Proton microbeams,their production and use

Well focused beams of protons and other ions provide a very powerful means of determining how the elemental composition of a sample varies over its surface. Observation of the X-rays from proton bombardment can provide great sensitivity in most cases, while detection of nuclear effects has special applicability for elements of low atomic weight. A focusing system using high precision magnetic quadrupoles was designed and built for use with the IBIS 3 MeV Van de Graaff generator. Measurements of the first order focusing and aberrations agreed satisfactorily with theoretical predictions. The focused beam of 3 MeV protons was measured to have a diameter of less than 4 μm. The target chamber, deflection system and display system are described and examples given of use of the system. Backgrounds in X-ray detection are discussed and limits of detection are given.