YBa 2 Cu 3 O 7−δ (YBCO) films were deposited with a low-fluorine modified trifluoroacetate metalorganic deposition (TFA-MOD) method on SrTiO 3 single crystals and buffered Ni–W metallic tape with a thickness ranging from 450 to 600 nm. The method consists in the substitution of yttrium and copper trifluoroacetates with Cu and Y acetates dispersed in propionic acid. A reduced pyrolysis time with respect to the usual TFA method is obtained. Apart from CuO, no traces of second phases are revealed by x-ray measurements. The films are compact without cracks, and exhibit a slight superficial porosity, but they still remain well connected, and therefore the observed porosity does not affect either the critical current density or the normal state resistivity values, which are indicative of high-quality YBCO films. Moreover, YBCO films were also obtained on Pd-buffered Ni–W, with a CeO 2 /YSZ/CeO 2 buffer layer architecture. These films show good morphological, structural, and superconductive properties with high critical temperature (higher than 91 K) and critical current density higher than 1 MA cm −2 at 77 K in self-field.
Trace amounts of the neptunium isotopes neptunium-237 and -239 are found naturally as decay products from transmutation reactions in uranium ores .   In particular, 239 Np and 237 Np are the most common of these isotopes; they are directly formed from neutron capture by uranium-238 atoms. These neutrons come from the spontaneous fission of uranium-238, naturally neutron-induced fission of uranium-235, cosmic ray spallation of nuclei, and light elements absorbing alpha particles and emitting a neutron.  The half-life of 239 Np is very short, although the detection of its much longer-lived daughter 239 Pu in nature in 1951 definitively established its natural occurrence.  In 1952, 237 Np was identified and isolated from concentrates of uranium ore from the Belgian Congo : in these minerals, the ratio of neptunium-237 to uranium is less than or equal to about 10 −12 to 1.