1. The natural abundance of 235U is 0,72 % (atomic percentage).
2. 4,99 g of natural uranium contain approx. 8,8396.1019 atoms of 235U.
1 nanogram of natural uranium = 2,53.1012 atoms
Uranium-235 is not added to natural uranium, it is extracted from natural uranium by a process called enrichment.
Uranium enriched with isotope 235 to approx 4 percent (natural U is 0.7 percent 235)
Uranium is a chemical element with three natural isotopes (234, 235, 238). The natural uranium has cca. 0,72 % uranium-235; uranium with a concentration of uranium-235 under 0,72 % is called depleted uranium; uranium with a concentration of uranium -235 above 0,72 % is called enriched uranium. Uranium in nuclear power and research reactors is used as metal, aloys, uranium dioxide, uranium carbides, uranium silicides, etc.
Isotopes Uranium 235 and uranium 238 are only natural isotopes of the element uranium.
Uranium 235 is 0.7 percent of natural uranium and is fissile
Depleted uranium is approx. 60% less radioactive than an equivalent mass of natural uranium.
1 nanogram of natural uranium = 2,53.1012 atoms
abundance of uranium in the earth crust; 2,5-3 ppm (mg/kg) abundance of uranium in the sea water: ca. 3 ppb (?g/kg)
Natural uranium has about 0.7 percent U235, this has to be increased to about 4 percent for use in natural water moderated reactors. The obtaining of uranium from mining and refining is described in the document linked below
Uranium-235 is not added to natural uranium, it is extracted from natural uranium by a process called enrichment.
To be absolutely correct is necessary to be known the exact percentage of 234U, 235U and 238U in the sample. The approximate mass for uranium with 85 % 235U 235,45.
Uranium enriched with isotope 235 to approx 4 percent (natural U is 0.7 percent 235)
Uranium is a chemical element with three natural isotopes (234, 235, 238). The natural uranium has cca. 0,72 % uranium-235; uranium with a concentration of uranium-235 under 0,72 % is called depleted uranium; uranium with a concentration of uranium -235 above 0,72 % is called enriched uranium. Uranium in nuclear power and research reactors is used as metal, aloys, uranium dioxide, uranium carbides, uranium silicides, etc.
Uranium is present in approx. 220 rocks and minerals.
Natural uranium has approx. 0,7 % 235U; uranium with more than 0,7 % 235U is an enriched uranium.
Uranim-234 is a rare natural isotope of uranium - the abundance is 0,0054 %.This isotope ha 92 protons, 142 neutrons and an atomic mass of 234,040 952 1(20).His halflife is 245 500 years.