SS Oberführer Viktor Brack writes a letter to Heinrich Himmler about the feasibility of mass sterilization using X-rays. He explains that preliminary investigations had revealed that low doses only produce temporary sterilization while higher doses which produce permanent sterilization also produce side-effects like burns. Viktor Brack then ignores this and recommends high-dose X-rays anyway.
"If any persons are to be sterilized permanently, this result can only be attained by applying x-rays in a dosage high enough to produce castration with all its consequences, since high x·ray dosages destroy the internal secretion of the ovary, or of the testicles, respectively. Lower dosages would only temporarily paralyze the procreative capacity. The consequences in question are, for example, the disappearance of menstruation, climacteric phenomena, changes in capillary growth, modification of metabolism, etc. In any case, attention must be drawn to these disadvantages.
The actual dosage can be given in various ways, and the irradiation can take place quite imperceptibly. The necessary local dosage for men is 500-600 r(oentgen), for women 300- 350 r. In general, an irradiation period of two minutes for men, three minutes for women, with the highest voltage, a thin filter and at a short distance, ought to be sufficient.
There is, however, a disadvantage that has to be put up with; as it is impossible unnoticeably to cover the rest of the body with lead, the other tissues of the body will be injured, and radiologic malaise, the so-called "Roentgenkater," will ensue. If the x-ray intensity is too high, those parts of the skin which the rays have reached, will exhibit symptoms of burns - varying in severity in individual cases- in the course of the following days or weeks.
One practical way of proceeding would be, for instance, to let the persons to be treated approach a counter, where they could be asked to answer some questions or to fill in forms , which would take them two or three minutes.
The official sitting behind the counter could operate the installation in such a way as to turn a switch which would activate the two valves which would activate the two valves simultaneously (since the radiation has to operate from both sides). With a two-valve installation about 150-200 persons could then be sterilized per day, and therefore, with 20 such installations as many as 3,000-4,000 persons per day."
Heinrich Himmler doesn't follow up on this proposal right away, so Brack will remind him of it in June 1942. At that point, Himmler will agree and has the procedure set up in Auschwitz.