for this anisotropy. The angular distributions of the four neutron groups associated with the B¹⁰ levels listed above, at E[subscript d] = 500 kev, indicates that at this energy stripping is unimportant for the 0.72, 1.74 and 2.15 mev levels, in agreement with the work of Pruitt et al. (1953) at E[subscript d] = 945 kev. The neutron group associated with the 3.58 mev level undoubtedly proceeds via ℓ = 1 stripping, but to obtain the observed position of the peak at this energy from Butler theory, it is necessary to assign a radius of 13.4 10⁻¹³ cm to Be⁹. The observed peak is twice as broad as that predicted by the theory, (undoubtedly a coulomb effect) and there is an isotropic background roughly one third the peak height, presumed due to compound nucleus formation. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A recording nuclear magnetic resonance spectrometer has been built and is in operation. The instrument is based upon a simple oscillating-detector of original design, for which the author presents a complete analysis of sensitivity and signal to noise ratio. This analysis is based upon the van der Pol oscillator and contains a theoretical estimate of the modulation noise in such an oscillator. Comparison with other methods shows the ultimate sensitivity of the oscillating detector to be the same as that obtainable by bridge methods, but the former is much more flexible. Although similar instruments are apparently in use, no details are given in the literature. Other features of the spectrometer are a 1200 lb. electromagnet and a lock-in detector of great stability. Some of the resonances recorded by the spectrometer are discussed. These are: (a) Cu⁶³ in the wire of the detector coil. (b) Br⁷⁹ and Br⁸¹ in NaBr and KBr solutions. (c) I¹²⁷ in Nal and KI solutions. (d) Sb¹²¹ in SbCl₅ and HSbCl₆. The copper signal provides a criterion of the sensitivity of the spectrometer. The measurement of the resonant frequency agrees with values reported by Knight for metallic copper. The resonance widths of the bromine isotopes are tenfold narrower than values given by Pound, an important discrepancy since it throws doubt upon our ability, at present, to calculate quadrupole moments from nuclear magnetic resonance. The iodine width in Nal agrees-with Pound's value. The antimony resonance in HSbCl₆ confirms work of Proctor (private communication). The resonant frequency in SbCl₅ is about .07% higher. This shift is an example of the chemical effect recently discovered for fluorine and nitrogen isotopes. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The construction and preliminary tests of a Beta-ray spectrometer designed to work at energies below 100 Kev is described. The instrument is of the small semi-circular focussing type using four counter pairs. The design is for reasonably high resolution and high transmission angle. The magnetic field is produced by a combination of plane coils designed to maintain field homogeneity to better than 1%. The magnet current is held to 1 part in 10,000 by means of an electronic circuit composed of D.C. and A.C. amplification stages controlling the grids of a bank of 6AS7 double triodes in series with the magnet windings. The counter windows and source backing are collodion films of the order of 0.1 μ. Work on this instrument is continuing. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A modular, multiwire drift chamber was built and tested in the M13 area. The resolution obtained with six sense wires, was in the horizontal drift direction σ(mean) < (79.9± .2)µm, with an angular resolution of (9.37±.02)mrads. With the drift chamber mounted in the first wire chamber position of the QQD-spectrometer, this corresponds to a resolution of 1.97mm FWHM at the position of the scattering target. In the vertical direction, using a charge division method, the best achieved resolution was < 2mm FWHM per wire, which gives an angular resolution of 71mrads or 15mm FWHM at the target position. The chamber was run at rates in excess of 10⁶ particles/sec. A multi-chamber system was tested, consisting of two modular four cell drift chambers for the horizontal direction, and one eight cell modular drift chamber, located in between and rotated by 90°, was used for the vertical position determination. The resolution for one four cell chamber was σ(mean) < (108.5± .9)µm, and for the eight cell chamber σ(mean) < (79.9± .2)µm. The angular resolution for this system was 1.37 mrad horizontally and 9.37mrads vertically; in connection with the QQD-spectrometer, this corresponds to FWHM of 0.267mm and 1.12mm respectively at the target spot. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A fifteen inch magnetic spectrometer using its fringing field to achieve double focusing has been developed and made ready for experimental work. Its power supply delivers continuously variable currents from 0-100 amperes. The current is stable to one part in ten thousand, being regulated by a transistor amplifier which drives a bank of parallel output power transistors. Interlocks are provided to protect the components against foreseeable hazards. The vacuum and detecting systems are complete, and the spectrometer has been tested with various alpha sources. The best resolution obtained was .57 per cent, but there should be much better resolving power inherent in the spectrometer, unrevealed because the sources used were fairly large. A resolution measurement of scattered protons when the beam from the Van de Graaff is put in to the spectrometer should determine the resolution more accurately. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In this thesis a small shift Mossbauer spectrometer developed by the author is described. An automatic multiplexing and printout system for eight scalers is described along with a digital electronic control system for the motor drive. Three-different suspension systems, for the transport portion of the linear drive -- (1) An air bearing suspension as developed by Wells (2) An oil supported teflon bearing suspension (3) A leadscrew suspension have been constructed. Mossbauer spectra for two sources – CO57 in Armco iron and CO57 in Pt195 -- against an enriched iron absorber have been taken with the latter two suspensions and have been compared with each other and with spectra taken on a commercial Mossbauer spectrometer. Theoretical calculations of the central Mossbauer line for the Armco iron source and enriched iron absorber have been made using the computer program written by Woodrow. These calculations are compared with the experimental spectra. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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