Cold fission

Cold fission or cold nuclear fission is defined as involving fission events for which fission fragments have such low excitation energy that no neutrons or gammas are emitted.

Cold fission events have so low a probability of occurrence that it is necessary to use a high flux nuclear reactor to study them.

The first observation of cold fission events was in experiments on fission induced by thermal neutrons of uranium 233, uranium 235 ^[1] and plutonium 239 ^[2] using the High Flux Reactor at the Institut Laue-Langevin in Grenoble, France. Other experiments on cold fission were also done involving ²⁴⁸Cm ^[3] and ²⁵²Cf .^[4] A phenomenological interpretation was proposed by Gönnenwein^[5] and Duarte et al..^[6]

The importance of cold fission phenomena lies in the fact that fragments reaching detectors have the same mass that they obtained at the "scission" configuration, just before the attractive but short-range nuclear force becomes null, and only Coulomb interaction acts between fragments. After this Coulomb potential energy is converted in fragments kinetic energies, which-–added to pre-scission kinetic energies—is measured by detectors.

The fact that cold fission preserves nuclear mass until the fission fragments reach the detectors permits the experimenter to better determine the fission dynamics, especially the aspects related to Coulomb and shell effects in low energy fission.^[7][8] and nucleon pair breaking. Adopting several theoretical assumptions about scission configuration one can calculate the maximal value of kinetic energy as a function of charge and mass of fragments and compare them to experimental results.

References

1. ^ C. Signarbieux et al.. "Evidence for nucleon pair breaking even in the coldest scission configurations of ²³⁴U and ²³⁶U", Journal de Physique Lettres Vol 42, No 19 /1981, DOI: 10.1051/jphyslet:019810042019043700, pp. 437-440
2. ^ M. Montoya. "Mass and kinetic energy distribution in cold fission of ²³³U, ²³⁵U and ²³⁹Pu induced by thermal neutrons", Zeitschrift für Physik A, Springer Berlin / Heidelberg, Vol 319, No 2 / June, 1984, DOI: 10.1007/BF01415636, pp. 219-225
3. ^ A Sandulescu et al. "The cold fission of 248Cm", Journal of Physics. G: Nucear and Particle. Physics, Volume 22/ 1996, DOI: 10.1088/0954-3899/22/7/003, pp. L87-L94
4. ^ S Misicu et al. "Orientations of fragments emitted in binary cold fission of 252Cf", Journal Physics G: Nuclear and Particle Physics, Volume 28 /October, 2002, DOI: 10.1088/0954-3899/28/11/309, pp. 2861-2874
5. ^ Gönnenwein, F.; Börsig, B. "Tip model of cold fission", Nuclear Physics A, Volume 530, Issue 1/ July, 1991, DOI: 10.1016/0375-9474(91)90754-T, pp. 27-57.
6. ^ S. B. Duarte. et al. "Cold fission description with constant and varying mass asymmetries", Physical Review C, Volume 57/ 1998, DOI: 10.1103/PhysRevC.57.2516, pp. 2516 - 2522
7. ^ Modesto Montoya, "Shell and coulomb effects in thermal neutron induced cold fission of U-233, U-235, and Pu-239", Radiation Effects and Defects in Solids, Volume 93, Issue 1 - 4 March 1986 , pages 9 - 12
8. ^ M. Montoya et al.., "Coulomb effects in low energy fission" Zeitschrift für Physik A, Springer Berlin / Heidelberg, Vol 325, No 3/September, 1986, DOI: 10.1007/BF01294620, pp. 357-362