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So who knows a thing or two about Strontium-90 and its decay?

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So who knows a thing or two about Strontium-90 and its decay?

Old 05-01-09, 08:17 AM
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So who knows a thing or two about Strontium-90 and its decay?

I sure don't, and that's why I'm posing this question for my wife's cousin. Here's the information:
For a paper, I'm trying to calculate the amount of heat generated by Strontium-90 as it decays.

Here's what I know:
Strontium-90 has a specific activity of 140 Ci/g
a Ci is 3.7e10 decays per second
Each decay has an energy of 0.20 MeV
There are 1.518e-16 BTU per MeV

from this I can calculate the heat produced per second per gram of Strontium-90

The tricky part comes in because Strontium-90 decays into Yttrium-90 which is also radioactive and has a specific activity of 555,000 Ci/s and each decay has an energy of 0.94 MeV

I don't know how to work the Yttrium into the mix. Do I just do the same calculation and add them together? Or how do I figure out how much yttrium is produced? Oh, and all radioactive decays are beta emissions in case that matters.
If you can answer her question, I'm sure she will be eternally grateful, and you can have the warm, fuzzy feeling of helping a fellow human being.
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Old 05-01-09, 08:22 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Interesting.
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Old 05-01-09, 08:30 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Do you realize this is a DVD forum?

Originally Posted by DavePack View Post
a Ci is 3.7e10 decays per second
And duh. Talk about stating the obvious.


Last edited by cpgator; 05-01-09 at 08:32 AM.
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Old 05-01-09, 08:32 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by cpgator View Post
Do you realize this is a DVD forum?
Sure I do. But I've been around this particular forum long enough to know there's a lot of folks out there with a wide range of knowledge. Just thought I'd throw it out there and see if it gets a bite. If not, well, at least I tried, and no harm done.
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Old 05-01-09, 08:46 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

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Old 05-01-09, 08:58 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

I guess you calculate separately and add.

http://dic.academic.ru/dic.nsf/enwiki/2839780

Strontium-90 (90Sr) is a radioactive isotope of strontium, with a half life of 28.8 years. 90Sr undergoes beta decay with decay energy of 0.546 MeV to the yttrium isotope 90Y, which in turn undergoes beta decay with half life of 64 hours and decay energy 2.28 MeV for beta particles to 90Zr (zirconium), which is stable.
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Old 05-01-09, 09:04 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by DavePack View Post
If you can answer her question, I'm sure she will be eternally grateful, and you can have the warm, fuzzy feeling of helping a fellow human being.
I'd rather have the warm, fuzzy feeling of ... oh, god dammit, you're making it too easy.
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Old 05-01-09, 09:14 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by kuroiinu View Post
I guess you calculate separately and add.

http://dic.academic.ru/dic.nsf/enwiki/2839780
If this doesn't satisfy you, I can ask some of the physicists here at work.

I guess the part I am not sure about is, does the stuff stay 90SR until it completely switches to 90Y, or is the a function where part of the material is SR, and the remainder is Y?
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Old 05-01-09, 09:23 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by jonw9 View Post
I guess the part I am not sure about is, does the stuff stay 90SR until it completely switches to 90Y, or is the a function where part of the material is SR, and the remainder is Y?
Given the relative half lives of Sr and Y (29 years and 64 hours, respectively), I think you will have both Sr and Y/Zr for a long time.

Last edited by Psi; 05-01-09 at 09:53 AM.
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Old 05-01-09, 10:05 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

There is no surer sign of decay in Strontium-90 than to see the rites of religion held in contempt.
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Old 05-01-09, 10:21 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

What I have received thus far:

Well, technically it's going to be a differential equation. You start with no YT, probably, and it will be produced at the rate stated, generating heat at that rate as it's created, and the YT is going to decay as well at it's own rate and the heat from that is going to be related to the amount of YT created. I could work it out pretty easily on paper, but typing it out gets a little complicated. You'll basically have an exponentially decaying rate of heat generated from the ST, then a more complicated function for the heat from the YT, which would grow until the decay rate of the ST fell to the decay rate of the YT, at which point it would also start to drop, eventually both going to zero at infinite time. You either need more information or you need to pick an amount of YT and ST if you just want to get one value.

Also, I hope that they meant specific activity of 550,000 Ci/g, not Ci/s.
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Old 05-01-09, 10:24 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

I'm concerned your energy numbers don't match to the various Wiki articles. I think 0.546 Mev and 2.28 Mev are the right numbers.

You can formally solve two differential equations, but the half-life of 64 hours is WAY less than 28.8 years. Within a few of the 64 hour lifetimes, a relatively small percentage of yttrium builds up, and while small, it is decaying much faster. You reach an equilibrium where it is decaying at the same rate as it is forming from the slower strontium decay. The total radiation from the gram of strontium will stabilize at twice the 140 Ci, half with the energy 0.546 Mev and half with 2.28 Mev.

Alternately, it can be viewed as 140 Ci, with total energy 2.826 Mev. Note that interesting result that more of the energy comes from yttrium decay. The strontium acts as a slow yttrium generator.
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Old 05-01-09, 10:36 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

BTW, does everybody who posted in this thread get listed as a co-author?
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Old 05-01-09, 10:47 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by Brian Shannon View Post


First thing I thought of when I saw the title.
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Old 05-01-09, 10:47 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Do you get super powers if you calculate wrong?
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Old 05-01-09, 10:55 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by jonw9 View Post
BTW, does everybody who posted in this thread get listed as a co-author?
I hope so. There's a lot of smart people I'd like to associate myself with here.
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Old 05-01-09, 11:38 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

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Old 05-01-09, 11:51 AM
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Re: So who knows a thing or two about Strontium-90 and its decay?

In for the co-author.
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Old 05-01-09, 12:06 PM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by antennaball View Post
In for the co-author.
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Old 05-01-09, 12:22 PM
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Re: So who knows a thing or two about Strontium-90 and its decay?

I always keep my Strontium-90 in the fridge.
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Old 05-01-09, 01:20 PM
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Re: So who knows a thing or two about Strontium-90 and its decay?

suprised it hasn't been asked, pics of your wife and if you wife's cousin is a female then those must be submitted to.
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Old 05-01-09, 01:39 PM
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Re: So who knows a thing or two about Strontium-90 and its decay?

It was hot day, really hot day for Northern California and I went to the fridge to get a cold diet coke, but I wasn't really looking, I took the first sip and wtf???? It was strontium-90!!!

So yeah, I learned my lesson.
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Old 05-01-09, 01:44 PM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Originally Posted by OldDude View Post
I'm concerned your energy numbers don't match to the various Wiki articles. I think 0.546 Mev and 2.28 Mev are the right numbers.

You can formally solve two differential equations, but the half-life of 64 hours is WAY less than 28.8 years. Within a few of the 64 hour lifetimes, a relatively small percentage of yttrium builds up, and while small, it is decaying much faster. You reach an equilibrium where it is decaying at the same rate as it is forming from the slower strontium decay. The total radiation from the gram of strontium will stabilize at twice the 140 Ci, half with the energy 0.546 Mev and half with 2.28 Mev.

Alternately, it can be viewed as 140 Ci, with total energy 2.826 Mev. Note that interesting result that more of the energy comes from yttrium decay. The strontium acts as a slow yttrium generator.

Damn, I was just about to post that.


I know that adamantium can cut right through it.
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Old 05-01-09, 01:52 PM
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Re: So who knows a thing or two about Strontium-90 and its decay?

Info and laughs -- no wonder I love reading (well, usually lurking) this forum so much.

Thanks everyone, I'll be sure to pass the info along.
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Old 05-01-09, 02:06 PM
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Re: So who knows a thing or two about Strontium-90 and its decay?

As the resident otter Ph.D. physicist here's my 2 cents - Sr90 is in secular equilibrium with it's daughter, Y 90. And your decay energy isn't correct. The Sr90 beta is 0.540 MeV and the Y90 beta is 2.27 MeV. I would assume that you are starting with a Sr-90 mix that is already in equilibrium for your formalism.

The formula for secular equilibrium if you want to see what the activity of the daughter is :

Ad(t) = Ap(0)(1-e^(-lambda(d)*t))

where lambda = .693/T(1/2)

..... otherwise you might need to start from scratch with the Bateman Equations...
http://www.neutron.kth.se/courses/tr...n/Bateman.html

Last edited by suziq999; 05-01-09 at 02:11 PM.
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