Production of fast evaporation residues by the reaction20Ne+208Pb at projectile energies of 8.6, 11.4 and 14.9 A.MeV

Velocity distributions and production cross sections of evaporation residues have been measured in the reaction²⁰Ne+²⁰⁸Pb at projectile energies of 8.6, 11.4, 14.9 A.MeV. Essential deviations from statistical model of deexcitation have been observed. Monte Carlo simulations involving emission of non-equilibrium particles have been used in order to reproduce experimental velocity, charge and mass distributions of evaporation residues and to estimate indirectly multiplicities of pre-equilibrium particles. Communicated by V. Metag     

Alpha decay studies of neutron-deficient radium isotopes

Neutron-deficient isotopes of radium have been produced in the reactions³⁵Cl+¹⁷⁵Lu,⁴⁰Ar+^170,171Yb, and³⁶Ar+^170,171Yb and separated in-flight with a gas-filled recoil separator. The activities have been identified on the basis of correlated alpha decay chains. The alpha particle energy E_α and the half-life T_1/2 of an isomeric state of the new isotope,^203m Ra, have been determined to be (7615±20) keV and (33 _?10 ⁺²² ) ms, respectively. An assignment of another decay with E_α = (7577±20) keV and T_1/2=(1.1 _?0.5 ^+5.0 ) ms to^203g Ra is made on the basis of one observed three-decay chain. Tentative evidence for the production of the new isotope²⁰²Ra is also given. The values E_α = (7860±60) keV and T_1/2=(0.7 _?0.3 ^+3.3 ) ms were measured. Improved decay data have been obtained for²⁰⁴Ra. The results are E_α = (7484±10) keV and T_1/2=(59 _?9 ⁺¹² ) ms. Earlier findings concerning the decay of two states in²⁰⁵Ra and an isomer in²⁰⁷Ra have been confirmed. Approximate values for cross sections have been determined for²⁰²Ra, produced using the³⁶Ar+¹⁷⁰Yb reaction and for²⁰³Ra,²⁰⁴Ra, and²⁰⁵Ra using the³⁵Cl+¹⁷⁵Lu reaction. The results are 2 nb (²⁰²Ra), 4 nb (²⁰³Ra), 40 nb (²⁰⁴Ra), and 800 nb (²⁰⁵Ra).     

A Helmholtz-Lie type characterization of ellipsoids,II

A closed convex surfaceS in is an ellipsoid if and only if for anyx, y εS there is an affinity mappingx ontoy and a neighborhood ofx inS onto a neighborhood ofy inS.     

Some analytical semigroups occurring in probability theory

One-parameter semigroups occurring in operator-limit distributions are investigated. The topological-algebraic background of the relevant monoids is discussed and Lie semigroup theory is applied to the Urbanik Decomposability Semigroup.     

Grain boundary segregation diagrams of α-iron

Based on thermodynamic analysis of interfacial segregation, the segregation enthalpy H ^o of a solute I in a given matrix was found to depend linearly on two mutually independent terms reflecting the type of interface and the solid solubility limit X _infI ^sup* at temperature T and can be written as In this equation, the structural dependence of interfacial segregation is contained in H ^*() which corresponds to the extrapolated segregation enthalpy of a solute with unlimited solubility in the matrix. The product [Tln(X _infI ^sup* )] is essentially constant with temperature, and can therefore be obtained from data for maximum solid solubility, [Tln(X _infI ^sup* )]_max. The parameter v>0 represents the relationship between the activity a _infI ^sup* of a solute at the bulk solid solubility limit in a given matrix and X _infI ^sup* , a _infI ^sup* =(X _infI ^sup* ) ^v , and is characteristic for the matrix. Using recent experimental data for silicon, phosphorus, and carbon segregation at well-characterized grain boundaries in oriented bicrystals of -iron, the averaged value was determined. Values of H ^*() range from -8 kJ/mol (general grain boundaries) up to +8 kJ/mol (special grain boundaries). These values are discussed and used for a more precise and generalized construction of grain boundary segregation diagrams of -iron.