Method and apparatus for producing electron beam diffraction patterns

An apparatus for producing electron beam diffraction patterns, comprising an electron beam device for producing a focussed electron beam, said electron beam having a density of less than one electron per square Angstrom;

• an object slide for the object to be examined, the object slide being located in the path of the focussed electron beam in a plane running transversely to the electron beam;
• an integrating image device or an integrating image material for producing an image of the electrons of the electron beam diffracted by the object, said object being a organic or biological substance having a periodic structure;
• an electrically controllable electron beam interruption device;
• and an interval tracing circuit coupled to the electron beam interruption device to periodically interrupt the focussed electron beam such that the beam interruption time is between one and ten seconds and the irradiation period is between 0.2 and two seconds, the interval tracing circuit including a first control circuit for adjusting the duration of the period during which the focussed electron beam is interrupted and a second control circuit for adjusting the duration of the irradiation period during which a pre-determined region of the object is to be irradiated by the focussed electron beam to thereby prevent said pre-determined region of said object from being altered by excessive or continuous irradiation.