What is the Relative Concentration of Helium at 3 Minutes After the Big Bang?

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SUMMARY

The relative concentration of helium at 3 minutes after the Big Bang is approximately 2-5 parts per 100,000 by mass. In a hypothetical scenario where 1 kilogram of normal matter is considered, this translates to about 250 grams of helium nuclei, aligning with the expected mass fraction of ~25%. The discussion also touches on the negligible contributions of helium-3 and lithium, with calculations indicating that the amount of lithium nuclei would range from 0.2 to 0.5 micrograms. The confusion arises from interpreting the concentration figures correctly, particularly in relation to the cosmic abundance of elements.

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  • Understanding of Big Bang nucleosynthesis
  • Basic knowledge of mass fraction calculations
  • Familiarity with isotopes, specifically helium-3 and lithium
  • Proficiency in scientific notation and unit conversions
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Homework Statement


the relative concentration by mass of helium at 3 minutes after the big bang is 2-5 parts per 100,000. If you had 1 kilogram of the normal matter from the universe at a time 3 minutes after the big bang, how much of it would be normal helium nuclei?

Homework Equations

The Attempt at a Solution


I have no idea.can someone help?
 
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If 2% of all apples are bad, and you have 10000 apples, how many apples are bad? The problem is as easy as this.
 
your mean is 1kg x 2x10^-5?but the answer is 250g. I only have the answer. I don't know how to get it
 
250 g sounds reasonable in terms of cosmology (the actual mass fraction was ~25%), but that doesn't fit to the given "2-5 parts per 100,000". Could that number refer to something else (like helium-3 or deuterium)?
 
IMG_1478376939.927361.jpg

I have table show that
 
That's what I expected. 25% 4He, so 250 g in 1 kg. The 3He contribution is negligible.
 
how about in 7Li. there isn't have%
 
What is unclear about "n parts in x"?
 
2-5 parts in 10 billion
 
  • #10
Yes, what is unclear about it?
 
  • #11
So It is 1kg x 2 parts in 10 billion?
 
  • #12
Sure. Well, 2 to 5.
 
  • #13
I have tried it before. 1kgx4x10^(-10)=4x10^(-10)kg. However the answer is 0.4mg=4x10^(-7)kg how to get it?
 
  • #14
there is the Q:If you could take a 1 kg handful of the matter in the universe 3 minutes after the big bang, approximately how much would be lithium nuclei?
 
  • #15
Should be 0.2 to 0.5 µg, not mg.
 
  • #16
my calculation is correct?
 
  • #18
thanks!
 

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