## Fission Physics Laboratory

### Area of research

Research in the field of nuclear fission physics were started in 1966 in the Republic of Kazakhstan in the Laboratory of reactor physics, later renamed as the Laboratory of fission physics, established in the Institute of Nuclear Physics.

### Background

From the very beginning the Laboratory began to develop the cooperation with the leading scientific centers: Physical-Energy Engineering Institute (PEE, Obninsk), Joint Institute of Nuclear Research (JINR, Dubna), Institute of Nuclear Research (INR, Kiev), involving the leading scientists such as Ignatyuk A.V., Zaika N.I., Oganesyan Yu. Ts., Selitsky Yu.A., Smirenkin G.N. in discussion and analysis of experimental data and performing of some important measurements at basic facilities of these organizations.

In 70-80s the Laboratory employed the talented young scientists, the graduates of the Physics Department of the Kazakh State University, including Beisin S.D., Mulgin S.I., Gruzintsev E.N., Rusanov A.Y., Zhdanov S.V. and others.

Under management of Okolovich V.N. the Laboratory designed and developed the highly sensitive measurement techniques for experimental studies of the characteristics of the preactinide nuclei fission such as integral cross-section of fission, angular and mass-energy distributions of fission fragments, the yields of delayed neutrons and others. The experiments were performed on the ion beams in the accelerators U-150 (Almaty), U-150 (PEE), U-200 (Dubna) and U-240 (Kiev).

As a result of these experiments the Laboratory obtained extensive information on the fission cross sections and angular distributions of fragments of target nuclei from gadolinium to bismuth in the reactions with light charged particles and 12С ions.

The next step of the Laboratory of Fission Physics activity implied the systematic large-scale studies of mass-energy distributions of fission fragments.

The interest towards the detailed study of fragments distributions by mass and energy was caused by the fact that these characteristics carry the important information about the static, dynamic and dissipative properties of nuclear matter. The studies were conducted on the beams of accelerated ions at the isochronous cyclotrons U-150 INP (Almaty) and U-400 (JINR, Dubna).

The detailed measurements were performed during fission of the heated pre-actinides nuclei from osmium 186Os to astatine 212At. The major experimental data were obtained for the first time. Moreover, due to substantial improving of the technique of the paired fragments spectrometry, the Laboratory reliably established (for the first time in the world) that the asymmetric fission component is observed during nuclei fission in the region of lead and its contribution to the total fragment mass yield is 0.3%. The results of this work, on the one hand, substantially broadened and extended the understanding of the mechanisms of the fission process, and on the other hand, promoted further research simultaneously in several areas.

In this regard the various countries (the USA, Belgium, Germany, Japan and France) started the intensive research of the component structure of the mass-energy distributions of fission fragments of actinide nuclei. Our laboratory, in particular, performed the systematic experimental study of the mass-energy distributions of fission fragments of nuclei from 232Th to 244Cm in the reactions with protons.

In close cooperation with the scientists from the Flerovsky Laboratory of Nuclear Reactions (FLNR, Dubna), our Laboratory conducted the research in the reactions with heavy ions jointly with the study of the fission process characteristics in the reactions with light charged particles. The measurements were performed on a two-arm TOF spectrometer DEMAS, installed on the channel of the ion beam in the cyclotron U-400M FLNR JINR (Dubna). The study of the characteristics of the mass-energy distributions of fission fragments in these reactions included the study of the droplet properties of these distributions and the impact of angular momentum on them.

During the operation time the Laboratory has gained the unique experimental data on the cross sections, angular and mass-energy distributions of fission fragments of nuclei from Xe to 108Hs, the thorough analysis which expanded the knowledge about many aspects of the fission reaction.

### Area of research

The study of the mechanism of formation of the charge, mass and energy distributions of fission fragments produced in reactions with charged particles in a wide range of excitation energies and the nucleon structure.

### Main scientific achievements

- • Gained unique experimental information about the mass-energy distributions of fission fragments for nuclei from 54Xe to 108Hs.

• Determined experimental values of fission barriers and effective moments of nuclei inertia.

• Established relationship between the dispersion of mass distributions of fragments with nuclear hardness in relation to the mass-asymmetric variation of the form. Determined values of hardness for nuclei with Z2/A~22.0-43.

• Experimentally determined location of the Businaro-Gallone point (above hardness is 0).

• For the first time discovered and studied asymmetry of low-energy nuclear fission in the lead area. Thus confirming the hypothesis about the existence of independent ways of nuclear fission (heteromodality). It is shown that heteromodality of fission is a universal property of nuclear fission in a wide range of nucleon composition.

• For the first time experimentally investigated appearance of shell effects in the mass-energy distributions of fragments with masses close to A/2 low-energy nuclear fission in the region of thallium. It was shown that these effects are stipulated by the effect of two strongly-deformed neutral shells formed in the resulting fragments with neutron numbers close to 52 and 68.

• For the first time identified isotopic invariance of charge distributions of fragments of actinide nuclei asymmetric fission at the excitation energies greater than 10 MeV.

• Developed systematics for calculation of fission fragments yield before and after neutrons emission from the fragments in the reactions with neutrons and protons of kinetic energy from 5 to 200 MeV on the target nuclei with Z = 90-97 and A = 230-250. Systematics was implemented in the form of software code PYF2.2. Source code can be found here.

The laboratory team members have published over 350 scientific works, including more than 200 published in the leading scientific journals in Russia and abroad, which gathered more than 1080 references in the world scientific literature and trained 3 doctors and 15 candidates (PhD) of physical and mathematical sciences.

### Important publications

- S.I. Mulgin, V.N. Okolovich, S.V. Zhdanov // Two-parametric method for silicon detector calibration in heavy ion and fission fragment spectrometry // NIM, Vol. 388, 1997, N 1, P. 254-259.
- M.G. Itkis, A. Ya. Rusanov // The fission of heated nuclei in reactions involving heavy ions: static and dynamical aspects // Physics of Particles and Nuclei, Vol.29, 1998,N2, P.160-200.
- S.I. Mulgin, K.-H. Schmidt, , A. Grewe, S.V. Zhdanov //Shell effects in the symmetric-modal fission of pre-actinide nuclei// Nuclear Physics A, Vol. 640, 1998, P. 375–388.
- José Benlliure, A Grewe, M De Jong, K-H Schmidt, S Zhdanov // Calculated nuclide production yields in relativistic collisions of fissile nuclei // Nuclear Physics A, Vol. 628, 2008, N 3, P. 458-478.
- S.I. Mulgin, V.N. Okolovich, S.V. Zhdanov // Observation of new channel in the proton-induced low-energy fission of nuclei from 233Pa to 245Bk // Physics Letters B, Vol. 462, 1999, P. 29–33.
- V. Pokrovsky, M. G. Itkis, J. M. Itkis, N. A. Kondratiev, E. M. Kozulin, E. V. Prokhorova, V. S. Salamatin, V. V. Pashkevich, S. I. Mulgin, A. Ya. Rusanov, S. V. Zhdanov, et al. // Fission modes in the reaction 208Pb(18O,f) // Phys. Rev. C 62, 2000, P. 014615.
- D.M. Gorodisskiy, S.I. Mulgin, V.N. Okolovich, A. Ya. Rusanov, S.V. Zhdanov // Isotopic and isotonic effects in fission-fragment mass yields of actinide nuclei // Physics Letters B, Vol. 548, 2002, N1, P. 45-51.
- M.G. Itkis, A.A. Bogatchev, I.M. Itkis, M. Jandel, J. Kliman, G.N. Kniajeva, N.A. Kondratiev, I.V. Korzyukov, E.M. Kozulin, L. Krupa, Yu. Ts. Oganessian, …, A Ya Rusanov, VM Voskresenski, AA Goverdovski, F Hanappe, T Materna, N Rowley, L Stuttge, G Giardina, KJ Moody. // Fusion-fission of superheavy nuclei // Journal of Nuclear and Radiochemical Sciences, Vol.3, 2002, N1, P.57-61.
- D.M. Gorodisskiy, S.I. Mulgin, A. Ya. Rusanov, S.V. Zhdanov // Isotopic invariance of fission fragment charge distributions for actinide nuclei at excitation energies above 10 MeV // Physics of Atomic Nuclei, Vol.66, 2003, N 6, P. 1190-1197.
- M.G. Itkis, A.A. Bogachev, I.M. Itkis, Ján Kliman, G.N. Knyazheva, N.A. Kondratiev, E.M. Kozulin, L. Krupa, Yu. Ts. Oganessian, I.V. Pokrovsky, E.V. Prokhorova, A. Ya. Rusanov // The processes of fusion-fission and quasi-fission of superheavy nuclei // Nuclear Physics A, Vol. 787< 2007, N1, P. 150-159.
- D.M. Gorodisskiy, K.V. Kovalchuk, S.I. Mulgin, A. Ya. Rusanov, S.V. Zhdanov // Systematics of fragment mass yields from fission of actinide nuclei induced by the 5–200MeV protons and neutrons // Annals of Nuclear Energy, Vol. 35, 2008, N2, P. 238-245.
- D.M. Gorodisskiy, S.I. Mulgin, A. Yu. Rusanov, S.V. Zhdanov // Modal approach to the description of fragment mass yields in neutron and proton induced fission of actinides at incident particle energies from 5 to 200 MeV, Book “Fission product yield data for the transmutation of minor actinide nuclear waste”, 2008.
- V.V. Pashkevich, A. Ya. Rusanov // The 226 Th fission valleys // Nuclear Physics A, Vol. 810, 2008, N1, P. 77-90.
- S.I. Mulgin, S.V. Zhdanov, N.A. Kondratiev, K.V. Kovalchuk, A. Ya. Rusanov // The modal structure of fragment mass and energy yields from the 10.3–30.0 MeV proton induced fission of 232 Th and 235 U // Nuclear Physics A, Vol. 824, 2009, N 1, P. 1-23.
- I.M. Itkis, E.M. Kozulin, M.G. Itkis, G.N. Knyazheva, A.A. Bogachev, E.V. Chernysheva, L. Krupa, Yu. Ts. Oganessian, V.I. Zagrebaev, A. Ya. Rusanov, F. Goennenwein, O. Dorvaux, Louise Stuttgé, Francis Hanappe, Emanuele Vardaci, E de Goés Brennand // Fission and quasifission modes in heavy-ion-induced reactions leading to the formation of Hs*.// Physical Review C, Vol.83, 2011, N 6, P. 064613/

**Head of Fission physics laboratory, Kvochkina Tatiyana Nickolayevna**