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 Some handy equations 
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Joined: Fri Jan 31, 2014 5:28 pm
Posts: 42
I discovered a cool website that lets you type in equations and it takes car of looking up data and unit conversions. I'm sure it does much much more, but I don't have the need to pay for the Pro subscription. I am not a mathematician or expert in nuclear engineering, so feel free to let me know if I've made any mistakes.

An example of half-life:

100(.5^(300 years/cesium-137 half life) ... lf+life%29

The 100 can be any number in Bq or grams or other units. Time can be entered in years, days or seconds, and any other isotopes can be used.

In the example above, no matter what number is entered, only about 1% cesium-137 remains after 300 year. In other words, if man stopped making Cs-137 today all but 1% will be gone in 300 years. That's good, but 1% of a really big number is still a really big number.

Another example of half-life:

120 Curies .5^(100 days/Iodine-131 half life) ... lf+life%29

To convert form amount of radiation to grams:

100 TBq/cesium-137 specific activity ... c+activity

The radiation amount can be entered as Becquerels or Cures and again any isotope can be entered and the software will look up its specific activity.

To convert from grams to amount of radiation:

(100 grams)(cesium-137 specific activity) ... ctivity%29

Finally, I made an equations to show how much Cs-137 from nuclear weapons test fallout is decaying in upper layers of the North Pacific ocean every day.:

(Please don't take these numbers too seriously, since estimates very widely as to the actual amount of radiation.)

69 PBq - 69 PBq(.5^(1 day/cesium-137 half life)) ... life%29%29

My result came out to 4.356 TBq per day, which wasn't that far off from the article I read that got me interested in trying to figure this out in the first place.

Sat Jul 26, 2014 9:10 pm
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Joined: Mon Jan 28, 2013 7:40 pm
Posts: 2885
Location: Illinois
Thank you. 8-)

South Beloit, Illinois - GMC200 Outside on HEPA air purifier, ground level, facing West.

Sat Jul 26, 2014 10:36 pm
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Joined: Fri Jul 11, 2014 10:36 am
Posts: 34
Fantastic reference, ammdb. Thanks for sharing. It's wonderful to know where to go to get straight answers to queries, and it starts with the contributors to the NETC website here who regurgitate all kinds of good info.

I'm trying to understand the actual gamma radiation doses we are being subjected to here in Portland, ME according to the EPA's readouts, which incidentally are some of the highest in the country. Maybe you can make sense of it? What does a constant reading of 350-400 cpm in the 600-800 Kev range (in a sixty mile circle between Portland and Bangor) mean healthwise for us and our kids? Should we be alarmed? Nobody in the mainstream media seems to be concerned about it. I don't believe they are even aware of it, or if they are then I need to know if they're part of a cover-up.

It all revolves around the secrecy surrounding this decommissioned NPP just north of us. Purportedly there is an ongoing maintenance program the details of which we aren't privy to that involve periodic releases of gases from these 60+ huge containment vessels. The company that owns it has filed for compensation to the tune of 9 million dollars a year for storage and maintenance of spent fuel going back to 1997 (it has been acknowledged in court it's the federal government's responsibility to dispose of it). As far as I know there are no full-time personnel on site. The two don't correlate. Sounds like a form of extortion to me, and if it is, that makes us the patsies.

Sun Jul 27, 2014 10:28 am

Joined: Fri Jan 31, 2014 5:28 pm
Posts: 42
Hi Grayling Skies,

The CPM question has come up before further down in this nuclear chat section. There's links to some good video's there.

I was also concerned about an EPA site in Billings MT, close to where I grew up, that was reporting averages around 500 cpm. This is what I posted after reading the EPA site and asking some questions.

ammdb wrote:

... People see cpm as a unit of measure like inches, and freak out when seeing cpm readings in the hundreds compared to an average off the shelf radiation detector that has background readings in the single or double digits. Please correct me if I'm wrong, but as I understand it, cpm is a relative number with many variables that affect it, and without knowing how the unit is calibrated, material being measured, and distance to the source, it doesn't give any information about the actual dose rate.

From what I've read about the EPA radiation monitoring sites, they pump air through a filter which traps isotopes in close proximity to the detector. Do to the inverse square law, it makes sense that these cpm readings are going to be way higher than without the filter. EPA sites are also using some sort of scintillation detector which is more sensitive and can measure all the different energies. Unfortunately, most people looking at the map and see average cpm readings in the hundreds near where they live, think that everyone is getting blasted with radiation, and don't know that they clicked on an EPA site showing normal background levels.

As for your concern about the spent fuel at the closed NPP in Maine, I would think that the dry cast are sealed, so as long as they're built correctly and taken care of, they shouldn't leak any radiation. I am by no means an expert and would be interested if others know more about this.

Having citizen radiation monitoring sites like netc is a great way of keeping the folks that are supposed to be maintaining NPP and spent fuel honest.

Mon Jul 28, 2014 7:57 pm
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Joined: Fri Jul 11, 2014 10:36 am
Posts: 34
Yes, guilty as charged - I'm one of those people freaking out. One day the readings here show level one, the next day they're at Defcon 5 or whatever. Both readings are still way above what's been considered normal for most other areas. Yes it's background radiation or else somebody in the National Guard dropped a depleted uranium mortar round on the firing range. It doesn't make sense, and the more I read about the different types of radiation the more confusing it gets. Freaking out isn't a good way to start a serious conversation with a newspaper reporter or a politician if you hope to elicit any empathy.

I like that scientific equation search engine you found. I like it a lot. I hope it's not too far above my own cognitive abilities because there are pieces of equations I want to run thru it to see what will come out the other end. Hopefully something that can help make sense of these Geiger counter and EPA readings.

I picked up a pretty good graduate studies book called Introduction to Radiation Protection - Practical Knowledge for Handling Radioactive Sources, Claus Grupen (2010) plus a couple of other related works, and also found dozens of free open college undergraduate courses in MIT's Nuclear Physics dept. archives. I'll start posting some of the good stuff here tomorrow.

Mon Jul 28, 2014 11:16 pm
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