Fission Product Yield Data for the Transmutation of Minor Actinide ...

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The results of Kibkalo agree completely with the experimental data, and the calculations of Zhdanov are very close; both sets of calculations almost coincide for the pre-case, whereas the mass distributions of Zhdanov are always below that of Kibkalo in the post-case. ALICE-91 produces a flat distribution at 160 MeV that agrees with the other calculations, except for a ‘bump’ in the fragment mass range of 130–145 that indicates the presence of a peak around A = 138. 6.3. PART B BENCHMARK EXERCISE The results of part B of the benchmark exercise have not been analysed in detail because of the serious inability to explain the various discrepancies in part A. Explanations for the observed discrepancies and inconsistencies can only be given after a thorough study of the models themselves and the different treatments of fission modes, multichance fission, neutron emission, etc. The results of part B of the benchmark are probably valuable for such a study and are included on the CD-ROM. 6.4. INFLUENCE OF MULTI-CHANCE FISSION Most of the discussion of the benchmark intercomparisons are included in Section 5.2. Here we present only some additional details on the effect of multi-chance fission as reflected in the benchmark calculations. 6.4.1. Superposition of preferred fission modes The reduction of the mass and excitation energy of the fissioning nucleus as compared with the composite nucleus could cause a change in the preferred fission mode, leading to a superposition of fission modes that may become noticeable in the mass distributions at higher energies. At 100 MeV (Fig. 6.2.10), the asymmetric and symmetric fission modes are about equal in the observed mass distribution. Maslov has calculated significant contributions up to 11th chance fission at this energy (see Fig. 3.1.1 of Section 3.1). Asymmetric fission is likely to dominate below 100 MeV, and according to Maslov’s calculations we can expect significant contributions from fissioning nuclides down to 231 U (9th chance fission) with a possible preference for the symmetric fission mode. However, the expected contribution is probably not sufficient to change the shape of the mass distribution significantly. At energies above 100 MeV, symmetric fission starts to dominate and the contributions from higher chance fission are more significant. The symmetric distribution from lower chance fission is superimposed by asymmetric distributions centred at lower fragment masses, as observed by Duijvestijn (Section 5.1.3.6), and the composite mass distribution is no longer symmetric in shape. 6.4.2. Change in peak positions and mass symmetry point in asymmetric fission The observed mass distribution is composed of contributions from lower mass isotopes of the target nucleus. Consequently, the mass of fission fragments from these contributions is also reduced. Since the position of the heavy mass peak also remains stable for the lower mass isotopes of the target nucleus due to shell effects, the position of the light mass peak changes to lighter masses and the valley becomes broader. Thus the heavy mass peak remains more or less unchanged in height and position, whereas the light mass peak becomes smaller and broader with a slope towards the light mass wing. As a consequence, the whole distribution should become broader and asymmetric in shape. The point of symmetry in the mass distribution, defined originally as the point where both fragments have equal mass (symmetric fission), changes from the position of first chance fission towards lower masses (broader valleys), with decreasing mass of the fissioning nucleus. When the composite mass distribution is considered, the symmetry point becomes the point above and below which the sums of the mass yields are equal and total 100%. However, this new point of mass symmetry is not defined solely by the mass of the target plus projectile, minus the total number of neutrons emitted. At higher excitation energies, symmetric fission becomes significant and the position of the composite symmetric peak will also be broadened towards lower masses with increasing energy. This behaviour should lead to a broad flattened plateau instead of a Gaussian shaped peak, particularly in those energy regions in which asymmetric fission has a noticeable contribution. 277
278 REFERENCES TO SECTION 6 [6.1] BROSA, U., et al., Nuclear scission, Phys. Rep. 197 (1990) 167–262. [6.2] SCHMITT, H.W., et al., Precision measurements of correlated energies and velocities of 252 Cf fission fragments, Phys. Rev. 137 (1965) B837. [6.3] ZÖLLER, C.M., Untersuchung der neutroneninduzierten Spaltung von 238 U im Energiebereich von 1 MeV bis 500 MeV, PhD Thesis, Technische Universität Darmstadt, Germany (1995). [6.4] VIVÈS, F., et al., Investigation of the fission fragment properties of the reaction 238 U(n, f) at incident neutron energies up to 5.8 MeV, Nucl. Phys. A 662 (2000) 63–92.
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Fission Product Yield Data for the
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AFGHANISTAN ALBANIA ALGERIA ANGOLA
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COPYRIGHT NOTICE All IAEA scientifi
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CONTRIBUTING AUTHORS Denschlag, J.-
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3.2.1. Introduction . . . . . . . .
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6. BENCHMARK EXERCISE . . . . . . .
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However, this CRP entered an entire
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‘Provisional masses’ are determ
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Three scientists were invited to pa
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8 (d) Prompt or delayed neutron emi
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[2.1.40] ITKIS, M.G., OGANESSIAN, Y
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[2.1.96] PATE, B.D., et al., Distri
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[2.1.152] JACOBS, E., et al., Produ
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16 2.2. MEASUREMENTS OF THE ENERGY
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FIG. 2.2.3. 94 Sr: best experimenta
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FIG. 2.2.15. 132 Te: best experimen
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FIG. 2.2.27. 146 Ba: best experimen
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3. EVALUATIONS 3.1. ACTINIDE NUCLEO
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3.1.2. Statistical model At least t
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J Â K=-J 2 2 2 ^ sym Krot ( U, J)
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nuclei with N > 144. However, for h
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neutron number. The observed fissio
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FIG. 3.1.6. 235 U(n,f) fission cros
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FIG. 3.1.10. 237 Np(n,f) fission cr
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from higher fission chances [3.1.43
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[3.1.48] DUSHIN, V.N., et al., Stat
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where Y S is our new standard, and
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TABLE 3.2.2. EVALUATED REFERENCE FI
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TABLE 3.2.2. EVALUATED REFERENCE FI
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TABLE 3.2.3. EVALUATED REFERENCE YI
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TABLE 3.2.3. EVALUATED REFERENCE YI
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The comparisons of our evaluated da
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TABLE 3.2.4. COMPARISON OF RECOMMEN
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TABLE 3.2.8. COMPARISON OF THE UNCE
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REFERENCES TO SECTION 3.2 [3.2.1] I
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where N C , N U are the modified an
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activities were recorded with a pro
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3.3.4. Results and discussion The r
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FIG. 3.3.10. Li Ze et al. data: com
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96 Annex 3.3.1 EVALUATED EXPERIMENT
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Li Ze et al. [3.3.8] Thierens et al
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100 Annex 3.3.3 EVALUATED DATA SET
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The range of target nuclides availa
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condensation of cross-sections by t
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(h) REFERENCE (C,80KIEV,171,1980) i
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uncertainties of the calculation. T
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4. SYSTEMATICS AND MODELS FOR THE P
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FIG. 4.1.2. 235 U total cross-secti
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FIG. 4.1.9. Total and mode separate
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4.2. SYSTEMATICS OF FISSION PRODUCT
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A - = (PA - NT)/2 (4.2.1b) 4.2.2.3.
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FIG. 4.2.4(a). 238 U + 5.5 MeV n, L
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FIG. 4.2.8(a). U238 + 300 MeV p, LS
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TABLE 4.2.1. EQUATIONS FOR SYSTEMAT
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values (points) and the derived fun
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distributions. Values of N(A) seldo
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FIG. 4.2.19. Systematic Z P paramet
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FIG. 4.2.21. Systematic Z P paramet
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FIG. 4.2.23. Nuclear charge displac
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FIG. 4.2.24. Number of protons emit
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epresenting model values and thus s
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FIG. 4.2.36. n T(A) for CF249T. FIG
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FIG. 4.2.41. U235T, line: model; po
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The FAST subroutine in the CYFP pro
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[4.2.28] BELHAFAF, D., et al., Kine
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4.3. FIVE GAUSSIAN SYSTEMATICS FOR
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Derived from measured data Fitted r
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FIG. 4.3.7. Mass distribution of 23
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FFIG. 4.3.12. Mass distribution of
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4.4. PHENOMENOLOGICAL MODEL FOR FRA
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where = 2mE is the wavelength, E
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FIG. 4.4.4. Fragment mass distribut
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fragment mass distributions are des
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FIG. 4.4.10. Fragment mass distribu
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P LD È Ê * E - 44. 7ˆ ˘ = Í1 +
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FIG. 4.4.13. Pre-neutron emission m
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FIG. 4.4.15. Post-neutron emission
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FIG. 4.4.17. Post-neutron emission
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fragment mass and charge distributi
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of the energy dependence of the fus
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4.5. MODAL APPROACH TO THE DESCRIPT
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This information was used for the p
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two neighbouring isotopes at differ
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FIG.4.5.2. Experimental relative ma
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Frequently, the yields Y i (M) are
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the nine optimum description parame
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TABLE 4.5.6. RELATIVE CONTRIBUTIONS
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TABLE 4.5.8. RELATIVE CONTRIBUTIONS
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Extracted values of s 2 M,S demonst
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FIG. 4.5.10. Fission fragment charg
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FIG. 4.5.12. Unchanged charge densi
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FIG. 4.5.16. Mass yield variance fo
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FIG. 4.5.20. Experimental mass yiel
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[4.5.24] GOVERDOVSKII, A.A., MITROF
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TABLE 4.6.1. FISSION PRODUCT YIELD
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TABLE 4.6.2. FIT PARAMETER VALUES O
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FIG. 4.6.2. Charge distributions fo
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model which is elucidated elsewhere
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the agreement is better. The observ
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inner barrier is much lower than th
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e determined in a self-consistent m
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FIG. 4.6.11. Overview of the coupli
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Page 267 and 268: 256 Valley heights and peak-to-vall
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Page 271 and 272: 260 Wahl uncert. margins Wahl uncer
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Page 301 and 302: 1. 290 Annex to Appendix I RECOMMEN
Page 303 and 304: 1.2. E n = 5.5 MeV 292 Nagy et al.
Page 305 and 306: 1.3. E n ª 8 MeV 294 Chapman (1978
Page 307 and 308: 1.5. E n = 14-15 MeV 296 Daroczy et
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Page 322 and 323: Zöller (1995) [II.7] E n = 13 (11.
Page 324 and 325: E n = 50 (45-55) MeV Post-neutron e
Page 326 and 327: Äystö et al. (1998) [II.9] E p =
Page 328 and 329: E n = 1.60 MeV Pre-neutron emission
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Page 332 and 333: E n = 99.5 (89-110) MeV Post-neutro
Page 334 and 335: Appendix III FISSION YIELD SYSTEMAT
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TABLE III.2. Ln(y)-LINEAR(E) FIT CO
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FIG. III.14. Dependence of paramete
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FIG. III.26. Comparison of the mass
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FIG. III.38. Comparison of the mass
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TABLE III.3. QUADRATIC FUNCTION FIT
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Uncertainty ratio or uncertainty Ad
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CONTENTS OF THE CD-ROM The attached
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This publication reports on a coord
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