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Earlier studies of spontaneous fission of heavy actinides found that the fission-fragment mass distribution suddenly changes from predominantly asymmetric to symmetric, when the mass number of the fissioning nucleus becomes larger than A_c = 257. We have measured for the first time fission-fragment mass and totalkinetic-energy (TKE) distributions of the excited compound nucleus ²⁵⁸Md∗ (Z = 101), populated in the reaction ⁴He + ²⁵⁴Es, using the rare radioactive target isotope ²⁵⁴Es with a short half-life, T1/2 = 275.7 d. The fission of ²⁵⁸Md∗ can be interpreted as involving three fission modes: one mass-asymmetric and two mass-symmetric fission modes, the lattermore » two are manifested by different TKE values. In this assumption, symmetric and asymmetric fission modes have nearly similar yields at the excitation energy of 15.0 MeV. The spectrum of 18.0 MeV can be explained as due to the increase of asymmetric fission mode.« less

The excitation functions for quasielastic scattering of ${}_{22}\mathrm{Ne}+{}_{248}\mathrm{Cm}$, ${}_{26}\mathrm{Mg}+{}_{248}\mathrm{Cm}$, and ${}_{48}\mathrm{Ca}+{}_{238}\mathrm{U}$ are measured using a gas-filled recoil ion separator. The quasielasticmore » barrier distributions are extracted for these systems and are compared with coupled-channel calculations. The results indicate that the barrier distribution is affected dominantly by deformation of the actinide target nuclei, but also by vibrational or rotational excitations of the projectile nuclei, as well as neutron transfer processes before capture. From a comparison between the experimental barrier distributions and the evaporation residue cross sections for Sg ( $Z=106$), Hs (108), Cn (112), and Lv (116), it is suggested that the hot fusion reactions take advantage of a compact collision, where the projectile approaches along the short axis of a prolately deformed nucleus. Overall, a new method is proposed to estimate the optimum incident energy to synthesize unknown superheavy nuclei using the barrier distribution.« less

In this work, samarium thin-films doped with a ²⁵²Cf radiotracer were used to study the effects of annealing on the release of fission fragments from electrodeposited films. An ammonium acetate molecular plating technique was utilized to perform the depositions. The fission fragment yields were measured using a unique technique involving the exposure of aluminum foils to the deposited material for a fixed time followed by gamma-ray spectroscopy to determine the rate at which the fission fragments implanted into the foils. Annealing of the electrodeposited films was found to have no effect on the release of fission fragments.

Separation of ²²⁵Ra (t_1/2 = 15 d) from its daughter isotope ²²⁵Ac (t_1/2 = 10 d) is necessary to obtain pure ²²⁵Ac for cancer alpha-therapy. In this study, microscale separation of ²²⁵Ra from its daughter ²²⁵Ac using BioRad AG50X4 cation exchange resin was achieved with good reproducibility across microdevices, and ≥90% purity was achieved for ²²⁵Ac, which is comparable to conventional chromatography. These results indicate the potential for greater use of microfluidics for biomedical radiochemistry. The modularity of the system and its compatibility with different resins allows for quick and easy adaptation to the various needs of a separation campaign.

Characterization of samarium thin films molecular plated from N,N-dimethylformamide solutions onto stainless steel substrates, with either mirrorlike or brushed finishes, was carried out using a Thermo Scientific K-Alpha x-ray photoelectron spectrometer. Survey scans of the two specimens showed the presence of samarium, carbon, and oxygen with minor amounts of sodium. High-resolution spectra were then taken of the Sm 3d, O 1s, and C 1s regions. Furthermore, the chemical compositions of the two samples were found to be very similar, with the key difference being the relative amounts of two carbon species. Spectra from the survey and narrow high-resolution scans ofmore » the Sm 3d, O 1s, and C 1s regions are reported herein.« less

In this paper, we describe the ¹⁴⁷Pm production yields and level of impurities from several targets that consisted of milligram quantities of highly enriched ¹⁴⁶Nd oxide irradiated at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory for durations ranging from 24 to180 h. A comparison between theoretical and experimental data are also presented, and attempts were made to empirically evaluate the neutron capture cross-sections of 41.3-d ^148mPm and 5.4-d ^148gPm. For a one-cycle irradiation (~24 days), ¹⁴⁷Pm yield reaches a maximum value of 101.8 MBq/mg (2.75 mCi/mg) at 60 days after the end of bombardment. Because ofmore » large neutron capture cross-sections of ¹⁴⁷Pm, the yield of ¹⁴⁷Pm does not significantly increase with longer irradiation. Our estimates of the thermal neutron capture cross-section and resonance integral for ¹⁴⁶Nd at 1.48 ± 0.05 b and 2.56 ± 0.25 b, respectively, were consistent with the reported values. The effective neutron capture cross-section of ¹⁴⁷Pm to ^148mPm was 53.3 ± 2.7 b - a factor of 2 lower than the 98.7 ± 6.5 b calculated from reported cross-sections. The measured σ_eff to the ground state (5.37-d ^148gPm) was 82.0 ± 4.1 b; ~34 % lower than the value of 139 ± 0 b calculated from reported cross-sections. In this work, we also describe the development of a chemical process based on extraction and ion-exchange chromatography for separation of ¹⁴⁷Pm from milligram quantities of ¹⁴⁶Nd and other impurities. Sequential separation of Pm from the Nd target and from other radioisotopic impurities (¹⁵³Gd and ^154&155Eu, ¹⁹²Ir, and ⁶⁰Co) was achieved using a LN extraction resin in HCl media followed by further purification of Pm from ⁶⁰Co and ¹⁹²Ir using a low cross-linking cation exchange resin. Based on these data, we estimated that two rounds of purification under our experimental conditions can provide a mass separation factor of > 104 between Pm and Nd. Our data indicate that curie quantities of ¹⁴⁷Pm with suitable chemical and radioisotopic purity for applications in beta voltaic batteries can be produced by irradiating gram quantities of highly enriched ¹⁴⁶Nd in the flux trap of HFIR for one cycle.« less

A new method has been developed for the isolation of ^223,224,225Ra, in high yield and purity, from a proton irradiated ²³²Th matrix. We report an all-aqueous process using multiple solid-supported adsorption steps including a citrate chelation method developed to remove >99.9% of the barium contaminants by activity from the final radium product. Moreover, we developed a procedure involving the use of three columns in succession, and the separation of ^223,224,225Ra from the thorium matrix was obtained with an overall recovery yield of 91 ± 3%, average radiochemical purity of 99.9%, and production yields that correspond to physical yields based onmore » previously measured excitation functions.« less