After throwing the letter into the mailbox, Chen Muwu kept looking forward to de Broglie's reply as soon as possible.
As long as he can get money from the little prince, he can continue to conduct electron diffraction experiments.
If there was no money, Chen Muwu would have no choice but to make lanterns for his nephew - and continue his fishing career in the Cavendish Laboratory as usual.
However, the tree wanted to be quiet but the wind was not stopping. As soon as he returned to the Cavendish Laboratory in the morning, before the chair under Chen Muwu's butt was warm, Blackett came to him with a stack of developed photographic films.
In May, after he and Kapitsa helped Chen Muwu find recoil electrons in the cloud chamber, Blackett continued to work on improving the cloud chamber.
Recently, he has finally succeeded in making great improvements to the Wilson Cloud Chamber based on the previous work.
Blackett only used simple mechanical structures such as levers, springs and rotating wheels to make the cloud chamber much more efficient than before.
Blackett also installed an additional mechanical shutter device between the radioactive source and the window of the cloud chamber, which would release alpha particles into the cloud chamber only when necessary.
After his improvement, this cloud chamber system can basically take pictures automatically. From the time the alpha particles enter the cloud chamber, it can complete a cycle every thirteen seconds on average.
Now that the cloud chamber's efficiency had been greatly improved, Blackett began using it to repeat Rutherford's proton discovery experiment countless times, and also took many photos.
The improved cloud room is good everywhere. The only inconvenience is that it takes too many photos.
A photo can be taken every thirteen seconds, so in an hour, nearly 300 photos can be taken.
After two or three days of experimenting, the entire table will be filled with photos.
Blackett's ability alone is completely incomprehensible.
So he could only hold a stack of photos and asked Chen Muwu, who had failed in the electron diffraction experiment and was too busy in the laboratory recently: "Chen, you haven't had anything to do recently. Can you help me look at some negatives and look for that one?" The trajectory of the proton?”
It's rude to come back without reciprocating. He had asked Blackett to help him a lot before. Now that his good friend has approached him, Chen Muwu has no reason to reject him.
He asked Blackett to put the photos on the table and looked at them one by one.
Each photo shows a bunch of thin white threads, estimated to number more than twenty.
Each thin white line represents the trajectory left by a charged particle in the cloud chamber.
Most of them are alpha particles passing through the cloud chamber, leaving a trajectory that does not change the direction of movement.
A small part is caused by the elastic collision between alpha particles and nitrogen atoms in the cloud chamber, resulting in two branches.
Only a handful of alpha particles hit the nucleus of a nitrogen atom and eject a proton, leaving a rare trail in the photo.
But what Blackett wanted Chen Muwu to look for was exactly the trajectory left after this last collision.
Four years ago, Rutherford bombarded nitrogen nuclei with alpha particles and discovered that a new particle occasionally appeared in this nuclear reaction.
After measuring the mass and charge of this new particle, Rutherford determined that this new particle was the nucleus H of hydrogen, or it could also be called the proton p.
Rutherford's explanation for this was that alpha particles were used to bombard the nitrogen nucleus, knocking out a proton, and at the same time turning the nitrogen on the target into carbon-13 (He+N→He+H+C).
He had not captured and observed this reaction from the cloud chamber, so he gave this task to Blackett, who had just enrolled in school at the time.
If you follow the explanation given by Rutherford, then the trajectory in the photo should be divided into three branches after the collision, representing the alpha particles themselves that were bounced back, the protons ejected from the nitrogen nucleus, and the residue after the protons were emitted. of atomic nuclei.
But the nuclear reaction that Chen Muwu remembered was completely different from the explanation given by Rutherford and Blackett.
Because after the alpha particle is incident, it is not bounced back at all, but is directly integrated into the nitrogen nucleus.
In this way, after the atomic nucleus emits a proton outward, it becomes not carbon-13, but oxygen-17 (He+N→H+O).
Therefore, there will not be three bifurcated trajectories in the photo at all. Regardless of whether protons are released or not, after the collision of alpha particles and nitrogen atoms, only two bifurcated trajectories will be produced.
No wonder Blake had a headache when faced with so many photos, because no matter how many photos he took, he could not find any three-branched trajectory in them.
But Chen Muwu was different. Knowing the real nuclear reaction situation, he began to carefully identify the individual special cases in the two bifurcated trajectories that were obviously different from most others.
He spent two days looking at the negatives for Blackett in the Cavendish Laboratory, but he could only find one such track among the large number of photos.
The past two days have made Chen Muwu a little dizzy.
He didn't want to look for more tracks, but came directly to Blackett with this photo.
Seeing Chen Muwu coming with the photo, Blackett looked very surprised: "Chen, have you found the trajectory of the hydrogen atom and are you here to tell me the good news this time?"
"Yes, not entirely," Chen Muwu handed over the photo in his hand, "I found the trajectory of the proton, but the branches of these trajectories are also two, not three as you said. .”
"What does it mean?"
Blackett was very happy to hear that the proton trajectory had been found, but he still didn't understand the meaning of the second half of Chen Muwu's words.
Chen Muwu pointed to a trajectory on one of the photos and said: "Patrick, look at this trajectory. Although it produces two bifurcations like other collision trajectories, the bifurcation here is somewhat different from the others. .
"The first trajectory is short and thick, and looks similar to the trajectory of nitrogen atoms after a collision.
"But the second thin and straight trajectory is obviously different from the alpha particle trajectory after the collision. It should be produced by a particle with less charge and high speed. I think this is the proton you are looking for. .”
"What does this mean?"
Blackett did not react to Chen Muwu's explanation for a while.
Although the trajectory of the proton he mentioned does seem to be thinner and straighter than the trajectory of the alpha particle, but...
“Where do the alpha particles that bounce back after the incident go?”
He raised his questions to Chen Muwu.
"It means that the reason why the alpha particle disappears is because it is not bounced back." Chen Muwu pointed his finger on the short and thick particle trajectory. "I just said that the trajectory of this particle is like a nitrogen atom. But it didn't say it was a nitrogen atom. In this photo, not only was the process of nuclear transmutation recorded for the first time, but a new isotope was also captured. I think the nucleus that left this trace was not carbon-13, but Oxygen-17."
(End of chapter)
