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Spontaneous Fission


Measurements of the Fission Neutron Multiplicity Distribution in Spontaneous Fission of Cm-244, Cm-248 and in Fission of U-233 and Pu-239 Induced by Thermal and Low Energy Neutrons.

Tech Area / Field

  • FIR-NOT/Nuclear and Other Technical Data/Fission Reactors

8 Project completed

Registration date

Completion date

Senior Project Manager
Glazova M B

Leading Institute
Khlopin Radium Institute, Russia, St Petersburg

Supporting institutes

  • Nuclear Physics Institute, Russia, Leningrad reg., Gatchina


  • European Commission / Joint Research Center / Institute for Reference Materials and Measurements, Belgium, Geel

Project summary

The purposes of this Project are precise multiparameter measurements of two-dimensional multiplicity distributions of the neutrons emitted simultaneously by each fragment with fixed mass and kinetic energy in the spontaneous fission of minor actmides Cm-244 and Cm-248, and in fission of the most important fuel cycle isotopes U-233, U-235, and Pu-239 induced by thermal and low energy resonance neutrons.

The need of the neutron multiplicity distributions' data stems from both the theory and the practical application tasks. First of all, these data are needed for creation of modern theoretical models of fission process because it presents information on deformation of both fragments, partition the energy released in the fission process between various degrees of freedom, distribution of excitation energy among fragments, and on the neutron-gamma competition in the deexcitation of fission fragments. Furthermore, these detailed data could help to elucidate the following important questions:

- fragment deformations in the vicinity of the scission point;

- energy balance for different fission modes,

- behavior of the fissioning system near the phase volume border,

- dynamics of the strongly deformed fissioning system at the descent from saddle to scission.

From the point of view of applied knowledge, the data on the variances of neutron multiplicity distributions as well as on the mean values of neutrons are needed for development of actmide-burner reactors within the framework of transmutation problem. It is known that the neutrons from spontaneous fission of Cm-244 give the main contribution in neutron radiation from a spent fuel. For the same reason, these data are necessary for improvement of the methods of nondestructive control used at the nuclear power stations, at the fuel storage pools and the reprocessing plants There is a need of these data for the IAEA safeguard system purposes.

The modernized and adjusted to the neutron beam experimental set-up of the KR1 based on a 400 1 twin Gd-loaded large liquid scintilator will be used for these measurements. The intensive quasi monochromatic neutron beam will be produced by means of a special system of four synchronized rotors with magnetic support placed at the stationary WWR-M research reactor of PNPI.

The experimental data obtained will be analyzed, intercompared and compared with those obtained formerly in the Cf-252 spontaneous fission The results will be then theoretically analyzed and treated from the point of view of the nuclear fission models.

A new neutron detector of another type with substantially improved characteristics is planned to be developed and used This detector is supposed to be 4 pi segmented one based on the neutron capture by Li-6 or B-10. This detector being position sensitive and with substantially suppressed background sensibility would be a promising step in the development of the neutron metrology technique It would permit performance of principal new experimental problems

Participation of the Japan Atomic Energy Research Institute is suggested at the stage of the experimental data processing, evaluation and treatment. Participation of the Institute for Reference Materials and Measurements (IRMM) is expected at the fission fragment detector designing and experimental data processing and theoretical model's treatment.


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