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a reply to: Phantom423

originally posted by: Hyperboles
that accident did not start a chain or nuclear reaction. pendulum? where does it fit in here.
a reply to: Arbitrageur

Yes, it did start a chain reaction. The chain reaction released so much radiation that the man stacking the blocks died 28 days later. All of the incidents described in that pdf are related to chain reaction accidents, why do you think they titled the paper "A review of criticality accidents"?

Criticality accident

A criticality accident is an uncontrolled nuclear fission chain reaction. It is sometimes referred to as a critical excursion

By the way, Chernobyl was a bigger accident where the nuclear chain reaction went supercritical, and again there was no impact loading to initiate that. Operators retracted too many control rods, and lost control of the chain reaction.

You made a demonstrably false statement about impact requirements for criticality, just as you made demonstrably false statements about using pendulums as timekeeping devices in varying gravitational fields, and other false statements too numerous to mention, which indicate a pattern of your misconceptions in the field of science. There's nothing wrong with having misconceptions, as long as they are corrected by evidence, but it's that last part which creates the most concern, failing to correct your misconceptions even when you are provided with contrary evidence.

that report is in error, there couldn't have been a chain reaction, they are lying, for what reason I do not know.
why use a detonator then in the weapons. super critical or otherwise if you get a chain reaction from some lousy bricks.
pendulum and others: all physical processes pertaining to time keeping/ flow have to tally with one another. there can be no contradiction. I hope understanding of all above comes to you, if you get your head out of the sand
a reply to: Arbitrageur

a reply to: Hyperboles
Wow... just wow... Hyperboles you absolutely have no clue it seems, its not even amusing to play this game anymore. You have no idea how any of GR works, no idea about atomic physics or nuclear physics and are calling people liars who have done more experimentation than you have ever hoped to even dream to do.

You constantly just want reality to shape around what you think it to be... its kind of troubling and a little bit sad to be honest.

If you said the sky was Green, and that anyone who says its Blue or Red depending on time of day are liars id not be too shocked anymore.

By what you just said, nuclear reactors don't work at all... they must be in a constant state of nearly exploding at any one time because that is the only way you get energy or radiation out of Uranium.

Wow,, just wow, you do have a problem with the English language, don't you? Brilliant conclusions, keep it up.
a reply to: ErosA433

a reply to: Hyperboles
There could be a language issue on your end, or else a complete lack of understanding of how the little Boy design worked, or maybe some of both. Let's look at this language of yours:

why use a detonator then in the weapons.

I have personally worked with high explosives (not nuclear), and in that context, a detonator is a specific type of device, also called a "blasting cap".

I'm not sure what you're calling a "detonator" in this schematic of the major "little boy" components:

en.wikipedia.org...


Are you referring to the Mark XV electric gun primers? The cordite bags? Nothing is labeled a "detonator" so this is a language issue in trying to figure out what you are talking about.

why use a detonator then in the weapons. super critical or otherwise if you get a chain reaction from some lousy bricks.

In the Los Alamos criticality accident mentioned earlier, the reflectors were tungsten-carbide blocks. The "Little Boy" design also employs Tungsten-carbide reflectors, see components labelled F, I and T.

The other thing I'd like you to notice in this illustration is that unlike smashing two protons together in a collider where we want a head-on impact, the design here is quite different where in some sense the mating pieces (subcritical masses) are designed to NOT impact with each other, which makes your language about "impact loading" difficult to comprehend. You can see the sort of "donut-shaped" projectile "S" is a stack of rings forming a hollow cylinder which is designed not to directly impact the other subcritical target mass "H", but to slide all the way around it, thus the objective is to join the subcritical masses together to create a supercritical mass, and not to "impact" or smash the two masses together like we try to do with protons.

So yes there seem to be some possible language issues, and/or maybe conceptual issues as well, but they seem to be on your end, because this design is not showing any "impact loading" of the two subcritical masses which are more designed to miss each other so "S" can slide around "H", rather than smash into it as "impact" suggests. So this design does not show what you say here:

originally posted by: Hyperboles
the amount of impact loading is huge otherwise you will not get the critical mass/density/gravity to start a nuclear process, so time compression has to be huge
a reply to: Arbitrageur

The design shows the critical mass is achieved by joining the two subcritical masses, not by "impact loading".

Here is another point of interest to further clarify it was joining of the subcritical masses which created the supercritical mass needed for the explosion. Additional bombs of this design were made but they were dismantled. One reason as I understand it was a safety concern that the bomb could go off accidentally if the two subcritical masses were joined by accident, let's say by the plane crashing, which possibly could happen even if the cordite powder bags were never ignited.

The replacement bombs presumably had better safety mechanisms to prevent them from going off accidentally, even if the plane carrying them had an accidental crash.

Lol joining? they are pulling your leg
a reply to: Arbitrageur

originally posted by: Hyperboles
that report is in error, there couldn't have been a chain reaction, they are lying, for what reason I do not know.

What does this even mean? Why couldn't there have been a chain reaction. Highly fissile material like 235Uranium, or 239Plutonium once over a certain mass and of certain geometry will be in a state of self-sustaining chain reaction. The Demon Core shown in Arbitrageur's post was a sphere of Plutonium designed to be 5% below the critical mass for a self sustained fission state. Materials in this close to critical mass and genometry typically self heat because the fission process is occurring within it, and the resultant energy absorbed. That is why Plutonium is used in Thermoelectric generators in satellites the material will constantly produce heat that can be used to power systems for a very long time.

The Demon core killed 2 people, both times caused by accidental experimental error.

The first was during neutron reflection experiments in which the core was placed into a tungston carbide castle, each piece of the reflector bringing the core closer to being critical, due to neutrons that would otherwise be lost are then being reflected back at the core. The experimentalist dropped one of the bricks onto the core, which was enough to compress the core and further reflect more neutrons into it causing it to enter a prompt chain reaction until he was able to lift the brick off of it. The result being he received a fatal dose of neutrons and died 25 days later. The other person in the room died 19 years later, receiving a far lower dose.

The second was an experiment to determine how close to critical the mass was, the core being placed in a hemisphere of beryllium (neutron reflector). The idea is to have a second hemisphere lowered over the top of it, and count the activity using scintillator counters. Now, the actual proper procedure was to have shims in place to prevent the two hemispheres from fully closing around the core, which would definitely make it go critical. So the process is, lower the top hemisphere and monitor activity at each position.

The experimentalist in question had taken to performing this test not using shims to maintain separation, but the edge of a screw driver. He had done it on many occasions, and it had been pointed out by many that one mistake would cause his death... non the less he thought he knew better and it wouldn't happen to him... on that day, the screw driver blade slipped and the hemispheres were allowed to close, causing the core to go critical. He described how he saw a flash of blue light in his eyes, and feel heat instantly over his skin, attributed to large burst of neutrons which are readily thermalized in water. To prevent a sustained reaction he was able to flip the top hemisphere off of the core. He however was a dead man walking, getting 5 times the dose the first victim of the core, and died 9 days after the incident. Other people present that day were tracked, all dying many years later, but many of the deaths attributed to radiation related complications and illnesses


So now that it is all spelt out in detail how the experiments and accidents occurred... tell me, how do you get a fatal dose of neutrons out of a piece of material without it going critical or entering a state where a chain reaction briefly occurs?

why use a detonator then in the weapons. super critical or otherwise if you get a chain reaction from some lousy bricks.

Your flippant and arrogant dismissal shows how little you understand nuclear technology and the control of run away conditions. When a mass like this goes critical, it doesn't instantly explode. If you think it does then you are very sadly mistaken. Surrounding a core with shielding would make it energy a super critical state and begin to produce large amounts of radiation and heat. There is a lag time between the initial critical state and the chain reaction entering an explosive state. The heat can cause physical and geometric changes in the material which can do three things... either prevent the core going into a explosive state, dropping it sub critical, melt the core or enter an explosive state. Typically you'd not want to melt the core as that is quite dangerous and tends toward the explosive state.

To get such a system to explode you need to hold the core in a super critical state, well over its critical point and maintain that critical mass. THEN it will explode, the chain reaction rapidly accelerating and producing heat and radiation contained within the device. In that state the energy density becomes so high that an explosion from the rapid expansion and liquefaction and vaporization of the device become inevitable simply from the amount of highly penetrating radiation being produced.

So the point of having a detonation mechanism is for safety.... there is a very good reason while modern high explosives are somewhat 'safe' these days... because too many people died using unstable materials in which mishandling can cause them to go off. Nitrate based blasting material in mines for example, are actually not that explosive in their normal state. Its with the addition of a blasting cap or energy delivery device which makes them explode. Until then, even tossing a cigarette on them doesn't have a huge probability to cause an explosion (id still not recommend it though, just in case) It is such if you are designing a nuclear device, you wouldn't want it so dangerously close to critical in a standby configuration. You would also want the core of it to be able to go critical very rapidly upon triggering. It is such that a typical device works on either gun type combination of the core material to a single super critical mass... or a configuration in which you melt and compress the core using high explosives to produce the criticality.

Clear? So exactly why make a statement demonstrating your ultimate lack of ability to comprehend any nuclear technology as to try and demonstrate you know better than everyone in the world?

pendulum and others: all physical processes pertaining to time keeping/ flow have to tally with one another. there can be no contradiction. I hope understanding of all above comes to you, if you get your head out of the sand
a reply to: Arbitrageur

A Pendulum is a composite mechanical object and its very operation is driven by the acceleration due to gravity... not the bending of space time directly. As we already discussed at exacerbating length... because a pendulum wont swing when placed at a lagrange point, does in no way mean time stops there. To claim that a pendulum clock is = to an atomic clock is to show supreme ignorance.

so you do need impact loading in a bomb don't you?
you need to read up on the pendulum in this thread and btw space is not bent
a reply to: ErosA433

a reply to: Arbitrageur

Maybe this question is somewhere among the many pages of this thread and if it is please show me where...

The question I have is simple... We all have an idea about what will happen when a nuclear bomb is dropped. Besides the destructive blast there will be radiation and nuclear fallout. The last two effects will cause areas to be contaminated in such a way that organisms in that area will suffer genetic mutations and cancer across many generations.

Now why do and can people live in Heroshima and Nagasaki as if nothing has happened.....? Why does everything grow and florish of the fauna and flora in Chernobyl as never before?

Maybe this is not the proper thread to ask this question....but I ask it here anyways.

a reply to: zatara

The difference between Heroshima and Nagasaki vs Chernobyl is simply the amount of nuclear material undergoing the reaction.

In the bombs it is only estimated that about 2lbs of Urianium underwent fission out of a payload of 140lbs for littleboy, and in fat man again, about 14lbs of plutonium for Fatman.

The rest of the payload would indeed have been spread out everywhere as it was vaporized. There would have been some neutron activation of surrounding material but the dust that eventually settled would have been roughly 140lb, leading to a higher background of radiation in the area, but not enormous levels

For Nagasaki, the bomb was detonated in a vally, and such, the destruction was somewhat different.


For Chernobyl on the other hand, a reactor went into melt down and exploded, the lower estimate of the amount of material that was ejected during the explosion which caused the top of the reactor to lift off and land on its side... was close to 15,000 lbs or It could have been higher. This material was also not smoothly spread into dust, but somewhat messily ejected in dust, chunks or slag, along with pieces of highly activated material... This is why the cleanup for Chernobyl is somewhat tricky and in many ways worse than the bombs.

While the bombs did cause a great many instantaneous deaths and obliteration, it was designed for this purpose, fall out mitigation wasn't at all a factor, but id still say conditions are more favourable... Chernobyl on the other hand... i hope you can see it was not the same, while loss of life might appear 'better' the consequences are worse to deal with

a reply to: zatara
a reply to: ErosA433
Good question by zatara and good answer by Eros. Actually I don't remember that question being asked before in this thread and it's a topic which interests me personally, partly because I'm a former radiation worker who handled controlled radioactive sources and had to wear a dosimiter badge at all times when I was at work to monitor my exposure. It's funny, the badges I wore look identical to the one in the James bond movie where they call it a "radiation shield", which is so funny, it doesn't shield you from anything, it just tells you how much you got zapped. It didn't even tell you that right away, you got a new badge every so often and the old one was measured so my employer could prove to regulators that their employees were under the established limits, which for me were the same as for workers working in a nuclear power plant.

To handle certain radioactive materials you need to go through training courses on the effects of radiation, but the course only goes so far and I wanted to know far more so I did additional research. Basically what I found is that a lot is known about high doses of radiation, but there is still uncertainty about the effects of low doses of radiation.

There is a hypothesis called the "The Linear No-Threshold" (LNT) model. There are still debates over whether this model is true or not. Some of the training I received seemed to imply there was a threshold below which it's probably not productive to worry about tiny radiation doses, because we are all subjected to background radiation (which varies by where you live, what foods you eat and other factors). For example, bananas are slightly radioactive, but I eat them all the time because the level of radioactivity is so small, even if that radiation may kill a cell or two, millions of cells are constantly dying in your body and being replaced, so what difference will a few more cell deaths make among those millions?

So if you can picture radiation that way, it seems like maybe there could be a threshold below which radiation doesn't usually affect us significantly, because we have evolved to deal with varying levels of background radiation, and now some research seems to support this idea of such a threshold:

The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data

The carcinogenic risk induced by low doses of ionizing radiation is controversial. It cannot be assessed with epidemiologic methods alone because at low doses the data are imprecise and often conflicting. Since the 1970s, the radiation protection community has estimated the risk of low doses by means of extrapolation from the risk assessed at high doses, generally by using the linear no-threshold (LNT) model.

The LNT relationship implies proportionality between dose and cancer risk...The advances during the past 2 decades in radiation biology, the understanding of carcinogenesis, and the discovery of defenses against carcinogenesis challenge the LNT model, which appears obsolete (2–6).

Life developed in a bath of ionizing radiation and solar ultraviolet radiation and created aerobic organisms requiring (a) defenses against the metabolically induced reactive oxygen species, (b) DNA repair, and (c) elimination of damaged cells. Several sets of data show the efficacy of these defenses to be much higher at low than at high doses and for fractionated or protracted irradiation than for acute irradiation.

So even though the LNT relationship was used for decades to estimate radiation risk, it may be an obsolete model, however some people still seem to advocate for its use, and it probably does lead to safer assumptions for safety even if the assumptions aren't really supported by observation. Even if there's a threshold, it's probably not the same for every person or animal also due to genetic variation.

The reason for for discussing whether LNT is true or false is I think the "threshold model" explains a lot of what is observed as the linked paper suggests. In Hiroshima and Nagasaki the radiation levels are probably below any such threshold which is why as you put it "people live in Hiroshima and Nagasaki as if nothing has happened". Chernobyl is a different story and radiation levels are definitely above any "safe" threshold in some areas, where radiation can be 10 or even 100 times above background radiation levels.

Why does everything grow and florish of the fauna and flora in Chernobyl as never before?

This is not completely true. Some species are doing well, but invertebrate populations have declined:

Reduced abundance of insects and spiders linked to radiation at Chernobyl 20 years after the accident

Effects of low-level radiation on abundance of animals are poorly known. We conducted standardized point counts and line transects of bumble-bees, butterflies, grasshoppers, dragonflies and spider webs at forest sites around Chernobyl differing in background radiation by over four orders of magnitude. Abundance of invertebrates decreased with increasing radiation, even after controlling for factors such as soil type, habitat and height of vegetation. These effects were stronger when comparing plots differing in radiation within rather than among sites, implying that the ecological effects of radiation from Chernobyl on animals are greater than previously assumed.

One reason why invertebrate populations are lower is they lay their eggs near the surface of the soil where high radiation exposure can damage the eggs.

Birds (which may feed on invertebrates) haven't done so well either, and this article questions some of the wildlife claims as "claims":

Did Chernobyl Leave an Eden for Wildlife?

In recent years, there have been reports that the area around the Chernobyl nuclear plant had become something of a wildlife playground. The reports suggested that animals like wild boar, wolves and moose had flourished in the 40-mile-diameter “exclusion zone,” which was contaminated by low-level radiation from the disaster in Ukraine 21 years ago.

But Timothy A. Mousseau, a biologist at the University of South Carolina and co-director of the university’s Chernobyl research initiative, said there had not been systematic studies of wildlife there. “When we sat down to review the literature, we realized that most of these claims were just that — claims,” he said...

Whatever the reasons, the study shows that for birds, at least, Chernobyl is far from a paradise; the contamination appears to have had an effect. “This was a big surprise to us,” Dr. Mousseau said. “We had no idea of the impact.”

Even this article talking about thriving wildlife mentions there are mutations observed, and they think even more mutated animals die and are eaten before scientists can observe them, though as long as breeding rates are high enough, wildlife populations can still thrive despite the mutated creatures which die:

Wildlife defies Chernobyl radiation

If the sun disappeared would the planets start orbiting Jupiter and if so will Jupiter start to warm up?

a reply to: wickd_waze
Imagine you have a ball tied to a string and you twirl it overhead in a circle to simulate the orbit of a planet.

When you let go of the string, the ball stops making its circle and continues in the direction it was going when you let go. If you did that with 8 balls of various sizes and "orbits", all 8 of them would similarly just keep going when you let go of the strings. I imagine that's more or less what the 8 planets would do, if the sun impossibly vanished. The moons orbiting Jupiter would keep orbiting Jupiter but I wouldn't expect any planets to do that, though I suppose there's a slim chance if the planets were in just the right position when it happened, an inner planet could pass close enough to Jupiter to be captured by Jupiter's gravity, though it's not something I would expect to happen, or try to calculate given the impossible circumstances.

Look at it this way, over 99.8% of the mass in the solar system is in the sun, so it's not like Jupiter is a close second.

a reply to: Arbitrageur

Thx for your extensive reply.. learned something new today... I had kind of hoped the impact of the radiation in these places were not as bad as expected but unfortunately there is no escape from that stuff. Same at those places where they tested these weapons. Beautiful places in the pacific completely wasted... Then I wonder.. what can be more important...or...is it really this important?

heck I don't think so. planets are actually falling vertically towards the sun. if the sun suddenly disappeared they would not fall vertically towards the centre of the sun any more, but would eventually essentially start falling vertically towards the centre of the galaxy
a reply to: Arbitrageur

originally posted by: Hyperboles
heck I don't think so. planets are actually falling vertically towards the sun. if the sun suddenly disappeared they would not fall vertically towards the centre of the sun any more, but would eventually essentially start falling vertically towards the centre of the galaxy
a reply to: Arbitrageur

"falling vertically towards the sun" - Is that an awkward way to say that they are orbiting the sun?

And yes, Arbitrageur is ignoring galactic orbital motion, for the sake of simplicity I would assume. He describes planet motion in sun reference frame which is a good approximation for human time scales.

Thanks, lots to ponder now when I’m thinking about it again.

What does a rocket push against in space to make it go forwards if there is nothing in space?

a reply to: moebius
Hyperboles doesn't understand reference frames and I gave up that he would understand them when his response was to screw them.

originally posted by: Arbitrageur
a reply to: Hyperboles
I understand your claim, but it's wrong because you don't know how reference frames work, therefore you have no explanation why you think there is g aboard the ISS reference frame (or at a Lagrangian point), yet the water just floats there in the middle as if g was zero. If g was non-zero in the ISS reference frame, then you'd see that water blob move in the direction of g.

originally posted by: Hyperboles
Lol screw the reference frames.

a reply to: Hyperboles
You still don't understand reference frames. The planets would not "eventually essentially start falling vertically towards the centre of the galaxy", my main objection being the word "start" because the planets are already orbiting the center of the galaxy, so that's not something that would "start" happening, it's already happening. If the planets weren't orbiting the galaxy along with the sun they wouldn't keep their orbits around the sun.

A secondary objection to this is that I'd be cautious of describing galactic orbits in the same terms as solar system orbits as you have done. I have no objection to saying the moon is falling toward earth (though technically they both orbit a common barycenter), or saying the planets fall toward the sun (though again, there are barycenters for those orbits as well). But remember that over 99.8% of the mass in the solar system is in the sun so you're only disregarding less than 0.2% of the mass of the solar system when you make that statement, quite reasonable if you're not concerned about gravitational interactions between planets. However, galaxies are not constructed with such a large proportion of mass in the center. As described here the Milky Way is more complicated than the solar system and the "falling toward the center" curve we see for the solar system similar to curve A in figure 8.17 is not the curve observed for galaxies like the Milky Way which is more like Curve B. It might be more accurate to say the sun is falling toward all the other mass in the Milky Way, than to say it's falling toward the center.

www.e-education.psu.edu...


This illustration shows another type of motion of the sun that's not described by "falling toward the center"; it moves above and below the galactic plane as it orbits:

Galactic_Motions

In this graphic, the white parts are above the galactic plane and the black parts below.

So again "falling vertically towards the centre of the galaxy" doesn't explain why the sun does makes that motion.

The tertiary objection is if you feel compelled to consider a larger view, why stop at the galaxy? The Milky way galaxy is also orbiting a point in the center of mass of the local group of galaxies, so why not consider those motions too? Or why not use the cosmic microwave background as a reference frame? I know, "screw the reference frames", your "wise insight" into reference frames.

originally posted by: zatara
a reply to: Arbitrageur

Thx for your extensive reply.. learned something new today... I had kind of hoped the impact of the radiation in these places were not as bad as expected but unfortunately there is no escape from that stuff. Same at those places where they tested these weapons. Beautiful places in the pacific completely wasted... Then I wonder.. what can be more important...or...is it really this important?

You're welcome but I don't fully understand your reply, such as "I had kind of hoped the impact of the radiation in these places were not as bad as expected", where we discussed Hiroshima, Nagasaki,Chernobyl and Marshall Islands. The current impact of radiation in Hiroshima and Nagasaki is not bad is what I was trying to say. But yes is other places it's bad like the latter two locations.

It's a lot better now than when atmospheric nuclear tests were being conducted, during which time and for some years afterward there wasn't any habitable spot on Earth to escape the radiation (I'm not sure about the north and south poles but those spots aren't very habitable). The large particulates from nuclear tests fell near the test site, but the really small radioactive particulates circled the globe for months or years before being deposited virtually everywhere the winds carried them, all over the globe. Thanks to half-lives doing what they do the danger in most places isn't as serious as it once was.

"unfortunately there is no escape from that stuff"

There is the New Zealand nuclear-free zone, if you can handle being upside down (joking about the upside down part).

"Then I wonder.. what can be more important." What can be more important than what? I'm not following your train of thought. At least it seems like testing has stopped for now, in most places except maybe North Korea? I remember a scientist with the Pentagon saying they were now trying to use some of the world's most powerful super computers to try to evaluate things like the stability and performance of nuclear stockpiles since they can't do actual testing anymore.

a reply to: Forensick
I always feel like puking when I hear some teacher say "There's no such thing as a stupid question, so go ahead and ask".

Their heart is in the right place, because they are encouraging people to ask questions which is good, however I personally do not believe there is no such thing as a stupid question. In any case there is a thread already dedicated to that specific question so please refer to that thread for ongoing specific discussion about that specific question:

What does a rocket push against in space?

Instead of calling it a stupid question, I'll say it's not only a loaded question but it's the wrong question to ask. The right question to ask is, "does a rocket need anything to push against in space?". Since the answer to that is "no" then that makes the question you asked irrelevant. This is the best site I ever found on rocket propulsion, which explains it in terms that anybody with a reasonable level of cognitive ability can understand:

Rocket Propulsion

Any further discussion on this topic, please take to the linked thread created specifically to discuss this question.