Search

We have studied the dependence of the production cross-sections of the isotopes 282,283112 and 286–288114 on the excitation energy of the compound nuclei 286112 and 290114. The maximum cross-sections of the xn-evaporation channels for the reaction 238U(48Ca,xn)286-x 112 were measured to be: σ 3n = 2.5 -1.1 +1.8 pb and σ 4n = 0.6 -0.5 +1.6 pb; for the reaction 242Pu(48Ca,xn)290-x 114: σ 2n ∼ 0.5 pb, σ 3n = 3.6 -1.7 +3.4 pb and σ 4n = 4.5 -1.9 +3.6 pb. In the reaction 233U(48Ca, 2-4n)277–279 112 we measured an upper cross-section limit of σ xn ≤ 0.6 pb. An increase of σ ER in the reactions of actinide targets with 48Ca can be due to the expected increase of the survivability of the excited compound nucleus upon closer approach to the closed neutron shell N = 184. The observed nuclear decay properties of the nuclides with Z = 104–118 are compared with theoretical nuclear mass calculations and the systematic trends of α-decay properties. As a whole, they give a consistent pattern of decay of the 18 even-Z neutron-rich nuclides with Z = 104–118 and N = 163–177.

Aiming at an increase in the identification ability and higher sensitivity in the experiments on the synthesis and study of the decay properties of superheavy nuclei, the separator VASSILISSA has been upgraded. After preparatory experiments, the experiment aiming at the synthesis of the isotope 283 112 in the reaction 48 Ca + 238 U was performed. The obtained results on the decay mode, half-life and production cross-section are in agreement with those obtained in our first experiment.

The upgraded separator VASSILISSA was used to confirm results of previous experiments on the synthesis of the heavy isotopes of the element 112 obtained in complete-fusion reactions of 48Ca and 238U. An additional reason was the non-observation of any events in the same reaction studied with the BGS separator at Berkeley. Limits of $280 \leq A \leq 286$ for the atomic mass number of the observed spontaneously fissioning isotope were measured. The obtained results on the decay mode, half-life and production cross-section are in agreement with those obtained in our first experiment.

neutron-rich isotopes 242,244 Pu, 243 Am, 245,248 Cm and 249 Cf with 48 Ca projectiles. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating in the decays of parent nuclides 286,287,288,289 114, 287,288 115, 290,291,293 116 and 294 118 produced in the 2n- to 5n-evaporation channels. The present observations can be considered to be experimental evidence of the existence of the “island of stability” of superheavy elements.

Summary We present results of the second experiment on the chemical identification of element 112. Similar to the first test in 2000, we aimed at the production of the spontaneously fissioning 283112 nuclei with T 1/2≈3min. A natU3O8 (with some Nd) target, 2mg of U/cm2 thick, was bombarded with 233-MeV 48Ca ions (the energy in the middle of the target layer). The nuclei recoiling from the target were thermalized in flowing helium. The target chamber was connected through a 25m long capillary to detectors of α-particles and fission fragments. All the equipment and detectors were kept at ambient temperature. According to the test experiments, of all the heavy elements produced in the bombardment, only Hg, Rn and At could be transported to the detectors. The first detecting device was similar to that used earlier – an assembly of 8 pairs of PIPS detectors coated with gold. Here one would observe the decay of element 112 atoms if they like Hg adsorbed on gold. The atoms which were not retained and freely passed through the PIPS detectors entered a new, flow-through ionization chamber, 5000 cm3 in volume, optimized for detecting fission fragments. The PIPS detectors and the ionization chamber were placed inside a large assembly of 3He – filled neutron counters to detect prompt neutrons from the fission events. In 22.5 days, a beam dose of 2.8×1018 ions was accumulated. More than 95 of the simultaneously produced α-active 185Hg (T 1/2=49 s) were found deposited already on the first pair of PIPS detectors; meanwhile, all the PIPSs did not detect any fission event. In the ionization chamber, eight fission events were observed in coincidence with neutron counts while the expected background was insignificant. Hence, the spontaneous fissions of the volatile activity can be conclusively attributed to the decay of element 112 produced in the fusion reaction 48Ca+ 238U, and formerly observed in Dubna physical experiments. Evaluation of the experimental data in terms of the adsorption enthalpies indicates much weaker interaction of element 112 with Au than that of Hg. One can conclude that in the given chemical environment, element 112 behaves like Rn rather than like Hg. The formation cross section of 283112 estimated from the data amounts to several pb. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions at JINR in November–December 2001.

This paper presents results of the experiments aimed at producing long-lived superheavy elements located near the spherical-shell closures with Z ⩾ 114 and N ⩾ 172 in the 244Pu + 48Ca and 248Cm + 48Ca reactions. The large measured α-particle energies of the newly observed nuclei, together with the long decay times and spontaneous fission terminating the chains, offer evidence of the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating from the parent nuclides 288, 289114 and 292116, produced in the 3n and 4n evaporation channels with cross-sections of about a picobarn. The present observations can be considered as experimental evidence of the existence of the “island of stability” of superheavy elements.

Experiments were performed on the preparation of volatile oxidation products from trace amounts of plutonium and on thermochromatographic (TC) separation of these species, taking into account the previously obtained data on different behaviour of some micro- and macrocomponents in the gas phase. The volatility of products formed by thermal oxidation of traces of U and 249Cf with an He-O2 (1 : 1 vol.) mixture was studied with the aim to simulate the behavior of Pu(IV) and Pu(VI) oxides. Hollow quartz columns were used. Under the experimental conditions, volatile UO2, UO3, and 249CfO2 were formed; the dioxides were deposited at 450±25°C, and UO3, at 250±25°C. The enthalpies of adsorption -ΔH a 0 of these compounds on quartz were calculated. Experimental evidence of existence in the gas phase of volatile uranic acid was obtained. The TC behavior of 238,239Pu traces was studied under conditions of thermal oxidation in an He-O2 flow at the oxygen concentration cO 2 varied from 50 to 10- 7%. In the cO 2 range of 50-5 × 10- 2%, deposition of volatile Pu species at 460±25 and 250±25°C was observed. The identical deposition temperatures and close values of -ΔH a 0 of the products of U and Pu oxidation suggest the transfer of Pu in the form of PuO2 and PuO3. In the cO 2 range from 50 to 1%, an abnormally volatile Pu species was detected, which was deposited at -105±25°C. Its -ΔH a 0, 41±6 kJ mol- 1, was close to that of OsO4. The deposition zones of 185OsO4 and of the highly volatile Pu species were superimposed. As cO 2 decreased, the yield of the highly volatile Pu species decreased; a similar trend is also characteristic of OsO4. This volatile Pu species was tentatively identified as Pu(VIII) oxide, PuO4.

The first attempt to chemically identify one of the recently discovered long-lived isotopes of superheavy elements, namely 283112 (3 min, SF), made at FLNR, Dubna is reported. The nuclide was produced by fusion of accelerated 48Ca with a target of natural U, which contained some Nd to simultaneously produce also short-lived Hg nuclides. According to test experiments with Hg, the expected lighter homologue of element 112, both elements can be isolated from the products of the bombardment in metallic state, and transported from the target in flowing He gas to a detection system, where spontaneous fission and alpha decays 49-s 185Hg) were registered using PIPS detectors. The surface of the detectors was covered with a thin layer of Au or Pd which ensured the detection of Hg with high efficiency due to its chemisorption on these surfaces. While about three SF events could be expected, not a single one was detected at an upper limit for the production cross section of about one picobarn. This may point to a "Rn-like" rather than "Hg-like" behavior of element 112. A new experiment is planned, in which both a "Rn-like" and a "Hg-like" species could be detected.

The stability of heavy nuclides, which tend to decay by α-emission and spontaneous fission, is determined by the structural properties of nuclear matter. Nuclear binding energies and lifetimes increase markedly in the vicinity of closed shells of neutrons or protons (nucleons), corresponding to ‘magic’ numbers of nucleons; these give rise to the most stable (spherical) nuclear shapes in the ground state. For example, with a proton number of Z = 82 and a neutron number of N = 126, the nucleus 208Pb is ‘doubly-magic’ and also exceptionally stable. The next closed neutron shell is expected at N = 184, leading to the prediction of an ‘island of stability’ of superheavy nuclei, for a broad range of isotopes with Z = 104 to 120 (refs 1, 2). The heaviest known nuclei have lifetimes of less than a millisecond, but nuclei near the top of the island of stability are predicted to exist for many years. (In contrast, nuclear matter consisting of about 300 nucleons with no shell structure would undergo fission within about 10−20 seconds.) Calculations3,4,5 indicate that nuclei with N > 168 should already benefit from the stabilizing influence of the closed shell at N = 184. Here we report the synthesis of an isotope containing 114 protons and 173 neutrons, through fusion of intense beams of 48Ca ions with 242Pu targets. The isotope decays by α-emission with a half-life of about five seconds, providing experimental confirmation of the island of stability.

The sorption was studied of element 104 (rutherfordium, Rf) and thorium on the strongly acidic cation exchanger DOWEX 50×8. The experiments were carried out on-line. Rf is strongly retained on cation exchange resins from diluted HCl/HF solutions in a concentration range of 0.05 to 0.1 M HCl and HF concentrations up to 0.01 M. This behaviour is similar to its pseudohomologue thorium and very different from its lighter homologue hafnium which is desorbed from DOWEX 50×8 at HF concentrations above 10 −3 M. The tested ion exchange system is suitable for fast on-line separation of element 106 (seaborgium, Sg) from all other contaminations and its decay product Rf. It, therefore, allows the indirect identification of Sg.

The work on isotopically pure 26 Al, 97 Ru, 178 W/ 178 Ta, 235 Np, 236 Pu and 237 Pu production was initiated because of intensive research on their applications in the biomedical field and environmental chemistry. The conditions for isotopically pure production have been investigated. This paper describes the data for the nuclear reactions of the radionuclide production, the different target designs and target chemistry procedures.

The heavy-element research program of the Dubna gas-filled recoil separator requires the use of rather exotic, strongly radioactive targets which can withstand long-term, high-intensity heavy-ion bombardments. A number of targets with thicknesses of 0.1–0.8 mg/cm2 deposited on various backings by different techniques such as electrospraying, mechanical painting with organic solutions, as well as molecular plating or electrodeposition from organic solutions were tested. The best results were obtained for electroplated targets deposited on 1.5 μm Ti backings. Isotopically enriched targets of 235,236,238U, 242,244Pu, and 248Cm mounted on rotating disks were irradiated by ions ranging from neon to argon with intensities up to 2 × 1013pps delivered by the U400 cyclotron. During two months of irradiation the total beam dose of the 34S ions applied to the target of 244Pu reached 2.5 × 1019. Collaborative Dubna-Livermore experiments were performed in 1993–1995 by employing the Dubna gas-filled recoil separator and resulted in the discovery of the new nuclides 262104, 265106, 266106, 267108, and 273110. The experiments aimed at the synthesis of element 114 are under preparation. Target fabrication methods and experimental results for nuclear physics studies at Coulomb energies are described.

In bombardments of $^{244}\mathrm{Pu}$ with $^{34}\mathrm{S}$ we discovered the \ensuremath{\alpha}-decaying nuclide $^{273}110$. We conducted an extensive off-line search of the raw data for event sequences which fit the expected pattern of implantation in a position-sensitive detector and subsequent decay of $^{273}110$ and its descendants. We observed one three-member sequence of genetically linked \ensuremath{\alpha} decays, resulting in ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=11.35 MeV, a half-life of 0.${3}_{\mathrm{\ensuremath{-}}0.2}^{+1.3}$ ms, and a production cross section of about 0.4 pb for $^{273}110$. Other possible $^{273}110$ event chains were also observed. The measured \ensuremath{\alpha}-particle energy for the N=163 nuclide $^{273}110$ provides direct evidence for a neutron shell closure at N=162. \textcopyright{} 1996 The American Physical Society.

Some short-lived isotopes of Hf, Ta and W, synthesized at the U-400 cyclotron of JINR-Dubna, have been isolated using a previously elaborated fast continuous method of chemical isolation of element 104 from nuclear reaction products. The products were transported by a NaCl aerosol jet, from the irradiated targets to a separation device in which Hf, Ta and W were isolated by using three coupled ion-exchange columns.

A fission ionization chamber has been designed to monitor neutron fluxes produced by the proton beam of the Van de Graaf accelerator in the 7Li(p, n)7Be nuclear reaction. A target producing neutrons is placed at the center of the chamber, which has a hemispherical shape. The neutrons escaping from the target are detected within the limits of a space angle a little larger than 2π sr. A 235U isotope is used as a fissile material. A U3O8 layer with a thickness of 300 μg/cm2 and an area of 80 cm2 has already been deposited on the surface of the inner hemisphere using electrolysis. The chamber is filled with a gas mixture of 97% Ar + 3% CO2. The detection efficiency of the chamber for neutrons with 1- to 150-keV energies is found to be 1.6 × 10–5. Using this chamber, it is possible to measure (with a statistical accuracy of 1%) the integrated neutron yield in a thick target exposed for ∼20 min to a proton beam with a current of ∼3 μA and an energy of 1942 keV, which is 60 keV above the threshold of the 7Li(p, n)7Be reaction. The design of the fission chamber is described, and the test results are presented.

In bombardments of ${}^{238}$U targets with 186-MeV ${}^{34}$S projectiles we discovered the $\ensuremath{\alpha}$-decaying nuclide ${}^{267}$108 with a half-life of ${19}_{\ensuremath{-}10}^{+29}$ ms, ${E}_{\ensuremath{\alpha}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}9.74$ to 9.87 MeV, and a production cross section of about 2.5 pb. The new nuclide was identified by measuring correlations in energy, time, and position to establish genetic links between its implantation in a position-sensitive silicon detector and subsequent $\ensuremath{\alpha}$ decay followed by $\ensuremath{\alpha}$ decays of known descendant nuclides.

An efficient radiochemical procedure for the chromatographic separation of carrier-free 178W radioisotope is described. 178W (T1/2=22 d) was produced by the U-200 accelerator (FLNR) via a natHf (α, 2n) 178W reaction. The energy of the α-particles was 36 MeV. The HfO2 target was dissolved in concentrated HCl in the presence of HF. The solution was evaporated to dryness and dissolved in 8 M HCl. The extraction was done in plastic columns filled with TBP impregnated resin (100–150 mesh). The flow rate was not higher than 1 mL/min. After carefully washing off the resin with 8 M HCl, the produced 178W was eluted with 1 M HCl. The efficiency was not less than 95%.

The short-lived isotopes of W and their descendants have been isolated from the products of the bombardment of144Sm with24Mg by a fast continuous ion-exchange method, using HF solution media. The feasibility of this method for isolation of element 106 is discussed.

A good separation of the pair Md-Fm was performed on a spheroidal cation exchanger OSTION by means of ammonium α-hydroxy-α-methylbutyrate. The sepation factors and the position of elution peaks for elements of pairs Md-Fm and Ho-Dy are similar.

Ion mobilities of carrier-free 239Np(V) have been measured in aqueous solutions, T = 298.1 (1) K. Ion mobilities of 239NpO2 + and its dependencies on pH of acidic inert electrolytes have been measured. In alkaline solutions the stoichimetric hydrolysis constants of NpO2(OH) as well as NpO2(OH)2 − have been obtained. Complex formations of 239Np(V) with oxalate, tartrate, sulphate, acetate and citrate ligands have been studied in neutral solutions.

The results of two experiments designed to synthesize element 115 isotopes in the {sup 243}Am+{sup 48}Ca reaction are presented. Two new elements with atomic numbers 113 and 115 were observed for the first time. With 248-MeV {sup 48}Ca projectiles, we observed three similar decay chains consisting of five consecutive {alpha} decays, all detected in a total time interval of 30 s. Each chain was terminated by a spontaneous fission (SF) with a high-energy release and a lifetime of about a day. With 253-MeV {sup 48}Ca projectiles, we registered a different decay chain of consecutive {alpha} decays detected in a time interval of 0.5 s, also terminated by spontaneous fission, but after 1.8 h. The decay properties of the eleven new {alpha}- and SF-decaying nuclei are consistent with expectations for consecutive {alpha} decays originating from the parent isotopes {sup 288}115 and {sup 287}115, produced in the 3n- and 4n-evaporation channels, respectively. Support for the assignment of the atomic numbers of all of the nuclei in the {sup 288}115 decay chain was obtained in an independent experiment in which a long-lived spontaneous fission activity, {sup 268}Db (15 events), was found to be chemically consistent with the fifth group of the periodic table.more » The odd-odd isotope {sup 288}115 was observed with largest cross section of about 4 pb. In the SF decay of {sup 268}Db, a total kinetic energy of 230 MeV and a neutron multiplicity per fission of 4.2 were measured. The decay properties of the 11 new isotopes with Z=105-115 and the production cross sections are in agreement with modern concepts of the role of nuclear shells in the stability of superheavy nuclei. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research.« less

We have studied the dependence of the production cross sections of the isotopes {sup 282,283}112 and {sup 286,287}114 on the excitation energy of the compound nuclei {sup 286}112 and {sup 290}114. The maximum cross section values of the xn-evaporation channels for the reaction {sup 238}U({sup 48}Ca,xn){sup 286-x}112 were measured to be {sigma}{sub 3n}=2.5{sub -1.1}{sup +1.8} pb and {sigma}{sub 4n}=0.6{sub -0.5}{sup +1.6} pb; for the reaction {sup 242}Pu({sup 48}Ca,xn){sup 290-x}114: {sigma}{sub 2n}{approx}0.5 pb, {sigma}{sub 3n}=3.6{sub -1.7}{sup +3.4} pb, and {sigma}{sub 4n}=4.5{sub -1.9}{sup +3.6} pb. In the reaction {sup 233}U({sup 48}Ca,2-4n){sup 277-279}112 at E*=34.9=2.2 MeV we measured an upper cross section limit of {sigma}{sub xn}{

We have studied the excitation functions of the reactions $^{244}\mathrm{Pu}$($^{48}\mathrm{Ca}$,$xn$). Maximum cross sections for the evaporation of 3--5 neutrons in the complete-fusion reaction $^{244}\mathrm{Pu+}^{48}\mathrm{Ca}$ were measured to be ${\ensuremath{\sigma}}_{3n}=2\phantom{\rule{0.3em}{0ex}}\text{pb}$, ${\ensuremath{\sigma}}_{4n}=5\phantom{\rule{0.3em}{0ex}}\text{pb}$, and ${\ensuremath{\sigma}}_{5n}=1\phantom{\rule{0.3em}{0ex}}\text{pb}$. The decay properties of $3n$-evaporation product $^{289}114$, in the decay chains observed at low $^{48}\mathrm{Ca}$ energy coincide well with those previously observed in the $^{244}\mathrm{Pu+}^{48}\mathrm{Ca}$ and $^{248}\mathrm{Cm+}^{48}\mathrm{Ca}$ reactions and assigned to $^{288}114$. Two isotopes of element 114 and their descendant nuclei were identified for the first time at higher bombarding energies: $^{288}114$ (${E}_{\ensuremath{\alpha}}=9.95\phantom{\rule{0.3em}{0ex}}\text{MeV}$, ${T}_{1∕2}=0.6\phantom{\rule{0.3em}{0ex}}\mathrm{s}$) and $^{287}114$ (${E}_{\ensuremath{\alpha}}=10.04\phantom{\rule{0.3em}{0ex}}\text{MeV}$, ${T}_{1∕2}=1\phantom{\rule{0.3em}{0ex}}\mathrm{s}$). We also report on the observation of new isotopes of element 116, $^{290,291}116$, produced in the $^{245}\mathrm{Cm}+^{48}\mathrm{Ca}$ reaction with cross sections of about $1\phantom{\rule{0.3em}{0ex}}\text{pb}$. A discussion of self-consistent interpretations of all observed decay chains originating at $Z=118$, 116, and 114 is presented.

This paper presents results of experiments aimed at producing long-lived superheavy elements located near the spherical shell closures with Z ≥114 and N ≥172 in the reactions of neutron-rich isotopes 244Pu, 245,248Cm and 249Cf with 48Ca projectiles. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating in the decays of parent nuclides 289114, 290,291,293116 and 294118 produced in the 2n and 3n-evaporation channels. The present observations can be considered to be experimental evidence of the existence of the “island of stability” of superheavy elements.

Isotopically pure 236Pu (>99.999% by activity) has been produced by irradiating U (95% 235U) with 4He ions and refining the product by electromagnetic mass separation. Further developments in the production of 237Pu are also reported, giving material containing, by activity, only 3 × 10−6% 236Pu and probably only ∼ 10−5% 238Pu.

We measured the average electronic charge $〈q〉$ of heavy ions with atomic numbers $Z=89$ through 116 traversing dilute hydrogen gas with velocities ranging from 1 to 2.6 times the Bohr velocity. We observe a strong linear dependence of the average charge on the velocity of the ions, and only a weak dependence on their atomic number Z. A more detailed examination of the experimental results shows that the $〈q〉$ values reflect the influence of the $5f$ electron shell on the properties of these elements.

This paper presents results of the experiments aimed at producing long-lived superheavy elements located near the spherical-shell closures with Z ⩾ 114 and N ⩾ 172 in the 244Pu + 48Ca and 248Cm + 48Ca reactions. The large measured α-particle energies of the newly observed nuclei, together with the long decay times and spontaneous fission terminating the chains, offer evidence of the decay of nuclei with high atomic numbers. The decay properties of the synthesized nuclei are consistent with the consecutive α-decays originating from the parent nuclides 288, 289114 and 292116, produced in the 3n and 4n evaporation channels with cross-sections of about a picobarn. The present observations can be considered as experimental evidence of the existence of the “island of stability” of superheavy elements.

We present the observation of the first decay event of the new nuclide {sup 292}116 in the running experiment on the synthesis of Z=116 nuclei in the reaction {sup 248}Cm+{sup 48}Ca. The experiment is in progress at FLNR, JINR, Dubna.

In bombardments of ${}^{244}\mathrm{Pu}$ targets with 114- and 120-MeV ${}^{22}\mathrm{Ne}$ projectiles we detected 69 $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\alpha}$ correlations linking $\ensuremath{\alpha}$ decays of ${}^{261}\mathrm{Rf}$ and ${}^{257}\mathrm{No}.$ We observed one $\ensuremath{\alpha}$ peak with ${E}_{\ensuremath{\alpha}}=8.30\ifmmode\pm\else\textpm\fi{}0.06$ MeV for ${}^{261}\mathrm{Rf}$ and peaks with \ensuremath{\alpha}-particle energies 8.07\char21{}8.40 MeV for ${}^{257}\mathrm{No}.$ The half-life of ${}^{257}\mathrm{No}$ was measured to be $25\ifmmode\pm\else\textpm\fi{}3$ s. No correlations were found between $\ensuremath{\alpha}$ decays and subsequent spontaneous fission events, from which we calculated an upper limit of 1.5% for the fission branch of ${}^{257}\mathrm{No}$ and estimated an upper limit of 3% for the \ensuremath{\alpha}-decay branch of ${}^{262}\mathrm{Rf}.$ The cross section of the ${}^{244}\mathrm{Pu}{(}^{22}\mathrm{Ne}{,5n)}^{261}\mathrm{Rf}$ reaction was measured to be about 4 nb at both ${}^{22}\mathrm{Ne}$ energies used. We also report on some results from ${}^{242}\mathrm{Pu}{+}^{22}\mathrm{Ne}$ and ${}^{238}\mathrm{U}{+}^{26}\mathrm{Mg}$ bombardments.

118 s); for the spontaneous fission (T1/257.522.9 114 s), the total energies deposited in the detector array were 213 62 and 221 62 MeV. The decay properties of the synthesized nuclei are consistent with the consecutive a decays originating from the parent even-even nucleus 288 114, produced in the 4n-evaporation channel with a cross section of about 1 pb. 288 114 and 284 112 are the heaviest known a-decaying even-even nuclides, following the production of 260 Sg and 266 Sg (Z5106) and the observation of a decay of 264 Hs (Z5108). The observed radioactive properties of 288 114 and the daughter nuclides match the decay scenario predicted by the macroscopic-microscopic theory.

A procedure for the preparation of a pure 97Tc isotope that can be used as a tracer in dilution mass spectrometry and accelerator mass spectrometry is described. The reaction 95Mo (4He, 2n) 97Ru was used. An enriched 95Mo(>90%) target (10 mg cm−2) was irradiated with 31.5 MeV 4He-ions for 70 h at 30 μA. The obtained 97Ru decayed (T1/2=2.9 d) to form 97Tc (99.9%) and 97mTc (1.7×10−2%). After cooling for 100 days the target was removed from the copper backing. The radiochemical procedure included dissolution of the target and two-fold distillation of 97Tc as Tc2O7 with HClO4. Over 98% of 97Tc was recovered after two distillations. The radioactive admixtures of 56,57,58Co, 54Mn, 65Zn produced from the copper backing were quantitatively retained in the precipitate in a distillation still. The obtained quantity of 97Tc was 3.5 μg. According to the calculation it contained less than 0.1% of 97Mo.

The results of the study enable us to conclude the following: the β decay of249Bk is accompanied by an L series of x rays from the daughter product Cf. The yield of this radiation is low: ω(Lα+Lβ+ Lγ) ≈ 10−4 (β disintegration)−1, but because of the high specific β activity of249Bk, 1 μg of this isotope emits ∼3.7·105 x-ray quanta per minute. This enables us to detect a fairly small amount of Bk (∼0.01 μg) on the basis of x rays in a period of 5–10 min. The rapid accumulation of the daughter product249Cf does not interfere with the determination of the249Bk on the basis of x rays. Even when the mixture contains equal numbers of Bk and Cf nuclei, the ratio of the Lα lines corresponding to them is 0.46. Therefore the composition of a mixture of249Bk+249Cf can be determined on the basis of x rays over broad ranges of variation of the relative concentrations of Bk+Cf, roughly from 0.03 to 80. It is important to note that for relative measurements it is not necessary to prepare special specimens, since x rays with energies of 15–20 keV are not strongly absorbed in the solution and in the walls of the chemical vessel.

The electromigration behaviour of carrier-free241Am−Am(III) in inert electrolytes, μ=0.1 (C10 4 − ), T=298.1(1) K, was studied. On the basis of the overall ion mobilities of241Am−Am(III) on pH between pH 5.5 and 12.9, the stoichiometric hydrolysis constants p 3 β3 =23.8(9), and pK1=6.9(2) were obtained. For K4 a limitation of pK4≧14.4(3) was possible, because no formation of anionic hydrolysis products in solutions pH≦12.9 was registered. The individual ion mobility of the241Am−Am3+ decrease in the range pH 5.5–3 from +6.85(15) up to +5.50(15)·10−4 cm2·s−1·V−1. Dependences of this effect on overall ionic strength, inert electrolyte anion, and the temperature of the electrolytes were studied in acidic and neutral solutions.

The formation of nuclides undergoing delayed fission with half-lives in the range of T1/2 1 s has been observed in fusion-evaporation reactions induced by 230 MeV 40Ca and 40Ar projectiles on isotopically enriched targets of 144Sm, 147Sm and 150Sm. The fission activity with T1/2 = 0.70+0.12-0.09 s produced in the 144Sm + 40Ca reaction has been found to be the most striking one. The origin of this activity is explained as being due to the β-delayed fission occurring in the chain . The discovery of β-delayed fission in the Hg region opens up valuable prospects for extending low-energy (E* ≤ Qβ+(EC)) fission studies to neutron-deficient nuclei of many elements belonging to the translanthanide part of the Mendeleev periodic table.

Mendelevium-256 was obtained by irradiating of Bk-249 with Ne-22 ions in the external beam of U-300 cyclotron. An efficient ionexchanging method of medelevium isolation and separation from nuclear reaction products have been developed in which a column with cation exchanger and zinc amalgam and 1M HCl solutions as eluents were used. Under these conditions mendelevium has been shown to be reduced and washed out as an alkaline earth element. The ionic radius of Md2+ has been estimated from a correlation of the elution peak positions with ionic radius of several divalent elements. This value was used to calculate the heat of hydration of Md2+ ion.