J.F. Wild

Chloride complexation of element 104

Abstract We have investigated the chloride complexation of element 104 and compared it to that of the actinides and Hf. The 65- s α-emitting isotope 261 104 was produced via the bombardment of 248 Cm with 18 O ions, and the recoil products were transported to a fast computer-controlled apparatus for performing chemical experiments. This system allowed the experiments to be repeated many times to compensate for the very small number or 261 104 atoms produced in each bombardment. The formation of anionic-chloride complexes with element 104 was compared to those with Hf, Cm, and Fm by testing their relative absorption onto a column containing a quaternary amine. The results show that in 12 M HCl solutions the chloride complexation of element 104 is clearly stronger than that of the trivalent actinides and is quite similar to that of Hf, which is expected to be its homolog in the periodic table.

Octupole deformation in 142,143Ba and 144Ce: new band structures in neutron-rich Ba-isotopes

Abstract New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

Studies of californium(II) and (III) iodides

Abstract The compounds CfI2 and CfI3 have been prepared in microgram quantities using high-vacuum techniques. These compounds were characterized by both X-ray powder diffraction and optical spectroscopy. Californium diiodide is prepared by H2 reduction of CfI3 at elevated temperatures and exhibits two crystalline modifications: the CdCl2-type rhombohedral structure with a0 = 7.434 ± 0.011 A and α = 35.83 ± 0.07°, and the CdI2-type hexagonal structure with a0 = 4.557 ± 0.004 A and c0 = 6.992 ± 0.006 A. Optical spectra taken of the samples reveal absorption bands in the wavelength region 300–1100 nm consistent with the presence of Cf(II). Californium triiodide exhibits the rhombohedral BiI3-type structure with a0 = 8.205 ± 0.004 A and α = 55.08 ± 0.01°. This structure is stable up t0 700°C; linear coefficients of thermal expansion were obtained for the temperature range 20–700°C. Optical spectra taken of CfI3 showed absorption-peak positions consistent with those expected by extrapolation from known CfCl3 and CfBr3 peak positions.

SEARCH FOR AN 80-ms SPONTANEOUS FISSION ACTIVITY IN BOMBARDMENTS OF 249Bk WITH 15N

Nitschke, M Fowler, A. Nurmia, .L. P. Somerville, Landrum, . W,. Lo!Jghee{;\, J, Silva, .and Eskola TWO-WEEK LOAN COPY This is a Library Circulating Copy wh may be borrowed two weeks. For a personal retention copyy call Divisiony Ext 6782. Preoan~d for the U.S. Department of Energy under Contract W-1405-ENG-48

Observation of enhanced nuclear stability near the 162 neutron shell

In bombardments of {sup 248}Cm with {sup 22}Ne the authors discovered two new isotopes, {sup 265}106 and {sup 266}106, by establishing genetic links between {alpha} decays of the 106 nuclides and SF or {alpha} decays of the daughter (grand-daughter) nuclides. For {sup 266}106 they measured E{sub {alpha}}=8.62{+-}0.06 MeV followed by the SF decay of {sup 262}104 for which they measured a half-life value of 1.2{sup +1.0}{sub {minus}0.5} s. For {sup 265}106 they measured E{sub {alpha}}=8.82{+-}0.06 MeV. They estimated {alpha} half-lives of 10-30 s for {sup 266}106 and 2-30 s for {sup 265}106 with SF branches of {approximately}50% or less. The decay properties of {sup 266}106 indicate a large enhancement in the SF stability of this N=160 nuclide and confirm the existence of the predicted neutron-deformed shell N=162.

Some nuclear properties of fermium-257☆

Abstract A total half-life of 100·5±0·2 days and an alpha-to-spontaneous-fission decay ratio of 475±10 have been measured for 257 Fm by counting in ionization chambers. Thermal-neutron fission cross sections for 257 Fm (2950±160 b) and its daughter, 253 Cf (1300±240 b), have been measured in a thermal-neutron column using mica as a fission-fragment track recorder.

A new isotope of curium and its decay properties: 251Cm☆

Abstract The nuclide 251Cm ( t 1 2 = 16.8 ± 0.2 min ) was produced by neutron capture from 250Cm with an approximate cross section of 80 barns. In the decay of 251Cm, we measured the energies and intensities of 12 γ-rays from which we constructed a level scheme for 251Bk and assigned configurations for six single-particle states in 251Bk and for the ground state of 251Cm ( 1 2 ) + . The levels of 251Bk fed by 251Cm β-decay are compared with those of 249Bk fed by 249Cm β-decay. We also compare our measured Qβ− value of 1.42 MeV for 251Cm with previous closed-cycle estimates.

Non-observance of monovalent Md☆

Abstract Cocrystallization experiments were reported in 1972 that indicated a monovalent state existed for Md. We recently repeated some of these experiments and performed a series of new ones in which we attempted to prepare Md(I) by reduction with Sm2+ in an ethanolic or fused KCl medium. The oxidation state of Md was determined by the amount of 256Md tracer (≥ 105 atoms) carried on precipitates of SmF 2 SmCl 2 , SmCl2, RbCl and Rb2PtCl6. Comparisons of the coprecipitation behavior of Md with the behavior of tracer amounts of the elements Es, Fm, Eu, Sr, Y and Cs showed that Md consistently follows the behavior of Fm2+, Eu2+ and Sr2+, rather than the behavior of Cs+. Therefore, we conclude that Md cannot be reduced to a monovalent oxidation state with Sm2+ and that the earlier claim for Md(I) is unsubstantiated.

Mössbauer studies of americium compounds

Abstract Mossbauer studies of several compounds of Am were made with 243Pu as a source and 243Am as an absorber. Isomer shifts, line widths, and resonance intensities were measured with various sources and absorbers for recoiless emission of the 84-keV γ-ray of 243Am. The pentavalent Am compounds KAmO2CO3 and KAmO2F2 gave five-peak absorption spectra attributable to electric hyperfine interaction. A complex spectrum, interpreted as a result of magnetic hyperfine interaction, was also observed for the system PuFe2/AmO2. The changes in isomer shifts with the Am oxidation state are attributed to increases in the electron density in the region of the nucleus caused by removal of 5f electrons, and consequently, an increase in the effective Coulombic nuclear attraction for the outer s and p electrons.

Separation of trivalent actinides from lanthanides by solvent extraction

Abstract A method is presented for separating the trivalent actinides, mainly Am and Cm, from trivalent lanthanides by the use of only two solvent extractants. The first solvent removes the heavy lanthanides, leaving the Am, Cm and the lighterlanthanides; the second removes the Am and Cm. Because additional complexing agents are not required, waste-disposal and corrosion problems are reduced. Overall separation factors may be as high as several thousand for the separation of Am and Cm from lanthanides in the fission waste products from reactor fuel processing.