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Positron emission

by cylinder
Tags: decay, emission, positron
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cylinder
#1
Sep26-10, 09:05 PM
P: 14
I've been wondering about positron emission. If a neutron has more mass than a proton, how can a proton turn into a neutron by releasing a particle with mass?

(source:http://en.wikipedia.org/wiki/Positron_emission)
Doesn't this violate the law of conservation of energy? Isn't Boron-11 heavier than Carbon-11?
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jtbell
#2
Sep26-10, 09:42 PM
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Quote Quote by cylinder View Post
Isn't Boron-11 heavier than Carbon-11?
Look them up.

http://www.nist.gov/physlab/data/comp.cfm

For C you need to use the "All isotopes" option.
cylinder
#3
Sep26-10, 09:53 PM
P: 14
But... Doesn't Boron have 6 neutrons and 5 protons, where Carbon has 5 neutrons and 6 protons? What am I missing here? Apologies, but my knowledge of nuclear physics is elementary, at best.

Vanadium 50
#4
Sep26-10, 10:24 PM
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Positron emission

Cylinder, jtbell gave you some excellent advice. Look them up.
cylinder
#5
Sep26-10, 10:34 PM
P: 14
Yes, I looked them up before I posted that. I'm sorry, I was just stating that I am confused about something else now: it looks like the masses of the nucleons don't add linearly. I understand if my new question is a bit off topic. Should I start a new thread?
granpa
#6
Sep26-10, 10:48 PM
P: 2,258
this is exactly the sort of thing that wolframAlpha was made for
http://www.wolframalpha.com/input/?i...1+and+boron-11



http://atom.kaeri.re.kr/ton/nuc1.html




heres a link to a monster jpeg. Consider yourself warned. its huge.
http://upload.wikimedia.org/wikipedi...rs_changed.jpg

heres another nice one
http://www.mathpuzzle.com/stability.html
inflector
#7
Sep26-10, 11:08 PM
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Quote Quote by cylinder View Post
Yes, I looked them up before I posted that. I'm sorry, I was just stating that I am confused about something else now: it looks like the masses of the nucleons don't add linearly.
The concept of nuclear binding energy is the piece you seem to be missing:

http://hyperphysics.phy-astr.gsu.edu...ne/nucbin.html

has a pretty good overview for this and the basics of nuclear mass and how it relates to nucleons.

Essentially, this binding energy (mass) difference is the source of the energy for both fusion and fission.
Drakkith
#8
Sep26-10, 11:17 PM
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The total mass of a nucleus is LESS than the total mass of the individual particles that make up the nucleus if they were not bound, because of nuclear binding energy.
cylinder
#9
Sep26-10, 11:24 PM
P: 14
Quote Quote by inflector View Post
http://hyperphysics.phy-astr.gsu.edu...ne/nucbin.html
Essentially, this binding energy (mass) difference is the source of the energy for both fusion and fission.
Oh wow, that is really cool. Thank you very much, that clarifies a lot.

Thanks for all of you guys' help!


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