Madame Wu Experiment: Doubts & Reasoning

In summary, the conversation discusses the experiment of Madame Wu where a strong magnetic field is used to polarize nuclei and scintillators are used to detect particles emitted in the decay process. The conversation also mentions a contradiction in the results and debates the importance of the direction of emission and the role of weak interactions in the experiment. Ultimately, it is concluded that there may be an error in the book referencing the experiment.
  • #1
Federica
12
1
Hi all,

I have some doubts regarding the experiment of Madame Wu. I know a strong magnetic field is used to polarise the ##^{60}Co## nuclei, then we have an anthracene scintillator on the top of the sample which will detect the electron produced in the decay: ##^{60}Co \rightarrow ^{60}Ni^{**} + e^{-} + \bar{\nu}_{e}##. Two others scintillators will detect the two gammas produced by the de-excitation of ##^{60}Ni^{**}##, one is set at 90° to the field (the 'equatorial counter') and the other one at 0° ('the polar counter').

Now, since I suppose the spins are parallel to the field, I would expect the polar counter to detect more photons than the equatorial one (as long as we have polarisation), but the opposite happens. And since the anti-neutrino is right-handed, the electron should be left-handed, which means the anthracene detector should detect more electrons when the field is on the downside. But once again, the opposite happens.

Can someone help me to understand what's wrong with my reasoning?
 
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  • #2
Which direction receives more photons depends on the direction of the magnetic field. Not that it would matter: Any preference is parity violation.
 
  • #3
Hello everybody!

I join the conversation since I also have some doubts about Wu experiment.

mfb said:
Any preference is parity violation.
Yes, you are right, but if the emission is in the opposite direction of the spin the weak interactions obey V-A structure, otherwise V+A... So, the direction of the emission is important.

From the attached graphs it seems there is a contradiction. Let's consider the graph about the beta asymmetry and the situation "B up" (a).
If the field is upward, the spin is upward. Since V-A structure implies the emission of the electrons opposite to the spin, I would expect to count less frequently than the situation in which the filed in downward (remember that in Wu experiment the scintillator is over the source). But the graph shows the opposite.

Where does my reasoning fail?
 

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  • #4
I'm not sure where you got these graphs from because the publication has it in the opposite direction, and it is quite clear:
The sign of the asymmetry coefficient, ##\alpha##, is negative, that is, the emission of beta particles is more favored in the direction opposite to that of the nuclear spin.
 
  • #5
mfb said:
I'm not sure where you got these graphs from because the publication has it in the opposite direction, and it is quite clear:

Those graphs are taken from "Introduction to Elementary Particle Physics", A. Bettini. Thank you for your prompt reply, it seems there's an error on the book then.
 

1. What is the Madame Wu Experiment?

The Madame Wu Experiment, also known as the Wu Experiment or the Wu-Segal Experiment, was a landmark experiment in nuclear physics conducted in 1956 by Chinese-American physicist Chien-Shiung Wu. It aimed to test the conservation of parity in weak interactions, and ultimately provided evidence for the violation of this fundamental symmetry.

2. What were the doubts and reasoning behind the Madame Wu Experiment?

The doubts surrounding the Madame Wu Experiment stemmed from the fact that it contradicted the long-held belief that parity was conserved in all physical interactions. This was a fundamental principle in physics, and the reasoning behind the experiment was to challenge this idea and provide evidence for its violation.

3. How did the Madame Wu Experiment challenge the established beliefs in physics?

The Madame Wu Experiment challenged the established beliefs in physics by providing evidence for the violation of parity in weak interactions. This was a significant discovery as it showed that the laws of physics were not symmetrical, and that the universe did not behave in the same way for particles and their mirror images.

4. What were the results of the Madame Wu Experiment?

The results of the Madame Wu Experiment showed that the weak nuclear force does not obey the principle of parity conservation. This was a groundbreaking discovery that changed the way physicists thought about the fundamental laws of nature and paved the way for further research and understanding in the field of particle physics.

5. How did the Madame Wu Experiment impact the field of physics?

The Madame Wu Experiment had a significant impact on the field of physics by challenging long-held beliefs and providing evidence for the violation of parity in weak interactions. This discovery opened up new avenues of research and led to further breakthroughs in understanding the fundamental laws of nature.

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