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In 2013 March and 2014 May, Voyager-1 (V1) experienced small but significant increases in the flux of galactic cosmic rays (GCRs) in the hundred MeV/n range. Additionally, V1 also saw episodic depletion of GCR flux around perpendicular pitch angles. We discuss the pitch-angle distribution and the time profiles of these events. In a previous paper, we interpreted the 2013 "bump" as the GCRs remotely sensing a shock that reached the magnetic field line passing through V1: particles gained energy as they were reflected on the approaching region of the stronger magnetic field of the disturbance. Here, we point out that energy gain is not restricted to reflected particles -GCRs passing through the disturbance also gain energy. The effect should be present in a broad range of pitch angles with the maximum increase of GCR intensity predicted to occur at the critical reflection angle. In this paper, the shock is not step-like, but a gradual increase of the magnetic field strength, B, taking a few days, in agreement with V1 measurements. This smoothens the profile of the predicted bump in the GCR flux. We also address the linear episodic decreases seen around perpendicular pitch angles. These events are interpreted in terms of adiabatic cooling behind the shock due to the slow weakening of B. We present simple numerical model calculations and find that a gradual shock followed by a slow decrease of B, as observed, may account for both the episodic increases and the anisotropic depletion of GCR fluxes.

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The efficiency of NaI(T1) scintillation counters for the detection of gamma rays is discussed and experimentally determined. Experimental efficiencies, based upon the number of counts above a bias equal to one-half the gamma ray energy and a solid angle defined to the crystal effective centre, for a three-inch-diameter by three-inch long (3 x 3) crystal are given for gamma ray energies of 0.51, 1.275 and 6.14 MeV. Gamma ray spectra at 1.275 and 6.14 MeV are extrapolated to zero energy in order to compare theoretical efficiencies, based upon the integrated primary absorption, with the experimental results. These results show that, with experience, one can expect accuracy to better than 5% at these energies. Tables are given of the theoretical efficiency for 3x3, 2¾ x 4½ and 5x4 crystals for several gamma ray energies and source-to-counter distances of from 0.1 cm to 1 m. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The energy of gamma rays from the reaction H² (p,γ)He³ has been measured as a function of incident proton energy in the range of proton energies from 1 to 2 Mev. The results were consistent with the assumption that the He³ is left in the ground state. The Doppler shift in gamma ray energy was measured for incident protons of energies 1 Mev. and 1.7 Mev. and was found to be consistent with the value calculated assuming that the He³ was not slowed down before emission of the gamma ray. This puts an upper limit on the lifetime of the intermediate state of 2 x 10⁻¹² sec. The angular distribution of gamma rays at an incident proton energy of 1.75 Mev. was of the form sin²θ + (.025 ± .007), and at incident proton energy of 1.00 Mev. was of the form sin²θ + (.043 ± .008). The excitation function, over a range of incident proton energies from 0.25 to 1.85 Mev., is fitted by a function of the form AEp⁰•⁶⁵. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The cross sections for the 0¹⁶ (p,ɤ) F¹⁷ transitions to the ground d-state and to an excited s-state of F¹⁷ have been measured in this laboratory and elsewhere, at different energies in the range from about 100 kev to 2.5 Mev incident proton energy. In this thesis an attempt is made to calculate these cross sections at several energies in the above range on the hypothesis of direct proton capture. Similar calculations have been made at the California Institute of Technology but have not been published. The standard formula for the cross section for an electric dipole transition from an incident p state to a final d-or s-state has been used. The matrix element appearing in this formula was split up into an angular part which can be evaluated exactly, and a radial integral which has to be calculated approximately. In the case of transitions to the excited s-state numerical calculations using tabulated wave-functions were made at center of mass proton energies of 150, 378 and 940 kev. The cross section at 150 kev was also calculated by the saddle point method using WKB approximations to the wave-functions, but this method was found to break down at energies above 200 kev due to difficulties with the WKB functions. Reasonably good agreement between the two methods was obtained at 150 kev. For transitions to the ground d-state the numerical method could not be used since tabulations of the required d-state wave-function are unavailable. Calculations were made only by the saddle point method at center of mass proton energies of 150, 378 and 500 kev. This method can not be used above 500 kev. The calculated ratio of [formula omitted] ≈ 9 at energies of 150 and 378 kev, and the absolute values of the cross sections agree reasonably well with the experimentally observed values. Some discrepancies are noted between these calculations and those carried out at the California Institute of Technology which are very briefly referred to in a preprint of an experimental paper, but a detailed comparison was not possible, as the details of those calculations are unavailable. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Two boron trifluoride proportional counters, one containing normal isotopic boron and the other boron enriched to 96% B¹⁰, have been irradiated with 4.87-Mev neutrons from the D +.D reaction. In addition to the reactions B¹⁰(n,α)Li⁷and B¹⁰(n,α)Li⁷* with Q-values of 2.79 Mev and 2.31 Mev respectively, two other reactions have been observed, (i) F¹⁹(n,α)N¹⁶and F¹⁹ (n, α)N¹⁶* with Q-values of -1.43±0.15 Mev and -1.77±0.15 Mev and (ii) either B¹⁰ (n,p)Be¹⁰ or B¹⁰ (n,t)Be⁸ with a Q-value of +0.35±0.20 Mev. Due to the presence of these two reactions, the analysis of complex fast neutron spectra by the use of such counters is not feasible. The Q-values for reaction (i) yield a value of the N¹⁶ mass of 16.01110±.00020 MU. Neutrons from a pulsed deuterium beam impinging on a tritium target were used to bombard a boron trifluoride proportional counter containing the normal ratio of B¹¹ to B¹⁰. The half-life of the activity and the energy of the particles emitted indicated that they were due to the immediate breakup of Be⁸ into two alphas after the 0.89 sec. beta decay of the Li⁸ formed by the B¹¹ (n,α)Li⁸ reaction. The process was found to have a cross section of the order of 10 millibarns for 14-Mev neutrons. The angular distribution of the non-resonant gamma radiation from the proton bombardment of C¹² has been measured and found to obey the relation:- I(ɵ)α0.02±.02 + sin²ɵ, for a proton energy of 1,580 kev. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The marked physical changes in potassium boro-hydride such as decrepitation and the development of a deep blue coloration when the solid compound is exposed to ionizing radiation stimulated a study of the effects of 50 Kvp X-rays on the alkali metal borohydrides to determine the nature of the radiation induced changes such as color center formation and chemical decomposition. Methods were developed to prepare the alkali metal borohydrides in a form suitable for radiation studies. Solvents studies showed that anhydrous hydrazine was an exceptionally good solvent for potassium borohydride, the solubility being 28.3 grams KBH₄ per 100 grams at 18.5° C. The handling of hydrazine as a solvent required the construction of special apparatus. A study of the use of hydrazine as a solvent for other ionic borohydrides and/or the growth of crystals suitable for spectroscopic work is incomplete. Therefore, the spectroscopic studies on radiation induced absorption bands was done mainly with thin pressed pellets. The borohydrides of rubidium and cesium were prepared by metathesis reactions from potassium borohydride via a sulfonium borohydride. The preparation of the previously unreported trimethylsulfonium borohydride is described. Color center formation was studied by spectroscopic methods only and the F and U type centers have been tentatively identified. The thermal stability and optical bleachability of some of the radiation induced absorption bands were examined. Chemical studies of radiation damage in potassium borohydride failed to show the presence of free alkali metal. Gaseous boron hydrides were also undetectable. Mass spectrometric examination of gaseous material evolved during irradiation showed only hydrogen to be present. No gas was evolved when heavily irradiated samples of potassium borohydride were dissolved in liquid ammonia. A discussion of methods and apparatus characteristic to the radiation studies such as the X-ray generator, radiation vessels, vacuum system, and a section on radiation dosimetry is included in the thesis. The intensity of X-rays generated by the Machlett OEG-60 X-ray tube was determined by the application of the included dosimetry data together with a calorimetric measurement of the output flux of the tube. At 50 Kvp and 28 milliamperes the intensity output was found to be 0.220 cal.min.⁻¹ cm.⁻² at the tube port. Some suggestions for further work are outlined at the end of the study. / Science, Faculty of / Chemistry, Department of / Graduate

Detailed calculations have been carried out which indicate that the small-angle scattering of fast neutrons by lead depends on the polarization, or spin orientation, of the neutrons. When the scattering of neutrons whose spin vectors point upward is observed in the horizontal plane, more neutrons should be found scattered to the right than to the left. For completely polarized 3.1 Mev neutrons, the theory predicts a maximum "right to left" intensity ratio of 14.5:1 at a scattering angle of 0.5°, the ratio decreasing to 1.6:1 at 5°, and approaching unity rapidly as the scattering angle increases. An attempt to detect this effect with neutrons from the reaction D(d,n)He³ failed because the degree of neutron collimation attainable, while satisfactory for most scattering experiments, was insufficient to permit investigation of neutron scattering at very small angles. A three crystal pair spectrometer has been used to investigate the complex gamma ray spectrum arising from bombardment of B¹⁰with deuterons of several energies between 0.8 and 2.2 Mev. Gamma rays of energy 4.46 ≠.04, 4.75 ≠ .03, 5.03 ≠ .09, 5.35 ≠ .05, 6.52 ≠ .05, 6.78 ≠ .07, 7.29 ≠ .04, 8.27 ≠ .09, and 8.87 ≠ .02 Mev have been assigned to transitions in B¹¹ and C¹¹, with excellent agreement in almost all cases with the energy level schemes proposed from other experiments. The excitation curves of three of the gamma rays have been found to rise smoothly between bombarding energies of 0.8 and 2.2 Mev, indicating that the reactions B¹⁰(d,p [symbol omitted])B¹¹l and B¹⁰(d, n [symbol omitted])C¹¹ are primarily of non-resonant character, at least in this energy region. / Science, Faculty of / Physics and Astronomy, Department of / Graduate