Question

The more readily fissionable isotope of uranium has an atomic mass of:
(A)- 234
(B)- 235
(C)- 236
(D)- 238

Answer 1

Uranium is a radioactive element that occurs naturally and has no stable isotope discovered yet. Naturally occurring uranium has its three isotopes, that is $^{238}U{{,}^{235}}U\text{ and}{{\text{ }}^{234}}\text{U }$and all these isotopes are radioactive.

Complete Step by step solution:
-The standard atomic weight of Uranium which occurs naturally is 238.02831.
-There are six known isotopes of Uranium, that are- $^{232}U{{,}^{233}}U{{,}^{234}}U{{,}^{235}}U{{,}^{236}}\text{U and }{{U}^{238}}$.
- The Uranium-238 and Uranium-235 isotopes of Uranium have the longest half-lives among other isotopes and are therefore found in appreciable quantities in the earth’s crust.
- $^{238}U$being the most stable uranium isotope with a half-life of $4.4683\times {{10}^{9}}$years is an alpha emitter and decays through the 18-member uranium-series into lead-206.
-$^{235}U$being the second stable uranium isotope decays through the 15-member uranium-series into lead-207. This isotope has a half-life of 703.8 million years.
-$^{234}U$is a naturally occurring uranium isotope which occurs in uranium ore as an indirect decay product of uranium-238 and extracted using isotope separation. This isotope of uranium has a half-life of 245,500 years.
-$^{233}U$ is a fissile isotope of uranium that fissions on neutron absorption but sometimes retains the neutron, becoming $^{234}U$. This isotope of uranium is produced by neutron irradiation of thorium-232 by absorption of neutrons and has a half-life of only 22 minutes. Thorium-233 undergoes decays producing protactinium-233 through beta decay.
-$^{232}U$have a half-life of 68.9 years and is a rare example of an even-even isotope. This isotope of uranium is a side product in the thorium cycle and is the fissile material as it emits intense gamma radiation.
-$^{239}U$is an isotope of uranium produced by exposing uranium-238 to neutron radiation in a nuclear reactor. This isotope has a half-life of about 23.45 minutes and decays into neptunium-239 through beta decay.

So, the correct answer is option B.

Note: Uranium is an element found everywhere in traces quantities. In 1938, two German physicists showed that it can split into two parts yielding energy. Uranium is a principal fuel for nuclear reactors and is the main raw material for nuclear weapons.