Donald N. Metta

THE EXTRACTION OF SELECTED M(III) METALS BY BIS 2‐ETHYLHEXYL PHOSPHORIC ACID IN N‐HEPTANE

Abstract The extraction of Y 3+ , Pm 3+ , Eu 3+ , Tm 3+ , Lu 3+ , Am 3+ and Cm 3+ from an aqueous chloride phase into a solution of (2-C 2 H 5 ·C 6 H 12 O) 2 PO(OH), HDEHP, in n -heptane has been studied as a function of the concentration of extractant in the organic phase and of hydrogen ion in the aqueous phase. From these data the stoichiometries of extraction have been deduced as: M A 3+ +2.5(HY) 2 o ⇌MY(HY 2 ) 2 o +3H A + where the subscripts A and O refer, respectively, to mutually equilibrated aqueous and organic phases. (The formulation of extracted entities is based solely upon established ratios and is in no sense to be interpreted in terms of established structure.) Corresponding to the stoichiometries, values of K , F and [H + ] obtained from the hydrogen ion dependency plots were inserted in the equation: K= K s F a /[H + ] b to obtain values of K s . ( K is the observed distribution ratio, F the equilibrium concentration of HDEHP in the organic phase, [H + ] the equilibrium concentration of hydrogen ion in the aqueous phase, and a and b the respective extractant and hydrogen ion dependencies.) The equation is applied specifically to a system embodying 1.0F (NaCl + HCl) at 22±2°C. The K s ( n -neptane) value is higher than the K s (benzene) value for each of the cations studied. Comparisons with extraction systems employing ( n -C 8 H 17 O) 2 PO(OH) and [C 4 H 9 C(CH 3 ) 2 CH 2 O] 2 PO(OH), respectively symbolized as HDOP and HDNOP, are made.

The reduction of plutonium(V) by aquatic sediments

Abstract The reduction of plutonium (V) to the (III) or (IV) state proceeds very slowly in distilled water or filtered natural waters, but rapidly in the presence of natural sediments. The reaction rate is nearly first-order and is proportional to sediment concentration. Fresh or heat-dried (105°C) sediments mediated a rapid reduction reaction but ashed (500°C) sediments, silica, kaolin, alumina and goethite mediated much slower rates. Rare earths strongly inhibit the reduction; the affinity (inhibition) constant of neodymium for the reducing site is 4·5 × 10 7 M −1 , whereas the affinity of neodymium for rare-earth binding sites is 5·0 × 10 5 M −1 . Some hours of pre-equilibration of sediment and liquid phase are necessary to achieve constant reduction rates.

The half-lives of 245Cm, 246Cm, 248Cm, 250Cf, 251Cf and 249Cf☆

Abstract The partial α-half-lives of 245 Cm, 246 Cm, 248 Cm, 250 Cf, 251 Cf and 249 Cf have been determined to be 8265 ± 180 yr, 4711 ± 22 yr, (3·84 ± 0·04) 10 5 yr, 13·08 ± 0·09 yr, 900 ± 50 yr, and 352 ± 6 yr respectively. Partial spontaneous fission half-lives of (1·80 ± 0·01) 10 7 yr and (4·22 ± 0·12) 10 6 yr were determined for 246 Cm and 248 Cm, respectively.

Copper Artifacts: Correlation with Source Types of Copper Ores

Six out of eight minor chemical elements, determined by spectroscopic and neutron-activation techniques, were found to be critical in computing a probability that a given copper artifact was derived from one of three types of copper ore: native metal, oxidized ore, reduced ore. Two elements, gold and tin, were apparently alloyed deliberately in many artifacts from both the Old World and the New World.

Fission cross-sections for 243Pu, 250Bk, 247Cm, 245Cm, 254mEs and 254Es, and odd-odd systematics☆

Abstract Fission cross-sections measured in back-to-back ion chambers in a graphite thermal column of a reactor are: 243 Pu, 196±16 barns; 250 Bk, 960±150 barns; 247 Cm, 108±5 barns; 245 Cm, 2040±80 barns; 254m Es, 1840±80 barns; 254 Es, 3060±180 barns. A more accurate beta decay half-life of 4·955±0·003 hours was found for 243 Pu. Of the 12 known thermal neutron fission cross-sections for odd-neutron and odd-proton target nuclei, only one cross-section is more than a factor of 2·3 from 1350 barns. A more striking uniformity is observed in the ratio of thermal neutron fission cross-section to target spin: eight of the ten known ratios are grouped at 600±320 barns per spin unit. The dependency of fission cross-section upon target spin is also shown by the three sets of isomers ( 254 Es, 242 Am, 244 Am) in which the higher fission cross-section of each pair is associated with the higher spin isomer. No simple correlation between fission cross-section and calculated compound nucleus level-density was found.

Decay properties of berkelium-249 and californium-249☆

Abstract The following decay properties have been measured: the alpha/beta branching ratio of 249Bk, (1·45±0·08) × 10−5, the alpha half-life of 249Cf, 345±15 yr, the spontaneous fission half-life of 249Bk, (1·87±0·09) × 109 yr, and the spontaneous fission half-life of 249Cf, (6·87±0·33) × 1010 yr, which appears to be anomalously long. Observations of the alpha particle spectra of these two nucleides are also reported.

Some new properties of 254Es and 255Es

Abstract Alpha decay of the 39.3 h 254m Es isomer was observed and further studies showed that this decay populates a 2 − excited state in 250 Bk, but decay to the 2 − ground state is highly hindered. The partial alpha half-life of 254m Es is 1.52±0.1 y. A lower limit to the spontaneous fission half-life of 254 Es was set at 2.5 × 10 7 y. The total decay and partial spontaneous fission half-lives of 254 Fm were redetermined as 194.4±0.1 min and 228±1 d, respectively. The pile neutron cross sections of 253 Es to produce the two isomers of 254 Es were measured as σ c = 13 b ( 254 Es ), σ c = 338 b ( 254 m Es ) . The partial alpha half-life of 255 Es has been measured as 1.38±0.08 y and the partial spontaneous fission half-life as 2440±140 y. The rotational band structure observed in the alpha decay of 255 Es is consistent with a 7 2 + spin.

236U/238U measurements in three terrestrial minerals and one processed ore☆

Abstract The 236 U/ 238 U ratio was measured mass spectrometrically in the following terrestrial uranium samples: uraninite with (2.3±0.8) × 10 −10 ; schroeckingerite with (2.0±2.0) × 10 −10 ; thucholite with (0.8±1.5) × 10 −10 ; and a processed ore with (6.2±2.2) × 10 −10 .

Alpha decay of 247Cm

Abstract An enriched sample of 247Cm (99.4 %) has been used to investigate the α-decay scheme of 247Cm. Seven α-groups with energies and intensities 5.265 (13.8 %), 5.210 (5.7 %), 5.145 (1.2 %), 4.983 (2.0 %), 4.941 (1.6 %), 4.868 (71.0 %) and 4.818 (4.7 %) were observed. Gamma-singles and αγ coincidence spectra showed the presence of 278.0, 287.5, 346.0 and 402.4 keV γ-rays. A two-parameter coincidence experiment established that the sources of the 402.4 and the 287.5 keV γ-rays were 4.868 and 4.983 MeV α-groups, respectively. The multipolarity of the 287.5 keV transition was found to be M1. The K conversion coefficient of the 402.4 keV γ-ray indicates an E1 multipolarity for this transition. The levels at 287.5 and 402.4 keV have been assigned to the 5 2 + (622) and 9 2 − (734) Nilsson states, respectively. The half-life of 247Cm was found to be (1.56±0.05) ×107 y from the α pulse analysis and mass spectrometric analysis of the sample.

Isotopic Abundances of Actinide Elements in Lunar Material

The abunldanzces of uranium and thorium were measured mass spectrometrically as 0.59 � 0.02 and 2.24 � 0.06 parts per million, respectively, in the fines of Apollo 11 builk sample. The ratio 235U/238U was 0.007258 � 0.000016, in agreement with terrestrial uranium. The following upper limits were set: 236U/238U≤3 x 10-9; parts per million of sample, 239Pu.≤1 x 10-9; 244Pu≤9 x 10-1l, and 247Cm ≤ 1.25 x 10-10. More alpha activity from 227Th and its decay products appears to be presenit than would be in equtilibrilum with the 235U in the sample. The search for other actinide and transactinide nuclides is continuing.