Q-Values of the (p,α) Reactions in Lithium-6, Lithium-7 and Nitrogen-15, and the B_ρ Values of Thorium C′ and Polonium Alpha-Particles

Abstract

ACCURATE values for the energy balance in nuclear reactions are important for establishing the scale of nuclear mass as well as providing confirmation of the Einstein mass–energy relation. During the past two and a half years, we have determined the Q-values for ⁷Li, ⁶Li and ¹⁵N (p,α) reactions, as well as the B_ρ for the α-particles from thorium C′ and polonium. A uniform-field magnetic spectrometer of the Cockcroft¹ design has been used in conjunction with a high-voltage accelerator. The magnetic field around the semi-circular particle-trajectories has been measured by determining the nuclear resonance-frequency of protons in a small sample of water, and converted to absolute values by using the value of the proton gyromagnetic ratio due to Thomas, Driscoll and Hipple². The diameter of the particle-trajectories has been measured absolutely and values of B_ρ (and hence energies) have been derived directly in terms of the spectrometer geometry and the above measurements. Reactions have been studied for 90° emission from a beam of 400-keV. protons, and the high-tension voltmeter scale calibrated by measuring the momentum of elastically scattered protons.