1. Measurements and calculations of the neutron spectrum in different irradiation channels of the TRIGA Mark II reactor, Slovenia R. Jaćimović 1, A. Trkov 2, M. Maučec 3 1 “Jožef Stefan” Institute, Ljubljana, Slovenia 2 IAEA, Vienna, Austria 3 HOLTEC International, Marlton, USA 1 st RCM of the IAEA CRP on Reference Database for NAA, Vienna, Austria October 2005

2. Introduction TRIGA Mark II reactor (250 kW) at the JSI from 1966. The k 0 -standardization method was introduced in 1987. TRIGA Mark II reactor (250 kW) –irradiation channels, –neutron spectral parameters, –neutron fluence gradients, –neutron self-shielding. Calibrated HPGe detector –absolutely calibrated point sources, –counting geometry.

3. Nuclear research reactor TRIGA Mark II (250 kW) - Short and long irradiation in the CC:  th ~ 10·10 12 cm -2 s -1 - Short irradiation in the PT and in the FPTS (up-to 30 min.)  th ~ 3.5·10 12 cm -2 s -1 - Long irradiation in the IC-40 (typically 20 hours)  th ~ 1.1·10 12 cm -2 s -1

4. Horizontal section of the TRIGA Mark II reactor (core No. 176)

5. Relevant nuclear data used for determination of f and  F. De Corte, A. Simonits, Atomic Data and Nuclear Data Tables, 85 (2003) 47-67.

6. Spectral parameters of the neutron fluence rate: f and 

7. Experimental and MCNP results for thermal neutron fluence rate

8. Comparison of experimental results for reaction rate with these of Monte Carlo calculations in 11 carousel channels at the TRIGA reactor. Parameter f was obtained only by simulation

9. Temporal variation of the neutron fluence rate in the IC-40 channel F(t) = 1 + k·t

10. The power of the TRIGA Mark II reactor reading from the safety channel 27. and 28.1.2003

11. Temporal variation of the neutron fluence rate in the IC-40 channel 20. and 21.1.2003 TH2: at the mean of the pool water at 0.5 m depth TH1: at the entrance near the reactor wall at 1 m depth

12. Axial and radial gradients of the neutron fluence rate Fe wire  = 0.4 mm Thermal neutron fluence rate: 58 Fe(n,  ) 59 Fe Fast neutron fluence rate: 54 Fe(n,p) 54 Mn From the same  spectrum !!!

13. Normalized specific activities of 59 Fe and 54 Mn vs. density for five matrices in the IC-40 and in the PT channels IC-40 PT IC-40PT

14. Specific activities and factors G th, F org and F inorg G th - not characteristic of nuclei, but depending of dimensions and composition of the sample G th,org = 1.01G th,inorg = 0.97 Cellulose Muscle H 2 O SiO 2

15. Axial and radial gradients of the thermal neutron fluence rate in different samples PTIC-40 -1.3%/cm 3.8%/cm 3.0%/cm 1.8%/cm

16. HPGe closed end coaxial detector (OR4) 40% relative efficiency at 1332.5 keV ( 60 Co) (dimensions are in mm)

17. Geometrical correction factor for absolute calibration for detector OR4 Detector OR4