Parker XRF, Instruction Manual

Page: 34 / 38

XRF Analyser Manual
32
The key processes in X-ray fluorescence
The two most important components of an XRF spectrometer are the vacuum tube,
which generates the probing electromagnetic radiation (usually X-rays), and the detector,
which responds to the X-ray photons released by the sample as a result of the radiation.
Vacuum tubes (in the form of the cathode ray tube) are familiar to many people as the
technology that used to be at the heart of every television. X-ray tubes operate along
exactly the same lines. In the most common design, a cathode is electrically heated to
stimulate the emission of electrons which are accelerated through an evacuated glass
tube towards a metal anode. The rapid deceleration of the electrons when they hit the
anode, which is usually made from copper, tungsten, or molybdenum, is accompanied
by the emission of X-rays. The energy of the emitted X-ray photons increases with the
voltage applied to accelerate the electrons whereas the number of photons increases with
the current flow. X-rays usually exit the tube through a beryllium window and are directed
towards the sample. The key elements of an x-ray tube are shown in the following
diagram.