A.A. Pleve

Experiments on the synthesis of neutron-deficient kurchatovium isotopes in reactions induced by 50Ti Ions

Abstract By bombarding Pb isotopes with 50 Ti ions, two new isotopes of element 104 (kurchatovium) with mass numbers 255 and 256 have been synthesized. The isotope 256 Ku has been formed in the reaction 208 Pb ( 50 Ti, 2n) and has a spontaneous fission half-life of about 5 msec. The odd isotope 255 Ku has been formed with a maximum cross section in the reaction 207 Pb( 50 Ti, 2n) and has a half-life of several seconds. The experimental results obtained, together with the available data on the properties of kurchatovium, substantially change the understanding of the stability of heavy nuclei with respect to spontaneous fission. In this connection the influence of the structure of the fission barrier on the properties of heavy nuclei is discussed. On the basis of the experimental data on the synthesis of Fm and Ku neutron-deficient isotopes in reactions induced by ions heavier than argon, the possibilitie s of synthesizing elements with Z≧106 are investigated.

Excitation energy of spontaneously fissioning isomer 242mAm

Abstract The excitation function for the reaction 243 Am(n, 2n) 242 Am leading to the formation of a spontaneously fissioning isomer has been studied. The mono-energetic 8–14.4 MeV. neutrons were obtaained from the reaction D(d, n) 3 He using a gaseous deuterium target. The excitation function has a distinct threshold character. The neutron energy corresponding to the reaction threshold is found to be 9.2±0.3 MeV in the c.m. system. The difference between this value and the threshold of the reaction leading to the ground state, equal to 2.9±0.4 MeV, is considered as the excitation energy of the spontaneously fissioning state of 242 Am.

Acceleration of 48Ca ions and new possibilities of synthesizing superheavy elements

Abstract At the JINR U-300 heavy-ion cyclotron, a 48Ca ion beam has been first produced. Compared with other ions, these ions have great advantages for the synthesis of transuranic and superheavy elements. The extreme neutron excess of the 48Ca nucleus enables one to approach the double magic nucleus 298114 in fusion reactions. In addition, the 48Ca nucleus itself being doubly magic, fusion reactions with it lead to the formation of compound nuclei with low excitation energies. This sharply increases the cross sections for reactions with a small number of neutrons emitted. The model experiments carried out to synthesize the isotope 252102 in reactions with different Pb isotopes have confirmed these advantages of 48Ca ions.

A study of the spontaneously-fissioning isomer of 242Am through the 241Am(n,γ) reaction

Abstract The excitation function for the 241 Am(n,γ) 242m Am reaction leading to the excitation of the 14 ms, spontaneously fissioning isomer has been studied in the range 0–6.5 MeV. The experimental results can be well explained taking into account the hypothesis of Strutinsky concerning the “shape isomerism”.

Population of the spontaneously fissioning isomer 244mfAm through the (n, γ) reaction

Abstract The excitation function of the 0.6 ms spontaneously fissioning isomer 244mf Am obtained in the reaction 243 Am(n,γ) 244mf Am was measured in the neutron energy range 0.3–4 MeV and compared to the results obtained for the spontaneously fissioning isomer 242mf Am.

The formation of a spontaneously fissioning isomer in the capture of neutrons by Am

Abstract The formation of a spontaneously fissioning isomer (T 1 2 = 13.1±0.1 msec ) was observed during the irradiation of Am243 with 14 MeV neutrons. The cross-section for the Am243 (n, 2n) Am242 reaction is about 0.15 mb. The results of this work together with the data previously obtained lead to the conclusion that an isotope of Am242 in an isomeric state undergoes spontaneous fission.

Experiments on the synthesis of neutron-deficient isotopes of kurchatovium in reactions with accelerated50Ti ions

ConclusionsA number of conclusions can be drawn from the aggregate of experimental results.The method of synthesis of transfermium elements in the irradiation of lead isotopes with ions with mass AI≥40 atomic units, investigated earlier [12] for the example of the reaction Pb(40Ar, xn)Fm, is also extremely effective using50Ti ions. The reactions Pb(40Ar, 2n)Fm and Pb(50Ti, 2n)Ku have approximately equal cross sections, which might have been expected on the basis of theoretical estimates. This permits us to hope that this method can be used successfully for the synthesis of heavier elements in the reactions induced by54Cr,55Mn, and58Fe ions.In all probability, the substantial changes in the systematics of the half-lives for even-even isotopes of kurchatovium are associated with the structure of the barriers to fission of these nuclei. From this standpoint, it seems important to investigate the properties of more neutron-deficient isotopes of kurchatovium, using, in particular, the reactions with204Pb, and to attempt to advance into the region of elements with Z≥ 106. On the other hand, a detailed theoretical analysis must be made of the data obtained on the basis of the modern theory of nuclear fission, which, in our opinion, will aid in a more reliable prediction of the properties of heavy and ultraheavy elements.