"Chen, what other experiments have you done?"

The more Rutherford listened, the more confused he became.

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

"At that time, the teachers, staff and students of the Cavendish Laboratory had left Cambridge University for the summer vacation, and I was bored in the Cavendish Laboratory by myself, so I found the source of alpha particles to bombard other targets to 'play'.

"When I was bombarding a boron crystal with alpha particles, I inadvertently blasted out a strange beam of particles from it.

"The fact that such particle beams cannot leave a trajectory in the cloud chamber and cannot be deflected in electric and magnetic fields indicates that they should be uncharged particles.

"At first, I thought that this kind of particle beam might be gamma rays with the above properties, but this kind of gamma rays, which can easily penetrate a few centimeters thick copper plates, are much harder than the gamma rays we usually see.

"I'm not sure if this thing coming out of the boron crystal is gamma rays, and I was going to do the next test.

Then at that point, Professor Eddington came to the door.

"He gave up his holiday at the seaside in Cornwall and went back to Cambridge University to study with me about the mechanism of the sun's luminescence.

"It was because of this that Professor Eddington and I turned to the question of nuclear fusion in the interior of the sun, and ignored the question of what the hard gamma rays that came out of the boron crystals were.

"Just a few days ago, Mr. Frederick discovered through calculations that there is a relative atomic mass gap in the equation of the nuclear reaction in which we have discovered a new element.

"He brought it up at the time and asked me where the mass had gone.

"I've been doing experiments for the past few days, and I've been thinking about this one thing all the time. After thinking about it, I thought about the experiment I had done before, and remembered whether the hard gamma rays emitted from this boron crystal could be neutrons.

"So in my free time, I repeated the experiments I did at the Cavendish lab last summer, and I felt that this kind of thing that was emitted was probably neutrons.

"That's why I sent you a telegram that day, asking you to come to Stockholm and find out with me."

The more Kapitsa listened to what Chen Muwu said, the more he felt that he had done a very correct thing to go against Rutherford's decision this time and sneak away to Sweden by himself.

This old crocodile is inevitably too unkind, why didn't he tell himself when he found such a big thing as a neutron?

Hearing Chen Muwu's description, Rutherford's face was still tightly knit, with a very serious expression: "Are you sure, did you find a neutron?" ”

Chen Muwu shook his head: "It's not sure yet, I'm waiting for you to arrive, and we'll further confirm this matter." ”

"Then tell me what you think."

Rutherford took out the pipe he was carrying, and when he was about to take out the tobacco bag, he suddenly realized that this was not the Cavendish laboratory, but Chen Muwu's site in Stockholm, and quietly put the pipe and tobacco bag back.

"Teacher, you can go smoke a bag of cigarettes, we just have to change places, I don't need a cyclotron for my experiment, and the place where I do the experiment is in another room."

"That's fine, whether the neutron is found or not, it doesn't hurt my skill in this bag of cigarettes."

Rutherford knew that Chen Muwu was playing a round for himself, and he was the first to walk out of the door of the cyclotron laboratory and come to the outside of the laboratory building.

Bohr also came out, and he was also a well-known smoker.

"Sir, try my serious Italian tobacco."

He pulled out his tobacco pouch and filled Rutherford's pipe before starting to fill his own.

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

Bohr helped Rutherford light his pipe, and found that the strong New Zealand man's hand holding the pipe had been trembling slightly.

The tone of his voice when he asked the question was a little excited, but also a little doubtful.

"I think Dr. Chen must have been able to confirm that he had discovered the neutron, which is why he sent you a telegram.

"He never did anything unprepared, and he couldn't have invited you from England to Stockholm because of the slightest hint of trouble."

Rutherford nodded, "I hope so." ”

Bohr knew that the next question he was going to ask might be the teacher's sadness, but he couldn't help but be angry: "Sir, did Dr. Chen really leave Cambridge University and move his academic research base to Sweden?" ”

It wasn't until the end of a bag of cigarettes that Rutherford finally answered Bohr's question: "I often lied to myself, saying that Chen came to Sweden just to do his friend the Crown Prince of Sweden a favor." In less than a year and a half, he'll be back at the Cavendish lab and will continue his experiments with us.

"But now you also see the scale of this prince's college, although I have never been to Copenhagen, but I have seen the letter you wrote and the postcard you sent me, your Institute of Theoretical Physics, is it completely incomparable to this school here?

"The building of a physics laboratory alone is much stronger than the Cavendish laboratory. If you could manage a place like this, would you go back to an old and dilapidated place like the Cavendish lab and continue experimenting?

Chen's decision to build his more advanced cyclotron in Stockholm instead of Cambridge speaks volumes.

"In the past five years at Cambridge University, Chen has not done anything to be sorry for us, but the Cavendish laboratory owes him a lot.

"No matter where others are, as long as we can continue to push the boundaries of physics, that's a good thing for you and me, isn't it?

"Let's go, let's go in and see how he found the neutron."

I don't know when, Cockcroft was already standing inside the door of the laboratory.

After Rutherford and Bohr finished smoking, they led the two of them to another laboratory according to Chen Muwu's instructions.

The interior of this laboratory is even more empty than the one that just happened to the cyclotron.

There was only one experimental table in the huge room, on which were the instruments that Chen Muwu needed to do the experiments.

Everyone in the room of the cyclotron just now all followed Chen Muwu to change positions, including Professor Bierman, a chemist - he also wanted to see what happened when Chen Muwu said that he had discovered neutrons.

Seeing Rutherford and Bohr returning after smoking, Chen Muwu began his introduction:

An alpha particle source, a collimation device, a thin boron crystal target, followed by a paraffin block, and at the end is a cloud chamber.

These instruments are all placed in a vacuum environment connected to a vacuum pump.

"At first, I found that the speed of this hard gamma ray is very fast, and in order to slow it down, I added a piece of paraffin wax to the back of the 'gamma ray', trying to make it absorb some of the energy by the paraffin wax, and then reduce the speed.

"What I didn't expect was that after this hard 'gamma ray' passed through the paraffin, the speed did not slow down, but became faster and faster.

"And what is coming out is no longer gamma rays, but positively charged proton beams.

"That is to say, this hard 'gamma ray' collides with the paraffin atoms inside the paraffin, and protons are shot out of it.

"At this point, I realized that something wasn't quite right, because I was all too familiar with the collision of gamma rays with atoms.

"Gamma rays are essentially electromagnetic waves, which in turn are photons with zero static mass. At most, the energy carried by gamma rays can only knock out the outermost electrons on the periphery of the atom, which is the kind of gamma ray scattering called the 'Zen effect'.

"Gamma rays can't have that much energy to knock out the protons in paraffin. It's like using a celluloid table tennis ball to hit a shot put, even if the speed of the table tennis ball is, it is estimated that it will be difficult for the shot put to move a large distance. ”

"But what if it's a new type of gamma ray? For example, the one with high energy can really punch out the protons in paraffin? ”

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

Chen Muwu didn't expect that he would still come.

At the beginning, the two of them regarded the neutron as a new type of gamma ray, and only then did they pass by the discovery of the neutron.

"It's very simple, to verify whether this thing coming out of the boron crystal is gamma rays or a new particle, that's what I'm going to do next.

According to Sir Rutherford, "instead of choosing "teacher" when addressing Rutherford in front of everyone, Chen Muwu adopted a more official term: "A neutron may be a particle formed by the combination of a positively charged proton and a negatively charged electron."

"The mass of the known electron is only nearly 1/2000th of the mass of the proton, so theoretically, the mass of the 'neutron' should be basically the same as the mass of the proton.

"If we assume that these particles are 'neutrons,' then if they collide with other particles of similar mass, such as protons, deuterium nuclei, helium nuclei, and so on, the trajectory of these particles after the collision in the cloud chamber should be able to determine how much energy they gained in the collision.

"In this way, it will be possible to verify whether the particles emitted from the boron crystals are the so-called new particle 'neutrons'."

"Chen, did you do this experiment? 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, and I have only just reproduced the experiment in the past few days, and I only have this idea at present, and I have not had time to do an experiment to test it.

"It just so happens that you and Professor Bohr, as well as James and Peter, are in 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, and for Chen Muwu, as long as he wanted to do it, it would be completely easy to make the experiment.

Was he waiting for himself, wanting to see it with his own eyes?

Rutherford thought it was a possibility.

Chen Muwu said that everyone was doing experiments together, but this incident made everyone gather in front of the experimental table, but it was a kind of hindrance.

And to put it bluntly, this experiment uses the 'neutrons' ejected from the boron crystal to collide with the hydrogen nuclei, deuterium nuclei and helium nuclei, and uses the trajectory of these nuclei recorded in the cloud chamber to reverse the energy and mass of neutrons.

As long as you can take a photo of the trajectory in the cloud room, the next measurement and calculation work can even be carried out in the study room.

Therefore, after Chen Muwu introduced his experimental ideas and devices to these onlookers, he politely invited everyone out.

Only Zhao Zhongyao and Cockcroft were left by his side, as well as Irena and Frederick Curie, the first five people.

Since the construction of the cyclotron in Stockholm, a high enough level of tacit understanding has been cultivated between the several of them.

Because Chen Muwu had already done this experiment at Cambridge University before, with so many people to help, after doing it again, their progress was very fast.

It took less than a day for them to take enough cloud chamber photographic negatives.

The next step is to calculate how much energy the hydrogen, deuterium, and helium nuclei get from the boron rays, respectively, to deduce what the specific properties of the boron rays are.

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

The mass of this new particle is about 1.0067 relative to the atomic mass.

- Chen Muwu knows that this data is not accurate, and the accurate quality of future neutrons is much worse.

But the others present did not know about it.

All they know is that, according to the current data, the sum of the masses of one proton and one electron is about 1.0078 relative atomic mass.

In this way, the mass of neutrons and "protons + electrons" is almost the same.

Although the former is less massively 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 everyone's carnival.

The electroneutral particles, which he had painstakingly searched for for more than ten years, were indirectly recorded by the photographic negatives of the cloud chamber, and Rutherford was overjoyed.

"Chen, you're amazing! You're 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 chapter)