Need knowledgeable thoughts... (1 Viewer)

[someth1ng]

Okay, the problem I have is that in my exam, I was asked in the multiple choice:
This is roughly what the question was:
"Why is Uranium-238 radioactive?"
The two possible answers I saw were:
1. The proton-neutron ratio
2. The mass of the nuclei was too large

I put in 2 as my answer on the grounds that:
• Uranium has no non-radioactive isotopes so it can't be concluded that the ratio is caused by radioactivity.
• All elements >83 in atomic number are radioactive and higher atomic number generally equates to larger mass. The only change between 83 onward against under 83 is the mass but the ratio is the same.
• After doing some research: two main factors contribute to radioactivity: the size of the nuclei and the proton-neutron ratio. In Uranium, this would be the size since if you consider the size, a 1.6 ratio is reasonable for the magnitude of the protons in the nuclei.

Thoughts? I personally think both answers can be considered wrong.

 

[zeebobDD]

this would be the size since if you consider the size, a 1.6 ratio is reasonable for the magnitude of the protons in the nuclei.

Thoughts? I personally think both answers can be considered wrong.

yes but the p:n ratio has to be 1:1.5, both answers can be correct, but the main reason would be proton:neutron ratio i think

 

[hayabusaboston]

yes but the p:n ratio has to be 1:1.5, both answers can be correct, but the main reason would be proton:neutron ratio i think

+1
agreed

 

[someth1ng]

It's only 1:1.5 up to around Lead according to my textbook.

 

[asdfqwerty]

i think any element passing 83 is unstable because the mass of the nuclei is too large, not because of its n ratio. i would have gone with number 2, but then i could be wrong as well.

you should check the band of stability graph and see where uranium-238 lies. then you can work out whether it's its mass or n ratio.

 

[someth1ng]

Well, sources say that the nucleus is too large to be stable but doesn't state the mass specifically.

 

[nightweaver066]

Well, sources say that the nucleus is too large to be stable but doesn't state the mass specifically.

Maybe stating that the nuclei mass is too large is a bit too general where as saying it's radioactive due to the proton-neutron ratio is more specific.

 

[someth1ng]

It was a multiple choice question...

 

[nightweaver066]

It was a multiple choice question...

I know, but multiple choice questions can sometimes give two or more correct answers.

It's about selecting the more correct answer.

 

[someth1ng]

But I'm questioning whether the neutron-proton ratio is applicable for Uranium since:
• Pb is 1.53 ratio.
• Larger molecules have higher ratios so 1.58 is reasonable to expect from Uranium to be "stable" as it is larger than Pb.

 

[delian]

I know, but multiple choice questions can sometimes give two or more correct answers.

It's about selecting the more correct answer.

Very true.

 

[someth1ng]

Very true.

I'll talk to the teacher when we get results.