A-level physics (particles) question!

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olivier_
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The proton number of uranium is 92 and the proton number of radon is 88. Which series of decays turns a uranium nucleus into a radon nucleus?

So this was a multiple choice question and the correct option was:

"alpha + beta minus + beta minus + alpha + alpha"

But I'm confused as to why this is correct, because to go from 92 to 88 you need to decrease by 4 not increase. Alpha is +2 and beta minus is -1 so wouldn't the decay equation give +2-1-1+2+2=+4 overall?

Or would the effect on the proton number of the uranium be the opposite in order to balance out the equation with the +4 so in fact the proton number is 92-4=88?
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Sinnoh
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You've got it the wrong way around. The uranium nucleus is losing nucleons in the alpha decay. Beta-minus decay increases atomic number.
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olivier_
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(Original post by Sinnoh)
You've got it the wrong way around. The uranium nucleus is losing nucleons in the alpha decay. Beta-minus decay increases atomic number.
Ty for the reply In my question I suggested two opposite ways of thinking about it, so which one did you mean is wrong??
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Sinnoh
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(Original post by olivier_)
Alpha is +2 and beta minus is -1 so wouldn't the decay equation give +2-1-1+2+2=+4 overall?
This is wrong

Or would the effect on the proton number of the uranium be the opposite in order to balance out the equation with the +4 so in fact the proton number is 92-4=88?
This is correct

The nucleus loses an alpha particle's worth of nucleons in the decay. Yes an alpha particle has 2 protons and 2 neutrons, so an atomic number of +2, but this is being lost from the original nucleus, so you have to subtract it.
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olivier_
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(Original post by Sinnoh)
This is wrong


This is correct

The nucleus loses an alpha particle's worth of nucleons in the decay. Yes an alpha particle has 2 protons and 2 neutrons, so an atomic number of +2, but this is being lost from the original nucleus, so you have to subtract it.
That cleared the confusion, tysm
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