K- Shell X-ray Intensity Ratios of Fe, Ag and Te via Electron Capture Decay Employing 2π geometry S. B. Gudennavar 1* , S.G. Bubbly 1 , Daisy Joseph 2 , P. V. Sreevidya 1 and Linu George 1 1 Department of Physics, Christ University, Bangalore-560 029, INDIA 2 Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai-400 085, INDIA. * email:shivappa.b.gudennavar@christuniversity.in Introduction Over the past decades, the studies on nucleus have led to many major developments that have transformed our lives. Even though X- ray fluorescence studies could be traced long back, the topic remains still relevant owing to the increase in the applications of the accurate values of the X-ray fluorescence parameters in various fields. The radioactive decay of the unstable nuclides results in the generation of X-rays. It has been reported that the values of K shell X-ray intensity ratios following electron capture (EC) decay are different from the theoretical values as well as those obtained via photon induced excitations [1]. Several researchers had already made attempts to study the K shell intensity ratios by photon excitation methods employing reflection geometries [2]. But there are very few reports on the measurements of K shell X-ray intensity ratios of elements following decay processes, probably due to the difficulty in procuring strong radioactive sources. The measurement of K shell X-ray intensity ratios of iron, silver and tellurium via electron capture decay of Co-57, Cd-109 and I-125 are discussed here. Since the electron capture sources themselves will undergo decay to generate target X-rays, the need for seperate sources to excite the targets can be eliminated. We have employed 2π geometrical configuration method for the present investigation, which was previously developed by our research group [3]. The method requires only weak sources that can be handled safely without any personal radiation hazards. This eliminates the need for heavy shielding materials such as lead. Thus, the method is relatively cost effective and free from radiation hazards compared to all other methods. The obtained results are discussed in the light of the effects of electron capture decay on X-ray emission probabilities. Experimental In the present investigation, we have employed an X-ray fluorescence spectrometer consisting of a Si(Li) detector (sensitive surface area 20 mm 2 , 3.5 mm thickness, Be window of thickness 12.5 m, FWHM-140 eV at 5.9 keV), connected to a PC based 8k multichannel analyser. The weak 57 Co , 109 Cd and 125 I EC sources were obtained from Radio pharmaceuticals Division, Therapeutic and Reference Sources Section, BARC, Mumbai. These sources (2 Ci) were prepared on a plastic disc and covered with aluminised mylar film of thickness 0.7 mg/cm 2 . The 57 Co source having half-life of 270 days decays by pure EC to the excited state of 57 Fe emitting characteristic X- rays of iron and γ rays of 122 keV (85%), 136 keV (11%) and 14.39 keV (8.5%). The 109 Cd source having half-life of 453 days decays by pure EC to the isomeric state of 109m Ag which subsequently makes a transition to ground state through the emission of 88 keV γ-ray (5%). Similarly, the 125 I source, which have a half-life of 60 days, decays purely through EC to the isomeric state of 125m Te, which subsequently decays to the ground state, either through the emission of a γ-ray of 35.4 keV (7%) or by the emission of internal conversion electron (93%). The Si(Li) X-ray detector spectrometer was calibrated using various gamma and X- ray sources. Fixing the 57 Co source right on the face of the detector, a nearly 2 geometrical configuration is adopted and the K X-ray spectra of iron was acquired for the live time of 2000s in four trials. The K X-ray spectra of silver and tellurium were also obtained in the similar way by placing the 109 Cd source and 125 I source for the live time of 2000s and 3000s respectively. The intensities of K shell X- rays are measured and the detailed analysis of the obtained spectra are done using Origin Pro software. The