X-ray methods questions and answers.
Chemistry is the branch of Science which deals with the structure of matter and composition of substances, their transformation, analysis, synthesis and manufacturing. To facilitate the study of Chemistry, it has been divided into various branches viz; Physical, Inorganic, Organic, Analytical etc. The knowledge of the basic concepts is absolutely essential for better understanding of the subject matter. To augment the ability of the students to understand the subject.
Q. How will you define X-rays?
Q. What is the basic principle of X-rays?
Q. What is Bremsstrahlung?
Q. Differentiate between Kα and Kβ?
Q. How for analytical purposes X-rays are obtained?
- Bombardment of a metal target with a beam of high energy electrons.
- By exposure of a substance to a primary beam of X-rays inorder to generate a secondary beam of fluorescent rays, and
- By a radioactive source whose decay process results in X-ray emission.
Q. What analytical information is provided by X-rays?
- Absorption of X-rays gives information about the absorbing material, just as in other spectral regions.
- The diffraction of X-rays permits analysis of crystalline materials with a high degree of accuracy and specificity.
- Wavelength measurement identifies the element in the excited state samples.
- Measurement of radiant power at given wavelength can be quantitative indicator of the composition of the sample.
Q. Which instrument can be used for X-rays measurement and what are its components?
Q. What detectors are being used in X-rays absorption and emission analysis?
- Photographic detectors
- Gas ionization detector
- Scintillation detector
Q. Make a comparison between X-ray absorption and X-ray emission?
- For general elemental analysis the X-ray emission is versatile than X-absorption. Emission has advantages of spectral line specificity and sensitivity of one or two orders of magnitude greater than absorption.
- X-ray emission is applicable to a wide range of elements without changing any instrumental parameter other than Bragg angle.
- X-ray emission methods are applicable to all elements having atomic number 11 to 92, with some practical and theoretical limitations, in the case of low atomic number elements.
- A unique advantage of the absorption edge method over emission is the elimination of matrix effect which is inherent in emission analysis.
- Concentration can be calculated from absorption edge measurement without recourse to the use of standards.
- The lower limit of detection by emission method is a function to peak to back ground ratio and the number of photons mounted.
Q. What do you know about X-ray diffraction?
Q. Why crystals diffract X-rays?
Q. Define Bragg law?
Q. What are the most important requirements of diffraction?
- The spacing between the layers of atoms must be roughly the same as the wavelength of radiation.
- The scattering centre must be specially distributed in a highly regular way.
Q. What are advantage and disadvantage of X-ray methods?
- X-ray methods are non-destructive in nature.
- X-ray analysis can be applied to amorphous or crystalline samples in any physical state of sub-division.
- There is no consideration of electrical and mechanical properties of samples.
Disadvantages of X-ray methods
- The accuracy of method depends upon the surface preparation, reliability of standards, stability of the X-ray tube output and number of X-ray photons counted.
- At one percent concentration level the line intensity and line to background ratio is sufficiently high.
- Instrumental and sample variables affect the analysis. Three variables can, however, be reduced to less than using standardized techniques and modern instruments.