The Feasibility of Converting Neptunium-237 into a Nuclear Weapon

Neptunium-237 has been discussed as a potential material for constructing a nuclear weapon, but its practicality compared to more commonly used isotope materials like Highly Enriched Uranium (HEU) and Weapons-Grade Plutonium (WGP) raises significant questions. While the Los Alamos team managed to demonstrate a critical mass of Neptunium 237 in a composite core with Uranium 235, making a usable bomb from bare neptunium-237 alone remains a theoretical possibility at best.

Isotope Properties and Decay Chain

Nepmutium-237 is part of the 4n1 decay chain, making it a by-product of nuclear reactors and plutonium production. It is also found in trace amounts in uranium ores, which pose a potential risk in terms of radioactive waste management. The isotopes neptunium-235, -236, and -237 are all fissionable, but experimental data confirms that only neptunium-237 has a critical mass of about 60 kg, only about 10 kg more than the commonly used uranium-235.

Critical Mass and Nuclear Reactions

The critical mass for neptunium-237 was reported by Science News to be approximately 60 kg. This means that with the right configurations, neptunium-237 could serve as the core of a nuclear weapon. However, the low neutron cross section of neptunium-237 suggests that it would be an inferior choice for a fission bomb, as it would be difficult to initiate a chain reaction with thermal neutrons.

Several studies, including the 2002 Los Alamos team report, indicate that a composite core with neptunium-237 and uranium-235 can achieve critical mass. This means that breaking down the process of weaponization into steps with a composite core can increase its feasibility. However, the challenges involved in isolating and purifying large quantities of neptunium-236 remain significant, making it a less attractive option.

Comparison of Isotopes for Nuclear Weapons

In practical terms, the critical masses of neptunium-235, -236, and -237 are, respectively, 66.2 kg, 6.79 kg, and 63.6 kg. Despite neptunium-236 having even lower critical masses than plutonium-239, the difficulties in purifying large amounts of neptunium-236 and the availability of plutonium and uranium make these options less viable for creating nuclear weapons.

Furthermore, the theoretical ease of using neptunium-237 to produce plutonium-238 for space programs does not translate into its use as a nuclear proliferation material. The current focus remains on highly-enriched uranium and weapons-grade plutonium due to their proven reliability and ease of manufacture.

Conclusion

While neptunium-237 can theoretically be used to create a nuclear weapon, the practical challenges and the availability of easier and more reliable materials make it a less attractive option. The critical mass and the physical properties of neptunium-237 may allow it to be used in certain scenarios, but the difficulties in achieving a chain reaction, combined with the availability of safer and more reliable materials, mean that neptunium-237 is unlikely to be a primary choice for nuclear weapon construction.

For more information on this topic, you may refer to relevant studies and reports such as those from Los Alamos National Laboratory and Science News.