Dan's Data letters #192
Publication date: 27-Oct-2007.Last modified 06-Dec-2012.
Lead foil makes the chicken sweeter
When microwaving a chicken, one often wraps tinfoil around the ends of the drumsticks to avoid overcooking them, as the foil reflects the microwaves.
If foil reflects microwave radiation, what other types of radiation does it reflect? If I'm sitting next to a ball of plutonium, would wrapping it (or myself) in tinfoil have any effect whatsoever?
Further to the idea of some sort of disaster involving radiation, a friend of mine once said that fat absorbs the least radiation of all foods. His suggestion was that, in the event of a radioactive disaster, one should loot the supermarket for butter or lard (to minimise ingestion of contaminated foods), and multivitamins (to enable digestion of the fats).
Eric
Answer:
Well, plutonium is an
alpha emitter, and a layer
of aluminium foil certainly will block alpha radiation A-OK.
But so will very thin paper, the layer of dead cells on the surface of your skin, or a few centimetres of air.
Plutonium has many alarming characteristics, but its direct radiation is only dangerous to humans if it's inside our bodies - if, for instance, you inhale plutonium dust, or the oxide smoke created when plutonium burns in air (which small flakes of plutonium will do spontaneously!).
The decay products of the various isotopes of plutonium include emitters of different, more alarming, kinds of radiation. If you're starting with the common isotopes, though - plutonium-239 and plutonium-244 - the half-lives are so long (24,100 years and eighty MILLION years, respectively...) that the rate of creation of those more active decay products is quite slow, and there won't be much of them to worry about at any given time unless you start out with a really large amount of plutonium.
Even the super-ferocious 87.7-year-half-life Pu-238, quite small pieces of which will glow brightly with the heat of their decay, can be rendered harmless by pathetically weak shielding - as long as the plutonium doesn't burn through that shielding, burst into flames, and ruin the day of your whole suburb.
(A really large amount of any kind of plutonium in one lump, of course, will immediately do something that will make your concerns about long-term radiation exposure entirely irrelevant. I talk about this some more in this previous column; all plutonium emits some neutron radiation, which if reflected back into a nearly critical lump of plutonium will cause it to go critical.)
Aaaanyway, when you're talking about the kind of radiation that may harm an earthling, you're talking about alpha, beta, high-energy electromagnetic, and just possibly also neutron radiation - which only the uncommon Pu-240 isotope emits in significant quantities.
Alpha is helium nuclei that can be stopped by just about anything, and beta (electrons) will be significantly impeded by quite thin shielding, including light metals like aluminium. So if you have to share a room with a strong beta source, then wrapping it in as many layers of aluminium foil as you can get your hands on may well help.
(Because of this easy shielding, sources that emit beta radiation alone only show up in the radiation-disaster leaderboard when something like a miscalibrated radiotherapy device exposes large numbers of patients to excessive radiation. The "orphan" sources that leave a trail of horrible deaths in their wake when ignorant people find them in a junkyard or something are always strong gamma emitters.)
Neutron radiation - which may come your way in significant amounts if you're near something in which nuclear fission is happening - is best blocked by something containing a lot of light nuclei, ideally hydrogen. Water, concrete (which has lots of chemically bound water in it), plastics; aluminium would be better than nothing, but aluminium foil probably wouldn't do anything significant.
And then there's high-energy electromagnetic radiation, X-rays and gamma rays. You want heavy nuclei to block them - lead sheet will work beautifully, iron may be some use, aluminium will do next to nothing. Light metals show up only faintly on an X-ray - actually, aluminium is one of the materials used to make lenses for focussing high-energy X-rays.
Regarding your friend's theory about avoiding radiation poisoning by eating lard and vitamins, I think it only makes any sense if we assume that the farms that make the food are all still happily chugging away in the middle of the fallout zone.
I think this is unlikely to actually be the case.
Canned food that was manufactured before the disaster will be uncontaminated. I, for one, would buy that before I started chowing down on lard.
Battery vs starter motor... to the death!
I have a Bosch 12V heavy duty sealed lead acid automotive battery in my car that's been giving me a bit of grief.
It's been drained flat (and I mean COMPLETELY flat) accidentally on a couple of occasions, and now when I go to start my car the starter motor usually needs a couple of turns of the key to get it to kick over and it does that nasty "groan" that I'm sure you've heard when your battery hasn't got a full charge. I'm at the point where I'm going to replace it as I'm just not confident that the car's always going to start.
Being the cheeky sod that I am, I took the battery in to Supercheap (where I bought it), as the battery has a 24 month warranty (its only about nine months old). They tested the battery and the alternator with a tester they have, and concluded that there's nothing wrong with the battery or my alternator, and thus the problem must be elsewhere - in any case, they said they can't replace the battery unless it fails their test.
I'm a little at a loss as what to do about this. Surely you can get a replacement of a product that is faulty in this country without having to jump through onerous hoops to do it? The battery MAY give enough charge to start the car right now, but its capacity is useless and I'm certain its overall power is severely degraded.
I don't want to end up sitting in the middle of nowhere trying to start a car with a dead battery at 3 AM. (I do a fair bit of driving outside the city at odd hours, so its entirely probable I would end up in this situation).
Is there anything that I can do, or should I just pony up with another $200 and buy a new one?
Trevor
Answer:
Do you really mean Sealed Lead-Acid, there? That usually means a
gel-electrolyte battery, not
the liquid-electrolyte standard automotive type.
There are "maintenance-free" automotive batteries, but they're still not really sealed - if they were, they'd pop when you charged them. Instead, they're just batteries that you can't (easily) top up, even though their semi-sealed cell caps still let vapour escape.
Running a car battery completely flat even briefly is, as you suspect, usually bad news. Automotive batteries are not made for deep discharge. Even leaving them in a low charge state for a while can greatly reduce their life.
On the plus side, "desulfator" gadgets actually, apparently, really can work, especially on liquid-electrolyte batteries that don't have trouble with crud building up next to the plates and being stuck there with no way to escape, which is what happens when the electrolyte is a gel.
You can get small desulfators that just connect across the battery terminals, so you can hook one up to your car battery in situ and have it work while you drive around.
I've actually got one of those, but haven't yet had a liquid-electrolyte battery that needs it (I tried it on a dead SLA - it didn't do a thing). I don't want to leave it hooked up across anything all the time, if only because it causes a lot of radio interference.
It's possible that your fancy brand-name battery really does still have adequate performance remaining.
If you did a lot of cranking when your battery was weak, you could have damaged the starter motor - they, like car batteries, are made to deliver a lot of power for a short period of time. A starter that's been cranking away for some time may suffer heat damage, even if it's not getting a lot of volts. Then, when you've got a full charge in the battery again, the damaged starter can draw a lot more current than normal, accelerating its own demise and injuring the battery further. I think this is a fairly common "death spiral" situation; any auto electrician should be able to diagnose it.
(It's also possible, of course, that the guys at the store just had their battery-tester set to the "motorcycle" setting.)
Another job for paper clips
In the recent LED torch article you linked to a CR123A charger at Quality China Goods.
The charger has a choice of two round pins or two flat pins. Do either of those work in an Australian power point? Or do you have to get the two flat pins and bend them? Or do you have to get some kind of adaptor? Any recommendations for that?
I notice on eBay, one or two of the similar chargers have adaptors included.
Also what is the difference between 3.0v/3.6v/3.7v CR123s? What would be better for the Ultrafire WF-501B?
David
Answer:
It's often possible to crank US-type two-flat-pins plugs into rough compatibility with
Australian sockets by the application of brute force,
ignorance
and a pair of pliers, but I don't recommend it.
Yes, it's better to use one of the universal adapters, which often have three holes of complicated shape on the front, and two standard Australian pins on the back.
(You can see the socket type in the second picture on this page.)
The three-to-two-pin adapter type is not a great idea for use with an earthed device; the earth wire will now be connected to nothing.
QCG have a simple two-pin version of the adapter, which should work fine with any un-earthed small device or power cord.
I wouldn't use any of these adapters to power something that draws a lot of current, because the terminals inside are necessarily not very well fitted to just about any shape of pin you plug into them. It's also easier for plugs to slide out of them partially, leaving live metal exposed between the plug and the adapter. And, of course, they do not convert voltage; you should only use a simple plug adapter, or the in-extremis bend-with-pliers trick, on devices that're able to accept 220-240V AC.
In the olden days, practically everything had a simple linear power supply and had to be made in a different version for 110-120V countries and 220-240V ones. Lots of cheap gadgets have "world compatible" switching PSUs these days, though.
On the subject of lithium battery voltage: As you've noticed, there's some confusion about the actual voltage of different flavours of lithium battery, because (like every other kind of battery) their voltage when brand new (or freshly charged) is higher than their nominal voltage.
Ordinary non-rechargeable lithium cells (of the lithium/manganese oxide type) are nominal-three-volt devices, but you can expect a brand new one to be 3.7 volts. Rechargeable lithium cells are nominally 3.6 volts, but when fully charged will be about 4.1 volts.
One-upmanship among battery purveyors results in umpteen permutations of these numbers.
For the Ultrafire WF-501B I reviewed, you want a couple of rechargeable 123s for peak brightness (and so that you can use the same batteries in other devices, like cameras), or a single 18650 cell for maximum battery life.
Slightly insulated for your protection
For your entertainment: The world's dodgiest transformer:
Matt
Answer:
This version
of the same thing was linked all over the place a little while ago.
A basic arc welder is very electrically simple - in extremis, you can arc-weld with just two or three car batteries in series - so it's not surprising that people in developing countries are winding their own.
The only part I don't get is the high selling price. The Afrigadget piece says the welders sell for about 14,000 Kenyan shillings, which is more than $US200 as I write this - not much lower than the price of a basic Chinese stick welder with similar specs here in the high-cost-of-living West.
You'd think that in nations where a bottle of rum costs a buck someone'd find a way to sell much safer Chinese welders for less than the price of these ingenious, but hideous, bodge jobs.
(If you'd like to feast your eyes on a lot of other welders made to a recipe that usually starts "dismantle three microwave ovens...", there are plenty of them on homemadetools.net!)
And now: Cockmongers.
You do the work and others earn the money?
These eBay listings (screenshot here) are a pretty shameless use of your article.
I would sue them.
Eugen
(whose reply address bounced; with any luck he's reading this page)
Answer:
Unfortunately, eBay don't make it very easy to complain about this sort of thing. It is literally
impossible to send them an e-mail about it through their "Contact Us" system.
The system forces you to categorise your complaint message, and there is no category for listings that rip off someone's off-eBay work, as these ones do. They are, as you say, a straight copy of my review of the R-Driver II, including the pictures, which they are unfortunately not hotlinking.
If a listing is a copy of your listing, there's an eBay complaint category for it. But if it's a copy of something else you wrote, there's no obvious way to complain,
After I put this page up, a reader suggested I try sending eBay a DMCA takedown notice. I wasn't very optimistic about this working, since I'm in Australia and the offenders are presumably in Hong Kong, but what the heck; I sent the notice via e-mail to eBay's Registered Agent.
After a while, eBay sent me a PDF application for their Verified Rights Owner (VeRO) Program, which I had to fax back to them with my details filled in.
So I did that, and lo and behold, they took down the listings. In future, I can apparently tell them about infringing pages by e-mail.
(UPDATE: I've done that a few times, now.)
This is quite a pleasing result, if of course it keeps working as it has so far. Before all of this, I'd tried contacting the seller multiple times; they kept saying they'd change the listings immediately, but didn't do a damn thing.
So the sellers still suck.
(Originally they were calling themselves "states.electronics", store-name "wm-electronic". Now they're calling themselves "au.electronics", store name "australia.electronics" {on US eBay here}; "states.electronics" seems to be back, too, with the store name "dragonext-store".)
But it would appear that if you're willing to go to the effort of faxing in one form, eBay actually do provide a way to get listings that rip off your work taken down.
The punishment is just the taking down of the listings, and the complaint process isn't dead easy, so ripping off other people's non-eBay work for your eBay listings would still appear to be a pretty safe scam.
But then again, eBay shouldn't take down a listing just based on one e-mail that alleges the listing is a copy of someone else's work - if they did, you could just copy a listing to your Google Pages site or whatever and make a nuisance of yourself.
