Lab Measurements with a Prototype Module of the LargE Area burst Polarimeter (LEAP)

The LargE Area burst Polarimeter (LEAP) is a proposed instrument optimized for measuring polarization and spectra of Gamma-Ray Bursts (GRBs). It is capable of measuring polarization from 50 keV to 1 MeV and spectra from 20 keV to 6 MeV. LEAP is a low-risk, wide field-of-view Compton polarimeter designed to be deployed as an external payload on the International Space Station for a 32-month mission. The instrument consists of seven LEAP Polarimeter Modules (LPMs), each containing a 12x12 array of scintillator-PMT detector elements. Two types of scintillators are used within each array. Some elements are made of plastic scintillator (a low-Z material ideal for scattering) and some are made of Cesium Iodide (a high-Z material ideal for photon absorption). A prototype of the instrument has been built to evaluate the design and to characterize the response to polarized photons. The prototype consists of a limited number of detector elements arranged in a 5x5 array. This prototype has been used to carry out polarization and spectral measurements of radioactive sources for multiple observation scenarios. Polarization measurements were made using two different partially polarized sources placed at various locations within the FoV. All measurements were compared with GEANT4 simulations to validate the simulations and our understanding of the full instrument design. The lab data has also been used to evaluate different algorithms for the polarization analysis. We will provide a description of the prototype and summarize results from the laboratory measurements.