标签: radioactive

The increased interest in long-life embedded applications such as remote data logging or utility meters brings up the eternal engineering question: how are we going to power these devices? These devices should operate on a small battery for 10, 20, or more years without any attention, often under difficult environmental conditions.   For shorter-life installations on the order of a few years, the battery decision analysis begins with some basic analysis of the current drain on the battery under various duty cycles and operational modes compared to the energy capacity of the battery (mA-hour). This can get fairly involved for applications with complicated operational cycles, but it's not too hard to at least put an upper-bound, worst-case number on requirements. However, when you need to run for a decade or more, the basic electrical analysis of load current and power versus capacity is only a small factor. Issues such as self-discharge, chemical deterioration and enclosure corrosion become major concerns.   Which is why I was intrigued when I read “Designing and Fabricating a Multiple-Decade Battery in Aerospace Defense Technology. The article detailed a thermoelectric generator (TEG) based on radioactive decay that could run for 150 years, in theory. The architecture used a two-step process which I had not read about before, where the decay generates light, and then that light generates power via photovoltaic cells. The authors allude to the low efficiency, but unfortunately give no numbers, although I suspect it is in the 5% range.   Behind this deceptively simple symbol is a complex world of electrochemical and even radioactive activity.   TEGs powered by radioactive decay have been used successfully for decades, especially for deep-space vehicles where solar radiation is minimal. These TEGs use a single-stage conversion process based on heat of radioactive decay rather than the photons of the two-step process, with Seebeck-junction thermocouples to generate the electrical power from the decay's heat.   This approach powers the Voyager 1 and 2 craft launched in 1977, which are still traveling and sending back data even as they have crossed the vague border of our solar system into exospace. (For a fascinating book on these spacecraft, see "Voyager: seeking newer worlds in the third great age of discovery" by Stephen J. Pyne; and note that their extraordinary journey was made conceivable by the space-mechanics insight of a graduate student working on his own.) There's some also work being done to use thermocouples to capture waste heat from engines, but how practical they will be (cost, reliability, size, efficiency) is still unclear.   Of course, you can theoretically make a decay-based battery last as long as needed by using more of the core material. The question is how long the rest of the assembly and electronics will last under the application's operating conditions before it deteriorates and falls apart, unrelated to the radioactive-decay mechanism itself. But, hey, if the battery doesn’t meet last 100+ years, no one from today will around from today to criticize the work?   I also saw two other articles on long-life batteries, albeit on "only" a few decades. “Choosing the Right Batteries for High-Tech Batteries" from NASA Tech Briefs looked at the attributes of various chemistries, and especially the many interesting sub-varieties of the lithium-battery family. In a word: it’s complicated. When you need a few decades of use, even at very low current levels or low-rate pulsed duty cycles, there are many factors which come into the analysis such as self-discharge and temperature ratings. The mA-Hr capacity becomes only one of many parameters to consider.   While the author of this article is from a leading vendor of such batteries (Tadiran) and perhaps has some bias, I'd rather hear from someone who has real units out in the field and a track record, and who has dealt with subtle manufacturing and production issues, rather than just an academic expert. The same vendor also had a piece "Power Your Wireless Sensors for 40 Years" which had some overlap with the previous piece, but added new information as well.   Are you involved in decisions for long-life battery selection? How do you assess basic capacity needed with complex operational cycles? How do you decide on the long-life chemistry and form factor that will work?

The increased interest in long-life embedded applications such as remote data logging or utility meters brings up the eternal engineering question: how are we going to power these devices? These devices should operate on a small battery for 10, 20, or more years without any attention, often under difficult environmental conditions.   For shorter-life installations on the order of a few years, the battery decision analysis begins with some basic analysis of the current drain on the battery under various duty cycles and operational modes compared to the energy capacity of the battery (mA-hour). This can get fairly involved for applications with complicated operational cycles, but it's not too hard to at least put an upper-bound, worst-case number on requirements. However, when you need to run for a decade or more, the basic electrical analysis of load current and power versus capacity is only a small factor. Issues such as self-discharge, chemical deterioration and enclosure corrosion become major concerns.   Which is why I was intrigued when I read “Designing and Fabricating a Multiple-Decade Battery in Aerospace Defense Technology. The article detailed a thermoelectric generator (TEG) based on radioactive decay that could run for 150 years, in theory. The architecture used a two-step process which I had not read about before, where the decay generates light, and then that light generates power via photovoltaic cells. The authors allude to the low efficiency, but unfortunately give no numbers, although I suspect it is in the 5% range.   Behind this deceptively simple symbol is a complex world of electrochemical and even radioactive activity.   TEGs powered by radioactive decay have been used successfully for decades, especially for deep-space vehicles where solar radiation is minimal. These TEGs use a single-stage conversion process based on heat of radioactive decay rather than the photons of the two-step process, with Seebeck-junction thermocouples to generate the electrical power from the decay's heat.   This approach powers the Voyager 1 and 2 craft launched in 1977, which are still traveling and sending back data even as they have crossed the vague border of our solar system into exospace. (For a fascinating book on these spacecraft, see "Voyager: seeking newer worlds in the third great age of discovery" by Stephen J. Pyne; and note that their extraordinary journey was made conceivable by the space-mechanics insight of a graduate student working on his own.) There's some also work being done to use thermocouples to capture waste heat from engines, but how practical they will be (cost, reliability, size, efficiency) is still unclear.   Of course, you can theoretically make a decay-based battery last as long as needed by using more of the core material. The question is how long the rest of the assembly and electronics will last under the application's operating conditions before it deteriorates and falls apart, unrelated to the radioactive-decay mechanism itself. But, hey, if the battery doesn’t meet last 100+ years, no one from today will around from today to criticize the work?   I also saw two other articles on long-life batteries, albeit on "only" a few decades. “Choosing the Right Batteries for High-Tech Batteries" from NASA Tech Briefs looked at the attributes of various chemistries, and especially the many interesting sub-varieties of the lithium-battery family. In a word: it’s complicated. When you need a few decades of use, even at very low current levels or low-rate pulsed duty cycles, there are many factors which come into the analysis such as self-discharge and temperature ratings. The mA-Hr capacity becomes only one of many parameters to consider.   While the author of this article is from a leading vendor of such batteries (Tadiran) and perhaps has some bias, I'd rather hear from someone who has real units out in the field and a track record, and who has dealt with subtle manufacturing and production issues, rather than just an academic expert. The same vendor also had a piece "Power Your Wireless Sensors for 40 Years" which had some overlap with the previous piece, but added new information as well.   Are you involved in decisions for long-life battery selection? How do you assess basic capacity needed with complex operational cycles? How do you decide on the long-life chemistry and form factor that will work?

Back in the mists of time, I wrote a blog about a Radiation Dose Chart. Following this, I built myself a DIY Geiger Counter ... but my Little Beauty didn't count. I didn't know whether this was simply due to the fact that I didn't have a source of radiation, so I sent it off to my friend David Ashton in Australia. Almost as soon as I'd dropped my Geiger Counter in the post, Nick Bricteux sent two radioactive marbles to me, thereby allowing me to proclaim in all honesty that I am the proud possessor of a pair of Radioactive Balls. Happily, Davis sorted out the problem, and he even wrote a column about it called How to make a Geiger counter count. And as soon as the little rascal was back in my hands (the Geiger counter, not David), I took a video of it clicking away in my office. But that's not what I wanted to talk to you about... A few days ago, a reader emailed me with a link to a can of uranium ore that you can purchase from Amazon.com. Give me strength! They really do sell just about everything these days, don't they? One funny thing about all of this is the section that says "Customers who viewed this item also viewed..." Would you care to make a guess? Well, how about: Canned Unicorn Meat A UFO Detector A 32 ounce container of Wolf Urine Lure A soil sample from Roswell Actually, all joking apart, I think I have sufficient Wolf's Urine on hand to satisfy my current and foreseeable requirements, and the canned unicorn is rather tasty (or so I've been told). But the really funny thing about the can of uranium ore page is the comments, for example: Example #1: Ran out of toothpaste, and remembered how you're supposed to be able to use baking soda to clean your teeth, so of course, I accidentally used this instead, and Wow! all I can say is, my teeth have never been cleaner! They sparkle, they tingle, and for some reason, they STAY clean now, no matter what. Example #2: Is this U-235 or U-238 I need the right isotope for my home-reactor with the correct atomic properties to ensure the flux capacity for power peaking. Example #3: I bought this product for my son's science fair project and now he has created a swarm of ZOMBIES. Please help they cut off our phone lines and locked us in the computer room. Our Address is 1234 Brainless Dr. Example #4: I have been using this product (well, I bought about a hundred of them), and I still have not gotten my super-powers. Is there anyway the manufacturer can send me some info and maybe a timeline as to how long this is supposed to take? I have these bits duct tape all over my body, but all I'm getting is an annoying rash and these weird lumps on my head and testicles. I hope this doesn't mean I'm getting some lame ass unicorn powers, because the one lump is on the side of my head and that would look bloody silly to have a Power Horn there. Not to mention I'll have to do some severe work on my jockey shorts if the horns sprout there. Example #5: Did not work as I expect! I buy for project, we make great reactor! Suddenly reactor turns too hot, big explosion! Now city is destroyed and horror movie is made about place... Worst of all we make Sweden angry! They say we give them radioactive animals! Is lie, we only contaminate little bit of Russia! I put picture of result in customer images. Not happy with this. Since there are approximately 350 such reviews on Amazon, this should keep us all busy for quite some time (I'd love to hear which comment you think is the funniest).  

A few weeks ago, I purchased a Geiger counter kit and constructed it. Brimming with excitement I powered it up and... nothing happened. Some folks said that they had the same kit and it worked; others said that they had the same kit and it didn't work (and they weren't very happy about it). A lot of folks offered suggestions, but by that time I had shipped my kit off to my friend – electronics expert David Ashton – in Australia. David approached the problem with gusto and abandon, and he just reported that he now has my counter counting furiously. The little scamp (the counter, not David) is now winging its way back to me as I pen these words. As an added bonus, David has kindly documented everything that he did – including a video – in the hopes that it will help others with the same kit. It is published in EE Times. As I say, my Geiger counter is now wending its weary way back to me as we speak. Quite apart from anything else, I can't wait to test the little rascal out with my two radioactive marbles. Now, before you bounce over to read David's Article, I can't help myself from showing you a short video he took. David had the same problem I did (before I received my radioactive marbles), which was that he didn't have a radioactive source. So he took my modified Geiger counter over to a Nuclear Medicine practice in a neighboring town (they do radiotherapy and various diagnostic tests using radioactive substances) and they very kindly let David have access to a radioactive source. Finally, as one last interesting aside, one commenter to my original blog mentioned that the "No-salt Salt" that you can buy (which replaces a lot of the Sodium Chloride with Potassium Chloride) is mildly radioactive. David tried this with my now-working Geiger counter as shown below...   And the result was... well, you can read all about this in David's Article (grin)