Revision of the ISO 8529 Standards Calculations of the (AmBe) neutron spectrum

1. Revision of the ISO 8529 StandardsCalculations of the (AmBe) neutron spectrum J.-L. Chartier

2. Production of the (AmBe) neutron spectrum • Homogeneouscompressed mixture • 2 types of (a , n) reactions a) 9Be +  12C + n + 5.701 MeV • Break up reaction b) 9Be +  8Be + ’ + n – 1.665 MeV - Fission of Am

3. Computational tools for calculations (1) • Code SPAR (RSICC CCC-0228_001) Calculations of stopping powers and ranges • Code Sources-4C (RSICC CCC-661) Code system for calculating (,n), spontaneous fission and delayed neutron sources and spectra • Code ‘Norio’ Code system for calculating (,n) and (,’n) neutron spectra. Distributed by N.Tsujimura (JAEA)

4. Computational tools for calculations (cont.) • Code MCNPX 2.6.0 Transport of neutrons and alphas • Code SRIM 2008 Stopping and Ranges of Ions in Matter • Microsoft Studio Developer Used for home-made Fortran softwares and modifications in SPAR code

5. Model of (AmO2 /Be) mixture • Spherical clusters of AmO2 Radius range from Rc= 0 up to 3 mm • Calculation of the a spectra at the cluster surface (modifiedSPAR code) for several values of Rc • Graphs : a) with MCNPX b) with SPAR* code

8. Characteristics of (AmBe) source type X3 • Capsule type X3, material stainless steel • Capsule diameter x height (mm) : 22.4 x 31 • Capsule lateral wall thickness (mm) : 2.4 • Source materials : Be 4.6g ; AmO2 0.37g • Nominal activity (appr.) : 37GBq (1 Ci) • Emission rate (appr.) : 2.2 (10**6) n/s • ISO spectrum : E average = 4.16 MeV

9. Calculations with Sources_4C code (1) • Option 1 : "homogeneous mixture" (tape 1) • Modification of the "tape 5 input data" by inserting the a spectrum calculated at the Rc cluster surface (tape 5) instead of 241Am a spectrum • Graphs: - theoretical neutron spectrum versus Rc - emission rate versus Rc (n/cm3) - average neutron energy versus Rc

10. Spectres-4C (AmBe) theoretical spectra

18. Calculations with Sources_4C code (2) • Taking into account the geometry of the neutron source type X3 with MCNPX 2.6.0 • Graphs: - emergent neutron spectrum versus Rc (average spectrum on a spherical surface surrounding the source – Tally F2) - emission rate versus Rc (n/cm3) - average neutron energy versus Rc

19. Sources-4C + MCNPX (AmBe) theoretical spectra

26. Calculations with Sources_4C code (3) Conclusions: • the general shape of the ISO reference spectrum is obtained, but: • Strong differences (peaks, resolution, …) • Much higher average energies • No spectral contribution of the break-up reaction in the low energy range • Sources_5A version

27. Calculations with Sources_5A code (1) • Version Sources_5A code • E.F. Shores,G.E. Mueller and G.A. Schlapper Appl. Rad. and Isot. 59 (2003) pp. 151-158 A new 9Be(a,n) cross-section evaluation for use in the Sources computer code • Should take into account the breakup reaction 9Be(a,a 'n) by modification of tape4 branching fraction file

28. Calculations with Sources_5A code (2) • Practically the same results as those with Sources_4C code !!!

29. Calculations with "Norio" code (1) • Norio Tsujimura, T. Yoshida and T. Momose (Nuclear Fuel Cycle Engineering Laboratories) JAEA Rad. Prot. Dos. (2007), pp. 1-6 Calculations of anisotropy factors for radionuclide neutron sources due to scattering from source encapsulation and support structures

30. Calculations with "Norio" code (2) • Same model : spherical AmO2 clusters embedded in thick Be target • Calculation of the a-particles spectrum at the sphere surface ( modified SPAR code) • Calculation of the theoretical neutron spectrum taking into account both reactions: - 9Be (a,n) and 9Be (a,a'n) - cross-sections and their angular distributions (JENDL file 2005)

31. Calculations with "Norio" code + MCNPX 2.6 • The "Norio" theoretical neutron spectrum is used as an input neutron spectrum in the input MCNPX file • The characteristics of the X3 type source (geometry, materials, …) are also included in the MCNPX input file • Calculation of the average emitted neutron spectrum on a spherical surface surrounding the source (Tally F2)

32. Calculated neutron spectrum of X3 source derived from ("Norio" + MCNPX) codes • Graphs: - neutron spectra (Tally F2) - emission rate versus Rc - average neutron energy

33. Norio + MCNPX (AmBe) theoretical spectra

34. Influence of the initial alpha spectrum (1)

35. Influence of the initial alpha spectrum (2)

43. Characteristics of the (AmBe) source type X4 • Capsule type X4,material stainless steel • Capsule diameter x height (mm): 22.4 x 48.5 • Capsule lateral wall thickness (mm); 2.4 • Source material: ‘same density as X3 source’ • Nominal activity (appr.): 111Gbq (3 Ci)

45. (AmBe) source type X4 • Fluence Z (tally F5) : 3.0129 E-3 n/cm² per p. • Fluence Y (tally F5) : 3.4083 E-3 n/cm² per p. • Eaver = 4.340 MeV • Fluence (tally F2) : 3.2914 E-3 n/cm² per p. • Eaver = 4.375 MeV

46. A few comments (1) • 2 series of results were presented • Neutron spectra obtained with‘Norio code’ are consistent with measured ones • Higher average energy • Continuation of calculations Which ones ? Estimation of uncertainties ?

47. A few comments (2) • Estimation of uncertainties is not easy - the manufacturer doesn’t want to communicate the radioactive material’s characteristics - the manufaturer doesn’t know the r.m.’s characteristics (density, …) with an accuracy lower than 20 to 30% - reproducibility of production ? - granulometry ?

48. A few comments (3) • For calculations modelling is necessary • How to validate a model when input data are not accurately known? • Calculations enable to visualize some modifications of the neutron spectrum with respect to selected input data • Normalisation of calculated results ?

49. Many thanks for your patience