A Man of Science and Engineering in Troubled Times Wandering in the Late Qing Dynasty

Chapter 712 Epilogue : Big and Small Neutrons
Li Yu went straight to Berlin.

The scientific community has already achieved initial results regarding the prediction about neutrons.

The first to achieve a breakthrough was Bot's team at the University of Berlin (Bot won the Nobel Prize in 1954, but not for the neutron).

From 1928 to 1930, Bothe and his students bombarded beryllium nuclei with alpha particles emitted by radioactive polonium and discovered strong penetrating radiation. The penetrating power of this radiation was many times greater than that of the known gamma rays, and it only slowed down by half after passing through a two-centimeter-thick lead plate.

In 1930, the two made their results public.

It just so happened that Wang Ganchang was awarded a government scholarship to study abroad this year and came to the University of Berlin to study under Meitner.

Meitner and Bothe did not belong to the same laboratory.

Wang Ganchang had a very strong intuition in physics. After seeing Bort's results, he immediately felt that beryllium rays were definitely not gamma rays, because no matter how strong the penetrating power of gamma rays was, it was impossible for them to penetrate a lead plate several centimeters thick.

Most importantly, he discovered a loophole in Bot's experiment: the detector used by Bot's team was a Geiger counter.

Wang Ganchang estimated that if a cloud chamber was used for detection, the properties of this ray could be better analyzed.

——This is absolutely the right direction.

Unfortunately, in history, when Wang Ganchang proposed to his mentor Meitner that he wanted to use a cloud chamber as a detector to study beryllium rays, Meitner refused, and his application was rejected twice.

Two years later, the Curies of France were also very close to discovering the neutron, but they also believed that this ray was an electromagnetic wave.

Just one month after the Curies announced their research results, Chadwick of the Cavendish Laboratory in the UK repeated Bothe's experiment using a cloud chamber and discovered the neutron.

After learning about this, Meitner said to Wang Ganchang with regret: "It seems that we are unlucky."

Wang Ganchang regretted this for the rest of his life.

Of course Li Yu would not let this happen again.

This is not only a personal honor for Wang Ganchang, but also a great incentive for China's scientific cause.

-

Royal Wilhelm Institute of Chemistry, University of Berlin, Germany.

Li Yu met Wang Ganchang and chatted for a while. When Li Yu mentioned Bote's experiment, Wang Ganchang expressed his helplessness: "It only takes a little improvement, and in a few months, there will be a big discovery. Unfortunately, I can't use the laboratory because I don't have the authority given by my supervisor."

Li Yu asked tentatively: "Are you sure?"

"I can't say for sure," Wang Ganchang said, "but it's pretty close. At least I can write a doctoral thesis based on it."

Li Yu smiled and said, "You are only in your first year of doctoral studies."

"It was only after I came here that I realized that there are many people who get their doctorate degrees at a very young age," Wang Ganchang said modestly.

Indeed, the three people born in the 00s have all become big names now: Heisenberg, Dirac, and Pauli.

Li Yu touched his chin and said, "Why not apply to return to China for half a year? I can provide a full set of experimental equipment, and maybe we can get some results."

"Return to China?" Wang Ganchang asked in surprise.

Li Yu said: "If you have a mature idea, there is no problem. The laboratory conditions at Datong University are not bad at all."

Wang Ganchang said: "I don't know if my supervisor will agree."

"It's okay," Li Yu helped him dispel his doubts. "It's only half a year, and there aren't so many rules and regulations in the doctoral stage. When you return with honors, not only will you graduate with a doctorate, you can also continue to do research and study."

"But here at the University of Berlin..." Wang Ganchang was young after all and did not dare to offend those bigwigs.

Li Yu smiled and said, "With me, they dare not not give me face."

This statement was so domineering. Wang Ganchang naturally knew Li Yu's status in the scientific field. With his support, the University of Berlin would never dare to say anything.

Wang Ganchang said, "Then I will ask my supervisor for leave, finish a few tasks this week, and then I can leave."

"Don't worry." Li Yu said.

They have no shortage of time now.

-

While Wang Ganchang was dealing with his own trivial matters, Li Yu met Einstein again at the University of Berlin.

He had just returned to Berlin with Romain Rolland after attending a pacifist meeting.

"Mr. Einstein, Mr. Romain Rolland." Li Yu greeted them.

Einstein put down his pipe and said, "It's a pity that there is no academician at this peace gathering."

"What topic?" Li Yu asked casually.

"Don't mention it," Einstein said speechlessly, "I shouldn't have had any hope in them."

Romain Rolland replied: "It is a peace conference on limiting the use of poison gas in war."

"Don't you find it absurd?" Einstein said. "It seems to me that it is completely futile to lay down rules and limits for the conduct of war. War is not a game, and therefore one cannot conduct it according to rules as in a game. Our struggle must be directed against war itself."

Romain Rolland, who was also an anti-war activist, asked, "So what do you think should be done?"

Einstein thought for a moment and said, "We can most effectively fight the war system by establishing an organization that completely refuses to serve in the military. Because military training is a mental and physical education in the art of killing, it hinders the growth of people's will to strive for peace."

Romain Rolland asked again: "If a European war breaks out again and one side is obviously the aggressor, what will you do?"

Einstein said: "I will unconditionally refuse all direct or indirect war service and will try to persuade my friends to take the same position, regardless of how I feel about the causes of a particular war."

Romain Rolland smiled and said, "As expected, Mr. Einstein tends to be unrealistic once he leaves the field of science. In today's Germany, disarmament is simply wishful thinking. Perhaps in the eyes of some politicians, they will think that your statement is very naive."

Albert Einstein said: “Violence breeds violence.”

Romain Rolland asked Li Yu: "Mr. Academician, are you willing to join our peace organization?"

"Sorry," Li Yu said, "I can't join."

"Why?" asked Romain Rolland.

Li Yu said: "Because there are crazy people in this world."

Albert Einstein said: “A madman cannot become the leader of a great nation.”

Li Yu spread his hands: "That's hard to say."

Einstein's commitment to peace was consistent. Although, in addition to Romain Rolland, other academic giants such as Millikan criticized his views in this regard as being somewhat "naive", many of Einstein's words were still quite prescient.

For example, in 1929, he told Zionist leader Weizmann: "If we cannot find a way to cooperate sincerely with the Arabs and sign a fair contract, then after 2000 years of suffering, we have actually learned nothing."

These words are still thought-provoking even a hundred years later.

Einstein's enthusiasm for the cause of peace is naturally related to the current situation in Germany.

The little mustache man was ready to make a move. The economic crisis allowed his power to grow continuously, and he declared that he wanted to avenge Germany in the First World War.

Long before he came to power, German society knew that this man would definitely expand the military and prepare for war in the future.

But these are not something Li Yu can control.

-

After saying goodbye to the two of them, Li Yu attended a small-scale quantum lecture organized by Pauli. Li Yu was very familiar with the content of this lecture: Zhao Zhongyao's positron paper.

The discovery of the positron had a great impact on the scientific community. Universities and research institutes around the world were studying it, after all, it was a new particle. After Pauli finished speaking, he chatted with Li Yu alone.

"Mr. Academician, in fact, I also did something that a theoretical physicist should not do." Pauli said helplessly.

"What's the matter?" Li Yu asked.

Pauli said: "I have proposed something that will never be experimentally detectable by man."

"Are you talking about the energy that was lost in...oh, Blackett's experiment?" Li Yu asked.

“Yes, I did want to call it the neutron at first,” Pauli said, “but you took that word.”

The two were talking about a strange experimental phenomenon discovered by Chadwick in 1914: when the nucleus of an element decays, it may become the nucleus of a new element and then add beta particles (actually beta rays), but Chadwick measured and found that the energy before and after was not conserved.

In other words, the energy of the original nucleus A after it decayed into nucleus B + β particle was not equal. To put it simply, he felt that the energy of the β particle was a little less.

This is the so-called "energy theft case".

Pauli continued, "At the beginning of this year, I went to Copenhagen, and Professor Bohr proposed a hypothesis that only statistical energy conservation exists for microscopic particles, and that individual particles may not conserve energy. But this is ridiculous."

Li Yu laughed and said, "You definitely refuted it to my face."

"That's for sure!" Pauli said, "We can't abandon the law of conservation of energy just for an experimental phenomenon! So, I personally guess that there is a kind of neutral particle in beta radiation that humans cannot detect. It is very small and just makes up for this part of the missing energy."

"It is indeed small enough," Li Yu said, "According to the mass-energy equation, the mass of this particle is millions of times smaller than that of an electron."

Pauli said: "So this particle may never be detected, and it would be unprofessional for a scientist to say that something will never be detected."

Li Yu agreed with Pauli's point of view: "It is difficult to detect because it has no charge, does not participate in electromagnetic interaction, and is so small. But even if there is no way now, it does not mean there will be no way in the future."

In fact, the first person to propose a reliable method to detect neutrinos was Wang Ganchang, who was about to return to China with Li Yu. He gave a method in 1941, but at that time he was in the war-torn country and could not conduct the experiment himself.

Li Yu asked again: "Since it can't be called Neutron, what name did you give it?"

"The little neutron. But I didn't publish anything in a public journal," Pauli said, and then explained, "I laughed at Dirac's prediction of the anti-electron, but I didn't expect it to come true."

It seems that even the "God of Counterattack" Pauli did not dare to predict new particles easily.

Li Yu smiled and said, "Little neutron? That sounds too bad. It's better to call it neutrino. And since Dirac succeeded, neutrino is still uncertain. You can write an article to make a prediction."

"Whatever," Pauli said, "it's impossible to find it anyway, and there is no theoretical basis for it."

Just a few years after Pao Da Shen said this, Fermi proposed the theory of β decay...

But even so, many people opposed the neutrino hypothesis for many years afterwards, including Dirac.

The two really ridiculed each other and loved and hated each other: Pauli opposed Dirac's positron prediction; Dirac opposed Pauli's neutrino prediction.

As for neutrinos, they were not discovered until 1956, and three types of them were discovered.

Although neutrinos are difficult to detect, they are the second most common particles in the universe, second only to photons. About trillions of neutrinos pass through our bodies every second, with the largest number coming from the sun.

-

This time, Li Yu returned to China with Wang Ganchang by taking the Trans-Siberian Railway, which was much faster.

After arriving at Shanghai Datong University, Li Yu started the experiment without stopping. In terms of equipment, he had no shortage of it.

Although Li Yu himself was not very good at experiments, Wang Ganchang could do it himself as long as he had the equipment and funds.

All Li Yu had to do was to remind him: "Perhaps what you are looking for is the neutron I predicted back then."

With this clear direction, the great secret treasure won’t escape!
While Wang Ganchang was busy with his experiments, the Curies in France were also conducting their research.

But as mentioned above, the Curies, like Bothe, were in the wrong direction. They believed that this new radiation was electromagnetic waves.

The Curies slowed down the radiation by passing it through paraffin wax before passing it through a Geiger counter.

According to the experimental expectations, when beryllium rays pass through paraffin, some of their energy will be absorbed and their speed will slow down.

But the result was surprising: the rays not only did not slow down, but became faster! And the detector results showed that the rays were actually protons!

The Curies believed that a beam of electromagnetic waves turned into particles through paraffin, which must be a collision. That is, the beryllium ray hit the paraffin and was absorbed, and then the protons were knocked out.

So the two of them completely reached a dead end in this direction.

In fact, it is easy for people in later generations to see that beryllium rays are definitely not electromagnetic waves, because the rest mass of electromagnetic waves is 0. Even if there is dynamic mass, it is impossible to have such high energy to knock out protons.

The photoelectric effect can use light to knock out electrons because electrons themselves are very light and are in the outer layer of atoms, so many of them are inherently unstable.

However, if you want to knock protons out of the nucleus, it is definitely impossible to do it with electromagnetic waves.

Of course, it cannot be said that the Curies were not capable enough, they just could not stand from a God’s perspective like Li Yu.

As for science, it is bound to require elimination and verification bit by bit. There must always be someone who does the preliminary work so that future generations can stand on their shoulders and achieve success.

Wang Ganchang's experiment lasted less than four months, but he discovered the neutron and calculated its mass.

Excited, he quickly wrote an experimental paper and announced at the end:

"The neutron predicted by Mr. Li Yu many years ago has been discovered!"

Since it was Li Yu's bold statement, he must let his own people find it.

Li Yu was of course happy for him, and exclaimed: "Another key to particle physics has finally appeared."

"You mean radioactivity?" Wang Ganchang said.

Li Yu said: "It will be able to do so many things in the future."

Wang Ganchang was still very sharp: "Use it to bombard other atomic nuclei?"

Li Yu smiled and said, "Your idea is very bold."

Since the discovery of neutrons, scientists around the world have begun bombarding atoms with neutrons, which opened Pandora's box.

In 1934, Fermi's team and the Joliot-Curies bombarded uranium with neutrons for the first time;

In 1938, Otto Hahn discovered that nuclear fission occurred when uranium 235 was bombarded with neutrons! Lise Meitner then published a paper giving a theoretical explanation.

Two days after Meitner finished writing his paper, the German authorities sent someone to find Hahn and began to study the atomic bomb project. They also found Heisenberg, Laue, Geiger, and Both, and called it the Uranium Club.

Fermi realized that in order to achieve a chain reaction, slow neutrons must be used, and he discovered that hydrogen-rich substances such as heavy water could slow down neutrons.

……

It is said that Wang Ganchang was the hero of the two bombs and one satellite.

After signing Wang Ganchang's article, Li Yu first published it in the domestic "Science Magazine" and then mailed it to the American "SCIENCE" to ensure that it would appear in the newspaper as soon as possible.

Soon, congratulatory letters came in from all over the place like snowflakes.

Li Yu opened a letter from the Cavendish Laboratory and said with a smile: "Mr. Rutherford said that they started looking for this neutral particle many years ago, but they have always been on the wrong track.

"And this one, from Professor Bot of Berlin University, praising your scientific intuition...

"With this achievement, you will definitely win the Nobel Prize along with Zhao Zhongyao."

"It's just like a dream!" Wang Ganchang was still very young, and was somewhat shocked by the sudden arrival of a famous figure, but he still said modestly, "If it weren't for the direction and resources given by the academician, I'm afraid I wouldn't even have the opportunity to go in the wrong direction."

Li Yu remembered what Meitner said and put it into practice: "We are lucky!"