Supressing background and increasing luminosity of a β-spectrometer of internal target type for an investigation of the (n, e) reaction

Abstract A method for reducing background and increasing transmission and luminosity of the β-spectrometer of internal target type for an investigation of the (n, e) reaction is proposed. The electron background of such spectrometers is shown to come mainly from scattering of the electrons which are produced outside the target by the target itself. This component of the electron background can be cancelled with the aid of an appropriate magnetic field. Using the method proposed, the β-spectrometer at the WWR-M reactor in Gatchina has been successfully modernized. The spectrometer in its present form incorporates a transport solenoid (instead of a lense) for guiding electrons away from the target situated in a tangential channel near the reactor core and for focusing them onto a magnetic shield slit, which is an electron source for a 45 cm radius double focusing iron-core magnet-analyser. Sensitivity of the β-spectrometer with the transport solenoid compared with that of the β-spectrometer with the lense is increased 7 times. Correspondingly, the time need for obtaining the same statistical accuracy as before is decreased by a factor of 49. Using the β-spectrometer, conversion electron spectra from the 115 In(n, e) 116 In, 133 Cs(n, e) 134 Cs and 121 Sb(n, e) 122 Sb reactions have been measured. Some of them are presented.