W.R. Daniels

Some short-lived isotopes of cerium and praseodymium☆

Abstract The following new β-decay chains of cerium and praseodymium were identified in the fission products of 235U: 147Ce(65 ± 6 sec)-147Pr(12·0 ± 0.5 min) and 148Ce(43 ± 10 sec)-148Pr(1·98 ± 0·10 min). The cerium half-lives were determined by measuring the relative amounts of the praseodymium daughter activities in samples milked from fission product cerium at suitable intervals. The praseodymium half-lives were obtained by direct observation of the decay of the milked samples. Studies of the radiations of 147Pr and 148Pr with β- and γ-scintillation spectrometers indicated total β-decay energies of 2·7 ± 0·2 MeV and 4·5 ± 0·4 MeV, respectively. A partial decay scheme for 147Pr has been proposed. The mass assignments of 5·98 hr 145Pr and the 12 min 147Pr were substantiated by (γ, p) reactions on enriched 146Nd and 148Nd. Similar irradiations of 150Nd produced some evidence for an ≈ 2·3 min activity attributable to 149Pr.

Radiochemical purification of tin and the half-lives of 121Sn, 123Sn, 125Sn and 125Sb☆

Abstract A procedure is given for the separation and radiochemical determination of tin isotopes in uranium fission product mixtures at least 2 days old. The half-lives of 121Sn, 123Sn, 125Sn and 125Sb were determined to be 26·85 ± 0·20 hr, 129·0 ± 0·5 days, 9·625 ± 0·025 days and 2·81 ± 0·05 years, respectively.

Decay of 24 min 146Pr

Abstract The radiations associated with the β-decay of 24 min 146 Pr have been studied with Ge(Li), Si(Li), NaI(Tl) and trans -stilbene detectors. Gamma-gamma and gamma-beta coincidence experiments were performed, and gamma-gamma directional correlations were measured for the 1.525–0.454 MeV cascade. The observation of a 3.6 MeV β-group in coincidence with the 0.454 MeV photopeak establishes the total β-disintegration energy of 146 Pr as 4.1±0.1 MeV. The β-ray spectrum is complex with an end-point energy of 4.1±0.2 MeV. The intensity of the 0.454 MeV γ-transition per β-disintegration was found to be 0.49, and the intensities of some 40 other γ-rays were determined. Most of these γ-transitions have been placed in the 146 Nd level scheme which includes excited states with energies has high as 3.819 MeV. The present data appear to be consistent with an assignment of either 1 − or 2 − for the ground state of 146 Pr.

Decay of 243Pu

The radiations associated with the β-decay of 4.96 h 243Pu have been studied with Ge(Li) and Si(Li) detectors and krypton- and xenon-filled proportional counters. Conversion electron lines of the more intense γ-transitions have been measured and tentative multipolarities have been assigned. A decay scheme incorporating some 20 γ-transitions is presented. The Nilsson assignments of 72+[624] for 243Pu and 52−[523] for 243Am are substantiated by the present data. The total β-disintegration energy of 243Pu is 580 ± 10 keV.

Attempts to produce superheavy elements by fusion of 48Ca with 248Cm in the bombarding energy range of 4.5–5.2 MeV/u

Abstract A search for superheavy elements which are expected to occur around the predicted nuclear shell closures at atomic number 114 and neutron number 184 was made in bombardments of 248 Cm with 48 Ca ions. We have carried out this search at energies close to the Coulomb barrier to keep the excitation energy of the compound nucleus Z = 116, A = 296 as low as possible. The experiments were performed at the accelerators SUPERHILAC (Lawrence Berkeley Laboratory (LBL)) and UNILAC (GSI) and used a variety of improved physical and chemical techniques for the isolation and detection of superheavy elements to increase the sensitivity relative to earlier experiments. The small-angle separator system (SASSY) at LBL and the separator for heavy-ion reaction products (SHIP) at GSI were used for shortlived nuclides, and several radiochemical techniques were applied for longer half-lives. Although a broad range of half-lives, 10 −6 to 10 8 s, and excitation energies, 16 to 40 MeV, has been examined, no evidence for the formation of superheavy elements with cross sections greater than 10 −34 to 10 −35 cm 2 was found.

Sorption and Migration of Radionuclides in Geologic Media

The interactions of a quartz monzonite, an argillite, an alluvium, and several tuffs with various radionuclides in selected phreatic waters have been studied. The sorption--desorption hehavior of Sr, Tc(VII), Cs, Ba, Ce, Eu, U(VI), Pu, and Am under ambient and 70{sup 0}C temperature conditions has been measured.

Actinide yields from the reactions of 40Ca and 48Ca with 248Cm

Abstract Radiochemical techniques were applied to determine the actinide yields for nuclides with mass numbers below and above that of the target from the reaction 48 Ca + 248 Cm at energies near the interaction barrier. This work was initiated in the hope that the very neutron-rich projectile 48 Ca might give access to new neutron-rich isotopes of target-like actinide elements by nucleon transfer reactions. However, for trans-target elements, the use of 48 Ca did not result in increased production rates for such isotopes compared with those obtained in previous investigations. In contrast, rather neutronrich isotopes of below-target elements were observed at a remarkably high cross-section level. This observation is interpreted as a massive mass drift towards symmetry for this system. These investigations have been extended to the system 40 Ca + 248 Cm to explore the effect of the very different neutron-to-proton N Z ratios of 40 Ca and 48 Ca on the production of heavy target-like products.

Decay of 245Pu

Abstract The radiations associated with the β-decay of 10.5 h 245 Pu have been studied with Ge(Li) and Si(Li) detectors, a xenon-filled proportional counter and conventional NaI(Tl) scintillators used in singles and coincidence configurations. The β-ray spectrum is complex with a 1210±40 keV end-point energy. The most intense group has a 930±30 keV end-point energy. Conversion electron lines of the more intense γ-transitions have been measured and tentative multipolarities have been assigned. A total of 70 γ-rays was observed in Ge(Li) singles spectra, and most of these transitions have been included in the 245 Am level scheme, which includes excited states at 19, 28, 47, 70, 87, 124, 134, 327, 396, 475, 757, 796, 887, 920, 958, 988, 1066, 1112 and 1185 keV. The present data are consistent with spin and parity assignments of 9 2 − for 245 Pu and 5 2 + for 245 Am. The total β-disintegration energy of 245 Pu is 1.26±0.03 MeV.

Discovery of a 7. 6-hour high-spin isomer of einsteinium-256

A 7.6-hour, beta-emitting isomer of /sup 256/Es has been produced via the (t,p) reaction by bombarding /sup 254g/Es with 16-MeV tritons. No evidence for an alpha branch was found. A number of gamma rays were observed, on the basis of which a partial decay scheme is proposed. It is concluded that the isomer has spin 7 or 8.

Radiochemical Separation of Actinides from Copper and Gold Catcher Foils from Heavy Ion Reactions with Actinide Targets

By M. M. FOWLER, W. R. DANIELS, Isotope and Nuclear Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA H. R. VON GUNTEN*, Radiochemisches Laboratorium, Universität Bern, CH-3000 Bern 9, Switzerland H. GAGGELER, Eidgenössisches Institut für Reaktorforschung, CH-5303 Würenlingen, Switzerland D. C. HOFFMAN, D. LEE, K. GREGORICH, Nuclear Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720, USA K. J. MOODY, Radiochemistry Division, Lawrence Livermore National Laboratory, University of California, Livermore, California 94550, USA M. LERCH**, G. HERRMANN*** and N. TRAUTMANN, Institut für Kernchemie, Universität Mainz, D-6500 Mainz, Fed. Rep. of Germany