INR RAS - innovations

Nondestructive control of fission materials

The development of new methods of neutron registration remains the actual problem for the control of radioactive materials movement. In case of large freight traffic and conveyer system of freight examination at the transfer points, customs terminals and junctions it is important to create a compact and transferable dosimeter which is capable of conducting the nondestructive express-analysis of the presence of radioactive materials in cargo containers and luggage of probable terrorists at a small exposure time in the real- time scale. Thus it is necessary to have, whenever possible, the greatest sensitivity to register minimum quantities of radioactive substances, especially of fissionable materials of various chemical forms. To solve the problem of developing an express monitor for the nondestructive detection of α -emitting isotopes of trans-uranium elements it is proposed to measure neutrons from (α, n)-reactions on the light elements using a FGRM detector. The neutrons formed in the given reactions are supposed to be registered with the help of the reactions ⁹Be(n, α)⁶He or ²³Na(n,p)²³Ne using the target material of beryllium- or sodium-oxalate correspondigly.

For the nondestructive control of fission materials it is important to minimize the mass of target material. Then it is also possible to use the other not so sensitive nuclear reactions. One can imagine an installation of the nondestructive control in the airports as follows: the conveyer passes the luggage through a frame-like tube filling with powder of target material. The length of the frame perimeter would be ~3 m. At a tube diameter of ~2 cm the total mass of the target substance in the frame would be ~500 g.

To evaluate the detector sensitivity we shall assume that the source of neutron radiation represents a homogeneous mixture of an alpha-emitting trans-uranium isotope with any light element, i.e. O, F, C, Al, etc. The yield of fast neutrons from such a composition can be set equal to 10^-6 per alpha particle for an evaluation. For the sensitivity of the device it is then possible to obtain the following values: at a distance of 0.5 m from the container, the device is capable to register 40 g Th-230, 20 g Pu-239, 2 g Pu-240, 0.2 g Am-241 or 0.004 g Cf-250 during an exposition time of 1 minute. By increasing the mass of target material the detector sensitivity increases linearly.

Person for contact: Dr. Lebedev Sergej, Phone: +7(495)850-42-61