afterglow

Chapter 279 Critical mass; not having and having but not using are two different things
In fact, Zhu Lingjing didn't know what Zhou Changfeng was referring to, but in view of the latter's identity, she guessed it intuitively.

This guy must be thinking about weapons, and in connection with the quality loss mentioned, it is undoubtedly because he thought of the energy burst in this process according to the mass-energy conversion formula E=MC.

Zhou Changfeng, who was full of expectations, immediately nodded and said: "Yes, so based on this discovery, it is theoretically possible to design an unusual...bomb."

Your span is too big, why did you suddenly jump to practical applications?

"Wait a minute." Zhu Lingjing was trying to recall the frontier research in physics in the past few years. She vaguely remembered that the academic circles seemed to be arguing about this experiment, and they always believed that the transuranium elements were formed in the process.

Is this article published in Nature reliable?The splitting of the nucleus?This is a bit shocking.

She smiled slightly, and said: "The research on the origin of all things is never accomplished overnight. The discoveries in this area are too novel, and it is not easy to apply them directly to practice. And the truth is uncertain. Let's see the reaction of the world's academic circles later. "

In the 30s, it was popular in the physics community to use neutrons to bombard various nuclei to explore the process and results, but when people bombarded uranium nuclei with neutrons, obvious radioactive phenomena were observed, which actually occurred nuclear fission, but people mistakenly It is believed that this is just the generation of new substances - transuranic elements.

Therefore, a series of contradictions appeared in theory, and the academic circles were full of disputes. Physicists all over the world tried the same experiment repeatedly, but until today they finally made subversive discoveries.

At that time, people's understanding of the world was still limited, and they were quite shallow in nuclear physics. The fixed thinking greatly hindered people from getting out of misunderstandings.

In fact, Qian's research group from Hangzhou University and Imperial Gezhi University has been infinitely close to the correct answer in the 36th year of Zhichang, but unfortunately they were confused by a strange element (isotope of yttrium), mistakenly thinking that it is also a transuranium element, products of nuclear fission.

Although the famous Fermi group, Curie group, and Qian's group all collapsed, the mystery that has caused human beings to stagnate on the road of nuclear physics exploration for four years has finally been revealed.

"Okay, but..." Zhou Changfeng thought for a while, and said seriously: "Uh... If this discovery is correct, I think we should start preliminary research as soon as possible, it is too amazing, the chain reaction, the energy released will be very, very many."

"It's a good word, but I think it depends on luck, or it must be luck." After dinner, Zhu Lingjing had nothing to do, so she simply continued to chat with him.

She blinked, looked at the small cup on the table and said: "At the microscopic level, although atoms are close to each other, the space around the nucleus is huge. For example, if this small cup is an atomic nucleus, its The electrons in the outer shell may be a hundred paces away, and the space in the middle is empty. How likely are the few neutrons released at the beginning of the reaction to hit the next nucleus exactly?"

Wow, realized so quickly what the problem with trying to maintain a self-sustaining chain reaction is?Straight to the root ah.

At least in this respect, Zhou Changfeng immediately looked up to her by two points.

This is like being in a shooting range, surrounded by some evenly arranged balloons, randomly shooting two shots, to ensure that at least one balloon is hit (so that the reaction can be self-sustaining), it is necessary to calculate at least how big the shooting range should be through theoretical calculations .

The result is... critical mass.

As we all know, Heisenberg miscalculated this data in history, and obtained an outrageous data with a radius of 54cm, that is, a full U13000 of 235kg, which caused the German side to think that this is completely impossible.

Of course, whether he did it on purpose or accidentally is a topic that people are talking about.

Due to the flood of information in the Internet age, the data conclusions that made people think about it decades ago have become known to everyone.

As we all know, the critical mass of high-abundance spherical U235 is about 52 kg, and the critical mass of high-abundance spherical Pu239 is about 17 kg.

In this regard, being a time traveler has a small amount of inherent advantages. At least if the scientists of Ming Dynasty miscalculated the critical mass, they could be corrected immediately.

But this is only a small part of the huge calculation project. The real fission weapon needs more complex calculations, and those are beyond the reach of Zhou Changfeng. We can only hope for the wisdom and energy of physicists and mathematicians .

Seeing that Zhu Lingjing was talking about this topic with great interest, Zhou Changfeng followed her words and said, "The probability is indeed very small, so a large lump of uranium is needed to increase the probability to certainty."

Zhu Lingjing thought that Zhou was just an amateur in this area. She said calmly, "Your understanding of this is a little shallow. You must know that the direction of motion of neutrons produced by fission is completely random in three-dimensional space."

"Your Highness, I know, so a specific mathematical analysis method must be introduced to calculate it."

"Hmm..." Zhu Lingjing pondered thoughtfully, "This way of thinking seems to have had similar problems before."

She is not a professional in this area either. Nuclear physics is only a category of physics. If mathematical models are to be considered, it is not a category she can think about.

"Your Highness, I mainly suggest starting preliminary research as soon as possible."

"But whether it's theoretically possible or not is unknown."

"Then you have to calculate and demonstrate first. If it works, continue. This discovery in physics is public, and other countries will definitely conduct research on it."

Although Zhou Changfeng tried his best to conceal his eagerness, Zhu Lingjing still felt strange. She looked him up and down and said calmly, "Be safe and don't be impatient. Your idea can be directly reported to the Ministry of War."

Zhou Changfeng, who was quite helpless, replied: "This idea is too advanced, and the officials who have to report do not know this kind of knowledge. They must think this is a fantasy, so it is more effective for you to speak, Your Highness."

"That's right." Zhu Lingjing couldn't help laughing, she raised her index finger, "You Bugang's class teacher, when you have free time, go to the university to find someone to discuss with, to be more authoritative, so I will pay attention to follow up on this joint name."

This answer is okay, there is drama.

The goal is basically achieved, so there is no need to stay for a long time, not to mention that I haven't even eaten dinner yet.

Ever since, Zhou Changfeng, who was hungry, left immediately.

"In a hurry, like a child who has found a new toy." Seeing him leaving quickly and disappearing in a blink of an eye, Zhu Lingjing couldn't help muttering.

Zhou Changfeng wanted to go home at first, but suddenly realized that Xia Xiaoshi was still living in her mother's house, and the house was empty now, so he turned back to Jiangxinzhou.

Although the first regiment of the marines had just loaded up and set off in Haizhou, there were units left behind in the station.

In Nanjing, which has just entered June, there are already signs of scorching heat, but it is not obvious.The next day, Zhou Changfeng arrived at Imperial Gezhi University early in the morning.

The small door made of stone and piled up like large building blocks is unique, and the aluminum alloy plaque in regular script is also very distinctive.

It is not easy for young people who can go to university these days, either from a wealthy family or unique talents.Unlike the flood of college students in later generations, today's college students are real talents-high professional quality, fast acceptance, and strong hands-on ability.

The monthly salary of ordinary college students can reach [-] yuan after graduation, and basically it only takes one year to break [-] yuan.

On the vast campus of this polytechnic college, almost all of them are male students, and the ratio of male to female may be less than twenty to one.

After several inquiries, Zhou Changfeng found Zhang Shilin, a Ph.D. (Bachelor) from the Department of Chemistry, whom he had met last year.

Ponds, wooden bridges, and waterside pavilions. Zhang Shilin was sitting alone on a bench holding a fishing rod. His hair and beard were messy, and his eyes were wandering.

This appearance is really too close to the image of "Frankenstein".

Zhou Changfeng stopped behind him for a long time without being noticed. His thoughts were interrupted until the fishing line trembled up and down, and he frantically threw the rod.

Then, he noticed someone standing behind him.

Zhang Shilin felt that the person in front of him looked familiar, and tried hard to think, but he just couldn't remember, "Ah, you are..."

"Last year, the train from Wuhan to Beijing." Zhou Changfeng reminded helplessly.

"Oh, I remembered, Zhou... yes, Zhou Changfeng! Nice to meet you."

"Why are you fishing here?"

"Oh, there is an obstacle in the research. After half a month of tossing, there is no progress. My husband asked me to come out to relax."

Doing academic work is really exhausting, and sooner or later you will get bald.

Zhou Changfeng was silent for a few seconds, and then bluntly stated his reason for coming.

"Is Chief Zhou actually paying attention to this aspect?" Zhang Shilin, who was a little surprised, said while re-baiting: "This news has only been out for a few days, and the academic world has not yet reached a conclusion."

"That's not important. I want to find a more authoritative scholar, can you recommend one or two?"

Zhang Shilin nodded, and replied without hesitation: "Mr. Xu Shangdanxu of our school, he is one of the leading figures in this field in our country."

"Where is he now?"

"It's in the school, it should still be in the laboratory building."

After thanking him, Zhou Changfeng quickly left and went straight to the laboratory building.

It is not a tall building, on the contrary, it has only three floors, but it is very wide.The black glazed tiles on the roof with angled eaves show a unique luster under the sunlight.

Here, he waited for half an hour.

Xu Shangdan, a nuclear physicist, gave Zhou Changfeng a somewhat contradictory impression. At first glance, he seemed like an amiable little old man, but he also felt that he had a sense of boundary that was inaccessible.

But Zhou Changfeng quickly figured it out. To put it bluntly, this is the admiration imprinted in the subconscious out of the awe of knowledge.

"...When the news came out, we were also very surprised, and hurriedly tried to reproduce the same experiment." Xu Shangdan stroked his beard and sighed: "It's a pity that we were blinded by appearances in the past and failed to see through the essence."

When physicists in Ming Dynasty bombarded uranium nuclei with neutrons, they accidentally produced an element with a half-life of 3.5 hours, which is an isotope of element 39 yttrium. This phenomenon is actually enough to prove nuclear fission.

But physicists didn't know the truth, and they were tricked by the isotope's physical properties into thinking that the element with a half-life of 3.5 hours was a transuranic element heavier than uranium.

"..." After briefly describing the loss of mass and the energy released during the fission process, Zhou Changfeng asked straightforwardly: "Dare to ask, sir, do you think this is feasible?"

Xu Shangdan said in a deep voice: "This requires knowing the reaction cross section of neutron-induced disintegration of uranium nuclei, that is, probability, space density, etc. Hopefully, I think there is."

Zhou Changfeng breathed a sigh of relief, and said with a smile: "This is enough. It is much faster to concentrate on research and tackle key problems than to spread it out now. Mr. Xu, please join me in joining the University."

"Have you tried to use it as a weapon now?"

"Of course, and we must strive to be the first."

"This...with all due respect, child, the power contained in it is too great." Xu Shangdan said solemnly, "This is not comparable to chemical energy. The speed of light is too fast, let alone its square. Even if only one gram of mass is converted into energy, it is probably equivalent to tens of thousands of tons of ordinary explosives."

Although people nowadays know nothing about the power of fission weapons, as a professional, Xu Shangdan can still judge the horror of its power by intuition when he knows the principle of its energy source.

"I know, but the use of weapons is not only to expand the territory, but also to protect the country. There are two completely different things between 'not having' and 'having but not using'. To put it bluntly, what you are concerned about is precisely some Western People don't care, the game between countries is not a child's play."

"Hey, that's right." Xu Shangdan looked out of the sunny window and was silent for a long time, "Besides, even if I don't agree, you will go find someone else."

Zhou Changfeng did not say a word, and acquiesced.

Next, the two briefly discussed critical mass.

"More than 30 years ago, I can't remember clearly, there was a British man named Pearson who published a newspaper to solve a problem publicly, that is, if a drunk person walks, the direction and size of each step are completely random. time, where is the best chance of finding him."

"Are you planning to use this as a reference to find the size and weight of the required uranium?"

"Maybe, the way of thinking is similar. In the 20th year of Zhichang, senior Li Cheng from Xi'an University summed up this problem and proposed a theorem and proof process called 'random walk theorem'. After walking out of the unit length left and right, the probability of returning to the original position is one, which means that it will return to the origin in the end.”

"Um……"

After a while, Xu Shangdan joked: "If you finally calculate an impossible number, will you people be very disappointed?"

Zhou Changfeng froze for a moment, not knowing how to answer.

If there is no nuclear deterrence, a large-scale conventional war will come every few decades, which is not a good thing for ordinary people, but politicians don't care.

He replied meaningfully: "The military is actually indifferent, but I think the powerful will be very happy."

(End of this chapter)