Production Of Heavy Nuclei Research Articles

Nuclear and chemical characterization of heavy actinides

Abstract Recent progress in the production of heavy nuclei far from stability and in the studies of nuclear and chemical properties of heavy actinides is briefly reviewed. Exotic nuclear decay properties including nuclear fission of heavy nuclei, measurements of first ionization potentials of heavy actinides, and redox studies of heavy actinides are described. Brief history of discovery of the transuranium elements is also presented.

Production of heavy trans-target nuclei in multinucleon transfer reactions

Problems of production and study of new neutron-enriched heavy nuclei are discussed. Low-energy multinucleon transfer reactions are shown to be quite appropriate for this purpose. Reactions with actinide beams and targets are of special interest for synthesis of new neutron-enriched transfermium nuclei and not-yet-known nuclei with closed neutron shell $N=126$ having the largest impact on the astrophysical r-process. The estimated cross sections for the production of these nuclei look very promising for planning such experiments at currently available accelerators. These experiments, however, are rather expensive and difficult to perform because of low intensities of the massive projectile beams and problems of separating and detecting the heavy reaction products. Thus, realistic predictions of the corresponding cross sections for different projectile-target combinations are definitely required. Some uncertainty still remains in the values of several parameters used for describing the low-energy nuclear dynamics. This uncertainty does not allow one to perform very accurate predictions for the productions of new heavier-than-target (trans-target) nuclei in multinucleon transfer reactions. Most of these parameters (nucleon transfer rate, nuclear viscosity, and fission barriers) are fundamental characteristics of low-energy nuclear dynamics. Determination of the values of these parameters (as well as their temperature dependence) is of significance in its own right. The available experimental data on the production of heavy nuclei in low-energy multinucleon transfer reactions are still insufficient and fragmentary. Several new experiments are proposed, these include those in which the role of shell effects in reaction dynamics can be better clarified.

Production of heavy nuclei in the interaction of 7Li ions with copper nuclei at an energy of 35 MeV per nucleon

The absolute values of the cross sections for the production of target fragments in the interaction of copper with 7Li ions at an energy of 35 MeV per nucleon were measured. The measurements were performed by recording the yields of radioactive nuclear residues with the aid of a semiconductor detector from ultrapure germanium. The charge and isobaric distributions in the mass-number range 22–69 amu were used to deduce the mass yield of reaction products and to calculate the total interaction cross section. The results are presented that were derived from a comparison with data obtained for 12C + Cu reactions and with estimates based on theoretical models.

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in massive stars

The production of heavy nuclei during explosive helium burning has been calculated using a hydrodynamical model of a 15-solar mass (Type II) supernova and an n-process nuclear reaction network. It is found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material, especially in the vicinity of Pt, nor are any actinides produced. These deficiencies reflect an inadequate supply of neutrons. However, some neutron-rich isotopes, normally associated with the r-process, are produced which may be significant for the production of isotopic anomalies in meteorites.

Production of Heavy Nuclei in the Par and Barbel Devices

In the Par and Barbel thermonuclear devices, heavy nuclei up to $A=257$ were produced by the exposure of ${\mathrm{U}}^{238}$ to intense neutron fluxes. If one tries to interpret the resulting abundance as a function of mass number by assuming that all higher nuclei resulted from multiple neutron capture in ${\mathrm{U}}^{238}$, there are difficulties in reconciling the high-$A$ data with standard semiempirical mass formulas and neutron-capture cross-section theories. Neither the general trend of abundance as a function of $A$, nor the odd-even fluctuation (for $A>249$) which is superimposed on this trend, is consistent with standard theory. In this paper we explore the suggestion that the high-mass isotopes resulted from neutron capture in odd-$Z$ nuclei (Pa and Np). We adopt a simplified model of the thermonuclear devices in which deuterium plus tritium burns to completion and resulting neutrons are captured by various heavy nuclei. We first estimate, in Sec. II, the number of uranium nuclei which will be transformed to odd $Z$ by the reactions ${\mathrm{U}}^{238}(n,p){\mathrm{Pa}}^{238}$; ${\mathrm{U}}^{238}(d,n){\mathrm{Np}}^{239}$, and ${\mathrm{U}}^{238}(d,2n){\mathrm{Np}}^{238}$. A production of about ${10}^{\ensuremath{-}3}$ Pa/U and \ensuremath{\le}${10}^{\ensuremath{-}3}$ Np/U is found and it is estimated that roughly these ratios will be available as targets for multiple neutron capture. In Sec. III statistical theory is used together with Seeger's semiempirical mass formula to calculate 20-keV neutron-capture cross sections for the nuclei $91\ensuremath{\le}Z\ensuremath{\le}93$, $238\ensuremath{\le}A\ensuremath{\le}257$. The average odd-$Z$ cross sections are systematically larger than the even $Z$, and those of Np are larger than Pa. The mass-yield curve can then be calculated for various neutron-flux values and in Sec. IV the results are compared with experiment. For both Par and Barbel, good agreement with the experimental abundance data is found using a 20-keV exposure of 7\ifmmode\times\else\texttimes\fi{}${10}^{24}$ neutrons/${\mathrm{cm}}^{2}$. For Par, a Np/U ratio of ${10}^{\ensuremath{-}3}$ is required while for Barbel the corresponding ratio is about 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$. In both cases the light end of the mass curve ($A<248$) is due to the uranium capture chain, while the heavy end ($A\ensuremath{\ge}250$) arises from capture by Np. A comparison is also made with less complete data from the Mike device, and it is found that for $A\ensuremath{\ge}245$ the data can be fit for $\ensuremath{\phi}=6\ifmmode\times\else\texttimes\fi{}{10}^{24}$ neutrons/${\mathrm{cm}}^{2}$ with Np/U\ensuremath{\simeq}1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$. We conclude that the formation of odd-$Z$ nuclei which undergo multiple neutron capture permits one to understand the mass-yield curves using standard semiempirical mass formulas and conventional capture-cross-section theory.