The New fIREBall*

Measurement of conversion electrons in coincidence with gamma rays promises new information on nuclear structure specifically about distinguishing coexistence from vibrational excitations. The Internal Conversion Electron Ball (ICEBall) mini-orange array of SiLi detectors, now located at the Nuclear Science Laboratory of the University of Notre Dame,  is being upgraded to the fInternal ConveRsion Electron Ball (fIREBall) array. The upgrade includes improvements to the filters allowing more of the beam to make it to the Si detectors, new designs for the magnet filters with optimized designs to improve detection efficiency, and new detectors. A combination of FreeCAD, COMSOL, and Geant4 was used to develop a working simulation to test a wide variety of shapes. Using the simulations, we have discovered shapes that could more than double the efficiency of ICEBall. We have achieved good agreement between experimental tests of the new magnet shapes with the simulation predictions, establishing the reliability of using simulations to design future magnet shapes. With the designs finalized, we are preparing for fIREBall’s first commission run, a repeat of a previous ICEBall experiment, a ^152,154Sm(α,2n)^154,156Gd reaction, to confirm/determine the improvements achieved, specifically in coincidence measurements. Details about the magnet design process and the upcoming commission run will be presented.