"Transuranic elements (rnurnielemen)?"

For colleagues in the lab, the term "element elemen" is naturally familiar; But rnurni is undoubtedly a new word, and it has attracted a lot of discussion.

When Sun Yuanqi wrote the word on the blackboard, everyone found that the meaning of the word was not difficult to understand: rn, the prefix means to leapfrog and exceed, such as rnlin, rnrin, etc.; urni, chemically "uranium". Taken together, the two words mean "transuranic".

What is a transuranic element?

Uranium is the heaviest element that can be found in nature, and chemists have been trying to discover heavier elements ever since 1789, when the German chemist Kraprot separated it from bituminous uranium. One hundred and twenty years later, chemists have discovered more elements, even determining that uranium has an atomic number of 92, but still no heavier element has been found.

Transuranic elements? Are there elements in the world with atomic numbers exceeding uranium? Everyone has this question in their minds.

"Yes, transuranic elements." Sun Yuanqi said with certainty, "There is no doubt that uranium is the heaviest element that can be found in nature." Elements that exceed uranium are largely absent in nature because most of them are unstable and have a very short half-life. The only way to discover and produce them is through artificial nuclear reactions. ”

Regarding the proposal of transuranic elements, Sun Yuanqi struggled for a long time, because there are generally two ways to prepare transuranic elements:

The first way, which is easier to achieve, is to accelerate the deuterium nucleus to bombard uranium-238, thus obtaining plutonium-239. Plutonium is an element with atomic number 94, and in this way, the concept of a transuranic element is confirmed. However, plutonium-239 has a fast fission rate, a small critical mass, a long half-life, and some nuclear properties are better than uranium-235, coupled with the high reserves of uranium-238 in nature, making plutonium-239 once the most important nuclear charge in early nuclear weapons. The atomic bombs dropped on the cities of Nagasaki and Hiroshima at the end of World War II were made with plutonium-239 cores. Of course, there are pros and cons, plutonium-239 is very toxic and expensive to produce, requiring the construction of complex production reactors and reprocessing plants to achieve industrial production.

The second way, best known, is to bombard uranium with neutrons. When an element is bombarded with neutrons, it often transforms the bombarded element into an element with an atomic number greater than 1. In this way, transuranic elements can be discovered in a steady stream. But there are two problems.

First of all, no neutrons have been discovered yet. Neutrons are not hard to find, especially now that particle accelerators have been invented, which can be used to accelerate α particles and then bombard lighter elements such as beryllium, boron or lithium. Although neutrons alone are unstable and have an average lifespan of only about 16 minutes, they are enough to do many things, such as bombarding uranium after acceleration.

The second is that once uranium is bombarded with neutrons, in addition to the emergence of new elements, the most likely phenomenon is nuclear fission, which is not only an extremely complex nuclear process, but also has great practical value, and once it is made public, it will attract the attention of the whole world. As soon as the hypothesis of uranium nuclear fission was proposed, all the physical laboratories in the world immediately boiled and quickly launched intensive research on this phenomenon. In less than a year, more than a hundred scientific papers on nuclear fission were published, which is unprecedented in the history of physics. Now that everyone is engrossed in the study of nuclear fission, the chain reaction will inevitably be discovered, and nuclear weapons will be on the horizon.

Of course, the discovery of chain reactions to the realization of controllable chain reactions is not achieved overnight, and it is even more difficult to use it to create nuclear weapons. Initially, all the research work carried out in the laboratory was to use uranium-235 to achieve a controlled chain reaction. Uranium-235 is a rare isotope that is found in only 0.7 levels of natural uranium. To achieve a nuclear explosion, a few kilograms to tens of kilograms of uranium-235 with a purity of more than 90 may be required. Before 1940, mankind had never obtained even a very small amount of pure uranium-235, and it was impossible to produce such a thing in "kilograms".

The pros and cons of these two aspects have been weighed by Sun Yuanqi for a long time. At this time, the concept of "transuranic element" was proposed, but he had already made up his mind in his heart: "Before, we irradiated molybdenum with deuterium nuclei and discovered the first man-made element technetium. In the same way, if we irradiate uranium with deuterium nuclei, will new elements be produced? I think the answer should be yes

"After the discovery of technetium, there must have been many people who thought about irradiating uranium with deuterium nuclei, but no results have been reported so far. Why? The reasons for this can be thought of by everyone, first of all, uranium is very precious, and ordinary people are not capable of doing this experiment; Secondly, before uranium is irradiated with deuterium nuclei, it must be accelerated with a large particle accelerator in order to obtain possible results. This kind of accelerator is currently only available in our Element Lab, which gives us an opportunity, and I believe that as long as we overcome the difficulties of small sample quality and difficult separation, we will definitely find something."

Why leak the first method? Sun Yuanqi has his own considerations:

Before nuclear fission was discovered, some of the properties of plutonium did not attract much attention from researchers. In addition, to achieve industrial production of purified plutonium-239, it is necessary to build a complex production reactor and reprocessing plant, at least Sun Yuanqi does not have this kind of research capability and industrial base for the time being, so he must give enough sweetness to the Sufficient Element Laboratory, and then use the reasonable excuse of "studying the preparation method of known elements", let them take a step first, in order to indirectly achieve their own goals. Even if the Elemental Lab doesn't take the bait, you can learn from the technology used in their experiments to separate plutonium. These technologies are not always kept secret from the director of the laboratory, right?

Every year, the Element Lab warmly invites Sun Yuan to work in the United States, but the actual work that Sun Yuanqi does for the laboratory every year is extremely limited, just a few points, judgments, and a formality. These words can actually be explained in the letter, but the laboratory still pays a lot of salary every year and invites Sun Yuan to come over. Perhaps, as the story goes

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