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

A scintillation counter for the measurement of extremely low specific beta activities has been developed which achieves its high sensitivity through the application of large amounts of radioactive substance, and the use of an efficient liquid scintillation phosphor. The counter can be used in two different ways; as a volume counter and as a multiple-sample counter. In the first type of counter the solid radioactive sample is mixed with the liquid phosphor to form a transparent paste; in the second type a smaller amount of solid sample is spread out on a large surface of cellophane and immersed in the scintillating fluid. Experiments have been made with K⁴⁰ , C¹⁴ , and S³⁵ to determine the range of application, sensitivity, and efficiency of the counters. The volume counter can be used to assay a wide variety of material and is especially suited for biological problems. Its sensitivity was found to be better than 10⁻¹¹ curies/gm., while that of the multiple-sample counter is of the order of 10⁻¹⁰ curies/gm.. These sensitivities can be measured with a good degree of reproducibility and are superior to the conventional methods, with the exception of the elaborate screen-wall counter method. / 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

[no abstract submitted] / 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

No description available.

No description available.