Program - Brookhaven National Laboratory

[3] and theoretically predicted [4,5] relative increased neutron multiplicity for the heavy fragments with
higher incident neutron energies has been studied. The impact is found to be noticeable on post-neutron
mass yields, which are the relevant quantities for a-priori waste assessments. The fission cross sections for
240,242 Pu at threshold and in the plateau region are being investigated within the ANDES project [6]. The
results show some discrepancies (up to 12 %) to the ENDF/B-VII evaluation mainly for 242 Pu around 1
MeV, where the evaluation exhibits a resonance-like structure not observed in the present work. The requested
target accuracy in design studies of innovative reactor concepts like Gen-IV is in the range of a few
percent. In order to be able to respond to requests for measurements of prompt neutron and gamma-ray
emission [7,8] in fission IRMM has also invested in setting up a neutron and gamma-ray detector array. The
neutron array is called SCINTIA and has so far been tested with 252 Cf(SF). For gamma-ray multiplicity
and spectrum measurements lanthanum- and cerium-halide detectors are being used, and first quantitative
results for 252 Cf(SF)and 235 U(nth, f) will be reported.
[1] E. Birgersson et al., Nucl. Phys. A817, 1 (2008). [2] A. Al-Adili et al., Nucl. Instr. Meth. A624,
684 (2010). [3] A. Naqvi et al., Phys. Rev. C34, 21 (1986). [4] K.-H. Schmidt and B. Jurado, Phys.
Rev. C83, 061601 (2011). [5] C. Manailescu et al., Nucl. Phys. A867, 12 (2011). [6] ANDES project,
http://www.andes-nd.eu/. [7] G.Rimpault in P.Rullhusen (Ed.), Proceedings of the Workshop on Nuclear
Data Needs for GenerationIV, Antwerp, Belgium, WorldScientific, ISBN981- 256-830-1, 2006, April 2005,
p.46. [8] G.Rimpault, A.Courcelle, D.Blanchet, Comment to the HPRL:ID H.3 and H.4, /http://www.oecdnea.org/html/dbdata/hprl/tmp/HPRLgammafission.pdf.
RA 2 11:00 AM
Dynamical Scission Model
N. Carjan, M. Rizea
National Institute of Physics and Nuclear Engineering ”Horia Hulubei”, PO Box MG-6, 077125,
Bucharest-Magurele, Romania
The sudden approximation has been recently used to calculate microscopic scission-properties during the
low-energy fission of 236 U [1,3]. The purpose of the present paper is to go beyond this mathematical
approximation and consider the real physical situation in which the scission process, i.e., the transition
from two fragments connected by a thin neck (αi) to two separated fragments (αf ) takes place in a short
but finite time interval ∆T . For this we follow the evolution from αi to αf of all occupied neutron states
by solving numerically the two-dimensional time-dependent Schrödinger equation with time-dependent
potential. Calculations are performed for mass divisions from AL = 70 to AL = 118 (AL being the light
fragment mass). The exact duration of the neck rupture is unknown. ∆T is therefore taken as parameter
having values from 0.25 × 10 −22 to 9 × 10 −22 sec. The resulting scission neutron multiplicities νsc and
primary fragments’ excitation energies E ∗ sc are compared with those obtained in the frame of the sudden
approximation (that corresponds to ∆T = 0). As expected, shorter is the transition time more excited
are the fragments and more neutrons are emitted, the sudden approximation being an upper limit. For
∆T = 10 −22 sec, which is a realistic value, the time dependent results are 20% below this limit. For
transition times longer than 6 × 10 −22 sec the adiabatic limit is reached. The spatial distribution of the
neutron emission points at scission is also calculated as function of the transition time ∆T . Together with
the current density, it provides a detailed picture of the emission mechanism and a hint for the angular
distribution of the scission neutrons with respect to the fission axis. Finally, the contributions of the light
and of the heavy fragments to νsc and to E ∗ sc are estimated.
[1] N. Carjan, P. Talou, O. Serot, Nucl. Phys. A 792(2007) 102 [2] N. Carjan, M. Rizea, Phys. Rev. C 82
(2010) 014617 [3] N. Carjan, F.-J. Hambsch, M. Rizea, O. Serot, Phys. Rev. C 85 (2012) 044601
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