Scission gamma rays
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CLEI Experiment
Scission Gamma Rays G. V. Danilyan1)* , J. Klenke2) , V. A. Krakhotin1), V. L. Kuznetsov1), 3) , V. V. Novitsky1), 4) , V. S. Pavlov1), and P. B. Shatalov1) Received March 27, 2009
Abstract—Gamma rays probably emitted by the fissioning nucleus 236 U∗ at the instant of the break of the neck or within the time of about 10−21 s after or before this were discovered in the experiment devoted to searches for the effect of rotation of the fissioning nucleus in the process 235 U(n, γf ) and performed in a polarized beam of cold neutrons from the MEPHISTO Guideline at the FRM II Munich reactor. Detailed investigations revealed that the angular distribution of these gamma rays is compatible with the assumption of the dipole character of the radiation and that their energy spectrum differs substantially from the spectrum of prompt fission gamma rays. In the measured interval 250–600 keV, this spectrum can be described by an exponential function at the exponent value of α = −5 × 10−3 keV−1 . The mechanism of radiation of such gamma rays is not known at the present time. Theoretical models based on the phenomenon of the electric giant dipole resonance in a strongly deformed fissioning nucleus or in a fission fragment predict harder radiation whose spectrum differs substantially from the spectrum measured in the present study. PACS numbers: 24.70.+s, 24.75.+i, 25.85.Ec DOI: 10.1134/S1063778809110027
INTRODUCTION While studying in detail, at the reactor of the Laue–Langevin Institute (Grenoble, France), a threevector correlation in the ternary fission of 235 U nuclei that was induced cold polarized neutrons, a large collaboration of researchers from various nuclearphysics centers discovered a shift of the angular distribution of light charged particles originating from this fission process [1]. The sign of the shift of this light-charged-particle angular distribution was determined by the direction of the neutron-beam polarization—that is, by the direction of polarization of the fissioning nucleus 236 U. The authors of [1] explained the effect that they discovered by the rotation of the 236 U nucleus before its disintegration to two fragments and called it a ROT effect. The above shift, which is determined by the geometry of the arrangement of the target and detectors for fission fragments and light charged particles, is seeming. Because of the addition of the radial and tangential 1)
Institute of Theoretical and Experimental Physics, Bolshaya Cheremushkinskaya ul. 25, Moscow, 117218 Russia. 2) Forschungs-Neutronenquelle Heinz Maier–Leibnitz (FRM II), 85747 Garching, Germany. 3) Institute for Nuclear Research, Russian Academy of Sciences, Troitsk, Moscow oblast, 142190 Russia. 4) Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia. * E-mail: [email protected]
velocities of a fragment at the instant of scission of the rotating nucleus 236 U, the trajectory of this fragment is in fact deflected from the initial direction of the deformation axis of 236 U, but it was with
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