Question

The ore of Uranium found in nature contains 92U23 and 92U235. Although both the isotopes are fissionable, it is found out experimentally that one of the two sotopes is more easily fissionable. (i) Name the isotope of uranium which is easily fissionable (ii) Give a reason for your answer. (iii) Write a nuclear reaction when Uranium 238 emits an alpha particle to form a Thorium (Th) nucleus.

Answer 1

U235 is the fissionable isotope of Uranium. Natural Uranium contains only about 0.7 percent U235.Uranium-235 is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a fission chain reaction. It is the only fissile isotope that is a primordial nuclide or found in significant quantity in nature.

Uranium-235 has a half-life of 703.8 million years. It was discovered in 1935 by Arthur Jeffrey Dempster. Its (fission) nuclear cross section for slow thermal neutron is about 504.81 barns. For fast neutrons it is on the order of 1 barn. At thermal energy levels, about 5 of 6 neutron absorptions result in fission and 1 of 6 result in neutron capture forming uranium-236.[9] The fission-to-capture ratio improves for faster neutrons.


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Answer:

23892U→l23490Th+42He

Explanation:

Uranium-238 produces thorium-234 by alpha decay.

An α-particle is a helium nucleus. It contains 2 protons and 2 neutrons, for a mass number of 4.

During α-decay, an atomic nucleus emits an alpha particle. It transforms (or decays) into an atom with an atomic number 2 less and a mass number 4 less.

Thus, uranium-238 decays through α-particle emission to form thorium-234 according to the equation:

23892U→l23490Th+42He

Note that the sum of the subscripts (atomic numbers or charges) is the same on each side of the equation.

Also, the sum of the superscripts (masses) is the same on each side of the equation.

α Decay