Gradient Magnet Design for Simultaneous Detection of Electrons and Positrons in the Intermediate MeV Range

TL;DR

This paper presents a novel compact gradient magnet spectrometer capable of simultaneously detecting electrons and positrons in the 2-500 MeV range, with improved efficiency and resolution for gamma-ray spectroscopy applications.

Contribution

The work introduces a tapered gradient magnet design and a prototype for simultaneous electron-positron detection, enhancing energy resolution and efficiency for intermediate MeV gamma-ray spectroscopy.

Findings

Gradient magnet enables simultaneous detection of electrons and positrons.

Optimal elliptical aperture improves signal efficiency for divergent beams.

Prototype demonstrates effective energy resolution and detection efficiency.

Abstract

We report the design and development of a compact electron and positron spectrometer based on tapered Neodymium Iron Boron magnets. We show that the tapered design forms a gradient magnetic field component allowing energy dependent focusing of the dispersed charged particles along a chosen detector plane using RADIA, a code developed by European Synchrotron Radiation Facility for solving three-dimensional magnetostatics configuration, and a fourth order Runge-Kutta Particle Tracking code. The mirror symmetric design allows for simultaneous detection of pairs i.e. electrons and positrons with energies from 2 MeV to 500 MeV. We have developed a prototype matching the design specifications. We investigate the effects of beam divergence on the energy resolution and signal conversion efficiency for a photo-stimulated luminescencebased Imaging Plates (IPs). The optimal entrance aperture of the magnet is found to be elliptical and bigger than that of conventional pinhole aperture-based spectrometer designs even for a divergent beam originating from a point source at 20 cm away (i.e. solid angle of ~8 milli steradians). The signal efficiency in BAS-IP of SR type ranges from 1% to 5% for a parallel beam incident on a circular aperture of 20 mm diameter type at a chosen detection plane whereas it drops by up to a factor of 3 in the presence of divergence of ~ 8 milli steradians. The proposed gradient magnet is suitable for the detection of low flux and/or monoenergetic type electron/positron signals with finite transverse sizes. It offers unparalleled advantages for gammaray spectroscopy in the intermediate MeV range.