• Dr. MEETA SAH

Sommerfeld, in his pioneering work of analyzing the effect of electrons present in different orbits on the nuclear charge, introduced two screening parameters σ_(1 ) and σ_2 in the Sommerfeld-Dirac relativistic energy expression. But the relativistic expression was used in the expanded form in the initial works and approximation was made to truncate the infinite series after a certain term. A number of researches and efforts were made since the introduction of screening parameters to get complete information about their behavior. Some authors questioned the need of two separate screening parameters but Sommerfeld gave a perfect justification for the need of two parameters σ_(1 ) for the screening effect of the electrons situated in orbits both internal and external to the one under consideration and σ_(2 )for the screening of nuclear charge by the electrons present in the orbits inner to the one under consideration. As the work on screening parameters progressed, precise and accurate energy data became available thereby enabling the research work to provide a comprehensive and reliable list of σ_(1 ) and σ_2 values. The present review paper gives an account of studies made on screening parameters right from the time of their inception to the work done during early seventies. As a lot of work is done after this period also, it would be justified for convenience of the reader to divide the entire work into segments. The later studies in this field would be analyzed in forthcoming review papers.

Screening parameter, fine structure, Sommerfeld- Dirac relativistic energy expression, spins doublets, elliptic orbits,

"SCREENING CONSTANTS IN X-RAY SPECTRA: A REVIEW", International Journal of Emerging Technologies and Innovative Research (www.jetir.org), ISSN:2349-5162, Vol.8, Issue 6, page no.a156-a161, June-2021, Available :http://www.jetir.org/papers/JETIR2106022.pdf

"SCREENING CONSTANTS IN X-RAY SPECTRA: A REVIEW", International Journal of Emerging Technologies and Innovative Research (www.jetir.org | UGC and issn Approved), ISSN:2349-5162, Vol.8, Issue 6, page no. ppa156-a161, June-2021, Available at : http://www.jetir.org/papers/JETIR2106022.pdf