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Topic: Radioactive Decay - Please explain  (Read 5249 times)

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Offline Azureilai

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Radioactive Decay - Please explain
« on: December 07, 2012, 12:46:02 PM »
So, my teacher taught us about radioactive decay in class and gave us some examples. But I have still no conception of how the formulas work. So, can someone please explain to me about Beta, Positron, Electron capture, and Alpha decay. I understand that it has to do with losing/gaining protons, neutrons, and electons, but I don't get how to write it in a formula.

Offline fledarmus

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Re: Radioactive Decay - Please explain
« Reply #1 on: December 07, 2012, 01:46:54 PM »
We can talk you through it, but you have to do all the work!

Let's pick a random isotope, say 53I128, since it can decay by most of those processes. a) What does the formula for the isotope mean? b) What does that tell you about the makeup of the nucleus of the atom? c) How many protons and neutrons are present?

1) Now, which decay would you like to start with? Pick one

2) Describe the process that is carried out to emit that particle. a) How would that affect the structure of the nucleus? b) What is the new number of protons and neutrons? c) What is the formula for the new isotope that is created?

3) Write all of the above into a chemical formula

Offline Borek

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Re: Radioactive Decay - Please explain
« Reply #2 on: December 07, 2012, 02:10:06 PM »
Note:

[tеx]^{128}_{\phantom{0}53}I[/tеx]

will be rendered as

[tex]^{128}_{\phantom{0}53}I[/tex]

(\phantom{0} is needed to nicely align the numbers).
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Azureilai

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Re: Radioactive Decay - Please explain
« Reply #3 on: December 07, 2012, 02:18:22 PM »
Ok, I will go with Alpha Decay.
I know it has 53 protons (since it the atomic number) 53 electrons and 128 as mass.

 I know that in Alpha decay, there is the 2He4+ that is emitted, but I don't know how to write the equation.

(the 4+ represent mass. Im not sure how to render it to the front)

Offline fledarmus

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Re: Radioactive Decay - Please explain
« Reply #4 on: December 07, 2012, 02:29:07 PM »
Wow, that's really cool Borek! Not sure I'll be able to duplicate it though...

Okay Azureilai, your alpha particle isn't quite right. The charge should be 2+, as in [tex]^{4}_{2}He^{2+}[/tex]

Can you explain why? How many protons, electrons, and neutrons does it have?

Now if you take your original atom and remove that many protons, neutrons, and electrons, what do you have left?

Offline Azureilai

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Re: Radioactive Decay - Please explain
« Reply #5 on: December 09, 2012, 01:46:13 PM »
The helium atom has 4 for mass, so 2 protons and 2 neutrons, but im not sure whether it has four electrons or nonre.

Offline fledarmus

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Re: Radioactive Decay - Please explain
« Reply #6 on: December 09, 2012, 09:03:59 PM »
It will have no electrons, because it is being kicked out of a nucleus which has no electrons. The only way you get electrons inside the nucleus is if you have electron emission or electron capture. (And the choices would be 2 electrons or none, not 4 electrons).

But anyway, so you have your iodine nucleus which has 53 protons and a mass of 128 (how many neutrons is that?) and you remove 2 protons and 2 neutrons as an alpha particle. What do you have left?


Offline Azureilai

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Re: Radioactive Decay - Please explain
« Reply #7 on: December 09, 2012, 09:23:32 PM »
It has 75 neutrons, and after I remove 2 protons an neutrons, it has 124 as mass and 52 protons and 73 neutrons, and no electrons. Is that right?

Offline fledarmus

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Re: Radioactive Decay - Please explain
« Reply #8 on: December 09, 2012, 09:32:10 PM »
You started with 53 protons and took away 2 - that isn't 52...

Offline Azureilai

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Re: Radioactive Decay - Please explain
« Reply #9 on: December 09, 2012, 11:12:49 PM »
ah, sorry, meant 51

Offline fledarmus

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Re: Radioactive Decay - Please explain
« Reply #10 on: December 10, 2012, 07:30:26 AM »
 :D  Almost there - what isotope do you end up with? You already know the number of protons and the atomic mass...

And with that information you can write the reaction formula you are looking for.

Offline Azureilai

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Re: Radioactive Decay - Please explain
« Reply #11 on: December 10, 2012, 08:27:24 AM »
So its Antimony with no electrons and 73 neutrons.

Offline fledarmus

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Re: Radioactive Decay - Please explain
« Reply #12 on: December 10, 2012, 08:57:28 AM »
No electrons in the nucleus, anyway  ;)

So how do you write the reaction? Starting material on the left, products on the right...

Offline Azureilai

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Re: Radioactive Decay - Please explain
« Reply #13 on: December 10, 2012, 06:58:53 PM »
So basically the original parent nucleus Iodine on the left, then arrow to the right, and an helium plus Antimony atom. Protons forboth of them will be put at the bottom left,mass will be at the top, so,
Iodine -- > Antimony+Helium (Except it will be written short handed with all the numbers in the right place.)

Offline fledarmus

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Re: Radioactive Decay - Please explain
« Reply #14 on: December 11, 2012, 10:03:45 PM »
Exactly! Now do the same thing with the other forms of nuclear reaction you asked about, starting with the same iodine parent nucleus

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