M. J. Nurmia

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.

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.

Chemical Properties of Element 105 in Aqueous Solution: Back Extraction from Triisooctyl Amine into 0.5 M HCl

Previous studies of the halide complex formation of element 105 and its anion exchange with triisooctyl amine (TIOA) were continued. The experiments were performed on a one-minute time scale with the computer-controlled liquid chromatography system ARCA II on a mixture of 34-s 2 6 2 Ha and 27-s 2 6 3 Ha produced in the 2 4 Bk( 0,5n) and 2 4 Bk( 0,4n) reactions at a beam energy of 99 MeV. The Ha isotopes were detected by measuring the spontaneous fission and α-activities associated with their decay, and the α-decays of their daughters, 4-s Lr, and 6-s Lr. Time-correlated pairs of parent and daughter α-particles were also registered. 2 6 2 , 2 6 3 Ha was absorbed on the TIOA columns from either 12 M HCl/0.01 M HF or 10 M HCl, and was subsequently eluted in 0.5 M HCl/0.01 M H F like its homolog niobium, and the pseudohomolog protactinium, and unlike the closest homolog, tantalum, which remains in the amine phase under these conditions. The effluent was divided into an early Pa fraction and a subsequent Nb fraction. By varying the cut between the Pa fraction and the Nb fraction in rough steps, it was shown that the elution of element 105 occurs closer to the Pa elution position, i.e., earlier than the elution of Nb. These results confirm the non-tantalum like behavior of element 105 in 0.5 M HCl/0.01 M HF, and corroborate previously suggested structural differences between the halide complexes of element 105, niobium, and protactinium, on the one hand, and those of tantalum on the other hand.

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.

Gas phase chromatography of halides of elements 104 and 105

On-line isothermal gas phase chromatography was used to study halides of261104 (T1/2=65 s) and262,263105 (T1/2=34 s and 27 s) produced an atom-at-a time via the reactions248Cm(18O, 5n) and249Bk(18O, 5n, 4n), respectively. Using HBr and HCl gas as halogenating agents, we were able to produce volatile bromides and chlorides of the above mentioned elements and study their behavior compared to their lighter homologs in Groups 4 or 5 of the periodic table. Element 104 formed more volatile bromide than its homolog Hf. In contrast, element 105 bromides were found to be less volatile than the bromides of the group 5 elements Nb and Ta. Both 104 and Hf chlorides were observed to be more volatile than their respective bromides.

Solution Chemistry of Element 104: Part I. Liquid-Liquid Extractions with Triisooctylamine

Liquid-liquid extractions of element 104 (Rf), Zr, Nb, Th, and Eu were conducted using triisooctylamine (ΠΟΑ), an organic soluble high molecular weight amine. Initial studies were conducted studying the extraction of Zr, Nb, Th and Eu from 12 M HCl in an organic phase of TIOA in benzene. Tracer loss due to thin sample formation was examined using Zr. Based on the tracer extraction results, Rf extractions were conducted with an aqueous phase of 12 M HCl and an organic phase of 1.0 M and 0.1 M TIOA in benzene. The Rf extraction results showed that 0.1 M TIOA in benzene extracts Rf to a greater extent than 1.0 M TIOA in benzene. This difference is attributed to Rf loss during thin sample formation. The extraction of Rf by ΤΊΟΑ is further evidence that Rf behaves similar to the group 4 elements.

The hydration enthalpies of Md3+ and Lr3+

Lawrencium (3-min 260Lr) and lighter actinides were produced in the bombardment of a 249Bk target with 18O ions and loaded onto a cation exchange column in 0.05 M α-hydroxyisobutyrate solution at pH=4.85, together with the radioactive lanthanide tracers 166Ho, 171Er and 171Tm. In elutions with 0.12 M α=hydroxyisobutyrate solution (pH=4.85), trivalent Lr was eluted exactly together with the Er tracer and Md was eluted close to Ho. Lr elutes much later than expected based on the known elution positions of the lighter actinides and the expected analogy to the elution positions of the homologous lanthanides. From the measured elution positions, ionic radii were calculated for Lr3+ and Md3+. Semi- empiricalmodels allow the calculation of the heat of hydration from the ionic radii, resulting in ΔHhyd≈-−3654 kJ/mol for Md3+ and ΔHhyd≈ -−3685 kJ/mol for Lr3+.

Solution Chemistry of Element 104: Part II. Liquid-Liquid Extractions with Tributylphosphate

Liquid-liquid extractions of element 104 (Rf), Zr, Nb, Hf, Th, and Pu(IV) were conducted using tributylphosphate (TBP) in benzene. Initial studies were conducted using Zr and Nb. The effect of TBP, HCl, chloride, and hydrogen ion concentrations on Zr and Nb extraction was examined. Based on the results from these experiments, it was decided to examine Rf extraction into 0.25 M TBP in benzene as a function of HCl, chloride, and hydrogen ion concentrations between 8 and 12 M. Studies of these extraction conditions were carried out using Zr, Hf, Th, Pu, and Rf. The 65-second Rf was produced via the Cm(0,5n) reaction at the 88-Inch Cyclotron at Lawrence Berkeley Laboratory. The results show that extraction for these elements increases or remains high as a function of HCl concentration. However, in the experiments in which the chloride and hydrogen ion were varied, Rf extraction differed from that of the group 4 elements and behaved more like Pu(IV).

The heavy element volatility instrument (HEVI)

Abstract We have constructed the heavy element volatility instrument (HEVI), an on-line gas chromatography system which is used to continuously separate halides according to their volatility. Both gaseous HBr and HCl have been used as halogenating agents. The detailed design of the apparatus is described and some preliminary results are presented. The experimental results are compared with those from a Monte Carlo code simulation based on a microscopic model for gas thermochromatography in open columns with laminar flow of the carrier gas. There is good agreement between the experimental results and the simulation.

Lawrencium chemistry: no evidence for oxidation states lower than 3+ in aqueous solution

Lawrencium (3-min 260Lr) together with other actinides, was produced in the bombardment of a 249Bk target with 18O ions. There was no sign of a reduction of Lr3+ in dilute hydrochloric acid by V2+ or Cr2+, although in the same experiments, Md3+ was reduced to Md2+ (E°=−0.2 V). The resulting limit for the reduction potential of the Lr3+/Lr1(2)+ couple is E° < −0.44 V.