**3. Conclusion**

120 Radioisotopes – Applications in Physical Sciences

check the validity of the angular dependency of experimental L X-ray cross sections. The experimental K X-ray cross sections were compared with theoretically calculated values and fairly good correspondence was observed. This means that the present measurements

In following the work of us (Han et al., 2009) experimental results of the angular distribution of characteristic X-rays were introduced. We preferred to use of *ILa* /*ILl*(θ) intensity ratios to obtain the values of alignment parameters (A2). In that case, the background subtraction problem is considerably reduced and statistical errors are significantly less. It was observed from measured intensities that L*a* and L*l* X-ray intensities for the L3 sub-state depended on the emission angle, meaning that L*a* and L*l* X-rays had an anisotropic spatial distribution. Thus, the L*a* to L*l* intensity ratios for a set of elements was determined and alignment parameters for each element were obtained using these ratios. In this study, three L subshells electrons were excited. Therefore, alignment parameter values are influenced by Coster–Kronig transitions from vacancies induced in the L1 or L2 sub-shells. L1 and L2 subshells have the same J= 1/2 value therefore the transferred vacancies are not-aligned and the observed anisotropy of the X-rays is attenuated. For this reason, corrected value of the alignment parameter was calculated using attenuation factor F. If photon energies exciting only L3 sub-shell electrons are chosen, the alignment parameter will be independent from

In more recently study (Han and Demir, 2011a), we investigated the angular distribution of characteristic L X-rays emitted from heavy elements (Pt, Au, Pb, Bi, Th and U) as a result of L shell vacancy production by 59.54 keV photon impact and angular distribution of Compton scattering photons from the same elements. Thus, emitted fluorescent L X-rays and Compton scattering photons from elements were simultaneously measured in the same experimental geometry. Earlier experimental investigations have been only performed on the angular distribution of L X-rays or Compton scattering photons. This is the first report of the angular distribution of L*i* (*i*= *l*, *a*, *β* and *γ*) X-rays fluorescent and Compton scattering differential cross sections for Pt, Au, Pb, Bi, Th and U at different angles in the same experimental geometry. It is well known that Compton scattering differential cross sections have angular distribution. The experimental investigation on Compton scattering differential cross sections at different angles was made to check the validity of angular distribution of experimental L X-rays fluorescent differential cross sections. The experimental Compton scattering differential cross sections were compared with theoretically calculated values and fairly good correspondence was observed. This means that the present measurements regarding angular distribution of L X-rays are reliable. In the meantime, L3-subshell alignment of Th and U ionized by 59.5 keV photons has been investigated by evaluating the angular dependence of L*i* (*i*=*l*, *a*, η, *β* and *γ*) X-ray lines. The angular dependence measurements were performed by measuring the fluorescence cross section, σ*Li* (*i*= *l*, *a*, η, *β* and *γ*) and σ*Ll*/σ*Lγ*, σ*<sup>L</sup>*η/σ*Lγ*, σ*La* /σ*Lγ* and σ*Lβ*/σ*Lγ* ratios at different angles. It was observed from the measurements that L*i* (i=*l* and *a*) X rays for the L3-subshell depended on the emission angle and had an anisotropic spatial distribution. On the other hand, there was no dependence of emission angle and any significant anisotropy for other L X rays. The both L*l* and L*a* X-rays originate from the filling of vacancies in states L3-subshell with *J* = 3/2. The results of measurements indicate that the L3-subshell vacancy states with *J* =3/2 are aligned, whereas L1, and L2 vacancy states with *J* =1/2 are non-aligned. Integral cross-sections for the L*i* (*i*= *l*, *a*, η, *β* and *γ* ) X-rays and L subshell fluorescence yields ω*<sup>i</sup>* (*i*= 1, 2 and 3) were also determined and results were compared with theoretically calculated

regarding angular dependency of L X-rays are reliable.

Coster–Kronig transitions

In the light of all these, above; data from different researchers show contradictory and the existing results on the angular dependence of fluorescence X-ray and the alignment of atoms with inner-shells vacancy following ionization are still controversial and quite confusing. Therefore, more experimental and theoretical investigations should be required to settle the present discrepancies
