First of all I wish to thank everyone who answered my message. Your comments
really helped me!

My name is Leonid. I live in Russia and my occupation is teaching russian
language to foreign
students via e-mail ( http://AmusingRussian.narod.ru ).

During last 2-3 years I was receiving many letters from my students where they
asked wherher
radiation level in Russia is high or not. This summer I've received more than
300 such mailings.
So , I've decided to test it. I need to purchase radiation dosimeter in order to
measure radiation level
in my house and in region where I am living now (St. Peterburg).

I've found company DRGB (http://www.dosimeter.ru ) in Yellow pages . Then I told
them my problem.
Because they seemed to be interested I offered them to exchange links with me.
So, I've put a link
to their site and they put a link to my site.

Today I went to DRGB again and asked them if it is possible to use their device
for searching source
of radiation. They answered that the device was specially designed for this
purpose.

Then I asked them how often the calibration must be done. They told me that
calibration must be done
once during 2 years. When these two years will be over it's better to make
upgrade of the dosimeter
than repeat calibration.

New models of DRGB-dosimeters appear as often as computers do. Actually the DRGB
- dosimeter
is device with CPU and software in flash-memory. So, the dosimeter has many
common with computer.
That's why DRGB-support team recommended me to make upgrade instead of ordering
calibrations.