Precision tests of calculated internalconversion 134 coefficients the

Precision tests of calculated internal-conversion 134 coefficients: the case of Cs. What is an Internal Conversion Coefficient (ICC) and why do we care? The internal conversion coefficient of a transition is defined as the ratio of the probabilities of internal conversion (green) to -ray emission (red). Importance: • Nuclear decay schemes – Spin and parity assignments, Transition rates, Branching ratios • Detector calibration W. E. Rockwell, Mount Holyoke College H. I. Park, J. Goodwin, N. Nica, V. E Iacob, J. C. Hardy Cyclotron Institute, TAMU Summer 2005 Impurities The major impurities found were 56 Mn, 122 Sb, 124 Sb, 134 Cs, 82 Br and 80 Brm. Problems Internal Conversion occurs when the energy from the de-excitation of a nucleus is transferred to an atomic electron and the electron is ejected. Experiment: • Made solutions of Cs. NO 3, Cs. Cl, Cs 2 CO 3 using very pure chemicals. • Made a thin circular layer of very diluted insulin on a 1 inch square of Mylar • Dropped 0. 05 ml of each solution on layer of insulin. • Dried drops using vacuum chambers and a dry box and covered with hat shaped tops • Neutron activated samples at TRIGA reactor in the Texas A & M University Nuclear Science Center 133 Cs(n, ) --> 134 Cs • Used a disposable vacuum bag to cut off hat-like top and covered sample with Kapton tape • Placed sample exactly 15. 1 cm from detector and took 3 -5 consecutive spectra. • Calculated ICC values depend strongly on how theory deals with the hole left by the departing conversion electron. • One approach assumes that it is filled instantaneously, while the other considers that it stays empty throughout the entire conversion process. • In S. Raman et al, Phys. Rev. C 66, 044312 (2002) experimental values of ICCs were used to help make the argument that the “no hole” theory fit the experimental data better. • The problem with the “no hole” theory is that in fact the electron leaves the atom in less time that it takes for the atomic hole to be filled. • Most calculated results of ICCs are only known to agree with experimental results on an average of a few percent, and there are some cases of much more significant discrepancies. • To date there are few exact measurements of ICCs with an uncertainty below one percent and this lack of precision makes it difficult to be definitive about the validity of either treatment of the hole. Decay Scheme Energy (ke. V) Results and Calculations K-shell ICC fluorescence yield N peak area detector efficiency Subscript K designates K-x rays, which result from internal conversion, and subscript designates the transition - rays. Ratio of the ICC of 134 Cs to 137 Ba The subscript 1 indicates 134 Cs and the subscript 2 indicates 137 Ba. From ENDSDF website * I would like to give a special acknowledgement to my advisor J. C. Hardy and to N. Nica who worked with and advised me on a day-to-day basis. Our Results: Ratio of the ICC of 134 Cs to 137 Ba