रंजन जर्मनी के वैज्ञानिक थे। इन्होंने एक्सरे की खोज की जिससे शल्य चिकित्सा के क्षेत्र में क्रान्तिकारी परिवर्तन आ गया।

The roentgen or röntgen is a legacy unit of measurement for the exposure of X-rays and gamma rays, and is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air . In 1928, it was adopted as the first international measurement quantity for ionizing radiation to be defined for radiation protection, as it was then the most easily replicated method of measuring air ionization by using ion chambers. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays and was awarded the first Nobel Prize in Physics for the discovery.