By the technique of adiabatic demagnetization, paramagnetic salts may be cooled to temperatures less than .1°K. By good thermal contact between crystals and paramagnetic salts, the antiferromagnetics MnSiF₆.6H₂0 and CoC1₂.6H₂0 were cooled to temperatures at which the hyperfine interaction energy of an introduced Mn⁵⁴ impurity was comparable to kT. This resulted in a preferential population distribution of the available energy states. The alignment of nuclear spin, induced by the crystalline field present at the active Mn⁵⁴ impurity, was measured by the anisotropic distribution of the ƴ-rays given off by the radioactive Mn⁵⁴. This data led to a determination of the crystalline field acting on the impurity ion in MnSiF₆.6H₂0 and to verification of theoretical calculations representing the anisotropy of ƴ-emission as a function of absolute temperature. Also by means of such data, a determination was made of the axes of alignment in the antiferromagnetic, CoC1₂.6H₂0 . / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The gamma rays resulting from the bombardment of B¹⁰ with protons of energies from 0.5 to 2.0 Mev. have been observed with a sodium iodide scintillation counter. Capture radiation, of energy E[subscript γ] = 8.81 ± 0.05 + 10/11 E[subscript p] Mev., showed a broad resonance at E[subscript p] = 1135 ± 15 kev. At this energy, the radiation had an angular distribution of the form 1 + (0.5 ± 0.05)cos²θ and a total cross section (3.5 ± 1.0) × 10[power -30] cm². Several lower energy radiations were also observed and assigned tentatively to cascade transitions in en. The cross section for the 430 kev. radiation from the reaction B¹⁰ (p, αγ)Be⁷ was measured to be 0.21 ± 0.05 bn. at E[subscript p] = 1.52 Mev. This radiation was found to be isotropic. A three crystal scintillation counter pair spectometer has been constructed and used to observe the gamma radiations from the bombardment of B¹⁰ with deuterons of energies from 0.6 to 2.0 Mev. The spectrometer incorporated a selection of those pulses in the side counters representing 0.5 Mev. energy release before they entered a triple coincidence circuit, responding to coincidence between the three counters. The improved energy resolution and background rejection allowed the complex gamma ray spectra from B¹⁰ + d to be resolved and interpreted. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A single crystal sodium iodide spectrometer has been developed for the investigation of gamma-ray spectra. The spectrometer was tested with the gamma-rays from the sources Eu¹⁵⁵,RaD, Na²², Zn⁶⁵, Co⁶⁰, and RdTh. The spectra from these sources have been obtained by analyzing the pulse height distribution from the scintillation counter with a single channel differential discriminator. A crystal mounting technique is described in which the crystals are mounted dry with a layer of magnesium oxide powder surrounding them to provide diffuse reflecting surfaces. With mountings of this type, 7% energy resolution has been achieved for gamma-ray energies of approximately 1 MeV. The expected pulse height distributions have been calculated and compared with the experimental distributions. The effect of multiple scattering events on the shape of the distributions is discussed,2and the effect of crystal dimensions on the resolution has been studied. It has been found that for the energy region 0.5 to 2.5 MeV the best resolution is obtained with small crystals. A search has been made for the presence of low energy gamma-rays in the decay of tritium, and it was found that within the accuracy of the experiment no gamma-rays were present. A preliminary report is presented on the investigation of possible scintillation produced in air by alpha particles. The effect has been shown to exist but no systematic study has been made. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The reaction Li⁶(p,γ)Be⁷ has been investigated using 0.4 to 1 Mev. energy protons incident on isotopically separated Li⁶ targets. Capture gamma radiation to the ground state and the 430 Kev. state in Be⁷ has been observed; some 62% of the transitions go to the ground state. The ratio of intensities does not change significantly with energy, nor with angle of observation at Ep = 750 Kev. The differential cross section with the counter at 90° to the proton beam and Ep = 750 Kev; is about 2 x 10⁻³²cm²/steradian. The combined angular distribution of the two gamma rays is 1 + (1.05 ± 0.15)cos²θ at Ep = 750 Kev. The Q value for the reaction is 5.66 ± 0.03 Mev. in fair agreement with that calculated from mass values. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An apparatus for the measurement of the lifetimes of gamma-ray transitions between nuclear excited states has been designed and constructed. With this apparatus, lifetimes as short as 1.5 x 10⁻¹⁰ seconds may be determined. This lower limit is shown to be inherent in the scintillation detectors available and not in the electronic circuits which are themselves capable of much better performance. Measurements have been carried out on several radioactive nuclei and have yielded the following results: (1) The two excited states of Ni⁶⁰ have half-lives less than 1.6 x 10⁻¹⁰ seconds. (2) The three excited states of Co⁵⁹ have half-lives less than 2 x 10⁻¹⁰ seconds. (3) No detectable half-life is found in the decay of Eu¹⁵²,¹⁵⁴. (4) An excited state with a half-life of 1.1 x 10⁻⁹ seconds is present in W¹⁸². We identify this transition as magnetic quadrupole. (5) A half-life.of 2.3 x 10⁻¹⁰ seconds is found for the .607 Mev transition in Te¹²⁴ which has previously been classified as electric quadrupole. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The development of scintillation counters for measurements of Ƴ-ray energies and fluxes is described, with particular emphasis on Y-rays in the energy range 2 to 20 Mev. A comparison has been made between the experimentally observed and theoretically predicted properties of these counters. A three-crystal pair spectrometer has been developed which measures only those Ƴ-rays which interact with the detector crystal by producing electron-positron pairs. This device has proved useful for investigating the pair production process for Ƴ-rays with energies only 150 Kev. above the pair production threshold, as well as for the investigation of the complex Ƴ-ray spectrum produced by the F¹⁹(p,αƳ)0¹⁶ reaction. A detailed study of the D(p,Ƴ)He³ reaction has been made. The Ƴ-ray energy indicates that the transition goes to the ground state of He³. The shift in Ƴ-energy with changing proton, energy was, observed, and fits the following relation: E[subscript] Ƴ = (5.50 ± 0.03) + ⅔ E[subscript]p Mev. The Doppler shift of the Ƴ-ray energy (frequency) as a function of the angle between the directions of the incident protons and emitted Ƴ-rays has been measured. The observed shift has the full value expected, assuming that the Ƴ-rays are emitted in a time short compared to the slowing down time of the intermediate He³ nucleus in the target. From these results an upper limit of 2 x 10¹³sec. can be placed on the half-life for the Ƴ-ray transition. The cross section for the reaction for incident protons of 1 Mev. is estimated to be 6 x 10⁻³⁰ cm² (± 50%). The excitation function has been measured from 250 Kev. to 1.8 Mev. and the angular distribution of the Ƴ-rays has the form (Sin² θ + b) where b = 0.046 ± 0.005 for 1 Mev. protons and b = 0.025 ±0.006 for 1.75 Mev. protons. These results, when compared with recent theory, indicate that the reaction is due to direct radiative capture of the protons. Preliminary measurements have been made on the T(p,Ƴ)He⁴ reaction. The Ƴ-ray energy measured relative to the Ƴ rays from the Li⁷(p,Ƴ)Be⁸ reaction is 20.3 ± 0.4 Mev. for 800 Kev. incident protons, indicating that the transition goes directly to the ground state of the helium nucleus. The angular distribution of, the Ƴ-rays measured in a plane containing the incident proton beam direction is predominantly Sin² θ with the addition of a small isotropic component. The present approximate measurements show a greater isotropic component than that obtained at higher proton energy by other workers. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Several new techniques for improving the statistics of counting small peaks on large backgrounds in a beta-spectrometer are presented. These arose from an attempt to reconcile the conflicting reports in the literature of gamma-transitions in Ra (B + C) above 1.02 Mev. Some success has been met with. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The angular distribution of the gamma-rays from the direct radiative capture reaction D(p,ɣ)³He has been measured for 70 KeV and 144 KeV protons in the laboratory system, using thin deuterated polyethylene targets. The study of this particularly simple reaction is of interest for determining some properties of the forces which bind nuclear particles to each other. In addition it plays a role in a number of astrophysical processes. The ground state of ³He is predominantly a symmetric ²S state with admixtures of a ⁴D state and ²S(m) state of mixed symmetry. These admixtues are related to specific components of the two body forces coupling the three particles. The measurements were made with a high current 180 KeV accelerator, built by the author, using an ORTEC duoplasmatron ion source. Technical problems involved in the development of the accelerator and the deuterated targets are discussed. The angular distribution at 144 ± 16 KeV in terms of Legendre polynomials P₁ is given in the centre of mass system by W(ɵ) = Aₒ[Pₒ+(.05±.02)P₁-(.94±.02)P₂-(.05±.02)P₃+(.03±.02)P₄] and at 70 ± 20 KeV the angular distribution is given by W(ɵ) = Aₒ[Pₒ+(.(.06±.04)P₁-(.93±.05)P₂-(.06i±.04)P₃+(.02±.05)P₄] The coefficients in the Legendre polynomial expansion are related to the various transitions between the continuum and bound states. Their significance in terms of the different components of the ³He ground state wave function is discussed. The absolute cross section (i.e. the coefficient Aₒ ) has not been measured. Plans for measuring it in the near future are discussed briefly. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (M.S. in Physics)--United States Naval Postgraduate School, California. / "Unclassified Instrumentation." Includes bibliographical references (p. 37). 16

>Magister Scientiae - MSc / High spin excited stats in¹⁹²Tl were studied using gamma-ray spectroscopy. The study included taking an active part in performing the experiment, understanding the experimental procedure, electronics and data acquisition in this experiment. The high spin states in ¹⁹²Tl were produced using a ³⁷Cl beam and ¹⁶⁰Gd target. The nine clovers of the AFRODITE array were placed at 90° and 135°. The target was thin, allowing the residual thallium nuclei to recoil in vacuum. Two weeks of data was acquired and analysed in this work. In addition more data was acquired in order to perform DSAM lifetime measurements, but this is beyond the scope of this work. The preliminary data analysis of the thin target data involved energy and time-gain matching calibrations as well as Doppler shift and gain drift corrections. Then the data were sorted into matrices and spectra for the actual analysis. The known level scheme of ¹⁹²Tl was extended by more than 50 new transitions placed in three new bands. A chiral partner to the yrast band in ¹⁹²92Tl was searched for but not found. But there is still a possibility such a band to be discovered, when the additional three weekends of data (including the DSAM lifetime measurements) undergo such an analysis.