Gyors neutronok / Fast neutrons

Research and applications with fast neutrons

Two beam lines are available for irradiations with fast neutrons. At the high intensity irradiation site a water and He-gas cooled beryllium target is used for producing p+Be and d+Be neutrons with broad spectra mainly for application purposes. The low intensity irradiation site is used for neutron physics research either with broad spectrum d+Be neutrons or with quasi-monoenergetic d+D neutrons produced using a D₂-gas target.

There has been a broad range of research and applications of the neutron sources within the frameworks of numerous collaborations with local groups of ATOMKI, other institutions in Debrecen and collaborators from Hungarian and international institutions.

Neutron physics

• Cross section measurements

• Neutron transport studies

• Integral measurements for validation of evaluated excitation functions and cross section data libraries

New cross section data have been measured for the excitation function of several neutron induced nuclear reactions in the E_n = 6-11 MeV neutron energy range using quasi-monoenergetic neutrons.

A search for discrepancies of cross section data was also performed via integral testing methods. In the first method cross sections integrated for well known broad spectra of d+Be neutrons were measured and compared with data of evaluated libraries and/or results of theoretical calculations for the excitation functions. In the second method, at fast neutron sources (d+Be, d+D, d+T, Pu-Be) with well known spectra, transmission type benchmark neutron transport experiments have been done for bulk media of different shielding materials (graphite, aluminum, iron, lead, bismuth, water, polyethylene and sand). The measured spectra of neutrons (leakage spectra) were compared to results of Monte-Carlo simulations performed using cross section data of different versions of evaluated neutron data libraries (ENDF, JENDL, JEFF). Several discrepancies of cross section data have been found using the two types of integral testing method.

Bio-medical applications

• Physical dosimetry of mixed neutron-gamma fields

• Radiobiological research with human cells, bacteria and small animals related to fast neutron radiotherapy

• Study of the effects of radio-protector and hypoxic radio-sensitizer compounds in mixed neutron-gamma fields

• Study of the synergic effects of neutron irradiation and infections by bacteria

• Biological dosimetry

These studies provided important radiobiological information that can be used in planning and assessment of effects of fast neutron exposition of human individuals (e.g. fast neutron radiotherapy, radiation protection related issues at nuclear and high energy physics installations and space applications, military applications etc.).

Agro-biological applications

• Induction of mutations in seeds of hybrids and inbred lines (rice, soybean, wheat, corn, onion, tomato, pea, bean etc.) for breeding purposes

• Study of neutron and gamma photon induced electron traps in different media (milk powder, bones, teeth etc.)

As a major result a new maize gene bank has been available at the Center of Agricultural Sciences of Debrecen University with 1500 maize lines with broad genetic variability, resistance and adaptability. The great genetic variability can be exploited after strict assessment and selection. Up to now three of the lines have been released after investigation of the distinctness, uniformity and stability (often referred to as the “DUS criteria”).

Radiation damage studies with fast neutrons

• Electronic and photonic devices: analogue ICs, memories, ASICs, light sources (LEDs and laser diodes), photo sensors (PM-tubes, a-Si Shottky sensors, p-i-n sensors, CCDs, CMOS active pixel sensors), optical materials (glues, glasses), optical fibers, optocouplers

• Thin layer structures: Si-SiO₂, amorphous Si, SiC, CVD diamonds

• Detectors: silicon diodes, silicon microstrip detectors, parallel plate ionization chambers

• Systems: tiltmeters

Fast Neutron Activation Analysis (FNAA)

• Materials used for packaging integrated circuits

• ICs produced by flip-chip bond technologies

• Activation of multi-chip modules

• Estimation of the effects of neutron activation on device characteristics of ICs

The aim of the radiation damage and FNAA studies is the development of radiation tolerant components, devices and systems that can operate in radiation environments with neutron component (e.g. nuclear installations, high energy physics experiments, space, avionics and military applications). Most of the results have been used for the development of different subsystems of the CMS, ATLAS and ALICE high energy physics experiments at the Large Hadron Collider at CERN (Geneva, Switzerland).

Results of the memory tests have been used for selecting the components of the on-board mass storage system of the SMART-1 satellite of the European Space Agency (ESA). SMART-1 spiraled its way to the Moon using solar-electric propulsion and carrying a battery of miniaturized instruments. Because of the small thrust of its ion propulsion engine the satellite was exposed by the harsh radiation environment of the van Allen belts of Earth for weeks during its long journey to the Moon.