GB1074625A - Improvements relating to magnetic spectrometers - Google Patents

Abstract

1,074,625. Particle spectrometers. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 6, 1964 [April 24, 1963], No. 16172/63. Heading H1D. A magnetic spectrometer suitable for introduction at an intermediate stage of a rectilinear particle path-e.g. in an electron microscopehas aligned entrance and exit apertures, and a non-uniform transverse magnetic field, such that charged particles of a desired mass or energy just perform one cycle of a trochoidal path in passing through the field, and therefore emerge from the spectrometer moving again along the axis. Polepieces 12 and 13 are mounted in an evacuated cylindrical container 1, half shown in Fig. 2, particles to be analysed entering through a central aperture in the upper closing diaphragm of the container (Fig. 1, not shown) and passing generally down the axis of the container, first through the non-uniform field between the inclined pole faces 31 and 32, and then through a tube 8, which acts as a magnetic screen and extends to a central, exit aperture in the bottom wall of the container, this aperture having an associated slit which is adjustable both in width and position. The magnetic field intensity and distribution are adjustable by adjustment of the magnet energizing current and-by rotation of the polepieces on their core members 14 and 15-of the inclination between the pole faces. If the planes of the latter intersect at a distance x = f from the axis, the flux density B in the direction between the pole faces is given by B = K/f-x, where K is a parameter dependent upon the magnet exciting current. Charged particles entering the spectrometer pursue a trochoidal path in this field, variation of the exciting current and pole face inclination permitting adjustment to a condition in which particles of a particular desired energy (eV, Fig. 5, not shown) just complete one cycle of the path in passing through the field, and therefore emerge from it travelling along the axis, and pass out through the spectrometer exit slit.