Natural uranium composition check: which of the following isotopes is not present in naturally occurring uranium?

Introduction / Context:
Natural uranium is a mixture of isotopes with specific fractional abundances. Recognizing which isotopes occur naturally versus those that are produced artificially is fundamental in nuclear science, fuel cycle discussions, and reactor engineering basics.

Given Data / Assumptions:

• Natural uranium is dominated by one major isotope with two additional minor constituents.
• Some uranium isotopes are produced through neutron capture or as decay products during reactor operations rather than being present in ores as-mined.
• This is a factual recall question.

Concept / Approach:
Natural uranium consists primarily of U-238 (about 99% by atom), a smaller proportion of U-235 (about 0.7%), and a trace of U-234 (much less than 1%). Isotopes like U-232 and U-236 are generally not present in natural uranium; U-236 is typically formed via neutron capture on U-235 inside reactors, and U-232 can arise in certain thorium–uranium fuel sequences or reprocessed materials, not as a natural ore constituent. Therefore, among the listed options, U-232 is not present in natural uranium.

Step-by-Step Solution:
Recall natural uranium isotopes: U-238, U-235, U-234.Identify isotopes formed during irradiation or special decay chains (e.g., U-232, U-236).Conclude U-232 is not a natural component of uranium ores.

Verification / Alternative check:
Introductory nuclear engineering texts list the natural abundances and note that U-236 and U-232 are signatures of irradiated/reprocessed material, not freshly mined ore.

Why Other Options Are Wrong:
U-238: Major natural isotope.U-234: Present in trace amounts via decay of U-238.U-235: Minor but crucial fissile isotope in natural uranium.U-236: Typically produced in reactors, but the question asks which is not present; U-232 is the clearest correct choice here.

Common Pitfalls:
Confusing U-236 with U-234; the former is not naturally present in significant amounts, whereas U-234 is a recognized trace constituent of natural uranium.

Final Answer:
U-232