Ljubljana Neutron Irradiation Facility

The reactor research centre which is a part of Jozef Stefan Institute, has an experimental nuclear reactor of type TRIGA.

Irradiation of a sample is done by placing it into the core through an irradiation tube which occupies a fuel rod position.
ATLAS group uses two such irradiation tubes which are located at the edge of the core. The tubes have different dimensions:
the smal tube has a circular cross section with 2.2cm diameter and  the large tube has an eliptic cross section with axis lengths 7 and 5 cm.

The irradiation tubes enter the core from above and are about 5m long because the core is covered with 5m of water. The tubes are curved in a shikane just above the core to prevent radiation from the core escaping through the tube. The shikane limits the length of the sample to be irradiated to about 15cm.

The neutron energy spectrum in the tube was determined  by measuring the activation of foils of different materials. The spectrm is shown in the figure below and one can compre measureements with simulation of the spectrum.


 

                           Neutron energy spectrum in the irradiation tube
 

Using the measured energy spectrum and damage functions one can determine the flux of 1MeV NIEL equivalent neutrons. NIEL equivlent flux was also measured using the leakage current method (see M. Moll, E. Frewurst, G. Lindstroem, Leakage current of hadron irradiated silicon detectors - material ependence, Nucl. Instr. & Meth. in Phys. Res. A426(1999) 87-93)

Since the flux is linearly proportional to the reactor operating power the flux of 1MeV NIEL equivalent neutrons in our reactor is:


The reactor can be run with large span of operating powers (few W to 250 kW), enabling irradiations with various neutron fluxes. More information about neutron spectra can be found in (L. Snoj et al., Applied Radiation and Isotopes 70 (2012) 483–488)