Reborn and become a Great Scientist

Chapter 337 76 Director Chen is hiding away

After being bombarded by alpha particles, the boron crystal will release a stream of high-energy neutrons.

This kind of thing was put into the magnetic field by Bot and walked around, and found that it would not deflect in the magnetic field environment, and the forward path still maintained a straight line.

Therefore, these emitted neutrons were mistaken by Bot as high-energy gamma particles, because this was the only electrically neutral particle that physicists at the time could determine.

As for the electrically neutral particle in the nucleus that Rutherford, director of the Cavendish Laboratory, had always envisioned, Bott didn't take it to heart at all, nor did he think they said this thing was a so-called neutron. .

After all, it only exists in the imagination of the British. As of his discovery, humans have not found any trace of neutrons.

To be conservative, we can only preconceptionally believe that the particle stream they bombarded is a common gamma particle in daily life.

Later, the Curies Jr. and his wife replicated Bert's experiment and obtained the same experimental phenomenon.

Their experimental equipment was better than Bot's, and they measured it more accurately. The energy of this high-energy "gamma particle" was about fifty trillion electron volts, far exceeding the highest known gamma particle at the time. value, several MeV.

Then the couple went a step further, using the high-energy "gamma rays" produced by alpha particles bombarding light atomic nuclei to attack other substances such as paraffin.

The chemical formula of paraffin is CH, a mixture of hydrocarbons. Although it is not crystalline, it is rich in hydrogen nuclei.

After continuing to bombard paraffin with this high-energy "gamma ray", a large number of protons will be bombarded from the inside, which means that the hydrogen atoms in the paraffin will be knocked out from the inside.

For other substances rich in hydrogen atoms like paraffin, the same effect can be produced after high-energy "gamma particle" bombardment.

The explanation given by Mr. and Mrs. Curie for this phenomenon is that it is also similar to the Compton effect.

The incident high-energy "gamma rays" collide with the electrons in the paraffin, transferring the energy to the electrons, causing them to obtain high enough kinetic energy, and then bombard the hydrogen nuclei in the graphite in the form of protons.

However, the problem arises again. The incident high-energy "gamma particles" have an energy of at least [-] MeV, but the emitted proton has an energy of only [-] MeV.

The difference between the two is almost ten times, a whole order of magnitude difference.

The existing theories cannot explain this strange phenomenon anyway.

The Curies, like Bert, forced themselves to create this strange experimental phenomenon, and used the knowledge currently possessed by physicists to give a "reasonable" theoretical explanation.

Of course, in addition to Bot, the two of them were also interfered by a senior physicist.

This senior was none other than Bohr, the pioneer of Nordic physics.

It seems that the more famous physicists are, the more they have an unforgettable "cinnabar mole" in their hearts, which they love deeply and hate deeply.

For Einstein, his cinnabar mole was "quantum mechanics."

Obviously, other people have no doubt about the correctness of quantum mechanics, and regard it as the magic weapon and the only way to calculate the laws of physics operating in the microscopic world.

Only a small number of physicists, headed by Einstein, have always been obsessed with quantum mechanics, that is, how to deny quantum mechanics and what means should be used to prove that quantum mechanics is incomplete and a wrong theory.

For Bohr, his cinnabar mole was the "law of conservation of energy."

Since Chadwick measured that the electrons produced during beta decay of the atomic nucleus have a continuous energy spectrum, which is inconsistent with the prediction of energy and momentum conservation during the two-body decay process, Bohr has questioned the conservation of energy and momentum. Two unbreakable physical laws in classical physics.

Later, Bohr, his assistant Kramers, and Slater, a college student visiting Copenhagen from the United States, jointly published a paper titled "Quantum Theory of Radiation", which proposed a theory that they later used Named after the initials of the three people's surnames, it is called the BKS theory. In short, it means that energy and momentum do not need to be conserved during the microscopic interaction of a single particle. They only need to be conserved at the macroscopic statistical level. .

Later, Compton of the University of Chicago used the conservation of energy and momentum to explain the phenomenon of gamma ray scattering, but at the same time he used the metaphor of light quanta proposed by Einstein, which is Huang's particle theory.

In order to oppose this statement, Bohr, who insisted not to believe that light is a particle, brought up the old story again and mentioned the BKS theory whose central idea is the non-conservation of energy and momentum. This temporarily comforted those who were frightened by insisting on the wave theory. Many physicists.

But later, Compton used the cloud chamber photos he took to clearly and unmistakably record the trajectories of the recoil electrons and scattered gamma rays. He also proved the conservation of energy and momentum at the microscopic level, which is beyond doubt. The irrefutable experimental phenomena completely negated Bohr and his BKS theory.

Although he experienced a tragic failure in academic research on the Compton effect, this incident did not convince Bohr, and the idea that energy and momentum were not conserved was not completely extinguished in Bohr's mind. A faint glow of fire still remained.

Later, this ray of fire encountered firewood that could make it burn brightly again. Someone made a more precise measurement of the energy spectrum of beta decay. The experimental results of this measurement once again confirmed one thing, that is, the atomic nucleus The beta decay energy spectrum of is not the discrete spectrum expected by the theoretical group, but a continuous spectrum that gradually decays.

The discrete spectrum can be established based on two assumptions. One is that beta decay will release a lighter nucleus and an electron, and the other is that energy and momentum are conserved before and after the reaction.

Therefore, if you want to explain the continuous energy spectrum observed experimentally, you must give up one of the assumptions.

After this experiment was completed, Bohr's heart was rekindled and he once again took up the issue of "non-conservation of energy and momentum".

So in the following time, Bohr reminded physicists all the time in his speeches that the law of conservation of energy does not necessarily apply to the single reaction process of pressed atoms.

Then Bohr was slapped in the face again. This time it was one of his students, Pauli, who was always known for his sharp language and love of sarcasm, who came out to deny him.Bohr wrote a letter to his good student Pauli, introducing his point of view on revisiting old things, and believed that if it is confirmed that energy is not conserved, it can explain why the sun can shine, which was still an unsolved mystery at the time. question.

In his reply to Bohr, Pauli was uncharacteristically uncharacteristic. When facing his former teacher, he did not make sarcastic remarks as usual, but calmly said that the theory proposed by Bohr was incorrect only on a theoretical level. Just prove this one by one.

Later, Pauli himself proposed a new hypothesis based on denying the first hypothesis mentioned above.

He believes that in the process of beta decay, in addition to releasing an electron and a lighter atomic nucleus, it will also release other new particles with zero rest mass, electrical neutrality and photons. , which will take away part of the energy, so there is an energy loss.

But because the new particles interact so weakly with other matter, they are difficult to detect with laboratory instruments.

The total energy of the new particles, electrons and recoiled nuclei is still a fixed value, so in beta decay, the law of energy conservation still holds, but because the energy ratio obtained by the new particles and electrons can flexibly change with each other, beta decay occurs The energy spectral lines of electrons are continuous rather than discrete.

Because it is a particle in the electric center, Pauli tentatively named this unknown new particle "neutron".

After Chadwick discovered the neutron, Pauli's "neutron" was renamed by Fermi, and its future name was finally determined - neutrino.

By 1956, it was confirmed that the neutrinos predicted by Pauli and Fermi were used in the reverse beta decay process in nuclear reactors. Bohr's artificial hypothesis of non-conservation of energy and momentum was finally proven to be wrong. A small blemish on the academic career of a great physicist.

When the Curies used the "beryllium rays" produced by bombarding beryllium with alpha particles and continued bombarding graphite to produce protons whose energy was inconsistent with the theoretical value, they also thought of the energy once proposed by Bohr, the giant of Nordic physics. and the assumption that momentum may not be conserved at the microscopic level.

Although the experiment of Compton effect confirmed that in his experiment of gamma ray scattering, energy and momentum were conserved.

But this does not mean that energy and momentum are still conserved in other microphysical processes. Maybe they found a counterexample in the "Beryllium Ray" experiment this time.

Curie and his wife inherited Bohr's theory and believed that the energy of high-energy "gamma rays" they measured was just an average value. If they bombarded a beryllium metal target with alpha particles, there might be "rays with higher energy" in the emitted rays. Gamma rays" exist.

In other words, at the macroscopic statistical level, energy is conserved, but in the microscopic collision reaction of individual particles with individual particles, energy is not conserved.

This hypothesis can well explain why there is a large energy difference between this high-energy beryllium gamma ray and the emitted proton.

So sometimes, these physicists are really strange. Whether it is Bohr or the Curies, they are unwilling to propose an unknown new particle that can satisfy experimental phenomena. Instead, they are always Think that there are errors in the existing theory and think about how to modify it.

Chen Muwu stayed at the Cavendish Laboratory during the summer vacation and re-enacted it alone, or in other words, conducted the experiment that discovered neutrons for the first time. Basically, he repeated the experiment designed by the younger and younger Curies.

The experimental device starts with a polonium-210 radioactive source that can emit alpha particles. After collimation and speed selection, the emitted alpha particles pass through an accelerating electric field and bombard a target composed of boron crystals, so that they can appear High-energy "gamma rays", as Botte and the Curies called them, are neutrons.

However, because neutrons are uncharged electrically neutral particles, the method of detecting neutrons cannot be to use a cloud chamber that can record particle motion trajectories through ionized water mist, and other methods must be thought of.

The best and simplest way is to use the bombarded neutrons to continue bombarding paraffin like the Curies did, and then let the further bombarded protons enter the cloud chamber with a magnetic field.

As long as it can be determined from the trajectory calculation in the cloud chamber that the particles produced by the secondary bombardment are protons, then it can be inferred that the alpha particles that were initially used to bombard the boron crystal were indeed neutrons.

If you are not at ease, you can also calculate the energy of the bombarded protons, and you will basically be sure.

Chen Muwu only needed to confirm in the laboratory that he had bombarded neutrons, and then everything would be fine.

This is equivalent to having a big killer in his hands, and all that remains is the question of when to make it public.

Is it at this year’s upcoming Solvay Conference, or next year when your school in Sweden starts?
In other words, even if it is done, it is still pretending not to know about it.

When Rutherford and the Curies are together, we can replicate the experiment and discover the neutron again in front of everyone.

Of course, no matter what, Chen Muwu must conduct this experiment himself first.

He only knew the general steps of the experiment, specifically how much to adjust the accelerating electric field, how thick to cut the boron crystal target, and how thick to cut the paraffin target. These were all things that he needed to figure out with a little bit of exploration.

After several months, Chen Muwu finally started working hard in the Cavendish Laboratory again and started experiments conscientiously alone.

But just because he wants to be alone without being disturbed doesn't mean he can really get what he wants.

Although some of the original assistants went abroad and returned to China, Chen Muwu's deputy in the laboratory, Chadwick, also returned to his hometown for vacation with his wife and children.

But that doesn't mean no one has free access to the private laboratory of the acting director of the Cavendish Laboratory.

"Chen, what are you doing hiding here mysteriously all day long? I'm going to get married soon, and you don't go over to help me? Could it be that you are hiding out?"

Kapitsa opened the door of the laboratory with a loud bang.

(End of this chapter)