Reborn and become a Great Scientist

Chapter 415 154 The belated neutron

"Chen, what other experiments have you done?"

Rutherford became more and more confused as he listened.

"Well, teacher, it's a long story, this was last summer, when I was at Cambridge University.

"At that time, the teachers, staff and students of the Cavendish Laboratory all left Cambridge University to escape the summer heat during the holidays. I was bored in the Cavendish Laboratory by myself, so I found the alpha particle source to bombard other targets. 'Play'.

“When I bombarded the boron crystal with alpha particles, I accidentally bombarded a strange particle beam from it.

“This kind of particle beam cannot leave a trajectory in the cloud chamber, nor can it be deflected in electric or magnetic fields, indicating that they should be uncharged particles.

"I initially thought that this particle beam might be a gamma ray that conforms to the above properties, but this kind of gamma ray can easily penetrate a copper plate several centimeters thick and is harder than the gamma rays we usually see. Much more.

"I'm not sure whether the thing emitted from the boron crystal is a gamma ray. I originally planned to conduct further experiments.

"Then at that moment, Professor Eddington came to the door.

"He gave up his holiday on the seaside in Cornwall and came back to Cambridge University to study with me the mechanism of the sun's light.

"It was precisely because of this incident that Professor Eddington and I turned our heads to study the issue of nuclear fusion inside the sun, thereby ignoring the question of what the hard gamma rays emitted from the boron crystal were.

"Just a few days ago, Mr. Frederick discovered through calculation that in the nuclear reaction equations of several of us who discovered new elements, there is a gap in relative atomic mass before and after the reaction.

“At that time, he brought up this matter and asked me where the mass that disappeared one after another in the reaction went.

"While I was doing experiments these days, I was always thinking about this thing. After thinking about it, I thought of the experiment I did before, and the hard gamma rays emitted from this boron crystal. Could it be neutrons?

“So in my free time, I repeated the experiment I did at the Cavendish Laboratory last summer, and I felt that the thing that was emitted was probably a neutron.

"So I sent a telegram to you, teacher, that day, hoping that you would come to Stockholm as soon as possible and find out with me."

The more Kapica listened to what Chen Muwu said, the more he felt that he had done the right thing by going against Rutherford's decision and sneaking to Sweden.

This old crocodile was too unkind. Why didn't he tell himself about such a big neutron discovery?

After hearing Chen Muwu's description, Rutherford still had a frown on his face and a very stern expression: "Are you sure what you discovered is a neutron?"

Chen Muwu shook his head: "I'm not sure yet. I'm waiting for you, teacher, to arrive so we can further confirm this matter."

"Then tell me what you think."

Rutherford took out the pipe he carried with him. When he was about to take out the tobacco bag, he suddenly realized that this was not the Cavendish Laboratory, but Chen Muwu's territory in Stockholm. He quietly took out the pipe and tobacco bag. Put it back.

"Teacher, you can go smoke a bag of cigarettes. We just need to change places. The experiment I am doing does not require a cyclotron, and the experiment is in another room."

"That's fine. Whether the neutron is discovered or not, it doesn't take less than my pack of cigarettes."

Rutherford knew that Chen Muwu was trying to smooth things over for him, so he was the first to walk out of the cyclotron laboratory door and outside the laboratory building.

Bohr also walked out. He was also a famous smoker.

"Sir, try some of my serious Italian tobacco."

He took out his tobacco bag and filled Rutherford's pipe first, then started filling his own bag.

"Nils, tell me, can Chen really discover neutrons this time?"

Bohr helped Rutherford light the pipe and found that the hand holding the pipe of this strong New Zealand man was shaking slightly.

His tone when asking questions was a little excited, but also a little doubtful.

"I think Dr. Chen must be able to confirm that he discovered neutrons, so he sent you a telegram.

"He never does anything unprepared, and he would never invite you to Stockholm from the UK just because of a slight disturbance."

Rutherford nodded: "I hope so."

Bohr knew that the next sentence he was about to ask might be the teacher's sadness, but he really couldn't help being angry: "Sir, Dr. Chen really left Cambridge University and moved his academic research base to Coming from Sweden?”

It wasn't until he finished smoking a bag of cigarettes that Rutherford finally answered Bohr's question: "I often lie to myself, saying that Chen came to Sweden just to do a favor for his friend the Swedish Crown Prince. It won't take more than a year and a half. , he will return to the Cavendish Laboratory again and continue to do experiments with us.

"But now you have also seen the scale of this Prince's College. Although I have never been to Copenhagen, I have seen the letters you wrote and the postcards you sent me. Isn't your Institute of Theoretical Physics completely incomparable with this one here? Compared to other schools?

"Just a physics laboratory building is much better than the Cavendish Laboratory. Ask yourself, if you could be in charge of such a place, would you go back to the old and shabby Cavendish Laboratory? place, continue to experiment?

"Chen built his more advanced cyclotron in Stockholm instead of Cambridge University, which is enough to explain his choice.

"Forget it, during the five years Chen was at Cambridge University, he did nothing to regret us. On the contrary, the Cavendish Laboratory owed him a lot.

"No matter where others are, as long as they can continue to promote the development of physics, that is ultimately a good thing for you and me, isn't it?

"Let's go in and see how he discovered the neutron."

At some point, Cockcroft had already stood inside the laboratory door.

After Rutherford and Bohr finished smoking, they followed Chen Muwu's instructions and led them to another laboratory.

The interior decoration of this laboratory is even emptier than the one at the cyclotron just now.

There was only one experimental table in the huge room, which contained the instruments Chen Muwu needed to conduct experiments.

Everyone in the cyclotron room just now followed Chen Muwu and moved their positions, including Professor Bierman, a chemist - he also wanted to see what happened when Chen Muwu said he discovered neutrons.

Seeing Rutherford and Bohr coming back after finishing their cigarettes, Chen Muwu began his introduction:

An alpha particle source, a collimation device, a thin boron crystal target, followed by a paraffin block, and finally a cloud chamber. These experimental instruments are all placed in a vacuum environment connected to a vacuum pump.

"I first discovered that the speed of this kind of hard gamma ray is very fast. In order to slow it down, I added a piece of paraffin behind the 'gamma ray' in an attempt to make it absorb part of the energy by the paraffin, and then reduce the speed. Come down.

"What I didn't expect was that after the hard 'gamma rays' passed through the paraffin, not only did they not slow down, but they actually got faster and faster.

“And the things that were emitted were actually no longer gamma rays, but positively charged proton beams.

"That is to say, this beam of hard 'gamma rays' collided with paraffin atoms in paraffin, and protons were ejected from it.

"At this point, I realized that something was not right, because I should be familiar with the collision of gamma rays with atoms.

"Gamma rays are essentially electromagnetic waves, and electromagnetic waves are photons with zero static mass. The energy carried by gamma rays can only knock out the outermost electrons on the periphery of the atom, which is what is called ' Chern effect' of gamma ray scattering.

"It's absolutely impossible for gamma rays to have that much energy to knock out protons from paraffin. It's like using a celluloid ping-pong ball to hit a shot put. No matter how fast the ping-pong ball is, it's probably hard to beat it. The shot put travels a great distance."

"But what if this is a new type of gamma ray? For example, the one with high energy can really knock out the protons in paraffin?"

It was not Rutherford or Bohr who asked the question, but Frederick.

Chen Muwu didn't expect that what was supposed to come would still come.

At first, Curie and his wife regarded neutrons as a new type of gamma ray, and they missed the discovery of neutrons.

"It's very simple. To verify whether this thing emitted from the boron crystal is a gamma ray or a new particle, that's what I'm going to do next.

"According to Sir Rutherford," Chen Muwu did not choose "teacher" when calling Rutherford in front of everyone, but adopted a more official statement, "neutrons may be a A particle composed of an electrical proton and a negatively charged electron.

"It is known that the mass of an electron is only nearly one-thousandth of the mass of a proton, so theoretically the mass of a 'neutron' should be basically similar to the mass of a proton.

"If we assume that this particle is a 'neutron', then let it collide with other particles of similar mass, such as protons, deuterons, helium nuclei, etc., and observe the collision of these particles in a cloud chamber. The trajectories should be able to deduce how much energy they gained in the collision.

"In this way, we can verify whether the particles emitted from the boron crystal are the so-called new particles 'neutrons'."

"Chen, have you done this experiment? What was the result?"

This time it was Rutherford who asked the question.

"Sir, after I thought that this might be a 'neutron', I went to the telegraph office and sent you a telegram. I have just reproduced the experiment in the past few days. I just have this idea at the moment and haven't had time to do the experiment yet. Perform testing.

"It just so happens that you, Professor Bohr, James and Peter all came to Stockholm, so I think we might as well do this experiment together."

Rutherford didn't know whether Chen Muwu was telling the truth or a lie. He always felt that this so-called verification test was not complicated at all. For Chen Muwu, as long as he wanted to do it, it would be easy to conduct the experiment.

Is he waiting for him, wanting him to witness it with his own eyes?

Rutherford thought it was possible.

Chen Muwu said that everyone was doing the experiment together, but this incident made everyone gather around the experimental table, but their hands were tied, which was an obstacle.

And this experiment, to put it bluntly, uses the 'neutrons' emitted from the boron crystal to collide with hydrogen nuclei, deuterium nuclei and helium nuclei, and uses the cloud chamber to record the trajectories of these nuclei after the collision is completed, thereby inferring The energy and mass of neutrons.

As long as you can take photos of the trajectory in the cloud room, the subsequent measurement and calculation work can even be done in the study room.

So after Chen Muwu introduced his experimental ideas and equipment to the onlookers, he politely invited everyone out.

Only Zhao Zhongyao and Cockcroft, as well as Irena and Frederic Curie, were the only five people left around him.

Starting from the construction of the cyclotron in Stockholm, the few of them have developed a high level of tacit understanding among themselves.

Because Chen Muwu had already done this experiment at Cambridge University before, so with so many people helping out, they made rapid progress after doing it again.

It only took them less than a day to take enough photos of the cloud chamber.

The next step is to calculate how much energy hydrogen nuclei, deuterium nuclei and helium nuclei obtain from boron rays, and to infer the specific properties of this boron ray.

After the experimental results came out, the conclusions obtained after calculations were quickly revealed.

The mass of this new particle is approximately 1.0067 relative atomic mass.

——Chen Muwu knew that this data was inaccurate and far different from the precise mass of future neutrons.

But no one else present knew this.

They only know that according to the current data, the sum of the masses of a proton plus an electron is approximately 1.0078 relative atomic mass.

From this point of view, the masses of neutrons and "protons + electrons" are almost the same.

Although the former has less mass than the latter, it seems acceptable.

After getting this result, everyone present was extremely excited.

Chen Muwu had no choice but to pretend to be excited and join in everyone's carnival.

Rutherford was so happy that the electrically neutral particles he had been searching for for more than ten years were indirectly recorded by the photographic plates in the cloud chamber.

"Chen, you are amazing! You are amazing!"

But at this moment, an English sentence with a Danish accent suddenly sounded in the laboratory: "Sir, I think there is something wrong with your hypothesis."

(End of this chapter)