| 摘要 |
<p>A block of radiation absorbing material has a central cylindrical canal in which a source of gamma radiation is placed. A second cylindrical canal in the block contains a stopper which may be turned from the outside, and which has a narrow slit in it. Slits in the block can be lined up with the slit in the stopper by rotating the stopper and thus allow the radiation out in a well defined region known from the geometry of the slits.</p> |
