A double-focussing, semicircular sector, magnetic spectrograph has been constructed for detecting and analyzing charged particles from nuclear reactions, with energy up to 10 Mev for protons and alpha particles. Particles emitted at a point outside the field and within a solid angle of 0.007 steradian can be brought to a point focus, also outside the magnet, by the magnetic field which varies as r^(-1/2) near an average radius of 16 inches. The ultimate momentum resolution p/δp limited by the second order aberrations and other irregularities of the actual arrangement is over 1000. with the 1/4 inch collecting slit usually employed for intensity measurement, the momentum resolution is p/δp = 230.
The magnetic spectograph has been used to determine accurately the energy release in a number of nuclear reactions initiated by protons or deuterons on Li^7, Be^9, B^(11), C^(13), N^(15) and O^(16). These measurements, incorporated with the great number of accurate disintegration energy measurements recently available, have been used to derive the masses of light nuclei up to F^(20) from the nuclear data exclusively.
