Introduction
X-ray fluorescence refers to the emission of x-rays from material that has been bombarded with high energy x-rays and gamma rays causing particle excitement. X-ray fluorescence finds its application in chemical analysis, element analysis and identification of flaws in some materials such as ceramics and metals. The phenomenon is used in the field of archeology, forensic science and chemistry. The term fluoresce as applied refers to the re-emission of absorbed radiation of specific energy to a different energy level (Jenkins, 1999).
Discussion
Short-wavelength X-rays or gamma rays cause ionization of atoms of the materials that these waves may be exposed. Ionization process refers to discharge of electrons from the particle of the material when it is irradiated with a radiation of great energy. The energy of the radiation is usually greater than the ionization potential of the material. Gamma or X-rays posses’ energy that is great enough to excite the electrons in the inner orbital of most atoms. Once an electron is excited, it is expelled from the atom causing instability in the structure of the atom. The electrons in the higher orbital move to the lower orbital causing an electron hole in the atomic structure (Jenkins, 1999).
Energy is released from the atom in packets referred to as photons. The energy is equivalent to the energy variation between two energy levels. All the elements in the periodic table have their characteristic energy for electronic orbitals. When an electron in the inner energy level shell is ejected, electron from the outer shell drops into the hole created. This process occurs in restricted modes called transitions which produce a fluorescent packet of energy with a distinctive energy. Planks law can be used to calculate the wavelength of the radiation.
Where h is the energy, c is the speed of light, E is the energy.
X-ray fluorescence is used as a nondestructive analytical method where the sample is not destroyed during its analysis. This form of analysis requires the irradiation of the sample with elevated energy X-rays and the resulting radiation detected by the detector. Since each element has distinctive energy, the elements in the sample can be detected. This can be used in determination of the elements in a sample of water or soil. X-ray spectroscopy is mainly used in bulk chemical analysis if major elements in rocks and soil. The method can also be used in detection of trace elements in rocks and sediments. The only time the method can not be used in element identification is in the case of isotopes of elements.
The sample should be prepared on a flat disc to ensure that the arrangement of the tube-material-detector is regular. The diameter of the disc should be between 20-50mm. the disc shape can be obtained from different ways depending on the nature of the sample. Metals can be machine shaped while minerals can be pressed after grinding into tablets. Monochrometors can be used to maintain the symmetrical geometry between the ample and detector. The angle should be defined accurately since the X-ray release lines are narrow. This can be achieved through the use of flat crystal with soller collimators or using curved crystal with slits (Jenkins, 1999).
X-ray fluorescence is an important physical phenomenon which can be used in a wide range of applications. The concept behind the phenomena is ejection of an electron from an element when it is irradiated with radiation of a definite energy. Once the electron is ejected, a photon of energy is released whose wavelength can be determined using Plank’s law.
References
Jenkins, R. (1999). X-ray fluorescence spectrometry. New York, NY [u.a.: Wiley.
