Alpha Decay

[victorias]

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1. Under what conditions would alpha decay happen since it is not as efficient at replacing the protons:neutrons ratio?

2. By how much does the number of neutrons decrease?
I was thinking 2 neutrons but looking at this example, it seems that the neutrons decrease by 8. What am I missing here?
U-238 (92 protons, 146 neutrons) -> Th-228 (90 protons, 138 neutrons)

 

[aldol16]

1. Under what conditions would alpha decay happen since it is not as efficient at replacing the protons:neutrons ratio?

1) In your smoke detectors. What specifically are you looking for in response to this question?

2) U-238 goes to Th-234. I don't know where you got your number.

 

[victorias]

In the case when you have more protons than neutrons, my book says that beta positive decay or electron capture tend to take place. Alpha decay can be used but it is not as efficient. So I am wondering when would alpha decay more likely happen? Alpha decay decreases protons by 2 and neutrons by 2, how exactly does it help us reestablish the p:n ratio?

 

[aldol16]

Alpha decay is more likely with massive particles that have large nuclei and large P:N ratios.

 

[NextStepTutor_2]

In the case when you have more protons than neutrons, my book says that beta positive decay or electron capture tend to take place. Alpha decay can be used but it is not as efficient. So I am wondering when would alpha decay more likely happen? Alpha decay decreases protons by 2 and neutrons by 2, how exactly does it help us reestablish the p:n ratio?

While this type of discussion is beyond the scope of the MCAT, we can use it to think about physics the way the MCAT wants. If this process is not nearly as efficient as some others, then it stands to reason alpha-decay would be limited. In actuality, this is the case. Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very “neutron rich” which makes emission of the alpha particle possible.

THIS link has a pretty interesting section on why alpha-decay occurs and goes into a bit more detail than would be needed for the MCAT.

hope this helps, good luck!