Torbjorn Sikkeland

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.

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.

EVIDENCE FOR THE PRODUCTION OF COMPOUND NUCLEI WITH ATOMIC NUMBER 110

Abstract Using a two-dimensional pulse-height analyzer in conjunction with a coincidence technique, we have measured angular correlation functions for coincident fragment pairs, the fission excitation function, and the most probable kinetic energy release for binary fission in the bombardment of 238 U with 40 Ar from the Berkeley HILAC. Evidence is presented that compound nuclei of Z = 110 are produced in these reactions.

Spallation reactions of californium-252 with helium ions

Cross sections were determined for Cf/sup 252/( alpha ,xn) and ( alpha ,pxn) reactions. The product of the ( alpha ,3n) reaction, Fm/sup 253/, was found to have a half life of 1.0 plus or minus 0.2 days and the most abundant alpha -particle energy was 6.95 plus or minus 0.05 Mev. From the decay of Fm/ sup 253/, the electron-capture daughter Es/sup 253/ was found to have an electron- capture to alpha -decay branching ratio of 8.5 plus or minus 1.0. (C.J.G.)

EFFECTS OF ANGULAR MOMENTUM ON KINETIC ENERGY RELEASE IN FISSION.

Values for the most probable kinetic energy release in fission following compound-nucleus reactions between various targets and ions are reproduced. with a standard deviation of 1.5 MeV. by the expression EK0 (MeV) = 0.0042 Z02/A013 + 0.075 E0. where Z0.A0 and E0 are respectively the atomic number. mass number and the excitation energy of the compound nucleus.

Ratio of 115Cd isomers produced in heavy-ion-induced fission☆

Abstract Isomeric cross-section ratios have been measured for the formation of 115Cd isomers in 12C-and 16O-induced fission in 197Au and 238U. The cross-section ratio (high spin/low spin) varied from 1·60 to 3·43 for the system 197Au + 12C ion energy ranging from 73 to 120 MeV. In the same energy range the ratio for the system 238U + 12C varied from 0·55 to 0·82. The average intrinsic spin, 〈lf〉, of the fragment that decays to the 115Cd isomer pair was estimated from a simple model. The cross-section ratio showed the same relative increase with 〈lf〉, for both targets. At the same value for 〈lf〉 the ratio is much larger for 197Au than it is for 238U. It is suggested that this difference is related to the fact that in the Au system, the 115Cd is produced in a more asymmetric division.

New californium isotope, 242Cf☆

Abstract A new isotope of californium has been produced in the bombardments of 233 U, 234 U, 235 U and 236 U with 12 C ions from the Hilac. It decays with a half-life of 3.4 ± 0.2 min by the emission of α particles with an energy of 7.39 ± 0.02 MeV. From an analysis of the excitation functions, it is concluded that the isotope has the mass number 242.