[en] Gamma-rays in coincidence with the α-particles from the decay of the ground-state of ²¹⁸Th have been observed in the ²⁰⁶Pb(¹⁶O,4n) reaction. A tentative decay scheme of ²¹⁸Th is proposed

[en] The groundstate and a negative parity band of ₂₂₂Th have been observed in the ₂₀₈Pb (₁₈O, 4n) ₂₂₂Th reaction by conversion electron and ν-ray spectroscopy identifying the evaporation residues in a recoil separator. The de-excitation pattern is characterized by strong E1 transitions interconnecting the levels of alternating parity. The yrast levels may be interpreted as a molecular-cluster band. (orig.)

[en] Based on correlations of spontaneous fission isotopes with their respected 2Z-N values, we predict that the isotopes ²⁶¹Md and 106²⁶², which have not yet been discovered, have a spontaneous fission mode of decay. (author)

[en] The authors have measured the fission-fragment mass and kinetic-energy distributions from chemically separated lawrencium fractions following the bombardment of ²⁵⁴Es with 126-MeV ²²Ne ions. The spontaneous-fission activity in the lawrencium fraction is due to ²⁶¹Lr (39-m half-life) and ²⁶²No is based on time correlations of nobelium K-X rays with spontaneous-fission events. ²⁶²No is the first nuclide discovered with 160 neutrons. They will interpret their results in terms of the bimodal fission recently discovered in the heavy actinides. Their preliminary results show that ²⁶²No fissions symmetrically

[en] The new isotope 12.3-minute ²⁵⁶Cf was produced via the (t,p) reaction on a ²⁵⁴Cf target, and a new 43-minute isomer of ²⁵⁸Md was produced via the (α,n) reaction on ²⁵⁵Es at the Los Alamos FN Tandem Van de Graaff facility. The mass and total kinetic energy distributions of the fission fragments from the spontaneous fission (SF) of the ²⁵⁶Cf were found to be very similar to those from SF of the lighter californium isotopes. The most probable total kinetic energy was nearly the same as that measured for ²⁵²Cf and ²⁵⁴Cf. The 43-minute ²⁵⁸Md decays by electron capture to 380-μs ²⁵⁸Fm, and therefore, we were able to study the mass and kinetic energy distributions from spontaneous fission of ²⁵⁸Fm. the mass distribution was narrowly symmetric, similar to that measured for ²⁵⁹Fm (SF), but much narrower than that reported for ²⁵⁷Fm (SF). The most probable total kinetic energy for ²⁵⁸Fm (SF) was measured to be 238 MeV, nearly as high as that of 243 MeV measured for ²⁵⁹Fm (SF), and much higher than the value of 198 MeV reported for ²⁵⁷Fm (SF). Thus, although a rather dramatic change in spontaneous fission properties occurs for fermium isotopes at N = 158, no such abrupt change was observed for the californium isotopes

No abstract available

[en] A multicomponent decay curve analysis technique has been developed and incorporated into the decay curve fitting computer code, MLDS (maximum likelihood decay by the simplex method). The fitting criteria are based on the maximum likelihood technique for decay curves made up of time binned events. The probabilities used in the likelihood functions are based on the Poisson distribution, so decay curves constructed from a small number of events are treated correctly. A simple utility is included which allows the use of discrete event times, rather than time-binned data, to make maximum use of the decay information. The search for the maximum in the multidimensional likelihood surface for multi-component fits is performed by the simplex method, which makes the success of the iterative fits extremely insensitive to the initial values of the fit parameters and eliminates the problems of divergence. The simplex method also avoids the problem of programming the partial derivatives of the decay curves with respect to all the variable parameters, which makes the implementation of new types of decay curves straightforward. Any of the decay curve parameters can be fixed or allowed to vary. Asymmetric error limits for each of the free parameters, which do not consider the covariance of the other free parameters, are determined. A procedure is presented for determining the error limits which contain the associated covariances. The curve fitting procedure in MLDS can easily be adapted for fits to other curves with any functional form. (orig.)

[en] Short communication. 1 refs

[en] By using the theory of Lindhard et al (K. Danske Vidensk Selsk., Mat.-Fys. Meddr. 33:14 (1963)) together with experimental data, a complete set of average ranges of ²³³U fission fragments in all existing natural elements was evaluated. This set includes ranges for the median light fission fragment, the median heavy fission fragment and the overall median fission fragment for each stopping element. (author)

[en] A very high efficiency liquid-liquid chromatography (LLC) system based on 5- and 20-μm diameter porous silica microspheres was used to effect radiochemical separations of metal ions that required very large decontamination factors and/or high speeds. The stationary phase was 25-30% (w/w) of di(2-ethylhexyl) orthophosphoric acid (HDEHP) in dodecane. Nitric acid was used as the mobile phase. The mass transfer coefficient term, C, was determined from height equivalent to a theoretical plate vs. interstitial linear velocity data for the elution of Ca²⁺ and compared with values calculated from the interfacial mass transfer coefficients measured in the corresponding liquid-liquid extraction system. The HDEHP high-efficiency LLC system was also investigated for possible use in enriching the naturally occurring isotopes of calcium. Isotopic exchange constants for ⁴⁰Ca or ⁴²Ca and ⁴⁸Ca were measured chromatographically as a function of temperature. The enrichment of calcium isotopes was attempted on coupled columns at low flow velocities