Why we will never leave our Solar System

[RC1062]

But not the radiation being talked about... ???

[Ydoow]

Erm, that\'s still radiation...

That\'s quanta of energy occasionally being released from the nucleus of an atom.

I guess we\'re splitting hairs over different EM waves, but my point is to say that even a Wood Fire radiates heat, and that isn\'t cancerous.

[semininja]

But not the radiation being talked about... ???

Whoops. I wasn\'t reading very closely...

[Misterspork]

Radiation can give us cancer so yes it would effect us...

The only way we would be able to leave the solar system is if we found out how to turn dark energy into electricity.

Then we could put heating wires into our space suits and use the dark energy to power it.

There are two types of radiation, and you are thinking of the wrong one:

The first is heat transmission by radiation, electromagnetic radiation. Essentially, all objects are emitters and absorbers of this radiation. As we absorb this radiation our atoms speed up(Heat). As you emit it your atoms lose heat energy. Good absorbers are good emitters. The only way this type of radiation can give you cancer is if the object emitting it on you is VERY, VERY, VEEERRYY hot, hotter than the sun(Hotter objects emit higher frequency electromagnetic radiation, AKA x-rays and gamma rays, but this doesn\'t happen normally) This means two things in space:

1. You don\'t need a medium to transfer heat, meaning the sun can heat you up.

2. You can cool down in space without anything to absorb the energy from you.

3. White is the best color to wear, because it is the worst absorber and emitter, meaning you cool down slowly and heat up slowly, staying at around the same temperature.

The radiation you are thinking of is the particles emitted by radioactivity. These particles typically are:

1. Alpha particles, which consist of 2 protons and 2 neutrons, and move at 50% the speed of light.

2. Beta particles, which consist of something similar to electrons, and move at ~75% C

3. Gamma rays, which are very high energy electromagnetic waves(not usually emitted by substances) traveling at C.

This can have adverse effects on DNA, especially gamma rays, giving you cancer if exposed to too much.

[Johno]

This confusion is part of the reason people think mobile phones can give you cancer.

Coincidentally, it MAY also be possible to get cancer from microwaves; but so far we are yet to turn up any clear evidence of a link.

[semininja]

Erm, the radiation from cell phones could have the potential to cause cancer, from what I\'ve read.

[Misterspork]

Erm, the radiation from cell phones could have the potential to cause cancer, from what I\'ve read.

I don\'t think radio waves would be able to give you cancer.

[mincespy]

Erm, the radiation from cell phones could have the potential to cause cancer, from what I\'ve read.

That\'s only heavy mobile use.

[semininja]

I don\'t think radio waves would be able to give you cancer.

There have been studies that might disagree with you. I\'m personally not entirely convinced, but I don\'t know for certain.

[RC1062]

To be fair to much of any electro magnetic radiation could give you cancer... And does...

It is all about the quantities.

[Awaras]

There have been studies that might disagree with you. I\'m personally not entirely convinced, but I don\'t know for certain.

Yeah, cellphone radiation has been classified as a class 2B carcinogen, alongside such dire health hazards as coffee, gasoline and pickled vegetables...

http://en.wikipedia.org/wiki/List_of_IARC_Group_2B_carcinogens

*edit*

Hmm... And DDT apparently. I was led to believe that DDT is much more hazardous than coffee or diesel fumes... Strange.

[Kryten]

Yeah, cellphone radiation has been classified as a class 2B carcinogen, alongside such dire health hazards as coffee, gasoline and pickled vegetables...

http://en.wikipedia.org/wiki/List_of_IARC_Group_2B_carcinogens

There\'s only one category lower than that, and they\'ve only ever put one thing in it. 2B means \'possibly causes cancer\', which includes things with a 1 in a million chance of being carcinogenic, and things with a 50:50 chance. The whole system isn\'t very useful, really.

[Johno]

I think the best way to describe it is that mobile phones haven\'t been ruled out as a carcinogen.

[Randox]

To be classed as a carcinogen, something needs to increase your chance of getting cancer by say 1 in a million. For contrast, in North America, the chance of getting cancer in general is between 1 in 2 and 1 in 3 I think. However, our bodies are terrifyingly complex, and while we understand a lot of the general mechanics, but we lack proper comprehension on how everything interacts. We\'ll know we understand our bodies when we can computer model every chemical process that goes on inside them (all at once), and use these models to predict health like weather models predict future weather patterns.

My point being, just because we think something is safe or dangerous doesn\'t always make it true, because we have to work around our own ignorance. Sometimes we vastly over or under estimate how much of something our bodies can actually deal with.

So I did some research, and apparently an unprotected human in hard vacuum has 10 seconds of useful conciousness, and 90 seconds (total, not after) before their injuries become fatal (and you apparently do need a full pressure suit, though just a pressurized breathing supply would give you much more time).

Here is the full description:

When the human body is suddenly exposed to the vacuum of space, a number of injuries begin to occur immediately. Though they are relatively minor at first, they accumulate rapidly into a life-threatening combination. The first effect is the expansion of gases within the lungs and digestive tract due to the reduction of external pressure. A victim of explosive decompression greatly increases their chances of survival simply by exhaling within the first few seconds, otherwise death is likely to occur once the lungs rupture and spill bubbles of air into the circulatory system. Such a life-saving exhalation might be due to a shout of surprise, though it would naturally go unheard where there is no air to carry it.

In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim’s mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin.

Within seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as “the bends.†Direct exposure to the sun’s ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold.

For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them. Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of “useful consciousness†would wane as the effects of brain asphyxiation begin to set in. In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim’s mouth and nose to near-freezing. Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosis would become evident.

At this point the victim would be floating in a blue, bloated, unresponsive stupor, but their brain would remain undamaged and their heart would continue to beat. If pressurized oxygen is administered within about one and a half minutes, a person in such a state is likely make a complete recovery with only minor injuries, though the hypoxia-induced blindness may not pass for some time. Without intervention in those first ninety seconds, the blood pressure would fall sufficiently that the blood itself would begin to boil, and the heart would stop beating. There are no recorded instances of successful resuscitation beyond that threshold.

And people have gone through this, since altitude machines are capable of producing hard vacuums, and on the rare occasion will do so by mistake.

[aphazael]

Hmm... And DDT apparently. I was led to believe that DDT is much more hazardous than coffee or diesel fumes... Strange.

The problem with DDT wasn\'t so much with human toxicity (iirc it was originally developed as a less toxic alternative to older pesticides), but rather with the effects it was having on wildlife (eg the California Condor)

[Richy teh space man]

I think the only thing stopping us from leaving our solar system is the radiation and technology needed to propel a ship fast enough.. which we would probaby have at some point in the future

Unless WW3 kicks off of course..

[nibula]

Inertial dampers

[Ydoow]

To be classed as a carcinogen, something needs to increase your chance of getting cancer by say 1 in a million. For contrast, in North America, the chance of getting cancer in general is between 1 in 2 and 1 in 3 I think. However, our bodies are terrifyingly complex, and while we understand a lot of the general mechanics, but we lack proper comprehension on how everything interacts. We\'ll know we understand our bodies when we can computer model every chemical process that goes on inside them (all at once), and use these models to predict health like weather models predict future weather patterns.

My point being, just because we think something is safe or dangerous doesn\'t always make it true, because we have to work around our own ignorance. Sometimes we vastly over or under estimate how much of something our bodies can actually deal with.

So I did some research, and apparently an unprotected human in hard vacuum has 10 seconds of useful conciousness, and 90 seconds (total, not after) before their injuries become fatal (and you apparently do need a full pressure suit, though just a pressurized breathing supply would give you much more time).

Here is the full description:

When the human body is suddenly exposed to the vacuum of space, a number of injuries begin to occur immediately. Though they are relatively minor at first, they accumulate rapidly into a life-threatening combination. The first effect is the expansion of gases within the lungs and digestive tract due to the reduction of external pressure. A victim of explosive decompression greatly increases their chances of survival simply by exhaling within the first few seconds, otherwise death is likely to occur once the lungs rupture and spill bubbles of air into the circulatory system. Such a life-saving exhalation might be due to a shout of surprise, though it would naturally go unheard where there is no air to carry it.

In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim’s mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin.

Within seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as “the bends.†Direct exposure to the sun’s ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold.

For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them. Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of “useful consciousness†would wane as the effects of brain asphyxiation begin to set in. In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim’s mouth and nose to near-freezing. Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosis would become evident.

At this point the victim would be floating in a blue, bloated, unresponsive stupor, but their brain would remain undamaged and their heart would continue to beat. If pressurized oxygen is administered within about one and a half minutes, a person in such a state is likely make a complete recovery with only minor injuries, though the hypoxia-induced blindness may not pass for some time. Without intervention in those first ninety seconds, the blood pressure would fall sufficiently that the blood itself would begin to boil, and the heart would stop beating. There are no recorded instances of successful resuscitation beyond that threshold.

And people have gone through this, since altitude machines are capable of producing hard vacuums, and on the rare occasion will do so by mistake.

O_O

That actually sounds surprisingly accurate from what I\'ve learned in Physiology. Very interesting that you can survive a full minute and a half and still make a full recovery. That\'s very impressive indeed.

[Bluejayek]

Yes, I mean gases and oxygen inside us that equal to 1 newton if you convert it.

a) Newtons are a unit of force, not pressure. What you instead want is a unit such as newtons/square meter

1 Newton is approximately the force exerted by gravity on an apple. If I have an apple sitting on my hand, it does not implode, so I have to assume if I have one newton pushing outwards it would not explode either.

Now for radiation.

As somebody else mentioned, there are two senses the word \'radiation\' is commonly used in scientifically. The first is as in 'Thermal Radiation'. All bodies emit radiation in the form of photons of light at all times. The amount of radiation emitted, and the wavelength of the photons, varies based on the temperature of the body. The stephan boltzman law of blackbody radiation gives:

P/A = sigma * T^4 for a black body. A black body is simply a perfect emitter of radiation. Most objects are not black bodies, and so there is an extra constant in front called Emmisivity represented by Epsilon. Emissivity varies between 0, for a perfect reflector, and 1, for a perfect black body radiator.

The wavelength of light emitted is a continuum, however it has a peak at lambda = b/T where b is the constant 2.9*10^-3K m (Kelvin Meters). This gives a peak wavelength of around 10 micrometers for a body radiating at room temperature. This is in the infrared and not in the visible spectrum (~0.4-0.8 micrometers is visible) which explains why you do not consantly see light emitting from everyday objects. However, if you heat something up, the wavelength will drop into the visible. This is where the expressions 'Red hot' 'White hot' 'Blue hot' come from. Each of these simply means the peak of the radiation is at that portion of the visible spectrum. White hot implies the peak is right in the middle of the visible, so you see all the visible wavelengths combined into white. Blue is even hotter, as now most of the radiation is at the very low wavelengths.

Now, you might ask, if all materials are constantly emitting radiation, why don\'t they simply shed all of their energy and cool down to absolute zero?

Good question. This is because everything else is also emitting radiation. For an environment in equilibrium, they are all emitting the same radiation. Each of the bodies then absorbs the radiation the others emit, keeping everything at a constant temperature. However, if there is a temperature differential between two radiating objects, there is a net energy transfer. To find the rate of energy transfer, you simply take the difference between the energy input, and the energy output.

Power/area in = epsilon * sigma * T_surroundings⁴

Power/area out = epsilon * sigma * T_object⁴

Net power/area = epsilon * sigma * (T_surroundings⁴ - T_object⁴)

The temperature quoted for space, 3K = -270C, is given by the radiation temperature of the cosmic microwave background. It\'s a microwave background because the wavelength is rather large, owing to the low temperature. Wavelengths are simply a form of electromagnetic radiation that has a low energy and hence a relatively long wavelength, 1mm-1m.

However, if you are currently being illuminated by a star, the local temperature will be much higher because the radiation from the star is clearly much more energetic then the microwave background. This is why keeping cool is often more of a problem then keeping warm; the energy in from the star is much more then the energy that you radiate out.

Having dealt with thermal radiation, let us move on to the other sense that the word is used. This is as in 'ionizing radiation'. This is the sort of radiation that can cause cancer. The term 'Ionizing' simply means that the radiation has enough energy to ionize an atom, which means to knock an electron off the atom. Electrons are bound to atoms by electric fields from the opposite charge of the electron and the positive nucleus of an atom. The binding energy varies between atoms, depending on which electron you are looking at, and how big the nucleus is. Electrons in higher shells (further out) tend to be more weakly bound then those closer in, as would be expected. However, a good average value for the binding energy of the outermost electron in atoms is -10eV. This means you require 10eV of energy to knock that electron out.

Now, 10eV (electron volts) of energy is not very much, that is 1.6*10^-18 Joules or 4.5 * 10^-25 kilowatt hours, to quote some units you may be familiar with. However, the important thing here comes from quantum mechanics. Electrons will only absorb energy in specific bits called quanta, and that quanta must be large enough on its own to knock the electron out. You cannot keep shooting less energy quanta of light (called photons) at the electron until you have given it enough energy to leave, they simply wont eb absorbed and the electron will carry on. You must fire a photon that has an energy greater then 10eV to knock that electron off. The energy of a photon of light is given by its wavelength through the relationship hc/lambda where h is plancks constant, 6.6 x 10^-34 m^2 kg/ s, c is the speed of light in a vacuum, 3 * 10^8 m/s, and lambda is the wavelength. This gives a wavelength of around 120nm to ionize atoms. This is called ultraviolet radiation, which is why it is recommended you do not use tanning beds, and wear sunscreen, as both the Sun and tanning beds emit UV radiation. Recall microwave radiation, such as used in cell phones, has a wavelength of above 1mm, and thus is far, far below the energy that can ionize atoms. However, it does heat water up as you see in a microwave, and since your brain is mostly water, shooting microwaves at it all day is likely not particularly great for it.

However, ultraviolet radiation only has enough energy to ionize a single atom, which isnt so bad. Higher energy forms of radiation, such as x-rays or gamma rays, can ionize many more atoms before their energy is used up, making them more dangerous. Fortunately, they also tend to be much rarer. While ultraviolet can be produced through black body radiation by objects at a few thousand degrees, it would take an object sitting at millions of degrees Kelvin to emit Xrays such as those seen in medical equipment. Fortunately, such objects are extremely rare, and backgrounds like these are not a problem. Practically, X-rays in diagonostic equipment are produced by another process. This is where an electron is accelerated very quickly at a target material. When the electron hits the target and slows down, the slowing down causes an emission of Bremstrahlung radiation, which simply means 'Braking radiation' in german. This radiation is high energy, and so is called X-rays. These are used as the higher energy radiation, the further it can penetrate through objects. Therefore, X-rays can penetrate through you, but less so through bones. This gives the contrast that you see on medical X-rays.

Gamma rays, some of the highest energy electromagnetic radiation, are produced by nuclear processes. They are emitted when the nuceleons (protons and neutrons) in the nucleus of an atom rearrange themselves following the emission of some other sort of radiation such as alpha or beta particles. This energy is very high energy because the energy differences inside the nucleus of the atom are very high. Therefore, gammas rays are very penetrating (can only be stopped by meters of lead), and have the potential to ionize many, many atoms.

The other two types of radiation I just mentioned, alpha and beta particles, are also emitted in nuclear processes. Alpha particles are a helium 4 nucleus, with 2 protons and 2 neutrons, emitted from an atom with an energy of around 5MeV (varies by decay). These particles are relatively large, and charges, so they interact readily with matter. This makes them easy to absorb, and they can be stopped by a thin absorber such as a thin sheet of plastic. Beta particles are electrons that are emitted in nuclear process with energies ranging from a few 100 keV to several MeV. They are intermediatly penetrating, to stop them you need a thick sheet of plastic or a thin sheet of aluminum.

The most important thing to realize about these sources of nuclear radiation is that they emit isotropically in all directions. That means that as you move away, the radiation intensity drops as 1/R^2. If you are 10m away, you get 100x less radiation then if you are 1m away. So, moral of the story, the best protection is distance.

The concern about ionizing radiation in generl is DNA mutation, and interference with other cellular process. If you knock an electron off of an atom in a DNA molecule, you will disrupt the bond, possibly causing one of the DNA bases to be removed, introducing a mutation. Other process can also be interfered with when certain key bonds are broken down, which is why in general ionization radiation is not a good thing.

Anyways, I hope that none of you read this, as you probably will have gotten bored, fallen asleep at your desk, and then gotten brain damage as your head fell to impact your desk, and I would not want that on my conscience.

Cheers.

[technoguy33]

If your statement is true, how do you explain cosmonauts staying aboard Mir for over a year at a time? I\'m sorry, but my Vulcan senses tell me this is illogical. The real question is 'Will we manage not to destroy each other by the time we get to that technology.'

[nibula]

there is no MIR enymore

[Guest]

That dosn\'t mean people didnt stay in MIR.

[Johno]

You know, one of the most amazing moments I can remember (in terms of Space) was the day that the Shuttle docked with Mir.

We\'d been at cold war for so long . . then the Berlin Wall came down . . and suddenly, because we have the will to do it, and because there were people up there that needed resupply (it wasn\'t their fault that their government had collapsed and couldn\'t pay the bills to build new Soyuz capsules for a few years), we were able to work through all the (enormous!) technical challenges of taking a docking module designed for Buran and adapting it to connect to the American shuttle.

Suddenly it was possible to believe that they weren\'t Americans and Russians up there; they were humans, and humans could do awesome stuff.

Cooperation has continued, but the euphoria of that time has given way to reality again. Sad, but it was inevitable.

[LukeTim]

What about Artificial Gravity?

That\'s perfectly possible using the centrifugal force of a spinning craft.

[RC1062]

a) Newtons are a unit of force, not pressure. What you instead want is a unit such as newtons/square meter

1 Newton is approximately the force exerted by gravity on an apple. If I have an apple sitting on my hand, it does not implode, so I have to assume if I have one newton pushing outwards it would not explode either.

Now for radiation.

As somebody else mentioned, there are two senses the word \'radiation\' is commonly used in scientifically. The first is as in 'Thermal Radiation'. All bodies emit radiation in the form of photons of light at all times. The amount of radiation emitted, and the wavelength of the photons, varies based on the temperature of the body. The stephan boltzman law of blackbody radiation gives:

P/A = sigma * T^4 for a black body. A black body is simply a perfect emitter of radiation. Most objects are not black bodies, and so there is an extra constant in front called Emmisivity represented by Epsilon. Emissivity varies between 0, for a perfect reflector, and 1, for a perfect black body radiator.

The wavelength of light emitted is a continuum, however it has a peak at lambda = b/T where b is the constant 2.9*10^-3K m (Kelvin Meters). This gives a peak wavelength of around 10 micrometers for a body radiating at room temperature. This is in the infrared and not in the visible spectrum (~0.4-0.8 micrometers is visible) which explains why you do not consantly see light emitting from everyday objects. However, if you heat something up, the wavelength will drop into the visible. This is where the expressions 'Red hot' 'White hot' 'Blue hot' come from. Each of these simply means the peak of the radiation is at that portion of the visible spectrum. White hot implies the peak is right in the middle of the visible, so you see all the visible wavelengths combined into white. Blue is even hotter, as now most of the radiation is at the very low wavelengths.

Now, you might ask, if all materials are constantly emitting radiation, why don\'t they simply shed all of their energy and cool down to absolute zero?

Good question. This is because everything else is also emitting radiation. For an environment in equilibrium, they are all emitting the same radiation. Each of the bodies then absorbs the radiation the others emit, keeping everything at a constant temperature. However, if there is a temperature differential between two radiating objects, there is a net energy transfer. To find the rate of energy transfer, you simply take the difference between the energy input, and the energy output.

Power/area in = epsilon * sigma * T_surroundings⁴

Power/area out = epsilon * sigma * T_object⁴

Net power/area = epsilon * sigma * (T_surroundings⁴ - T_object⁴)

The temperature quoted for space, 3K = -270C, is given by the radiation temperature of the cosmic microwave background. It\'s a microwave background because the wavelength is rather large, owing to the low temperature. Wavelengths are simply a form of electromagnetic radiation that has a low energy and hence a relatively long wavelength, 1mm-1m.

However, if you are currently being illuminated by a star, the local temperature will be much higher because the radiation from the star is clearly much more energetic then the microwave background. This is why keeping cool is often more of a problem then keeping warm; the energy in from the star is much more then the energy that you radiate out.

Having dealt with thermal radiation, let us move on to the other sense that the word is used. This is as in 'ionizing radiation'. This is the sort of radiation that can cause cancer. The term 'Ionizing' simply means that the radiation has enough energy to ionize an atom, which means to knock an electron off the atom. Electrons are bound to atoms by electric fields from the opposite charge of the electron and the positive nucleus of an atom. The binding energy varies between atoms, depending on which electron you are looking at, and how big the nucleus is. Electrons in higher shells (further out) tend to be more weakly bound then those closer in, as would be expected. However, a good average value for the binding energy of the outermost electron in atoms is -10eV. This means you require 10eV of energy to knock that electron out.

Now, 10eV (electron volts) of energy is not very much, that is 1.6*10^-18 Joules or 4.5 * 10^-25 kilowatt hours, to quote some units you may be familiar with. However, the important thing here comes from quantum mechanics. Electrons will only absorb energy in specific bits called quanta, and that quanta must be large enough on its own to knock the electron out. You cannot keep shooting less energy quanta of light (called photons) at the electron until you have given it enough energy to leave, they simply wont eb absorbed and the electron will carry on. You must fire a photon that has an energy greater then 10eV to knock that electron off. The energy of a photon of light is given by its wavelength through the relationship hc/lambda where h is plancks constant, 6.6 x 10^-34 m^2 kg/ s, c is the speed of light in a vacuum, 3 * 10^8 m/s, and lambda is the wavelength. This gives a wavelength of around 120nm to ionize atoms. This is called ultraviolet radiation, which is why it is recommended you do not use tanning beds, and wear sunscreen, as both the Sun and tanning beds emit UV radiation. Recall microwave radiation, such as used in cell phones, has a wavelength of above 1mm, and thus is far, far below the energy that can ionize atoms. However, it does heat water up as you see in a microwave, and since your brain is mostly water, shooting microwaves at it all day is likely not particularly great for it.

However, ultraviolet radiation only has enough energy to ionize a single atom, which isnt so bad. Higher energy forms of radiation, such as x-rays or gamma rays, can ionize many more atoms before their energy is used up, making them more dangerous. Fortunately, they also tend to be much rarer. While ultraviolet can be produced through black body radiation by objects at a few thousand degrees, it would take an object sitting at millions of degrees Kelvin to emit Xrays such as those seen in medical equipment. Fortunately, such objects are extremely rare, and backgrounds like these are not a problem. Practically, X-rays in diagonostic equipment are produced by another process. This is where an electron is accelerated very quickly at a target material. When the electron hits the target and slows down, the slowing down causes an emission of Bremstrahlung radiation, which simply means 'Braking radiation' in german. This radiation is high energy, and so is called X-rays. These are used as the higher energy radiation, the further it can penetrate through objects. Therefore, X-rays can penetrate through you, but less so through bones. This gives the contrast that you see on medical X-rays.

Gamma rays, some of the highest energy electromagnetic radiation, are produced by nuclear processes. They are emitted when the nuceleons (protons and neutrons) in the nucleus of an atom rearrange themselves following the emission of some other sort of radiation such as alpha or beta particles. This energy is very high energy because the energy differences inside the nucleus of the atom are very high. Therefore, gammas rays are very penetrating (can only be stopped by meters of lead), and have the potential to ionize many, many atoms.

The other two types of radiation I just mentioned, alpha and beta particles, are also emitted in nuclear processes. Alpha particles are a helium 4 nucleus, with 2 protons and 2 neutrons, emitted from an atom with an energy of around 5MeV (varies by decay). These particles are relatively large, and charges, so they interact readily with matter. This makes them easy to absorb, and they can be stopped by a thin absorber such as a thin sheet of plastic. Beta particles are electrons that are emitted in nuclear process with energies ranging from a few 100 keV to several MeV. They are intermediatly penetrating, to stop them you need a thick sheet of plastic or a thin sheet of aluminum.

The most important thing to realize about these sources of nuclear radiation is that they emit isotropically in all directions. That means that as you move away, the radiation intensity drops as 1/R^2. If you are 10m away, you get 100x less radiation then if you are 1m away. So, moral of the story, the best protection is distance.

The concern about ionizing radiation in generl is DNA mutation, and interference with other cellular process. If you knock an electron off of an atom in a DNA molecule, you will disrupt the bond, possibly causing one of the DNA bases to be removed, introducing a mutation. Other process can also be interfered with when certain key bonds are broken down, which is why in general ionization radiation is not a good thing.

Anyways, I hope that none of you read this, as you probably will have gotten bored, fallen asleep at your desk, and then gotten brain damage as your head fell to impact your desk, and I would not want that on my conscience.

Cheers.

I thought a single photon could only release one electron? Though if it is higher in energy it is able to release electrons from atoms with higher ionisation energies.