Yu. S. Korotkin

Experiments to produce isotopes of superheavy elements with atomic numbers 114–116 in 48Ca ion reactions

Experiments have been performed to synthesize isotopes of elements 114–116 in fusion reactions between 48Ca ions and 246, 248Cm, 243Am and 242Pu target nuclei. The detection of reaction products by recording spontaneous fission and α-decay events allowed us to set upper limits of 5 × 10−35 cm2 and ≈ 2 × 10 −34 cm2 on the production cross sections for superheavy elements with 2 h ≦ Tsf ≦ 1 y and 2 h ≦ Tα ≦ 10 d, respectively.

Experimental Studies of the Formation and Radioactive Decay of Isotopes with Z = 104—109

B y Y U . T s . O G A N E S S I A N , M. H U S S O N N O I S * , A . G . D E M I N , Y U . P . K H A R I T O N O V , H . B R U C H E R T S E I F E R * * , O . C O N S T A N T I N E S C U * * * , Y U . S . K O R O T K I N , S . P. T R E T Y A K O V A , V . K . U T Y O N K O V , I. V . S H I R O K O V S K Y , and J. ESTEVEZ, Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna, USSR

On the stability of the nuclei of element 108 withA=263–265

In bombarding209Bi and207, 208Pb targets by55Mn and58Fe ions the yields of “cold fusion” reactions have been determined using a sensitive technique for detectingT1/2≧1 ms spontaneous fission and theα-decay of heavy actinide elements. It has been shown that theA = 263–265 isotopes of element 108, including the even-even isotope264108, undergo mainlyα-decay. The obtained results, together with the known data on the properties of the isotopes of elements 104 and 106, provide evidence for the enhanced stability of theZ=108 nuclei against spontaneous fission.

On the nuclear properties of the isotopes 256103 and 257103

Abstract The isotopes 256 103 and 257 103 were synthesized by bombarding 243 Am with 18 O ions. The assignment was based on the excitation functions of the reactions 243 Am( 18 O, 5n) 256 103 and 243 Am( 18 O, 4n) 257 103. The isotope 256 103 has a complicated alpha spectrum in the range 8.35 ≦ E α ≦ 8.60 MeV. An intense group of alpha particles has E α = 8.42 MeV. The measured half-life for 256 103 is about 35 sec. The obtained experimental data permit as to conclude that 257 103 has T 1 2 ≈ 35 sec and 8.5 ≦ E α ≦ 8.6 MeV . The experiments were performed on the external beam of the 310 cm cyclotron of the Laboratory of Nuclear Reactions, JINR.

Results of the searches for superheavy nuclei in the Cheleken Penninsula geothermal waters

The water rich in heavy volatile metals form the Cheleken Penninsula hot springs was passed through a column containing 850 kg of anion exchange resin. The spontaneous fission activity (SF) of the samples was measured by neutron multiplicity detectors. The counting rate of spontaneous fission events was 0.5 per day for 9 kg of saturated resin. After 170 kg of the resin had been treated with acid solutions and hydroxides had been precipitated from the eluate with alkali, the counting rate for the precipitate was about five per day. From measurements of theα/SF ratio it is concluded that the activity cannot be traced back to a contamination by actinides, except to a contamination by pure252Cf, which, however, seems to be unlikely. Thus the explanation of the observed effect as being due to the spontaneous fission of a new naturally occurring isotope of a superheavy element is considered to be the most probable one.

Selective concentration of the lanthanides with simultaneous purification from scandium

The solvent extraction of the rare earth elements, yttrium and scandium with trioctylphosphine oxide in the presence of strong complexing and various salting-out agents has been studied. As a result, a technique was developed for the extractionchromatography recovery of the rare earth elements and yttrium with simultaneous purification practically from all the elements, including scandium, usually present in the mineral samples.

Observation of nucleon clusters in the spontaneous decay of234U

The emission of Ne and Mg nuclei was detected in the spontaneous decay of234U with probabilities of, respectively, (3.9 ±1.0) × 10−13 and (2.3 ±0.7) × 10−13 relative toα-decay. The upper limits of this kind of decay for235U and236U have been established. Systematics of half-lives for cluster emission are found to be similar to the Geiger-Nuttall dependence forα-decay. Some evidence for the presence of hindrance to cluster emission from the odd-mass nuclei233U and235U is obtained.

Selective extraction of the transplutonium and rare-earth elements by trioctylphosphine oxide

In the studies of nuclear reactions of heavy ions with heavy nuclei it is often necessary to determine the yields of TPE. Trioctylphosphine oxide (TOPO) has high selectivity with respect to trivalent TPE and rare earths. The possibility of using target or catcher materials as salting-out agents in the extraction of TPE with TOPO from solutions containing DTPA and lactic acid was investigated. The influence of the concentration of Pb, Bi, Cu, Ni, nitric acid and TOPO on the distribution coefficients was established. The advantages of application of the method for the extraction chromatographic separation of TPE and rare earths from the other elements produced in the interaction of ions with heavy elements are shown.

Synthesis of260Ku in the irradiation of249Bk by15N ions

Conclusions1.In the249Bk(15N, 4n)260Ku reaction an isotope of kurchatovium (element 104) is obtained which decays by spontaneous fission with a half-life of ∼0.1 sec. This result is in complete agreement with conclusions of earlier works [1, 3, 5] in which260Ku was synthesized in other combinations of target and particle:242Pu+22Ne,246Cm+18O.2.The failure to observe260Ku with T1/2≈0.1 sec at Berkeley [10, 11] resulted from improper experimental arrangements and data processing.3.The detection of the spontaneous fission of nuclei of an unknown isotope when background is properly considered and suppressed permits the identification of the Z and A of the nuclei under study.

The spontaneous fission half-life of249Cf

The authors describe a method for determining the spontaneous fission half-life of Cf 249 which is comprised in the preparatory stages of berkelium 249 separation by extraction chromatography and in the analytic stages of the detection of fission fragments using dielectric track detectors consisting of polyethylene terephthalate and muscovite. The half-life was calculated in the basis of the mass and composition of the sample material, the exposure time, the recording efficiency, and the number of recorded fission tracks, and was determined to be (8.5 plus or minus 0.5) multiplied by ten to the tenth power years after averaging measurement results. The ratio of the probabilities of Cf 249 decay by alpha particle emission and spontaneous fission was calculated from the ratio of their respective intensities.