Construction and application of a high-resolution β-ray spectrometer connected with a tandem accelerator

Abstract A high-resolution iron-free β-ray spectrometer with a focusing angle of π√(13) 2 =324.5° has been constructed and connected with a 6 MV tandem accelerator. The focusing principle of this “flat” spectrometer involves radial focusing and axial defocusing at the exit slit which is curved. The “image” of a point source is a curved line, and the image of a line source is identical with that of a point source. The extra degrees of freedom due to this focusing principle are used to obtain a resolving width independent of all aperture angle terms up to the third power, and the only fourth-order term is that with ϕ 2 r × ϕ 2 z ( ϕ r and ϕ z are radi and axial aperture angles, respectively). The dispersion is D = 6.5. The stationary orbit has a radius of r 0 =30 cm. The magnetic field is produced by five pairs of coils. The maximum electron energy is 4.5 MeV and the corresponding electric power 45 kW. A typical pair of values for resolution (fwhm) η and fractional solid angle ω is η =2.2 × 10 −4 and ω =0.6 × 10 −2 . The spectrometer is situated in an iron-free brick building nearby a 6 MV tandem accelerator whose beam can be focused at the source position of the spectrometer to a spot of 0.5 × 5 mm 2 . The spectrometer was widely applied to study conversion line energies and intensities both from radioactive sources and from Coulomb-excited nuclei. At favorite cases momentum ratios can be measured with 2 × 10 −6 precision (internal error), and intensity ratios with 1 per cent. In this paper results are mostly given for energy values.