A 4 π dilepton spectrometer: PEPSI

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Vol. 335; no. 3; pp. 479 - 486
• Main Authors: Buda, A., Bacelar, J.C.S., Bałanda, A., van Klinken, J., Sujkowski, Z., van der Woude, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.1993
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/0168-9002(93)91233-D

A novel positron-electron pair spectroscopy instrument (PEPSI) was designed to measure transitions in the energy region 10–40 MeV. It consists of Nd 2Fe 14B permanent magnets forming a compact 4 π magnetic filter consisting of 12 positron and 20 electron mini-orange-like spectrometers. The response function of PEPSI has been measured with mono-energetic beams of electrons from 5 to 20 MeV. The PEPSI spectrometer was used for measuring the internal pair conversion coefficient ( α π ) of the 15.1 MeV M1 transition from a J π = 1 + state to the ground state in 12C. Our experimental value of α π = (3.3 ± 0.5) × 10 −3 is in good agreement with theoretical estimates.