Of course, the "marksmanship" configuration is not to completely abandon research, but only to put it on hold for a while, because low-yield nuclear bombs, or tactical nuclear weapons, can basically only be designed with "marksmanship", but at present, tactical nuclear weapons are far less significant to China than strategic nuclear weapons, and in addition, scientific research is insufficient, so there can only be trade-offs.

Hu Weidong chose the "implosion method" configuration as the first direction of research, so that it is necessary to compare the routes of uranium bullets and plutonium bullets, because plutonium bullets cannot adopt the "marksmanship" configuration, at least under the conditions of Jishu during World War II. Therefore, if you choose to start with the "marksmanship", the plutonium bullet route can only go to the side first to cool down for the time being

The original biggest advantage of the uranium bomb route was that it was relatively simple to design and process enriched uranium into a nuclear bomb, because it could adopt a "marksmanship" configuration with relatively low difficulty and much higher reliability, but since Hu Weidong decided to use the "implosion method" design, this advantage was completely meaningless. However, the long storage period of uranium bombs is relatively low, and the cost of maintenance and replenishment is much lower, and it can keep the nuclear arsenal stable at a certain size, which is also a great advantage, but there are also many shortcomings and limitations of this route

Uranium refining is difficult, and the use of uranium as a "nuclear explosive" is actually detrimental to the miniaturization of nuclear weapons, which is a hurdle that cannot be bypassed in the manufacture of hydrogen bombs. What's more, China is a uranium-deficient country, and uranium-235 accounts for only 0.7% of natural uranium, of which only about 0.5% can be extracted. The utilization rate of natural uranium is too low, and in China's national conditions, the uranium bomb route is a bit too extravagant

Plutonium, on the other hand, is different because it can be converted from uranium-238, which accounts for more than 99% of the total natural uranium, which is undoubtedly very attractive to China, which lacks uranium. In addition, there are differences in the chemical properties of plutonium and uranium, and relatively simple chemical methods can be used for separation and purification, which is less difficult and less expensive. In addition, if plutonium-239 is used as the "nuclear explosive" of an atomic bomb, the required mass is only a fraction of that of a uranium bomb, which is of great significance for the miniaturization of nuclear weapons.

But plutonium bullets also have their flaws and limitations. First of all, plutonium has special physical properties (Note 1). Processing is very difficult, which is a big challenge for China, which has a weak industrial base, especially the "911 Project" for secrecy. Basically, there are very few foreigners involved. You can only rely on the Chinese's own science and technology. As a result, the difficulty has skyrocketed countless times. The second is that plutonium bombs can only be made into complex implosion configurations, and the design and production are much more difficult than marksmanship, but since China intends to build a hydrogen bomb. No matter how difficult this road is, it has to be crossed, so there is no need to discuss this flaw.

However, there are three drawbacks in plutonium bombs, because plutonium-239 has a much shorter half-life than uranium-235 (less than 1/30,000), and weapons-grade plutonium also contains some plutonium isotopes with shorter half-lives (because they can also participate in nuclear reactions, and it is more difficult to separate than uranium-235 and uranium-238, so they generally do not choose to remove). A small decrease in the content of nuclear fuel will lead to a significant increase in the critical volume (so weapons-grade uranium requires more than 90% uranium-235 content), so the life of plutonium bombs is much shorter than that of uranium bombs, and they cannot be stored for a long time, and the nuclear fuel must be replaced every once in a while, which naturally increases the maintenance cost.

Because of this problem, countries that choose to focus on the plutonium route will naturally be limited in their ability to expand their nuclear arsenals, and the relatively frequent replacement of nuclear fuel will not only greatly increase maintenance costs, but also reduce security and secrecy. In addition, plutonium-239 needs to be produced by reactors, and because of its large size and obvious characteristics, the reactor is relatively difficult to keep secret, and at the same time, it cannot be transferred, and the production capacity may be damaged due to the destruction of hostile countries, while uranium-235 is purified with a centrifuge, which can be transferred to a safer place in a short time if necessary

The short half-life also brings another problem, that is, the radioactivity of plutonium-239 is much stronger than that of uranium-235, which only needs simple protection, and the reactor will also produce a variety of more radioactive short-half-life nuclides

In addition to radioactivity, the toxicity of plutonium and plutonium compounds is also a big trouble, although Hu Weidong knows that the so-called "a piece of plutonium can poison all living things on the earth" on the Internet in later generations is purely false, but plutonium is highly toxic is undeniable, even those who refute the rumors also admit that the toxicity of plutonium is "similar to nerve gas", although as long as it is not inhaled into the body, there is no need to worry, but it will definitely cause certain danger to the lives and health of researchers and all participants in the production and processing process in the future

Although the plutonium bomb route has various shortcomings, due to China's inherent lack of uranium, this route must be studied, not to mention that many of the jishu processes are also indispensable for the future disposal of nuclear power plant waste

However, Hu Weidong still decided to start uranium bombs in the Shiyan stage, so as not to take the plutonium bomb route but be stuck in the processing link and delay time, which caused China to miss the best opportunity to enter the game. After the first atomic bomb is exploded, it is not too late to turn the center of gravity back to the plutonium bomb route, anyway, there must be some time before the hydrogen bomb explosion, and at the same time, the plutonium produced by the reactor will also accumulate more, and the material technology and machine tool jishu will be at least stronger than now, and the progress of research will be faster than now.

Note 1: In general, plutonium has six allotropic forms, and a seventh (ζ) exists at high temperatures and a limited pressure range. These allotropes have very different densities and crystal structures. Therefore, plutonium is very sensitive to changes in temperature, pressure and chemical properties, and the volume of each allotrope varies greatly with the phase transition, and the density also varies with the allotrope.

The presence of many allotropes causes the state of plutonium to be variable, for example, the α form is present in pure plutonium at room temperature. It is a monoclinic structure with low symmetry, so it is friable, strong, compressible, and has low conductivity (α type of plutonium is a poor conductor of heat and electricity, which is extremely rare in metals. ）。 However, if the temperature is increased slightly, it will be transformed into a β that is malleable and malleable. This makes plutonium processing very difficult, especially for China, which is just entering the threshold of an industrial country (to be continued......