Artificially produced fissile materials — Which of the following isotopes are primarily man-made (do not occur naturally in useful amounts) and are produced through breeding reactions?

Introduction:
The nuclear fuel cycle leverages breeding to create fissile isotopes from fertile materials. Recognizing which fissile nuclides are man-made clarifies how reactors extend fuel resources beyond naturally occurring fissiles.

Given Data / Assumptions:

• Natural uranium contains ~0.7% U-235 and ~99.3% U-238.
• Thorium in nature is almost entirely Th-232.
• Breeding converts fertile isotopes (U-238, Th-232) into fissile isotopes (Pu-239, U-233).

Concept / Approach:
Determine which listed isotopes are principally produced in reactors: U-233 (from Th-232) and Pu-239 (from U-238) are classic bred fissile materials. By contrast, U-235 is naturally occurring in significant, mineable quantities.

Step-by-Step Solution:
U-235: Naturally present; enriched for most power reactors.U-233: Produced via Th-232 → Th-233 → Pa-233 → U-233.Pu-239: Produced via U-238 → U-239 → Np-239 → Pu-239.Hence, the primarily man-made isotopes among the options are U-233 and Pu-239.

Verification / Alternative check:
Fuel-cycle references document the thorium–uranium and uranium–plutonium breeding chains and their reaction sequences.

Why Other Options Are Wrong:

• U-235 is naturally occurring; while enrichment is industrial, the isotope itself is not primarily man-made.

Common Pitfalls:
Assuming “all fissile nuclides are man-made” or confusing enrichment with breeding.

Final Answer:
Both (b) and (c)