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Element No. 102

Description: By the use of a radically new method they have succeeded in identifying unambiguously an isotope of element 102. In other careful experiments conducted over a period of many months they find that they are unable to confirm the element 102 discovery work of Fields et al. reported in 1957. The experiments at Berkeley were performed with the new heavy ion linear accelerator (HILAC) over a period of several weeks and culinated the chemical identification of an isotope of fermium (Fm{sup 250}) as the daughter of an alpha-particle-emitting isotope of element 102 (102{sup 254}). The method used to detect the isotope of element 102 was essentially a continuous milking experiment wherein the atoms of the daughter element 100 were separated from the parent element 102 by taking advantage of the recoil due to the element 102 alpha particle decay. The target consisted of a mixture of isotopes of curium (95% Cm{sup 244} and 4.5% Cm{sup 246}) mounted on a very thin nickel foil. The target was approximately 0.5 mg/cm{sup 2} thick and was covered with 75 {micro}gm/cm{sup 2} aluminum to prevent curium 'knockover'. The curium was bombarded with mono-energetic C{sup 12} ions at energies from 60 to 100 Mev. The transmuted atoms were knocked into helium gas to absorb the considerable recoil energy. It was found that with a sufficient electric field strength practically all of these positively charged atoms could be attracted to a moving negatively charged metallic belt placed directly beneath the target. These atoms would then be carried on this conveyer belt under a foil which was charged negatively relative to the belt. Approximately half of the atoms undergoing alpha decay would cause their daughter atoms to recoil from the surface of the belt to the catcher foil. The catcher foil was cut transversely to the direction ...
Date: June 4, 1958
Creator: Ghiorso, A.; Sikkeland, T.; Walton, J.R. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Attempts to Confirm the Existence of the 10-Minute Isotope of102

Description: In many score of experiments conducted in various ways over a period of many months they find that they are unable to confirm the element 102 discovery work of Fields et al. reported in 1957. These experimenters ascribed to an isotope of element 102 an alpha particle activity having an energy of 8.5 {+-} 0.1 Mev and a half-life of approximately 10 minutes. It was reported to be produced by bombardments of a 1 mg/cm{sup 2} curium target with 0.03-0.10 mter-microamperes of C{sup 13} ions of about 90 Mev energy in the internal beam of the Nobel Institute 225 cm cyclotron. Our attempts to reproduce this activity were made with the monoenergetic ion beam available from the Berkeley heavy ion linear accelerator (HILAC). Curium with a similar isotopic composition was used, except that instead of one target they used six separate electroplated targets, four with 0.4 mg/cm{sup 2} curium and two with 0.1 mg/cm{sup 2} curium. These were mounted in vacuum so that the heavy ion beam could pass through and knock the transmutation recoils into 0.9 mg/cm{sup 2} palladium foils. After a suitable bombardment the six catcher foils were dissolved in a few drops of concentrated aqua regia and an actinide element fraction quickly separated from palladium by elution with 2M HCl from a column packed with Dowex-1 anion exchange resin. It was possible to examine a trans-plutonium fraction within 8 minutes from the end of bombardment. A wide range of energies (60-100 Mev) of both C{sup 12} and C{sup 13} projectiles and (+6) ion currents up to 0.2 microamperes were used. In order to compare these bombardments with those which were reported to have produced the 8.5 Mev alpha activity one can compare the amounts of the other alpha particle activities that are produced in such bombardments. The ...
Date: June 4, 1958
Creator: Ghiorso, A.; Sikkeland, T.; Walton, J.R. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Spontaneous fission properties of {sup 252,254}No and {sup 256,258}[104] and the disappearance of the outer fission barrier

Description: The mass and total kinetic energy distributions from the spontaneous fission of {sup 252}No, {sup 254}No, {sup 256}[104], and {sup 258}[104] were measured. The results, in combination with earlier measurements for {sup 256}No, {sup 258}No, and {sup 262}No, show a sharp transition from asymmetrical mass division in {sup 256}No to symmetrical division for {sup 258}No and {sup 262}No. On the other hand, all isotopes of element 104, including {sup 260}[104], appear to yield broadly symmetrical mass distributions. The total kinetic energies around 200 MeV for the 104 isotopes indicate that they fission by the low-energy mode of bimodal fission. Recent calculations of static potential energy surfaces including higher-order asymmetric deformations suggest that the outer fission barrier is well below the ground state in energy, which accounts for the observance of the symmetric mass division.
Date: September 1, 1993
Creator: Wild, J. F.; Hulet, E. K.; Lougheed, R. W.; Moody, K. J.; Bandong, B. B.; Dougan, R. J. et al.
Partner: UNT Libraries Government Documents Department

NOBELIUM: TRACER CHEMISTRY OF THE DIVALENT AND TRI-VALENTIONS

Description: In the absence of oxidizing or reducing agents the chromatographic and coprecipitation behavior of element 102 is similar to that of the alkaline earth elements. After oxidation with ceric ions, the behavior is that expected of a trivalent actinide. The conclusion is that nobelium is the first actinide for which the +2 oxidation state is the most stable species in aqueous solution.
Date: February 1, 1968
Creator: Maly, Jaromir; Sikkeland, Torbjorn; Silva, Robert & Ghiorso, Albert.
Partner: UNT Libraries Government Documents Department

Structure and formation mechanism of the transfermium isotope {sup 254}No.

Description: The ground-state band of the Z=102 isotope {sup 254}No has been identified up to spin 14, indicating that the nucleus is deformed. The deduced quadruple deformation, {beta} = 0.27, is in agreement with theoretical predictions. These observations confirm that the shell-correction energy responsible for the stability of transfermium nuclei is partly derived from deformation. The survival of {sup 254}No up to spin 14 means that its fission barrier persists at least up to that spin.
Date: December 17, 1998
Creator: Reiter, P.
Partner: UNT Libraries Government Documents Department

New, heavy transuranium isotopes

Description: In this report, we offer our most recent results concerning the decay properties for five new isotopes of Md, No, Lr, and for {sup 258m}Md. In additions to these successful experiments, we have also conducted searches for {sup 263}(105), {sup 264}(105), {sup 272}(109), and superheavy elements from bombardments of {sup 254}Es with heavy ions. {sup 2} An exciting finding in the course of this work is a new fission phenomenon, which we have termed bidmodal fission''. This is described in a subsequent section. The final part summarizes our conclusions based on the unexpectedly long half-lives and surprising fission properties of the heaviest nuclei. 27 refs., 19 figs.
Date: October 22, 1990
Creator: Hulet, E.K.
Partner: UNT Libraries Government Documents Department

Role of the second barrier upon mass division in the spontaneous fission of the heaviest elements

Description: In the region where theorists had earlier predicted the disappearance of the outer fission barrier or of it dropping below the ground-state, we have measured the mass and total-kinetic-energy distributions from spontaneous fission of {sup 252}No, {sup 254}No, {sup 256}[104], and {sup 258}[104]. The results, in combination with earlier measurements for {sup 256}No, {sup 258}No, and {sup 262}No, show a sharp transition from asymmetrical mass division in {sup 256}No to symmetrical ones for {sup 258}No and {sup 262}No. On-the-other-hand, all isotopes of element 104 including {sup 260}[104] appear to yield broadly symmetrical mass distributions. The total-kinetic energies around 200 MeV for the 104 isotopes indicate they fission by the low-energy mode of bimodal fission. Based on the hypothesis that the second barrier is responsible for asymmetrical mass distributions and when it disappears, for symmetrical ones, these observations for the isotopes of element 104 are in accord with 1976 calculations of the heights of the second fission barrier relative to the ground-state. Some recent calculations of static potential-energy surfaces and of barrier heights deduced from half-lives for spontaneous fission indicate the second barrier is from 0 to 2.9 MeV above the ground-state for the No and 104 isotopes. However, shape degrees-of-freedom have been limited in these calculations so that they fail to provide realistic heights for the outer fission barrier. For the few cases where higher-order asymmetrical deformations are included, this barrier height is well below the ground-state and, for these nuclides, we observe symmetric mass division only. Without more extensive calculations of potential-energy surfaces for comparison with our findings, we are unable reach a firm conclusion on the role of the second barrier upon mass division in fission.
Date: October 1, 1993
Creator: Hulet, E. K.
Partner: UNT Libraries Government Documents Department

Biomodal spontaneous fission

Description: Investigations of mass and kinetic-energy distributions from spontaneous fission have been extended in recent years to an isotope of element 104 and, for half-lives, to an isotope of element 108. The results have been surprising in that spontaneous fission half-lives have turned out to be much longer than expected and mass and kinetic- energy distributions were found to abruptly shift away from those of the lighter actinides, showing two modes of fission. These new developments have caused a re-evaluation of our understanding of the fission process, bringing an even deeper appreciation of the role played by nuclear shell effects upon spontaneous fission properties. 16 refs., 10 figs.
Date: September 26, 1989
Creator: Hulet, E.K. (Lawrence Livermore National Lab., CA (USA))
Partner: UNT Libraries Government Documents Department

Physics division annual report 1999

Description: This report summarizes the research performed in the past year in the Argonne Physics Division. The Division's programs include operation of ATLAS as a national heavy-ion user facility, nuclear structure and reaction research with beams of heavy ions, accelerator research and development especially in superconducting radio frequency technology, nuclear theory and medium energy nuclear physics. The Division took significant strides forward in its science and its initiatives for the future in the past year. Major progress was made in developing the concept and the technology for the future advanced facility of beams of short-lived nuclei, the Rare Isotope Accelerator. The scientific program capitalized on important instrumentation initiatives with key advances in nuclear science. In 1999, the nuclear science community adopted the Argonne concept for a multi-beam superconducting linear accelerator driver as the design of choice for the next major facility in the field a Rare Isotope Accelerator (WA) as recommended by the Nuclear Science Advisory Committee's 1996 Long Range Plan. Argonne has made significant R&D progress on almost all aspects of the design concept including the fast gas catcher (to allow fast fragmentation beams to be stopped and reaccelerated) that in large part defined the RIA concept the superconducting rf technology for the driver accelerator, the multiple-charge-state concept (to permit the facility to meet the design intensity goals with existing ion-source technology), and designs and tests of high-power target concepts to effectively deal with the full beam power of the driver linac. An NSAC subcommittee recommended the Argonne concept and set as tie design goal Uranium beams of 100-kwatt power at 400 MeV/u. Argonne demonstrated that this goal can be met with an innovative, but technically in-hand, design. The heavy-ion research program focused on GammaSphere, the premier facility for nuclear structure gamma-ray studies. One example of the ground-breaking research with ...
Date: December 6, 2000
Creator: Thayer, K., ed. & Physics
Partner: UNT Libraries Government Documents Department

Chemical properties of the heavier actinides and transactinides

Description: The chemical properties of each of the elements 99 (Es) through 105 are reviewed and their properties correlated with the electronic structure expected for 5f and 6d elements. A major feature of the heavier actinides, which differentiates them from the comparable lanthanides, is the increasing stability of the divalent oxidation state with increasing atomic number. The divalent oxidation state first becomes observable in the anhydrous halides of californium and increases in stability through the series to nobelium, where this valency becomes predominant in aqueous solution. In comparison with the analogous 4f electrons, the 5f electrons in the latter part of the series are more tightly bound. Thus, there is a lowering of the 5f energy levels with respect to the Fermi level as the atomic number increases. The metallic state of the heavier actinides has not been investigated except from the viewpoint of the relative volatility among members of the series. In aqueous solutions, ions of these elements behave as a normal trivalent actinides and lanthanides (except for nobelium). Their ionic radii decrease with increasing nuclear charge which is moderated because of increased screening of the outer 6p electrons by the 5f electrons. The actinide series of elements is completed with the element lawrencium (Lr) in which the electronic configuration is 5f/sup 14/7s/sup 2/7p. From Mendeleev's periodicity and Dirac-Fock calculations, the next group of elements is expected to be a d-transition series corresponding to the elements Hf through Hg. The chemical properties of elements 104 and 105 only have been studied and they indeed appear to show the properties expected of eka-Hf and eka-Ta. However, their nuclear lifetimes are so short and so few atoms can be produced that a rich variety of chemical information is probably unobtainable.
Date: January 1, 1981
Creator: Hulet, E.K.
Partner: UNT Libraries Government Documents Department

Evidence for bimodal fission in the heaviest elements

Description: We have measured the mass and kinetic-energy partitioning in the spontaneous fission of five heavy nuclides: /sup 258/Fm, /sup 259/Md, /sup 260/Md /sup 258/No, and /sup 260/(104). Each was produced by heavy-ion reactions with either /sup 248/Cm, /sup 249/Bk, or /sup 254/Es targets. Energies of correlated fragments from the isotopes with millisecond half lives, /sup 258/No and /sup 260/(104), were measured on-line by a special rotating-wheel instrument, while the others were determined off-line after mass separation. All fissioned with mass distributions that were symmetric. Total-kinetic-energy distributions peaked near either 200 or 235 MeV. Surprisingly, because only a single Gaussian energy distribution had been observed previously in actinide fission, these energy distributions were skewed upward or downward from the peak in each case, except for /sup 260/(104), indicating a composite of two energy distributions. We were able to fit accurately two Gaussian curves to the gross energy distributions from the four remaining nuclides. From the multiple TKE distributions and the shapes of the mass distributions, we conclude that there is a low-energy fission component with liquid-drop characteristics which is admixed with a much higher-energy component due to closed fragment shells. We now have further evidence for this conclusion from measurements of the neutron multiplicity in the spontaneous fission of /sup 260/Md. 25 refs., 9 figs.
Date: August 1, 1987
Creator: Hulet, E.K.; Wild, J.F.; Lougheed, R.W.; Dougan, R.J.; Landrum, J.H.; Dougan, A.D. et al.
Partner: UNT Libraries Government Documents Department

Discovery of a new mode of nuclear fission

Description: We measured the mass and kinetic-energy partitioning in the spontaneous fission of /sup 258/Fm, /sup 259/Md, /sup 260/Md, /sup 258/No, and /sup 260/(104). Surprisingly, these energy distributions were skewed upward or downward from the peak in each case, except for /sup 260/(104), indicating a composite of two energy distributions. We interpret this as a new mode of fission in which there is mixture of liquid-drop-like and fragment-shell-directed symmetric fission.
Date: January 1, 1986
Creator: Hulet, E.K.; Wild, J.F.; Dougan, R.J.; Lougheed, R.W.; Landrum, J.H.; Dougan, A.D. et al.
Partner: UNT Libraries Government Documents Department

New fission valley for /sup 258/Fm and nuclei beyond

Description: Experimental results on the fission properties of nuclei close to /sup 264/Fm show sudden and large changes with a change of only one or two neutrons or protons. The nucleus /sup 258/Fm, for instance, undergoes symmetric fission with a half-life of about 0.4 ms and a kinetic energy peaked at about 235 MeV whereas /sup 256/Fm undergoes asymmetric fission with a half-life of about 3 h and a kinetic energy peaked at about 200 MeV. Qualitatively, these sudden changes hve been postulated to be due to the emergence of fragment shells in symmetric fission products close to /sup 132/Sn. A quantitative calculation that shows where high-kinetic-energy symmetric fission occurs and why it is associated with a sudden and large decrease in fission half-lives. The study is based on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. The implications of the new fission valley on the stability of the heaviest elements is discussed. 33 refs., 12 figs.
Date: January 1, 1986
Creator: Moeller, P.; Nix, J.R. & Swiatecki, W.J.
Partner: UNT Libraries Government Documents Department

Recent searches for superheavy elements in deep-inelastic reactions. [Approximately 7 MeV/. mu. ]

Description: New attempts have been made to synthesize superheavy elements (SHE) by nuclear reactions that may possibly form the products at low excitation energies. Survival of the superheavy elements would then be enhanced because of reduced losses from prompt fission. Classical and diffusion-model calculations of deep-inelastic reactions indicate there should be detectable yields of SHE formed with less than 30 MeV of excitation energy. Accordingly, superheavy elements have been sought in such reactions where targets of /sup 248/Cm and /sup 238/U have been irradiated with /sup 136/Xe and /sup 238/U ions. In the most recent experiments, targets of /sup 248/Cm metal (3.5 to 7 mg-cm/sup -2/) were bombarded with 1.8-GeV /sup 238/U ions from the UNILAC accelerator. The longer-lived SHE and actinides near the target Z were chemically separated, and the yields of a number of isotopes of Bk, Cf, Es, and Fm were measured. An upper limit of 30 nb was obtained for the formation of 1-h /sup 259/No. In addition to the off-line chemical recovery and search for SHE, an on-line experiment was performed to detect volatile SHE with half-lives of a minute or more. All experiments to produce and detect superheavy elements were much less than optimum because of premature failures in the Cm-metal targets. The outcome and status of these experiments and the implications of the actinide yields in estimating the chances for forming superheavy elements in the /sup 248/Cm + /sup 238/U reactions are discussed. 5 figures, 1 table.
Date: October 1, 1980
Creator: Hulet, E.K.; Lougheed, R.W. & Nitschke, J.M.
Partner: UNT Libraries Government Documents Department

Calculated fission properties of the heaviest elements

Description: A quantitative calculation is presented that shows where high-kinetic-energy symmetric fission occurs and why it is associated with a sudden and large decrease in fission half-lives. The study is based on calculations of potential-energy surfaces in the macroscopic-microscopic model and a semi-empirical model for the nuclear inertia. For the macroscopic part a Yukawa-plus-exponential model is used and for the microscopic part a folded-Yukawa single-particle potential is used. The three-quadratic-surface parameterization generates shapes for which the potential-energy surfaces are calculated. The use of this parameterization and the use of the finite-range macroscopic model allows for the study of two touching spheres and similar shapes. The results of the calculations in terms of potential-energy surfaces and fission half-lives are presented for heavy even nuclei. The surfaces are displayed in the form of contour diagrams as functions of two moments of the shape. 53 refs., 15 figs., 1 tab.
Date: September 1, 1986
Creator: Moeller, P.; Nix, J.R. & Swiatecki, W.J.
Partner: UNT Libraries Government Documents Department

Prompt neutron multiplicities for the transplutonium nuclides

Description: The direct determination of the average prompt neutron emission values is reviewed, and a method of comparing different sites of neutron emission multiplicity distribution values is described. Measured and recommended values are tabulated for these nuclides: /sup 241/Am, /sup 242/Am, /sup 242/Cm, /sup 243/Cm, /sup 244/Cm, /sup 246/Cm, /sup 247/Cm, /sup 248/Cm, /sup 250/Cm, /sup 245/Cm, /sup 249/Bk, /sup 246/Cf, /sup 249/Cf, /sup 250/Cf, /sup 252/Cf, /sup 254/Cf, /sup 251/Cf, /sup 253/Es, /sup 254/Es, /sup 244/Fm, /sup 246/Fm, /sup 255/Fm, /sup 252/No, /sup 254/Fm, /sup 256/Fm, /sup 257/Fm. 59 refs., 24 tabs. (LEW)
Date: January 1, 1985
Creator: Holden, N.E. & Zucker, M.S.
Partner: UNT Libraries Government Documents Department

Neutron multiplicities for the transplutonium nuclides

Description: This paper continues, with respect to the transplutonium nuclides, earlier efforts to collate and evaluate data from the scientific literature on the prompt neutron multiplicity distribution from fission and its first moment <nu> = ..sigma..nuPnu. The isotopes considered here for which P/sub nu/ and or <nu> data (or both) were found in the literature are of americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), and nobelium (No).
Date: January 1, 1985
Creator: Holden, N.E. & Zucker, M.S.
Partner: UNT Libraries Government Documents Department

Heavy isotope production by multinucleon transfer reactions with /sup 254/Es. [101 MeV /sup 16/O, 98 MeV /sup 18/O, 127 MeV /sup 22/Ne]

Description: Fast automated on-line and quasi-on-line radiochemical techniques were applied to search for new isotopes, to measure their decay characteristics, and to study the cross sections of the heaviest, most neutron-rich actinide isotopes in reactions of /sup 16,18/O and /sup 22/Ne projectiles with /sup 254/Es as a target. The measured yields for isotopes up to Lr-260 are three or more orders of magnitude higher than in any other reaction used so far. A comparison with data for similar transfers from /sup 248/Cm targets is made. Transfer cross sections are extrapolated for the production of unknown, neutron-rich isotopes of elements 101 through 105, and the unique potential of /sup 254/Es as a target to make these exoctic nuclei accessible is demonstrated. 18 refs., 2 figs., 1 tab.
Date: January 1, 1985
Creator: Schaedel, M.; Bruechle, W.; Bruegger, M.; Gaeggeler, H.; Moody, K.J.; Schardt, D. et al.
Partner: UNT Libraries Government Documents Department

Rapid disappearance of shell effects in the fission of transfermium nuclei

Description: In the last fifteen years we have learned that nuclear shells have a very broad and pervasive impact on the fission process. In the first few decades after the discovery of nuclear fission, the nucleus was treated as a drop of liquid with smoothly varying attractive and repulsive forces. Although this model still forms the underlying basis for fission, we also observe large effects from the superimposition of shell corrections derived from coupling the quantum states of individual nucleons. The consequences of single-particle coupling on the fission process can be striking and may often overshadow that originating from the intrinsic liquid-drop component. Here, we point out several major features attributable to shell effects in the spontaneous fission (SF) of the lighter actinides, the sudden transition to symmetric fission in the fermium isotopes, and finally new experimental information indicating another transition in the SF of transfermium nuclides due to the disappearance of shell perturbations. In each transition, the abruptness is surprising, and for the moment, such rapid changes in fission behavior lack a theoretical rationale.
Date: January 1, 1983
Creator: Hulet, E.K.
Partner: UNT Libraries Government Documents Department

Calculated masses and half-lives for nuclei in the region 100 less than or equal to Z less than or equal to 110

Description: We have calculated nuclear masses and the corresponding ..cap alpha..-decay energies O/sub ..cap alpha../ and ..cap alpha.. half-lives T/sub ..cap alpha../ by use of the folded-Yukawa macroscopic-microscopic model, for nuclei at the end of the peninsula of known elements. We have also calculated, by use of the modified oscillator model, fission half-lives for even-even nuclei with Z between 100 and 110. The results agree well with data in this region, but an interpretation of the experimental data required further and extensive theoretical studies of odd particle effects. 13 references.
Date: January 1, 1984
Creator: Leander, G.A.; Moeller, P.; Nix, J.R. & Howard, W.M.
Partner: UNT Libraries Government Documents Department

Table of radioactive elements

Description: As has been the custom in the past, the Commission publishes a table of relative atomic masses and halflives of selected radionuclides. The information contained in this table will enable the user to calculate the atomic weight for radioactive materials with a variety of isotopic compositions. The atomic masses have been taken from the 1984 Atomic Mass Table. Some of the halflives have already been documented.
Date: January 1, 1985
Creator: Holden, N.E.
Partner: UNT Libraries Government Documents Department