A. Ghiorso

Sassy, a gas-filled magnetic separator for the study of fusion reaction products

Abstract A gas-filled on-line recoil separator at the Berkeley SuperHILAC is described. The separator consists of a magnetic dipole and a quadrupole doublet. The system is filled with He at a pressure of about 1 Torr (∼ 130 Pa). It separates particles according to their average magnetic rigidity. This allows a separation of evaporation residues, scattered target atoms and beam projectiles in a nuclear reaction. The separation time is in the order of 10 −6 s; the transmission is about 50% for evaporation residues, less than 10 −3 for scattered target-like recoil ions and transfer products, and about 10 −15 for full energy beam projectiles. Experimental data over a wide range of reactions are given and it is shown that the average charge of the recoils is determined by the atomic shell structure of the moving ionized atom in the gas.

Spontaneous fission of light fermium isotopes; New nuclides 244Fm and 245Fm

Abstract The spontaneous fission half-lives of 246 Fm and 248 Fm were determined. The new nuclides 244 Fm and 245 Fm were identified and their decay studied.

Nobelium: Tracer Chemistry of the Divalent and Trivalent Ions

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. Nobelium is the first actinide for which the +2 oxidation state is the most stable species in aqueous solution.

261Rf; new isotope of element 104☆

Abstract We have discovered a 65 s, α-particle emitting isotope of element 104, rutherfordium, by bombarding 248Cm with 18O ions. The identification of the isotope as 261Rf is based on milking the 26 s daughter, 257No.

The search for element 102

SYNTHESIS AND IDENTIFICATION of chemical elements with atomic numbers greater than 100 (fermium) have been accomplished with extremely small amounts, literally on a one‐atom‐at‐a‐time basis. At the present time these elements can only be formed with accelerated ions, ranging from neon to helium, that bombard targets from uranium to einsteinium. Because of their minuscule transmutation cross sections, such experiments are extremely difficult to perform, and often the results are subject to error and uncertainty of interpretation.

Decay properties of the new isotope 243Cf and of 244Cf

Abstract A new isotope of californium 243 Cf has been produced in the bombardments of 235 U, 236 U and 238 U with 12 C ions. At the same time new values for the half-life and α-particle energy observed in the decay of 244 Cf were obtained.

DETERMINATION OF THE No(II)--No(III) POTENTIAL FROM TRACER EXPERIMENTS.

Abstract The value of the standard oxidation potential of the No(II)No(III) couple in aqueous solution was estimated from the average behavior observed during repetitive series of experiments with 50–100 atoms per experiment. The distinction between No(II) and No(III) was made on a few atoms at a time basis by multiple solvent extractions with di(2-ethylhexyl)orthophosphoric acid (HDEHP) using the column elution technique of extraction chromatography. By comparing the extraction of nobelium from dilute acid solutions containing different oxidants with the extraction behavior of tracer quantities of radioactive elements of known standard oxidation potentials, the standard potential of the half-reaction No(II)No(III)+ e − was estimated to be −1·4 to −1·5 V.

The New ELement Mendelevium, Atomic Number 101

We have produced and chemically identified for the first time a few atoms of the element with atomic number 101. Very intense helium ion bombardments of tiny targets of 99{sup 253} have produced a few spontaneously fissionable atoms which elute in the eka-thulium position on a cation resin column.

OBSERVATIONS IN THE REACTION OF TWO MAGIC NUCLEI: 208Pb AND 48Ca

Abstract Excitation functions for compound-nucleus and transfer reactions have been measured with 48Ca ions on 208Pb targets. A comparison is made with the 40Ar-on-208Pb reaction to explain the observed anomalous behavior of the transfer reactions and a surprising cutoff of the (48Ca, 3n) exit channel. The former effect is interpreted as an enhancement of the tunneling gap between the projectile and the target while the latter is seen as a consequence of the angular momentum of the compound nucleus.

A search for superheavy elements with half-lives between a few minutes and several hundred days, produced in the 48Ca+248Cm reaction

Abstract The results of recent unsuccessful attempts to synthesize and identify superheavy elements at the Lawrence Berkeley Laboratory SuperHILAC are described. A thin 248Cm target was irradiated with 48Ca ions at an average energy in the target of 255 MeV. Direct counting of thin recoil foils for short-lived spontaneous fission activity was done. Two long irradiations were also made and radiochemical group separations for the superheavy elements were carried out. In the first radiochemical experiment, a thin superheavy element sample was prepared and has been continuously counted for spontaneous fission events in a dual surface barrier coincidence counter. In the second experiment, two superheavy element fractions were obtained and were counted for spontaneous fission events; the two fractions contained those elements that co-precipitated with copper sulfide from either an acid or basic solution.