1. LABORATORIO DE ANÁLISIS POR ACTIVACIÓN NEUTRÓNICA (LAAN) CLEA NUCLEAR ENGINEERING DEPARTMENT ATÓMICO BARILOCHE CENTRO ATÓMICO BARILOCHE COMISIÓN NACIONAL DE ENERGÍA ATÓMICA ARGENTINA

2. RA-6 reactor Main Purpose: Teaching for the School of Nuclear Engineering at Instituto Balseiro  ther in core : 7x10 12 n.cm -2.s -1 (max) Others: NAA personnel training material testing Beams :Boron Neutron Capture Therapy (BNCT) Neutrography PGNAA Operation & core configuration: on request

3. FACILITIES FOR NAA: RA-6

4. Neutron Activation Analysis Laboratory (LAAN) Sergio RIBEIRO GUEVARA Eric DORVAL María ARRIBÉRE “Consultants”Abraham KESTELMAN nucl. measurem. Erhard ACHTERBERG nucl. data evaluation RA-6 Francisco LESZCZYNSKI

5. FACILITIES FOR NAA: RA-6 Only Instrumental NAA At RA-6: irradiation boxes 1 pneumatic transfer system (1 sec. traveling time) 10% eff. HPGe (n-type) + electronics In 2 wooden “buildings”, for low background counting 30% eff. HPGe (p-type) + electronics LO-AX HPGe (planar) + electronics Biological and geological sample preparation rooms

6. NEUTRON FLUX MEASUREMENTS RA-6 started operation in 1983 Fuel: originally 93% enriched U from RA-3 Neutron spectrum was characterized between 1990-1992 in four irradiation positions (E5, F5, D8, I6) and was followed until now. Expected re-fueling: May-August? 2006 Fuel: 20% enriched U The neutron spectrum has to be characterized in at least two positions (E5, I6) or equivalents. Good news: the fuel is fresh, the history will be well known

7. 90’s calibration for the parametric method Goal: estimate elemental concentrations from integral nuclear parameters Høgdahl + Wescott conventions, assuming almost isotropic flux Measurement of working cross sections for some particular reactions Routine: irradiations with monitors for thermal, epithermal and fast neutrons For short irradiations: Mn, Au, Al For intermediate irradiations: Sc, Au, Al or Ni For long irradiations (>10 h): Co, Au, Ni Gamma self shielding: easy to address Neutron self shielding: were estimated and, if significant, avoided

8. 90’s calibration for the parametric method “multielement” flux calculation Slope:  0 /I*

9. TOOLS PC 3.4 GHz processor, 2 GB DDRM, 120 Gb HD, 800 MHz bus Software: Mandrake 10.1 Community Linux Platform Applications taken from libraries under the GNU public license Differential cross sections from ENDF-VI and JEF-2.2 libraries Nuclear grade materials for activation measurements RA-6: MCNP code

10. Planned approach The first positions to be characterized are in the core center, where flux is expected to be isotropic The assumptions for the flux characterization in the core center are:  linear anisotropy  flux modeled by Maxwell+ 1/E joint by the Horowitz-Tretiakoff function  the response functions will be computed using the differential cross sections with data taken from current libraries  validation by irradiation of monitors Neutron self shielding, Cd factors, foil borders effects are computed when needed

11. Planned approach  Au, almost independent of the “joint function” or Cd cut-off  Co, slight dependence on the “joint function” and/or Cd resonances  Mn, dependent of the “joint function” and/or Cd resonances  Sc, dependent of the “joint function” and the Cd cut-off Next irradiations: first check on the modeling. All monitors bare and under different cadmium thicknesses MCNP: a handout with his first calculations for the Fe and i6 irradiation positions has been prepared. First choice of monitors:

12. Planned approach + CRP To be defined…  Comparison of the analytical flux with MCNP for the core center and reflector  Explore the possibility to perform corrections for neutron self attenuation and cadmium factors by MCNP  Obtain a better estimate the effect of the sample irradiation can and other containers