Reborn and become a Great Scientist

Chapter 417 156 Chen Muwu’s Miracle Year

Where do positrons come from?

This is a question that everyone present began to think about after the excitement.

"Chen, where do you think this positively charged positron came from? Is it possible that there is something wrong with the cloud chamber? It is not actually a particle track, but a dust track inside?"

Kapitsa directly threw the problem back into Chen Muwu's hands.

The latter nodded seriously: "It's very possible. Let me look for it on other photographic films to see if there are any other tracks."

Rutherford felt in his heart that Kapitsa was just messing around, so why did Chen Muwu also join in the mess?

He has just calculated that the charge-to-mass ratio of this particle is the same as the charge-to-mass ratio of the electron, but the size of the deflection in the magnetic field is different.

This clearly shows that they are positively charged electrons. Why did he agree with Kapitsa and say that it was a particle of dust that accidentally entered the cloud chamber?

But let Chen Muwu look for it again. If there are positrons on only one photographic film, it is probably an accidental phenomenon. Maybe at a certain moment, a beam of cosmic rays happened to enter the cloud chamber.

But if positron trajectories also appear on other photographic films, it means that it is very likely that this experiment of bombarding boron crystals with alpha particles did produce a second product, positrons, in addition to neutrons.

In fact, Chen Muwu was not sure whether he could find another positron trajectory in the photographic film.

Boron has two stable natural isotopes in nature, boron-10 and boron-11.

The abundance of the former is about 20%, while the abundance of the latter is about 80%.

Only after the alpha particle undergoes a nuclear reaction with boron-10 to generate nitrogen-13 can it quickly release a positron and then decay into stable carbon-13.

And if a nuclear reaction occurs between alpha particles and boron-11, the reaction product is relatively stable carbon-14 and a neutron. Carbon-14 is not prone to further decay.

The proportions of boron-10 and boron-11 vary among different boron samples, but generally the latter has a higher proportion.

When Chen Muwu was at the Cavendish Laboratory, he was lucky enough to discover a positron from a boron crystal.

This time at Prince's Academy in Stockholm, he got lucky again.

Originally, the proportion of boron-10 is small, and when nitrogen-13 releases positrons, it is possible in all directions.

Can the released positrons happen to enter the cloud chamber?

Can we discover new tracks from other photographic films?

Chen Muwu was fetching water from fifteen buckets in his heart, feeling up and down.

Unless the second track can actually be found, he can't give definite information.

Fortunately, because neutrons were used to bombard hydrogen nuclei, deuterium nuclei, and helium nuclei for calculations, everyone took a large number of photographic films, much more than what Chen Muwu had done in the Cavendish Laboratory.

From these photographic films, it is not difficult to find a photo of the trajectory of a positron.

It cannot be said that it is not difficult. Perhaps it should be said that Chen Muwu is relatively lucky.

After calculation, the reappearance of the positron trajectory shows that its charge-to-mass ratio is still the same as that of the electron, but it is deflected in the opposite direction in the magnetic field.

If the trajectory only appears once, it can be said to be dust. However, if the trajectory of positrons appears on the two photographic films with different spatial and temporal environments, it is already certain that positrons will appear in the reaction product.

Next is another question, where do positrons come from?

Because Chen Muwu had discovered neutrons, answering this question suddenly became much simpler.

"This is what I think about the positron."

Chen Muwu continued to write on the scratch papers he used to calculate positron trajectories, and everyone around him put their heads closer.

"Now that neutrons have been discovered, and the mass of neutrons is basically the same as the mass of protons, we can make such an assumption.

"The positive charge of the alpha particle is 2, and its relative atomic mass is about 4, so it can be considered that the alpha particle is a helium nucleus composed of two protons and two neutrons combined together.

“Correspondingly, the boron crystal on the target, I don’t know whether it should be boron-10 or boron-11, their nuclei should be composed of five protons and five or six neutrons.

"I think we only need to test what type of products can be obtained on the target after being bombarded by alpha particles, and then we can roughly know where the neutrons and positrons in the counter reaction come from.

"Professor Bierman, you are the president of the International Union of Pure and Applied Chemistry. You are better than all of us here in testing chemical products.

"I'm going to have to work hard for you again this time."

This time, Chen Muwu almost got off the mark again and mentioned all the things like nitrogen-13 and carbon-14.

Chen Muwu knew that carbon-13 exists naturally in nature, and Professor Aston of the Cavendish Laboratory had also measured this isotope when measuring the masses of various isotopes.

Carbon-14 has not yet been discovered by the chemical community, and Chen Muwu also knows this.

But he was not sure whether nitrogen-13 was known to the chemical community or not. Anyway, there happened to be a chemistry professor Bierman who was also in Stockholm, so he asked him to personally test what the boron crystal became after being bombarded.

Chen Muwu took down the bombarded boron crystal target from the experimental device that had been closed long ago and handed it to Bierman.

Bierman went to do the identification, but the results of Zhao Zhongyao and Cockcroft's use of gamma rays to bombard deuterium nuclei were not yet available.

The few people who stayed suddenly didn't know what to do next.

"Chen, actually, have you already known where this positron comes from?"

Rutherford suddenly approached Chen Muwu and asked.

Chen Muwu nodded subconsciously and shook his head: "I just have a general idea.

"It turns out that in your imagination, Sir, the neutron is composed of a proton and an electron.

“So after a proton captures an electron, it becomes a neutron.

"But at the time when you proposed this theory, people had never thought that there was such a thing as a positively charged electron in the universe.

“Since the trajectory of the positron has been clearly recorded on the photographic film in the cloud chamber, is it possible that the proton actually released a positively charged electron outward and then turned into a neutron?

"Positively charged electrons can easily encounter a large number of negatively charged electrons in the surrounding environment. Perhaps they will annihilate. That's why a proton captures a negative electron and produces a neutron. An illusion."

Chen Muwu gave an answer that was completely contrary to the facts, but sounded very reasonable. We cannot talk about this in detail, as we may unknowingly talk about neutrinos as we talk about it.

Among these people in Stockholm, there was Bohr from Copenhagen.

Before and after the discovery of neutrinos, this gentleman once again put forward his view that energy is not conserved at the observer level.

Chen Muwu was afraid that the topic would turn to the conservation of energy, so he made up a wrong use.

Let us first understand the properties of positrons and positrons and the properties of positron and negative beta decay before mentioning neutrinos.

Otherwise, if you take too big steps, you will easily lose your legs.

Chen Muwu's original intention was to fool Rutherford by giving an answer that sounded reasonable at first glance but was actually wrong.

But he didn't expect that he would do something wrong again.

Because a few days later, Zhao Zhongyao and Cockcroft also conducted experiments on bombarding deuterium nuclei with gamma rays.

The experiments they measured showed that the binding energy of the deuterium nucleus was 2.2 megaelectronvolts, and the mass of the neutron was calculated to be 1.0084 relative atomic mass units or 1.0090 relative atomic mass units.

No matter which value is used, it is larger than the known relative atomic mass unit of 1.0078, the sum of the proton mass plus the electron mass.

Once this result comes out, it not only shows that the neutron is not an "affiliated binding system in which protons and electrons are combined" as Rutherford imagined in his hypothesis, but should be a basic, "inexhaustible" system. New particles for "redividing".

It seems that everyone is happy with this result, but there is another problem.

Neutrons are not a bound system composed of protons and electrons, so are protons a bound system composed of neutrons and positively charged positrons?

Rutherford thought of a new possibility at this moment.

He was about to express his point of view to Chen Muwu, but then he thought again and couldn't help but shake his head.

Protons and electrons can form a bound system because one of them is positively charged and the other is negatively charged.

But neutrons themselves are uncharged, while positrons are positively charged. There is no electrical opposite between the two. What force can bind them together?

Rutherford also felt that Chen Muwu's statement just now seemed very unreliable.

Because it has been ten years since I discovered the proton in 1919.

In the past ten years, people have seen a large number of protons and electrons in various experimental phenomena in the trajectory of the cloud chamber.

But only Chen Muwu has found neutrons, let alone positrons, which have basically never been seen before.

It can be seen that even if, as Chen Muwu said, the proton radiates a positron and then decays into a neutron, then this reaction is definitely not common and cannot happen easily.

Of course, there is another possibility, that is, what Chen Muwu said is wrong. The positrons do not come from protons, but have another source.

Of course, no matter what, the discovery of neutrons and positrons in one breath is a very big event for physics.

It can even be said that only half of 1928 has passed. The two particles discovered by Chen Muwu in Stockholm can already be declared to be the most important and eye-catching scientific discovery of the year.

Compared with these two particles, the cyclotron previously invented by Chen Muwu and the two new chemical elements produced on the cyclotron are also very important scientific discoveries, but...

Rutherford suddenly remembered that he had compared the year when Chen Muwu first arrived at Cambridge University to 1905 for Einstein.

Because in that year, Chen Muwu achieved countless results in physics and astronomy.

Rutherford felt that in 1928, Chen Muwu seemed to have regained his second spring and achieved so many results again.

And in Rutherford's eyes, these results were even more powerful than the previous one.

Maybe 1923 was not Chen Muwu’s miracle year, but 1928 was?

Shortly after, Bierman also gave his own test results.

He detected two isotopes of carbon from the bombarded boron crystal target:

"Dr. Chen, in this target, the product of a nuclear reaction is carbon-13, which is an isotope of carbon that chemists have found in nature.

"The other reaction product is a new isotope of carbon, carbon-14 with a relative atomic mass of 14.

"I reviewed relevant information and papers and found out that this is a new isotope of carbon that has never been discovered before!"

Biermann was thrilled.

But he saw everyone's reaction, especially the expression on the face of Rutherford, the leader of the Cavendish Laboratory.

Apparently, they didn't seem to pay much attention to the new carbon isotope they detected.

Bierman thought about what Chen Muwu had done at Prince's College in Stockholm these days.

Bierman had only a partial understanding of the results in physics, but he still had a say in chemistry.

Just for new elements, Chen Muwu has discovered two types in the cyclotron.

Compared with new elements, it is just a new isotope, which is really not worth mentioning.

Chen Muwu never made any comment on Bierman's test.

Whether he did not discover nitrogen-13, which decayed quickly, or whether he thought carbon-14 was unimportant, although there were many shortcomings, Chen Muwu did not point them out.

This time he agreed with Bierman's point of view. Carbon-14 produced in the laboratory is not good carbon-14. Only carbon-14 found in nature is good carbon-14.

The next step is to organize the results in physics and chemistry that have been achieved at Prince's College in recent times into papers for publication.

Everyone knew that Chen Muwu was going to start the Journal of Prince's College, so no one mentioned publishing the paper in other journals.

Only Rutherford, in his name, went to the telegraph office and took a telegram to the editorial office of Nature in London, asking them to place an advertisement in a prominent position in the latest issue of the journal.

"The neutron has finally been discovered. Details will be found in the first issue of "Journal of Prince's College" to be published soon."

(End of this chapter)