After World War II the denazification process began. When Jensen faced the proceedings, he turned to Werner Heisenberg, a prominent member of the "Uranverein", for a testament to his character – a document known as a "Persilschein" (whitewash certificate). Heisenberg was a particularly powerful writer of these documents; as he had never been a member of NSDAP, he had publicly clashed with NSDAP and the Schutzstaffel (SS), and was appointed by the British occupation authorities to the chair for theoretical physics and the directorship of the "Max-Planck Institut für Physik" then in Göttingen. Heisenberg wrote the document and convinced the authorities that Jensen had joined the Party organizations only to avoid unnecessary difficulties in academia.