Radiation Physics

Q1 . a ) Moseley 's law concerning the relationship between wavelength of a characteristic X-ray photon and the atomic number Z of an excited element can be expressed by the following equations (Beiser 1995 .Here ? is wavelength of the X-ray photon corresponding to electronic transition from ni to nf

RH 1 .097 107 m-1 is Rydberg constant

Z is atomic number of the excited atom

ni and nf are respectively initial and final orbit numbers of the electron undergoing transition

Thus this law states that energy of an electron in an excited atom

with atomic number Z is directly proportional to (Z-1 )2 and inversely proportional to the square of the orbit number

Q1 . b ) It is interesting to see how the general form of Moseley 's law can be predicted form the Bohr 's theory (Serway , Moses and Moyer 1997

Bohr 's theory gives energy of an electron in the nth shell of an one electron system having charge Ze in its nucleus as (1

Now let us consider a multi electron system with Ze charge on its nucleus and one of the K shell electrons being knocked off from its orbit , leaving a hole in K shell

Now let us consider an electron in nth shell , which can drop to this empty hole giving emission of a characteristic X-ray photon . This electron will see an effective charge of (Z - 1 )e in the nucleus as the K-shell electron is very near to the nucleus and it shields the nucleus...