ɪt hɐz ɐn ˈæktɪv sˌiːˈɛs aɪ tˌiːˈɛl sˌɪntɪlˈeɪʃən ʃˈiːld ɚɹˈaʊnd ðɪ ˈɛksɹˈeɪ slˈæʃ ɡˈæmɚɹˈeɪ dɪtˈɛktɚ, ˈɔːlsoʊ ʌv sˌiːˈɛs aɪ tˌiːˈɛl, wɪððə tˈuː kənˈɛktᵻd ɪn ᵻlɛktɹˈɑːnɪk ˌæntɪkoʊˈɪnsɪdəns tə ɹᵻdʒˈɛkt ʌnwˈɔntᵻd tʃˈɑːɹdʒd pˈɑːɹɾɪkəl ᵻvˈɛnts ænd tə pɹəvˈaɪd ðə ɹᵻkwˈaɪɚd ˈæŋɡjʊlɚ kˌɑːlɪmˈeɪʃən.
It has an active CsI(Tl) scintillation shield around the X-ray/gamma-ray detector, also of CsI(Tl), with the two connected in electronic anticoincidence to reject unwanted charged particle events and to provide the required angular collimation.