1900: A physics genius wandering around Europe

Chapter 691 Nuclear Emulsion Method! Shocking Results! Proof of Meson Theory! The Hadron Era! The Mystery of the Weak Force!

Cavendish Laboratory, UK.

Rutherford was a conservative leader.

Under his guidance, Cavendish University expanded in size, but its research remained focused on fields such as nuclear physics and radioactivity.

Even with the recent additions of cosmic rays and particle physics, these can still be included in nuclear physics.

In real history, his successor, George Bragg, was quite the opposite.

After becoming Cavendish's fifth director, the latter abandoned his original expertise in nuclear physics and instead vigorously developed niche disciplines such as biophysics, opening up new directions for the laboratory.

That's why Watson and Crick were able to study DNA in Cavendish later.

It is too difficult for traditional physics to make breakthroughs, while biophysics, as an interdisciplinary field, is a blue ocean.

However, Rutherford was a big shot after all, and no matter how difficult it was, he thought about breaking through rather than bypassing it.

Although he has had less and less time since becoming president of the Royal Society, he has gradually begun to withdraw from front-line research work.

However, he still sets aside fixed time each week to personally train and guide students, regardless of whether they are novice graduate students or senior researchers.

At this moment, in the office.

A young man is giving a work report.

"Studies on condensation phenomena in cloud chambers have revealed an anomalous phenomenon: steam passing through nozzles undergoes a high degree of ionization."

"Next, I proved that the reason was that the rapidly expanding steam was supersaturated."

"This phenomenon can be avoided by improving the design and operation of steam turbines."

"This is my improvement to the cloud room."

After listening, Rutherford nodded in satisfaction and said:
"Powell, although you've only been in the lab for a short time, you've adapted very well."

"This small improvement is very useful for cloud rooms."

Upon hearing this, Powell smiled happily.

He is 25 years old and a native Englishman.

As the son of a craftsman, his parents could not afford his tuition.

However, through his intelligence and hard work, he won a scholarship to Cambridge University and had the opportunity to become Rutherford's doctoral student.

This was the result he had always dreamed of.

At that moment, faced with his mentor's praise, he simply chuckled.

Such a small improvement is nothing in Cavendish, a place teeming with experts.

Rutherford continued:

"However, this project is just for you to practice."

"If you really want to graduate with a doctorate, you must produce innovative results."

“I’ve recently come up with a new research topic that I think is quite suitable for you. Let’s see if you can complete it.”

Wow!
Upon hearing this, Powell appeared excited.

As a doctoral student, the most important thing is what kind of research topic your supervisor can provide.

Everyone in academic circles knows that Professor Bruce's projects are at least Nobel Prize level.

Although Powell was unable to go to Borneo to apply for a PhD there.

But Professor Rutherford is a super big shot second only to Professor Bruce.

The other party's research topic is unlikely to be too bad either.

Moreover, both of these big shots were of the same caliber to him.

Powell said with a look of anticipation:

"Professor, please tell me, I will definitely study it carefully!"

Rutherford smiled slightly and said:

"Recently, many people have been studying cosmic rays, and they almost all use cloud chambers."

"But cloud rooms have one notable feature."

"When cosmic rays enter a cloud chamber, their extremely high speed makes them easy to penetrate the cloud chamber, resulting in incomplete trajectories."

"Therefore, cloud rooms are getting bigger and bigger now."

"The gaseous material in the cloud chamber is unlikely to effectively block the movement of cosmic rays."

"Moreover, it is very bulky and not suitable for carrying around."

"So, I was thinking, could we consider designing a new type of cosmic ray detector?"

Wow!
Powell looked shaken.

The ideas of these big shots are truly amazing.

While others were painstakingly studying various cosmic rays in cloud chambers, Professor Rutherford was thinking about inventing entirely new instruments.

This is an exaggeration.

But even though it's a good idea, he has no idea where to start.

What's the difference between this and "Go and deal with Tang Sanzang and his disciples"?

The supervisor only needs to say a few words, and the graduate students will be running around like crazy.

Rutherford, as if reading Powell's mind, smiled and said:

"Young man, calm down."

"I'm not the kind of mentor who just offers a vague idea and lets students do whatever they want."

"I already have an idea for this, I just hope you will give it a try."

Upon hearing this, Powell immediately looked ashamed and, moved, quickly said:
"Professor, I understand."

Rutherford smiled slightly, saying that young people all go through a growth process.

He suddenly asked:
"Let me ask you a question."

How did Professor Becquerel of France discover the radioactivity of uranium?

Powell paused, unsure of the question's meaning, but immediately replied:
"In 1896, Professor Becquerel discovered that uranium salts could darken photographic plates."

"Therefore, radioactivity was discovered."

Rutherford said excitedly:

"That's right!"

"This shows that the particles can interact with the photographic film, demonstrating their presence."

Traditional photographic negatives are made of latex, which is essentially composed of silver bromide and gelatin.

"I'm wondering if it's possible to design a special latex, or improve existing latex so that it can detect the properties of particles."

"When charged particles enter the latex, they collide with silver bromide, forming a photosensitive phenomenon and leaving tracks. After development and fixing, the properties of the particles can be observed."

"Based on the particle size in the latex and the collision patterns of silver bromide, the velocity and charge of the charged particles can be determined."

"If it is a neutral particle, we can measure the properties of its secondary particles after colliding with other particles, and then deduce the properties in reverse."

"Most importantly, latex is a solid-like substance with a density thousands of times greater than that of vapor in a cloud chamber, which can effectively block the movement of particles."

"Therefore, if the trajectory of a cosmic ray in a cloud chamber is several meters, it may only be a few millimeters in the latex."

"In this way, many complex phenomena can be displayed simultaneously on a small latex photograph."

"That's my thought."

Wow!
Powell was completely stunned.

This is simply a way to turn something rotten into something magical.

No one had ever thought of using photographic negatives to study cosmic rays.

Cosmic rays—that's such a high-level field of physics research.

Photography technology is already a common, low-end technology.

These two things have actually been linked together.

"It's incredible!"

Powell was not blindly praising Rutherford; he quickly understood Rutherford's intentions.

"When charged particles pass through silver bromide crystals, the latter capture electrons to form silver atoms, thus leaving a black mark."

"By combining the number of silver atoms and particle density with kinematic formulas, we can deduce the mass, velocity, and charge of the incident particle."

After listening, Rutherford smiled slightly and said:

"Ruzi can be taught."

Powell looked excited.

It would be wonderful if this idea could actually be realized. Compared to cloud rooms, it has many advantages such as being lightweight, simple, and economical.

He smiled and said:

"Professor, I think this kind of latex shouldn't be called latex, but rather 'nuclear latex'."

Rutherford said with a smile:

"Let's name it after you've implemented it."

Powell awkwardly scratched his head, but his heart was filled with fighting spirit.

In the days that followed, he threw himself into the experiments.

He increased the silver bromide content in traditional latex to increase the probability of collision.

In addition, he improved the sensitivity and thickness of the latex to make it more suitable for cosmic ray research scenarios.

Finally, he developed a method for measuring the relationship between track length and energy.

After making improvements, Powell conducted experiments using known particles such as electrons and protons, and found that the results were very good.

Rutherford was very satisfied.

"You could try studying cosmic rays."

So, Powell began studying cosmic rays with great excitement.

Although Blackett is no longer in the laboratory, he left behind a lot of related materials.

Powell quickly gained a deep understanding of cosmic rays.

On this day, while studying cosmic rays using his self-created latex method, he suddenly discovered a strange track.

Based on his calculations, he quickly concluded that the mass of this charged particle was 273 times that of an electron.

The young Powell was unaware of the significance of this number.

"It seems like there's no particle with that mass value."

So he took the experimental data and went to Rutherford.

After watching the whole process, Rutherford frowned slightly.

"Could it be that a new particle has been discovered?"

However, he suddenly had a flash of inspiration and exclaimed in shock:
"wrong!"

"Why does the mass of this particle seem somewhat similar to the π meson predicted by Cheng Dao?"

Wow!
Rutherford immediately stood up; even he was shocked by the conjecture.

If the π meson is indeed discovered, it would be an absolutely groundbreaking achievement for the physics community.

"Powell, get Chadwick together and have him study the strong properties of this new particle."

Powell's face was trembling with excitement.

He may have inadvertently confirmed the existence of the π meson!
"Oh, God!"

"Please don't joke with me!"

He immediately informed Chadwick, who was also extremely shocked upon hearing the news.

The two quickly discovered through experiments that this new particle, which has a mass 273 times that of an electron, interacts strongly with both protons and neutrons.

"It's highly likely to be a π meson!"

Ultimately, after further experimental verification, Rutherford made the final decision:
"This is the pi meson!"

"It carries a positive charge, so it must be a π+ meson!"

Chadwick said excitedly:
"Powell, you're going to be famous!"

Wow!
Powell was so excited that he didn't know what to say.

1929 October.

Powell's paper on the discovery of the π+ meson using the nuclear emulsion method was published in Nature.

The news caused an instant sensation in the physics community!
"Oh, God!"

"A new particle has been discovered!"

"Has the particle physics predicted by Professor Bruce finally begun to appear?"

It shocked countless people!
Not long after Anderson discovered the muon, a new particle has now emerged.

This has greatly excited the entire physics community.

Elementary particles represent the most fundamental rules of physics.

Once we understand the properties of elementary particles, we can understand the world at its most fundamental level.

The discovery of the π+ meson proved the correctness of Li Chengdao's meson theory.

"The second quantum field theory has been successfully declared!"

"Like father, like son!"

Countless people sighed.

Professor Bruce created quantum field theory and proposed quantum electrodynamics, and his eldest son, Li Chengdao, proposed meson theory.

One explains electromagnetic force, the other explains strong force; they're simply unbeatable.

Borneo.

When Li Chengdao heard the news, even with his composure, he couldn't help but dance with joy.

"Great!"

His theory was finally proven.

No one can understand this feeling.

At this moment, his state of mind finally underwent a transformation.

Soon, everyone's attention turned to Powell's nuclear emulsion method.

"This method is so ingenious!"

"Cosmic rays can be studied with such simple materials and manufacturing processes."

"Moreover, it is better and more suitable for studying cosmic rays than cloud chambers."

Leading figures in the field of cosmic rays, such as Zhao Zhongyao, Compton, and Anderson, have published articles offering objective evaluations of this new method.

"The nuclear emulsion method has the advantages of good spatial resolution and continuous sensitivity, and is suitable for complex reactions and studies involving multiple charged particles."

"Of course, it also has some drawbacks."

"It requires development and fixing, so the measurement results cannot be obtained immediately, and it also requires microscopic observation."

But in any case, adding a new measurement method is always a good thing.

Nuclear emulsion method allows more people to study cosmic rays.

Powell's name immediately resonated throughout the physics community.

In real history, after graduating, Dr. Powell worked at the University of Bristol in the UK.

It was there that he invented the nuclear emulsion method and thus discovered the π meson.

Later, physicists used this method to discover various hadrons, such as the K meson.

Particle physics has entered the hadron era!
Nuclear emulsion method and cloud chamber method have become the two most important methods for studying cosmic rays.

In addition, the former also plays a very important role in the field of nuclear physics.

Qian Sanqiang and He Zehui, a married couple from China, discovered the ternary and quaternary fission phenomena of uranium using the nuclear emulsion method.

Previously, physicists believed that uranium nuclei could only be divided into two halves.

With the discovery of the π meson, physicists began to study its properties.

Soon, it was discovered that the π meson, like the muon, also decays, and has an extremely short half-life.

This raises a completely new question.

With the discovery of more particles, several new decay mechanisms have emerged in addition to the previously known beta decay.

The reason why alpha decay and gamma decay are not mentioned here is because these two types of decay are relatively simple and do not involve changes in particles.

Beta decay, which involves the conversion of neutrons and protons, is more complex.

Beta decay, muon decay, and π meson decay are all weak-force-dominated decays.

This has further drawn physicists' attention to the weak force.

Now, of the four fundamental forces, only the weak force and gravity lack corresponding quantum field theories.

Obviously, most people think that the weak force is easier to study than gravity, since there are already so many phenomena to study in the former.

Thus, a study on weak forces began to emerge.

Meanwhile, another groundbreaking discovery has been made in the field of nuclear physics!
(End of this chapter)