XEMIS: A new Compton camera with liquid xenon

In the context of medical imaging system, we develop an innovative technique, called 3 gamma. It consists in a direct 3D reconstruction of each decays of ⁴⁴Sc radionuclide with a resolution below the centimeter. This breakthrough in instrumentation technique is only possible by the use of a new detection medium (liquid xenon) and a new detection structure compared with conventional imaging technique. Thanks to an ultra-low noise front-end electronics (below 100 electrons ENC) operating at liquid xenon temperature and a fast UV sensitive PMT, high spatial resolution and high energy resolution are achievable in 3D. This is particularly important for Compton imaging since all interactions in the medium have to be identified to derive the incoming gamma ray direction. A prototype (XEMIS1) is now in test at Subatech and shows promising results. We achieve an energy resolution of 8.9 % (FWHM) at 1.2 MeV with an electric field of 1kV/cm. All the cryogenic system is fully operational with a high purification rate and shows a very good stability. I will review all these aspects and introduce the next step of the project, XEMIS2, a larger prototype dedicated to the 3 gamma imaging of small animals.