Cairo University

MTPR Journal

 

X-Rays of Heavy Elements for Nanotechnological Applications: W and Pb Ions

& doi: https://doi.org/10.1142/9789814504898_0041
Sultana N. Nahar
Department of Astronomy, The Ohio State University, Columbus, OH 43210, USA

Vol./Issue: 13 , id: 383

Heavy elements can absorb or emit hard X-rays and hence are commonly implemented in various high energy nanotechnological applications. The absorptin or emission occurs mainly through the 1s-2p (Kα) transitions, and the process can be used as the source for production of radiation or electron in the applications. For enhanced productions of electrons and photons in the nanobiomedical applications, investigations have focused on the K-shell ionization of the atom or ion. This is because of the well-known rise in photoionization at the K-shell ionization threshold. However, experimental investigations to find any evidence of this rise has not been successful. We have developed a new method called Resonant Theranostics for biomedical applications, where we show that the energy for the rise is related to 1s-np, particularly to 1s-2p transitions which appear as resonances in the photoionization for heavy elements. The energy for the 1s-2p transitions varies some with the ionic state of the element and gives a narrow band resonant energy for the element. The strength of the process depends on the oscillator strength of the transitions. This report will demonstrate these through illustrations of the resonant energy range and strengths of photoabsorption due to K-alpha transitions using some elements, such as tungsten (W, Z=74) and lead (Pb, Z=82). An X-ray photon can ionize a high-Z element by ejection of a K-shell electron. This will create a hole or vacancy which, through the Auger process, will be filled out by an upper shell electron with emission of a photon. Such process at the resonant energy can lead to Koster-Kronig cascade giving out a number of photons and electrons as the element goes through various ionic states and can be modeled using the oscillator strengths. Such emissions are highly desirable in radiation therapy application. Present illustrations will include electric dipole allowed transitions for nine ionic states, from hydrogen to fluorine like ions. The 2p subshell is filled beyond fluorine. The number of transitions in each ionic state is different because of different number of 2p electrons. There are 2, 2, 6, 2, 14, 35, 35, 14 and 2 transitions in H-, He-like, Li-like, Be-like, B-like, C-like, N-like, O-like, and F-like ions respectively, with a total of 112 Kα transitions for each element to occur in the event of breaking of the ionic states, such as, due to Auger process. The Kα transitions are found to be in hard X-ray region of 57 - 63 keV (0.22 - 0.20 Å) for W, and 71 - 80 keV (0.17 - 0.16 Å) for lead.