Showing papers by "Glenn T. Seaborg published in 1986"

The chemistry of the actinide elements

Abstract: One.- 8. Americium.- 9. Curium.- 10. Berkelium.- 11. Californium.- 12. Einsteinium.- 13. Transeinsteinium Elements.- Two.- 14. Summary and comparative aspects of the actinide elements.- 15. Spectra and electronic structures of free actinide atoms and ions.- 16. Optical spectra and electronic structure of actinide ions in compounds and in solution.- 17. Thermodynamic properties.- 18. Magnetic properties.- 19. The metallic state.- 20. Structural chemistry.- 21. Solution chemistry and kinetics of ionic reactions.- 22. Organoactinide chemistry: properties of compounds having metal-carbon bonds only to ?-bonded ligands.- 23. Organoactinide chemistry: properties of compounds with actinide-carbon, actinide-transition-metal ? bonds.- 24. Future elements (including superheavy elements).- Appendix I.- Nuclear spins and moments of the actinides.- Appendix II.- Nuclear properties of actinide nuclides.- Author Index (Volumes 1 and 2).- Subject Index (Volumes 1 and 2).

Actinide production in reactions of heavy ions with Cm-248

Abstract: Transfer reactions of heavy ions with $^{248}$Cm targets are evaluated for their usefulness in producing unknown neutron-rich actinide nuclides. Cross sections for the production of nuclides in the region 91\ensuremath{\le}Z\ensuremath{\le}100 were determined radiochemically from bombardments with $^{18}$O, ${\mathrm{}}^{86}$Kr, and $^{136}$Xe ions. The systematic trends in the cross sections for these reactions can be understood in terms of the Coulomb potential and the stabilizing effect of the reaction Q values, which tend to favor the production of nuclei with Zg${Z}_{\mathrm{target}}$ with low excitation energies. Extrapolation of the product yields into unknown regions of charge and mass indicates that the use of heavy-ion transfer reactions to produce new neutron-rich above-target species is limited. Substantial production of unknown neutron-rich below-target species is expected in reactions with heavy projectiles like $^{136}$Xe and $^{238}$U.

Production of cold target-like fragments in the reaction of 48Ca+248Cm.

Abstract: Yields for isotopes of Rn through Pu have been measured in the reaction /sup 48/Ca+/sup 248/Cm at an energy of 248--263 MeV (1.04--1.10 times the Coulomb barrier). Despite the low bombarding energy, high and essentially constant integral yields of about 1 to 2 mb for the elements Rn through U were observed. There is evidence that these nuclides are produced with little excitation energy.

Summary and Comparative Aspects of the Actinide Elements

Abstract: This chapter is intended to provide a unified view of selected aspects of the physical, chemical, and biological properties of the actinide elements. The f-block elements have many unique features, and a comparison of the lanthanide and actinide transition series provides valuable insights into the properties of both. Comparative data are presented on the electronic configurations, oxidation states, redox potentials, thermochemical data, crystal structures, and ionic radii of the actinide elements, together with a miscellany of topics related to their environmental and health aspects. Much of this material is assembled in tabular and graphical form to facilitate rapid access. Many of the topics covered in this chapter, and some that are not discussed here, are the subjects of subsequent chapters of this work, and these may be consulted for more comprehensive treatments. This chapter provides a welcome opportunity to discuss the biological and environmental aspects of the actinide elements, subjects that were barely mentioned in the first edition of this work but have assumed great importance in recent times.

Attempts to produce superheavy elements by fusion of 48Ca with 248Cm in the bombarding energy range of 4.5–5.2 MeV/u

Abstract: A search for superheavy elements which are expected to occur around the predicted nuclear shell closures at atomic number 114 and neutron number 184 was made in bombardments of 248 Cm with 48 Ca ions. We have carried out this search at energies close to the Coulomb barrier to keep the excitation energy of the compound nucleus Z = 116, A = 296 as low as possible. The experiments were performed at the accelerators SUPERHILAC (Lawrence Berkeley Laboratory (LBL)) and UNILAC (GSI) and used a variety of improved physical and chemical techniques for the isolation and detection of superheavy elements to increase the sensitivity relative to earlier experiments. The small-angle separator system (SASSY) at LBL and the separator for heavy-ion reaction products (SHIP) at GSI were used for shortlived nuclides, and several radiochemical techniques were applied for longer half-lives. Although a broad range of half-lives, 10 −6 to 10 8 s, and excitation energies, 16 to 40 MeV, has been examined, no evidence for the formation of superheavy elements with cross sections greater than 10 −34 to 10 −35 cm 2 was found.

Incomplete and Complete Fusion in Intermediate Energy Heavy Ion Reactions

Abstract: The yields, angular distributions and differential range spectra have been measured for individual target residues from the interaction of 8.5 MeV/A 16O, 19 MeV/A 16O, 35 MeV/A 12C and 85 MeV/A 12C with 154Sm. From the measured data, fragment isobaric yields and velocity spectra were deduced. The results are compared to the predictions of a modified Boltzmann master equation model of precompound particle emission.

Actinide yields from the reactions of 40Ca and 48Ca with 248Cm

Abstract: Radiochemical techniques were applied to determine the actinide yields for nuclides with mass numbers below and above that of the target from the reaction 48 Ca + 248 Cm at energies near the interaction barrier. This work was initiated in the hope that the very neutron-rich projectile 48 Ca might give access to new neutron-rich isotopes of target-like actinide elements by nucleon transfer reactions. However, for trans-target elements, the use of 48 Ca did not result in increased production rates for such isotopes compared with those obtained in previous investigations. In contrast, rather neutronrich isotopes of below-target elements were observed at a remarkably high cross-section level. This observation is interpreted as a massive mass drift towards symmetry for this system. These investigations have been extended to the system 40 Ca + 248 Cm to explore the effect of the very different neutron-to-proton N Z ratios of 40 Ca and 48 Ca on the production of heavy target-like products.

Fast and slow processes in the fragmentation of 238U by 85 MeV/nucleon 12C.

Abstract: Target fragment distributions were measured using radiochemical techniques for 48 different fragments (28:SA:S185) from the interaction of 85 MeV/nucleon C with SU. The laboratory system angular distributions are forward peaked and generally flat beyond 90 o • When compared to similar distributions from the 85 MeV/nucleon 0+ Au reaction, the U target fragment distributions are less forward peaked, consistent with lower momentum transfer. The (A=80-120) fission fragment distributions were symmetric about 90 o in the moving frame, indicative of a \"slow\" process in which statistical equilibrium has been established. The average fissioning system angular momentum was deduced to be 25-35hbar. The observation that the fragments with low N/Z showed more anisotropic distributions than fragments with high N/Z was accounted for in firestreak model calculations as being due to a single reaction mechanism with varying amounts of deposition energy. The lightest (A<60) and heaviest (A = 139-169) members of the central fission-like bump in the mass distribution had moving frame angular distributions that were asymmetric in the moving frame. Furthermore, the heavy fragment complement of the 46Sc distribution was similar in shape to the Gd distribution, suggesting these fragments were produced in a new intermediate energy reaction mechanism, a fast, non-equilibrium, very asymmetric fission of a heavy nucleus. * Present Address: Los Alamos National Laboratory, Los Alamos, N.M. t Present Address: UCSF, Radiologic Imagery Lab., S. San Francisco, CA 94080 This work was supported in part by the U. S. Department of Energy under contract DEAC03-76SF00098 and DE-AM06-76RL02227, task agreement DE-AT06-76ER-70035, Mod. A009, the Swedish Natural Science Research Council, the BFMT (Bonn) and the Norwegian Research Council for Science and the Humanities.