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This is in computer:storage because that's one of several applications.
Certain radionuclides exhibit positive beta decay. They emit positrons when decaying into another element. One of the most stable of these seems to be potassium forty, with a half-life over an aeon, though others exist with
much shorter half-lives. These can be used as sources of positrons.
Now, suppose you have an evacuated chamber like a cathode ray tube with a lump of potassium forty, or maybe carbon eleven, at one end. Using an electric field, you steer the beam of positrons into a side compartment where it collides with some kind of dense matter, releasing gamma rays as they annihilate the electrons in it. These gamma rays are then used to generate electricity which powers the whole thing. At the other end of the chamber is a further screen with which the positrons collide, producing gamma rays. This is scanned with a second electrical field like a CRT monitor, and the "display" is fed back into the first set of electrical coild. If this field is then switched on and off, it can store digital information like a Williams tube. That's the storage bit.
Also, you have smaller, triode-like devices. These are evacuated chambers with a positron source and two compartments, the beam of positrons being steered in a similar way to the memory tube, with a similar detector at the other end. This is functionally similar to a transistor or valve, and can therefore be used to build logic gates.
Finally, the Williams tube-style device can be adapted for use as a raster-scan display by covering the front with phosphor, placing a mirror in the appropriate position and providing lead shielding to protect the viewer from the gamma rays.
The result of all this is that a digital computer can be built out of positronic devices, as in Asimov. It would be rather radioactive and the devices might fail quite quickly due to the gradual decay of the positron sources and the production of argon thirty-nine, but it would have the advantage of being self-powering. No external source of energy would be needed for it. It would just sit there working until it wore out. Argon thirty-nine is fairly stable and decays by negative beta emission, so that wouldn't mess it up.
Possible applications would be automatic space probes and robots mining other planets and moons.
Of course, this could all be done with ordinary beta emitters, but it wouldn't have the SF cachet of positrons.
I know this is somewhat WICTTISITMWIBNIIWR, but it does actually have an advantage.
Thermionic integrated circuits
http://www.junkbox....ronTubesIndex.shtml
Wonder if this would be doable with positronics [nineteenthly, Jan 28 2010]
[link]
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//These gamma rays are then used to generate electricity which powers the whole thing.// |
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Can you go into more detail about this bit? |
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Yes. The gamma radiation ionises the stuff in the way and the electrons released generate a current. I'm imagining something like the photovoltaic effect. |
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Alternatively, the energy from the gamma rays becomes heat and this is used to produce a current. |
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Nice. I expect a prototype of Data's positronic brain by next Thursday. |
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All i need to do is build a brain sufficiently complex to design a slightly more complex brain than itself which can design a brain slightly more...well, i think you see where i'm going with this. |
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[+] This is clearly destined to be the new steampunk. |
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I wonder what hangups and/or challenges might the digital positronic brain singularity get stuck on? Does it necessarily approach a positive feedback loop? |
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Yes, enormous doses of radiation, and of a kind which is particularly penetrating, but maybe not something to worry about so much if it's in space or on another planet, much though i'd like to see the things in action here on Earth. Even there, maybe the answer is to bury them in a cavern and communicate with wires and radio signals. |
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The thing is, for Asimov it was clearly a throwaway concept that was just supposed to sound good and had nothing essentially to do with the Laws of Robotics or anything the devices were actually supposed to do (though maybe platinum and iridium would be good ways of capturing positrons, i don't know - dense though, aren't they?), but it isn't totally unworkable. Pretty rubbish for miniaturisation purposes because it needs a vacuum to work, but self-powering. The radioactivity also seems quite appropriate for the times when the Robot stories were being written. |
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Yes, but it has a short half-life. It does turn into boron, so it wouldn't reduce the hardness of the vacuum in itself, and boron-eleven is stable. It'd be a more efficient source of positrons but it wouldn't last as long. |
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//for Asimov it was clearly a throwaway concept// |
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I think you've got the wrong SF author in mind, here: should
be Blish, rather than Azimov. The artificial intelligences in
_Cities in Flight_ used vacuum tubes, an anachronism which
"dated" the books, rather spoiling my enjoyment of them.
You've invented an excuse for that! Now, if you could work
on an explanation for the slide rules? |
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// The artificial intelligences in _Cities in Flight_ used vacuum tubes // |
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The "City Fathers" ? Yes, that's correct |
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// wrong SF author in mind, here: should be Blish, rather than Azimov // |
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Eh ? "Positronic Brains" are definitely an Asimov-ism. |
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Oh, and we want royalties on this stuff. |
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//Eh ? "Positronic Brains" are definitely an Asimov-ism.// |
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Yes, I realize that. Sorry I wasn't clearer. "wrong SF author"
was an ill-judged bit of rhetoric. I meant that the mental
contortion required to see vacuum tubes as futuristic is
more applicable to Blish than to Asimov. |
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I understand what you're saying but i'm not sure this is it. They'd probably be quite large because they'd need shielding to prevent interference. I have long been keen on the idea of a higher level of integration within a valve/tube, because it's not completely unfeasible - radio sets sometimes used valve-based integrated circuits pre-war in that they would stick more than one functional valve/tube in the same evacuated "package". |
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However, there is a way of joining the two together, justification-wise. Multivac was a physically vast computer which i think did exist in the positronic robot universe. The trouble with that, though, is that it's described as using relays. |
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From the Encyclopedia Galactica article on "Google" |
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The advent of Digital Positronic technology in the 2nd
decade of the 21st century accelerated the trend away
from miniaturization and towards economies of scale.
Server farms grew to the size of cities, and were intensely
radioactive. For this reason, most were relocated to the
Kuiper belt. |
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Google was an early adopter, and solved the lightspeed-lag
problem with predictive algorithms. The precise fraction
of queries answered before they were submitted was a
closely guarded secret, but generally believed to exceed
50%. No evidence has ever been found to substantiate
rumors that Google served web pages that did not yet
exist. |
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A small industry (the so-called "dataminer 29ers") grew up
on the economic model of intercepting Google's
transmissions, and selling them to hackers who believed
that, if they could crack the encryptation, they could
become rich in the financial markets. |
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Massive hardware infrastructure and advanced software
alone would have allowed Google to dominate the galactic
infosphere, but widespread belief in its near-omniscience
gave it a crushing advantage in any negotiation. Despite
this, Google maintained a more-or-less benign, laisez-faire
policy until, in 2030, the Google board of governors
appointed, as CEO, an AI programmed with the company
motto "Don't be evil, or, through inaction, allow evil to
be." |
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The result was the disastrous 2032 information embargo
against the People's Republic of China, resulting in
widespread famine, several interesting new viruses
(including the notorious HIV-5.2 which could infect humans
via cyber-sex), and the obliteration of the island of
Taiwan. |
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The "grassroots" campaign in favor of the embargo
subsequently proved to be 87% AI sockpuppets directed by
the Government of Tibet in Exile, which itself was a facade
(the real Tibetian government having been gutted and run
as a botnet by the Russian Mafia). |
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Google responded by reprogramming its CEO with the
famous "Prime Directive" prohibiting interference in
planetary affairs. The CEO was also programmed to be a
devout Dao-ist. This worked out well, except for minor
glitches, such as the massive reprintings, every few years,
of _The Lathe of Heaven_ |
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[Mouseposture], that's the kind of writing that makes the Halfbakery such a special place (in a good way). If the servers were left on Earth, it would explain how the planet became radioactive without the later Robots novels' explanation. |
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// valve-based integrated circuits pre-war // |
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// Multivac was a physically vast computer ?? |
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Why the past tense ? Ooops, have we let something slip ... |
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As you can see from my link, the war was apparently Vietnam! |
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Concerning Multivac, i think he's pretty vague about when it was. The robot stories have specific dates but i can't remember if Multivac is mentioned in them. |
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