R. W. Lougheed

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.

The use of electrodeposition methods to prepare actinide targets for cross-section measurements and accelerator bombardments

Abstract We have prepared targets of many of the actinide elements, e.g., U, Pu, Am, Cm, Bk, Cf, Es, and Fm, for use in a comprehensive series of fission cross-section measurements. Other experiments requiring actinide targets have involved accelerator bombardments, e.g., irradiation of 253 Es and 257 Fm at the HILAC, and symmetry studies of neutron-induced fission, e.g., recent studies of 257 Fm and 258 Fm fission. The experimental techniques require the targets be uniformly deposited in a thin layer on various backing materials such as Al, Ni, Pt, Be, Cu, and stainless steel. The backing materials ranged in thickness from 0.007 cm to 150 cm with target diameters ranging from 2 to 250 mm. In most cases the rarity of the nuclide required a deposition method that produces high yields, ≥90%. The various methods developed to produce acceptable targets may be summarized as follows: Electrodeposition technique (1) Dilute nitric acid electrolyte: Useful for actinides on a tracer level where high yields and small target area are desirable (e.g., einsteinium, fermium targets on a beryllium backing plate). (2) Isopropyl alcohol-dilute nitric acid electrolyte: Useful for actinides from tracer to microgram levels where uniformity of deposit is critical (e.g., berkelium, curium, einsteinium targets for Physics VIII cross-section experiment). (3) Ammonium chloride electrolyte: Useful for deposition of massive amounts ( 2 ) of actinides over large areas (180 cm 2 ). Also useful for deposition of actinides that are subject to hydrolysis in dilute acid (e.g., preparation of 232 U, 238 Pu, 242m Am targets on nickel foils for fission cross-section measurement). Chemical replacement technique . (1) The method is useful for plating uranium on aluminium. The preparation of 1-mg/cm 2 deposits on 1-mil aluminum is typical. Following deposition, it is usually necessary to determine the absolute amount of the actinide in the targets. This quantity is most often determined by absolute alpha counting. In the case of targets with high activity levels (10 6 –10 11 α dis/min) and large backing plates (8-in. diam.), a new low-geometry counter has been designed, built, and calibrated for this purpose. Uniformity of sample deposition has been monitored through alpha counter scanning techniques.

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.

Alpha decay of 255Md, 256Md and 257Md

Abstract The α-decay of 255Md,256Md and257Md has been studied following production of these isotopes in a series of helium-ion bombardments of an einsteinium target. The mendelevium was collected as the atoms recoiled from the target during bombardment. Following chemical purification the mendelevium was separated into various mass fractions in an electromagnetic isotope separator. The α-particle emission of each fraction was examined with the following results: 255 Md ,T 1 2 = 27±3 min , α/total = 0.100±0.014, Eα = 7.340±0.005 MeV ; 256 Md , T 1 2 = 77±5 min , α/total = 0.099±0.005, Eα = 7.16±0.015 MeV (16±2 %), Eα = 7.23±0.01 MeV (63 ±4%), Eα = 7.33±0.03 MeV (4±1 %), Eα = 7.46±0.03 MeV (5±1 %), Eα = 7.49±0.02 MeV (6±1 %), Eα = 7.67±0.03 MeV (2±1 %), Eα = 7.72±0.02 MeV (4±1 %) ; 257 Md , T 1 2 = 300±20 min , α/total MeV . The observed α-decay rates are compared with calculated values derived from α-decay theory. Lower limits have been determined for the partial spontaneous fission half-lives:255Md > 12 d,256Md > 2 d, 257Md > 6 d.

Radiopolarography of mendelevium in aqueous solutions

Abstract The possible existence of a monovalent ion of mendelevium has been examined further by radiopolarography. Experiments were conducted in several aqueous media with 241 Am, 249 Cf, 254 Es, 255,256 Fm and 256 Md tracers. Half-wave amalgamation potentials of Md in tetramethylammonium perchlorate and in LiCl were identical within the experimental errors at −1.755 ± 0.005 V vs the saturated calomel electrode, in good agreement with an earlier study by radiocoulometry in an ammonium acetate medium. No shift in the half-wave potential of Md was observed due to NH 4 + or Cl − ions; hence, these ions do not act as complexing agents for Md ions present during electrochemical reductions. The shift in the half-wave potential observed in the presence of citrate as a complexing agent was characteristic of the reduction process Md 2+ → Md 0 (Hg). In noncomplexing media, the slope of the logarithmically transformed wave of Md was ∼ 30 mV, consistent only with a reversible, two-electron reduction process. All of our results provide evidence for electrochemical reduction of the Md 2+ ion only and disprove the existence of an the intermediate Md + ion in aqueous solution with properties like those of Cs + , Ag + or Cu + .

Hyperfine Structure in the 253 Es Emission Spectrum. II. Nuclear Spin, Nuclear Magnetic Dipole Moment, and Energy Levels of Es ii*

Fifty-three emission-spectrum lines of einsteinium have been observed. The interval between the ground level 5I8 and the first excited level 3I7 of Es ii has been found to be 938.66 cm−1. The hyperfine structure confirms that the nuclear spin of 253Es is 72. A value of μI = (+5.1±1.3)μN was obtained for the nuclear magnetic dipole moment.

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

Fission Cross-Section Measurements of 247 Cm, 254 Es, and 250 Cf from 0.1 eV to 80 keV

The fission cross sections of Cm, Es, and Cf are measured with the Rensselaer intense neutron spectrometer from 0.1 eV to 80 keV. The cross sections are normalized to the U ENDF/BV broadened cross section. Fission areas and resonance widths are determined for lowenergy resonances in Cm. The Es and Cf fission cross sections are the only reported measurements for these isotopes. The Es isotope is the heaviest odd-odd isotope ever measured over this energy range. The thermal fission cross sections for Cm, Es, and Cf are determined by extrapolation of the low-energy region of the cross section and are in good agreement with other reported measurements. Resonance integrals are reported for the energy range of 0.1 eV to 80 keV, and the areas for Cm and Cf resonances are also reported. The previously reported Cm fission cross section was corrected for fission in Cm.

Hyperfine structure in the 253 Es emission spectrum, III: Extension of the line list, levels of Es i and Es ii, nuclear magnetic-dipole and quadrupole moments*

New observations of the einsteinium emission spectrum have increased the number of observed lines from 53 to 290 in the wavelength range 2600–6900 A. Ten lines have been assigned as transitions to the 5f11 7s2 4I15/2° ground state of Es i on the basis of reversal and hyperfine structure. The next odd level is 4I13/2° at 8759.25 cm−1. The lowest even level is 6I15/2 of the 5f11 7s7p configuration at 17 802.89 cm−1. The lowest level of the 5f106d7s2 configuration is 6I17/2 at 19 367.93 cm−1. Fifteen lines are classified as The lowest level transitions between Es i levels. Twenty-three lines are assigned as transitions to the two known lowest of Es ii. The hyperfine constants a5f = 0.033±0.001 cm−1 and bf = 0.48±0.06 cm−1 have been derived by an analysis of the hyperfine structure of assigned Es ii lines. From these constants for 253Es, we obtained a nuclear magnetic dipole moment of +3.6±0.4μN and a quadrupole moment of +6.0±0.8 b.

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.