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

2. Production of the (AmBe) neutron spectrum
Homogeneous compressed mixture
2 types of (a , n) reactions
a) 9Be +   12C + n MeV
Break up reaction
b) 9Be +   8Be + ’ + n – 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 (modified SPAR 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 ; AmO g
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. (AmBe) theoretical spectra
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. (AmBe) theoretical spectra
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
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. (AmBe) theoretical spectra
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) : E-3 n/cm² per p.
Fluence Y (tally F5) : E-3 n/cm² per p.
Eaver = MeV
Fluence (tally F2) : E-3 n/cm² per p.
Eaver = 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