How do black holes work?

Lou Bloomfield Leave a comment

How do black holes work?

As you assemble more and more mass together in a small volume, the gravity there becomes stronger and stronger. At first, it becomes more and more difficult to throw a ball upward hard enough to make it sail away from the mass into space. Eventually, you need a cannon to get the ball to leave. And by the time you get enough mass together, the gravity becomes so strong that light itself begins to have trouble escaping. Light falls in gravity, just like anything else. But it travels so fast that you barely notice it falling. However when the gravity becomes strong enough, light falls enough to cause some weird effects. A black hole forms when the gravity is so strong the even light is unable to escape from the mass.

What exactly does the bone do with the X-rays that the skin doesn’t?

Lou Bloomfield Leave a comment

What exactly does the bone do with the X-rays that the skin doesn’t?

The skin’s atoms are too small to experience the photoelectric effect with X-rays. Most X-rays go right through skin and soft tissue. However calcium atoms are large enough to experience the photoelectric effect and thus absorb many of the X-rays. Bones cast a shadow on film, which is how an image of your bones is formed.

On an X-ray result picture, why is the film in the background blue? Is this the …

Lou Bloomfield Leave a comment

On an X-ray result picture, why is the film in the background blue? Is this the only way it will show up? If so why?

The X-ray image itself is formed by tiny black silver particles, just as in a normal black and white photographic negative. If those particles were supported by a clear plastic sheet, then the X-ray should appear either clear or black and have no color. The blue you are referring to must be caused either by a colored pigment in the plastic X-ray film sheet or by a colored light used to illuminate the X-ray. I suspect the later. Fluorescent lamps tend to be bluish and the ones used to view X-rays are probably particular blue. It probably increases the apparent contrast in the image so that small variations in density become visible.

How do the “user-friendly” MRI machines work vs. the old catacomb type? (the o…

Lou Bloomfield Leave a comment

How do the “user-friendly” MRI machines work vs. the old catacomb type? (the opened vs. closed types)

The shape of the MRI machine is dictated primarily by the strong magnetic field it uses to record information about protons in a person’s tissues. This field needs to be very uniform over a large region of space and the simplest way of producing such a uniform field is with a huge coil of current-carrying wire. The person would go inside the coil, in the uniform field and other parts of the MRI machine would record the information. While the coil could be dressed up to look more like a tubular hole than a coil of wire, it was still very confining. Newer MRI machines use two smaller coils of current carrying wire, one above the other, to create a uniform field for imaging. This arrangement is trickier because the two coils must be shaped very carefully to ensure that the field is appropriately uniform. Moreover, most MRI machines use superconducting wires in these coils to achieve very high magnetic fields. Since superconducting coils must be cooled to very low temperatures, they require liquid helium coolants and sophisticated thermal insulation. While the single coil magnets required only a single refrigerator and insulating chamber, those with two coil magnets required two refrigerators and insulating chambers. That increases the expense of the magnet and its operation, but produces a more open imaging region.

You said that in the Three Mile Island Incident, it overheated due to the lack o…

Lou Bloomfield Leave a comment

You said that in the Three Mile Island Incident, it overheated due to the lack of cold water. How did that happen? Isn’t that a huge oversight?

The loss of cooling water was unexpected and was caused by a pump failure. The broken pump was actually part of the power-generating loop, not the reactor core-cooling loop. When everything was working properly, water flowing through a loop that included the reactor core transferred heat to water flowing through the generating plant loop. But when the generating plant loop shut down, the reactor core loop had nowhere to deposit its heat and the water in it boiled. Backup cooling water evidently did not exist, did not work, or was not sufficient to keep the reactor core from over heating. I don’t know whether it was poor design or poor maintenance that caused this disaster.

Why can’t you make nuclear weapons with any old element?

Lou Bloomfield Leave a comment

Why can’t you make nuclear weapons with any old element?

Only a few elements/isotopes are fissionable, meaning that only a few elements/isotopes have nuclei that shatter when struck by a neutron. Moreover, only a few of this fissionable nuclei release more neutrons than they take to fission. Of naturally occurring isotopes, only Uranium 235 is suitable for nuclear weapons. Plutonium 239 is also suitable, but it must be made artificially in a nuclear reactor.

When a plane drops a nuclear bomb, what sets the detonation process into effect?

Lou Bloomfield Leave a comment

When a plane drops a nuclear bomb, what sets the detonation process into effect?

The altitude at which the bomb explodes affects its results. Near or on the ground, the blast would cause incredible local damage, but less long-range damage. Above the ground, the blast would cause less local damage, but more long-range damage. So the bomb-makers build altitude sensing equipment into the bomb; probably a pressure sensing or radar-based altimeter. When the bomb has determined that it is at the right height, it triggers. High explosives assemble the critical mass as quickly as possible (typically by crushing the central sphere with carefully shaped high explosive charges). Once the fissionable material exceeds its critical mass, the chain reaction starts and the bomb explodes.

What is the difference between the nuclear bomb and the H-bomb?

Lou Bloomfield Leave a comment

What is the difference between the nuclear bomb and the H-bomb?

The fission bomb (uranium or plutonium bomb) derives its energy from the shattering of large nuclei; those in uranium or plutonium. The H-bomb (hydrogen, thermonuclear, or fusion bomb) derives most of its energy from the fusion or coalescence of small nuclei; those in hydrogen. The H-bomb releases more energy per kilogram than the fission bombs and can be made larger than the fission bombs. However, triggering a hydrogen bomb requires the enormous temperatures of a fission bomb.

If we were ever to have a nuclear war, would we have to live underground?

Lou Bloomfield Leave a comment

If we were ever to have a nuclear war, would we have to live underground?

The long-term effects of nuclear war would come primarily from the release of radioactive isotopes into our environment. Large nuclei, such as that of uranium 235, have many more neutrons than protons. These neutrons “dilute” the repelling protons and made these large nuclei less unstable. But once a large nucleus shatters into fragments of medium size, these fragments acquire electrons and become “normal” atoms with medium sized nuclei. Unfortunately, these medium sized nuclei need fewer neutrons than they wind up with and they are generally unstable. While they resemble normal atoms chemically, they contain unstable cores and eventually decay. The decays release energy and this energy can do chemical damage to surrounding material. If the atom has been incorporated into a biological system (e.g. a person), it can do chemical damage to that biological system, perhaps causing cancer or genetic damage. To avoid this insidious damage, people would have to stay away from the fallout chemicals. That would be a difficult task, even underground.