Off-line target thickness measurement setup
The thickness measured by quartz crystal thickness monitor or by weighing method may not be very accurate. For the absolute thickness measurement of thin free standing foils the following method is used.
The steps followed are:
5.484 MeV alpha particles from 147Am radio active source are allowed to pass through the foil.
The particles are detected by a solid state surface barrier detector.
The spectrum is recorded in a multi-channel analyzer.
The multi-channel analyzer is callibrated to measure energy.
The specific energy loss of the 5.484 MeV alpha particle in the foil material determined from theoretical value.
The thickness of the foil is determined by measuring the energy lost by the particles while passing through it and comparing with theoretical value.