T529

The Measurements of Electronic X rays
Correlated with Pionic X rays

Our group has been studying a pion capture process in molecules, especially inhydrogen compounds, in the liquid and gas phases. We have already revealed that thevalence electrons and chemical structure influence the pion capture and transfer processes[1-4]. When pions are captured in atoms or molecules, the pions are in high excited states atfirst, and then cascade to lower states by emitting pionic X rays (pX rays) or Auger electrons.
In the latter case, electronic X rays (eX rays) are also emitted. In the present study, weexamined the correlation between the eX rays and particular pX rays to understand the pion
capture mechanism microscopically.
The measurements were performed at pm-channel of KEK-PS. In this experiment,
we constructed a new measuring system consisting of three Ge detectors, which allowed us
to take correlation spectra of eX and pX rays in a lower energy region and more effectively.
We measured these X rays for Zn, Mo, Ag, Sn and Ta metals and Zn, Mo and Sn oxides.
4The typical pion beam intensity was about 1x10 p- per pulse.
The eX rays observed in the spectra are classified into two types. Some are thecharacteristic eX rays of target (atomic number Z) atoms emitted as a result of their
ionization by the pion beam, and the others are attributed to those triggered by the Auger
processes in the pionic cascade. Due to strong screening effect, the eX-ray energies ofpionic atoms are close to the characteristic eX rays of Z−1 atom, and they are shifted to ahigh-energy side. We show Z dependence of the energy shift in Fig.1. With the present
apparatus and counting statistics, it is difficult to identify the pion transition state incorrelating with these X rays.
Atomic and molecular states after the pion capture were also studied from therelation between eX rays and pX rays emitted in the pion capture process. In this purpose,
we extracted eX ray signals correlated with pX ray from the obtained spectra and thenexamined the difference in the fine structure of KX rays (the ratio of Ka to Kb X rays)
between Sn and Sn oxide. However, as shown in Fig.2, the number of correlated events istoo small to discuss on the difference quantitatively.
We are now developing a vacuum chamber for efficient detection of extremely low-energy X
rays, and improving the geometrical arrangement of the setup.

References[1] A. Shinohara, J. Shintai, T. Muroyama, M. Furukawa, T. Miura, Y. Yoshimura, T. Saito, T.
Ohdaira, and N. Imanishi, Phys. Rev. A, 53, 130-138(1996).
[2] A. Shinohara, T. Muroyama, C. Murata, M. Furukawa, T. Miura, T. Saito, A. Yokoyama,and S. Kojima, Phys. Rev. Lett., 76, 2460-2463(1996).
[3] A. Shinohara, J. Nucl. Radiochem. Sci., 1(1), 33-37(2000).
[4] A. Shinohara, T. Miura, A. Yokoyama, K. Takamiya, T. Kaneko, T. Muroyama, T. Saito, Y.
Hamajima, H. Muramatsu, S. Kojima, H.Baba, and M. Furukawa, Radiochim. Acta, 89, 849852(2001).

Figure Captions
Fig.1
Atomic-number dependence of the energy shift of Ka ray.
The vertical axis shows the difference in the energy of eX rays between Z−1 and Z atom
divided by the eX ray energy of Z−1 atom. As the atomic number Z is larger, the ratio ofenergy shift becomes smaller.
Fig.2
Observed photo spectrum in the electronic X-ray region for a Sn target.
Spectrum A is a single spectrum, and spectrum B shows coincidence events with(6-5) pX
ray. The numbers in parentheses indicate the main quantum-number transition of the pion
deexcitation