[Reduction of the surface dose of Co 60 rays in a tissue depth of 0 to 3 mm by means of a magnetic field (author's transl)].

In an air gap of 10 centimeters of width lying over a U-shaped iron core, a magnetic field with an intensity of B greater than or equal to 0,069 Tesla is produced by two permanent magnetic plates. This field is arranged behind the diaphragm unit of a Co-60 gammatron at right angle to the direction of radiation, so the surface dose can be reduced until a depth of 3 millimeters. This magnetic field diffracts the secondary electrons emanating from the diaphragms of the gammatron in such a manner that they cannot contribute to the surface dose within or beyond the irradiation field. Depending on the size of the irradiation field, the magnet allows to reduce the dose by 30% at most in a tissue depth of 5 to 10 mg/cm2. Measures were taken by means of a soft radiation chamber for different tissue depths within and beyond the irradiation field.