Yu. Dudchik
A.N. Sevchenko Institute of Applied Physics Problems of Belarusian State University
Belarus

Address for correspondence:
Dudchik Yury - 
A.N. Sevchenko Institute of Applied Physics Problems of Belarusian
State University,
Kurchatov str., 7,
Minsk 220045,
Belarus
e-mail: dudchik@bsu.by

I. Balukho
A.N. Sevchenko Institute of Applied Physics Problems of Belarusian State University
Belarus

Iren Balukho - 
Kurchatov str., 7,
Minsk 220045

N. Kolchevsky
A.N. Sevchenko Institute of Applied Physics Problems of Belarusian State University
Belarus

Nickolai Kolchevsky -
Kurchatov str., 7,
Minsk 220045