Probably a stupid car question...

[Treesh]

...but when I was having my alternator fixed the other day, I got to thinking about how a car makes its electricity. My father-in-law told me he could take the battery out of his older car and it would run fine without a battery because the car generated its own charge.

How would he start the car without the battery?

If it's a manual, just pop the clutch.

[Lissa]

... the higher the energy of the incident radiation, the more shielding required. It's not simply getting better reactions or smaller masses or using different methods to gather energy from standard radioactive decay ...

I agree with Lissa on this point. One can say "choose a better nuclear reaction", but nature really doesn't offer one. You can say "choose better shielding materials" but even the best possible still take pretty good thicknesses to work.

The Catch-22 is that if you use low energy reactions, you don't need as much shielding but then the pile has to be much larger to get a sustained reaction. If you use high energy reactions, you can make the pile smaller, but you then need more shielding. Optimizing just for weight, you still end up with something more suitable for railroad engines than cars or trucks. And that optimization involves using some nasty materials and insufficient containment for purely mechanical accidents.

On a (slightly) unrelated note, just how dense does the shielding have to be to impart Bremsstrahlung from Nitrogen-16 decay? I mean, just how energetic is that beta particle event?

Alpha and Beta decay is a non-issue outside the human body. Your own skin will stop the most energetic betas. The problem with Alphas and Betas is when they happen inside the human body. Externally, they're not a threat, internally they're very much one.

[--Pete]

Hi,

If it's a manual, just pop the clutch.

Usually will not work. It will work if your battery is too low to turn the starter motor. Or if you don't have a starter motor (I went a whole summer without one at Los Alamos). But if you don't have a battery at all, you probably cannot get the generator or alternator turning fast enough to supply enough power for the coil. Hence, no spark, no start. That's why aircraft use magnetos.

--Pete

[Zarathustra]

P.P.S.: Probably a stupid car question: The fuel consumption estimate shown in my girlfriend's VW, how trustworthy would it be? (horribly phrased, I know)

The biggest factor I've found (and this caught my eye since I got a 2011 VW GTI in November) is just how you drive it. But the sticker gives a pretty accurate ballpark. It's my understanding that those estimates are not written by the manufacturer.

[Taem]

...but when I was having my alternator fixed the other day, I got to thinking about how a car makes its electricity. My father-in-law told me he could take the battery out of his older car and it would run fine without a battery because the car generated its own charge.

How would he start the car without the battery?

After the car was started.

But it’s his tale, not mine! My "modern" car can't do anything unless every component is fully operational it seems.

---

P.P.S.: Probably a stupid car question: The fuel consumption estimate shown in my girlfriend's VW, how trustworthy would it be? (horribly phrased, I know)

The biggest factor I've found (and this caught my eye since I got a 2011 VW GTI in November) is just how you drive it. But the sticker gives a pretty accurate ballpark. It's my understanding that those estimates are not written by the manufacturer.

As someone else mentioned in this thread, I also have a Mustang GT, but a 2005 model. When I first got the car, I drove it an average of 75-80-MPH in the long stretches on the 101-freeway from where I live to work; my MPG was coming in at 25-26. Now, I drive more conservatively at 65-70-MPH and my MPG is pretty spot on at 23. Both are outstanding numbers for a V8 engine with 6-gears, but I found it interesting that most informal sites I visit claim the best MPG you can achieve for your money is 55-MPH, but that info is either outdated, or incorrect and I can prove it with my car! The "best MPH" for fuel conservation ratio has to vary based on wind resistance and the aerodynamics of the car, combined with the fuel to energy ratio vs. payoff in regards to how fast your traveling. Maybe 55-MPH was the best for cars of the 80's and 90's whose engines weren't as well built the same as they are today, or perhaps its the sportscar build itself, but in any case, not all cars are developed equally it would seem!

EDIT: I should mention that over 80-MPH, even by a hair, and my MPG dropped significantly!

[--Pete]

Hi,

... the best MPG you can achieve for your money is 55-MPH, but that info is either outdated, or incorrect ...

Basically, it is incorrect. As you discovered, different cars behave differently. Different drag coefficients, different gear ratios, different power curves, etc. I had a '66 Austin-Healey 3000 Mk3. It got its best gas mileage (25 mpg) at 4000 rpm in 4th gear overdrive. That worked out to 88 mph. At 55 mph (2500 rpm 4/OD), I would barely get 20 mpg, and in city driving, that dropped to about 15.

--Pete

[Treesh]

Hi,

If it's a manual, just pop the clutch.

Usually will not work. It will work if your battery is too low to turn the starter motor. Or if you don't have a starter motor (I went a whole summer without one at Los Alamos). But if you don't have a battery at all, you probably cannot get the generator or alternator turning fast enough to supply enough power for the coil. Hence, no spark, no start. That's why aircraft use magnetos.

--Pete

Didn't realize that. Good to know. Thanks.

[kandrathe]

On a (slightly) unrelated note, just how dense does the shielding have to be to impart Bremsstrahlung from Nitrogen-16 decay? I mean, just how energetic is that beta particle event?

From Wolfram|Alpha... Nitrogen 16. During its decay back to O16, it gives off 5-7 MeV high energy gamma radiation. From Wiki, "Condensate from the condenser is typically retained for 10 minutes to allow for decay of the 16N. This eliminates the need to shield and restrict access to any of the feed water piping or pumps."

For gamma / neutron radiation, here is source for computing necessary shielding.

I still believe it is possible with better engineering. For example, Toshiba has developed a 10MW compact reactor measuring 20 feet x 6 feet. I like the part where they use U238 as a part of the shielding, but over time it becomes enriched and contributes to the total fuel - an ingenious type of breeder reactor. A little too big, and far more power than is needed for a car sized vehicle (150 Kw). So, not an easy proposition to scale this down to 1/66 the energy output, and size by 1/10, but hardly the stuff of science fiction.

[--Pete]

Hi,

For example, Toshiba has developed a 10MW compact reactor measuring 20 feet x 6 feet.

Did you skip the part that said "The core heat source for this plant is quite compact; it is only about 0.7 meters in diameter and about 2 meters tall. This section of the plant would be at the bottom of the 30 meter deep excavation inside a sealed cylinder, a location that helps to provide the driving force needed for natural circulation cooling and that provides an impressive level of nuclear material security."

Somehow, I just don't think driving around with the equivalent of a 30 m (~100 ft) deep hole is going to be practical. And it's not just the equivalent shielding that you need, it's the loss of the ground heat pump effect. So, add shielding, add coolant/heat transfer fluid pump. Add who knows what to make it accident safe and to prevent the wrong people from getting weapon grade material.

--Pete

[Lissa]

On a (slightly) unrelated note, just how dense does the shielding have to be to impart Bremsstrahlung from Nitrogen-16 decay? I mean, just how energetic is that beta particle event?

From Wolfram|Alpha... Nitrogen 16. During its decay back to O16, it gives off 5-7 MeV high energy gamma radiation. From Wiki, "Condensate from the condenser is typically retained for 10 minutes to allow for decay of the 16N. This eliminates the need to shield and restrict access to any of the feed water piping or pumps."

Errr...there's no gamma with the decay, just a beta. Given, you have an electron moving at relativistic speeds, but it's just an electron which will be stopped by your skin if the decay happens external to your body. If the N16 decays in your lungs however, there is definite damage potential.

For gamma / neutron radiation, here is source for computing necessary shielding.

And you'll note that there are given thicknesses required to stop any gamma or neutrons. It's well known that you need 7+ thicknesses to cut the radiation to near 0 levels and it's going to depend on how powerful a gamma or neutron source is (case in point, when I was at the University of Arizona, we had a 5 Cu Co60 source. We had a couple feet of lead to act as shielding, but even still, when the source was raised to irradiate a sample, you could still measure a slight rise in radiation outside the room where the source was stored (when placing samples in the irradiation chamber while the source was lowered, we were required to wear finger dosimeters and we had to make sure that when we reached in, we had to do so that the lead shielding blocked our body and head). Given the amount of lead we needed for just a 5 Cu source, the amount of lead/uranium/other dense material for a reactor, even a small one, would be considerable.

I still believe it is possible with better engineering. For example, Toshiba has developed a 10MW compact reactor measuring 20 feet x 6 feet. I like the part where they use U238 as a part of the shielding, but over time it becomes enriched and contributes to the total fuel - an ingenious type of breeder reactor. A little too big, and far more power than is needed for a car sized vehicle (150 Kw). So, not an easy proposition to scale this down to 1/66 the energy output, and size by 1/10, but hardly the stuff of science fiction.

The problem isn't better engineering, we're designing reactors now that are passively safe, it takes an act of sabotage to make them meltdown now. The problem still remains, depending on your source strength, you're going to need a certain amount of shielding and that shielding can weigh a lot.

Another aspect is this, the Russians have created suitcase and hand gernade size nukes, we know minaturization is possible, the problem is the shielding and it always will be. You can't use coulombic forces to stop a neutron or a gamma like you can with a beta or an alpha, so the only way to really stop them is material that will increase the chance of interaction and potentially back scatter to the source till the harm said radiation is nil.

[Lissa]

Add who knows what to make it accident safe and to prevent the wrong people from getting weapon grade material.

--Pete

Weapons grade material isn't the thing watched most closely, it's the things required to make an implossion happen properly; high grade switches, high grade explosives. Without those things, the best you'll get that weapons grade material to be is a conventional explosive dirty bomb (spreading radioactive material about with conventional explosives).

[LochnarITB]

Add who knows what to make it accident safe and to prevent the wrong people from getting weapon grade material.

--Pete

Weapons grade material isn't the thing watched most closely, it's the things required to make an implossion happen properly; high grade switches, high grade explosives. Without those things, the best you'll get that weapons grade material to be is a conventional explosive dirty bomb (spreading radioactive material about with conventional explosives).

Bah, it only takes C-4, photo strobes and a metal salad bowl. I saw it in a movie!

[--Pete]

Hi,

OK, I have to be a bit careful here.

high grade switches

Trivial, today. Run of the mill SCRs (silicon controlled rectifiers) have a turn on time of 1.5 to 2.0 µs. Much better than what they had at Los Alamos in '45.

high grade explosives

Comp C and HMX appear to be relatively easy to get in the arms market. I've made my own PETN, nitroglycerin, and trinitrotoluene (and that was when I was in high school). With a little care and a little knowledge, some combinations of those (or mixtures of those) can be used to generate a spherical wave. If you know what you're doing, you can get consistently uniform and pure material.

Bah, it only takes C-4, photo strobes and a metal salad bowl. I saw it in a movie!

That movie scared the crap out of me. There were a few errors, but they came damned close (too damn close) to getting it right.

--Pete

[Lissa]

Hi,

OK, I have to be a bit careful here.

high grade switches

Trivial, today. Run of the mill SCRs (silicon controlled rectifiers) have a turn on time of 1.5 to 2.0 µs. Much better than what they had at Los Alamos in '45.

Not so trivial in other countries. You also have to have a special license to get those level of switches. It is monitored very, very closely.

Likewise, the bombs used on Hiroshima and Nagasaki were over the necessary amount of material because of the lack of technology. In Little Boy, the main Uranium pit was almost a critical mass by itself, it took slamming another large piece of Uranium into is to cause the reaction to go. Given it was about 1.5 critical masses, it detonated for about 9 kT. A test reactor used by Los Almos in the 70s was just slightly over a critical mass (it was used for flux experiments) and a sphere with a cylinder cut out of it and said cylinder was allowed to travel through the sphere to test fast flux interactions. Said reactor was taken out to the test range and the cylinder was block to stay in the sphere, needless to say, they got a detonation that was roughly twice what Hiroshima was. Nagasaki was above a critical mass (if I remember what my professors said, it was around twice what was necessary) as they weren't sure if they could get a good enough implossion to detonate the plutonium pit, they did get it to detonate for around 20 kT.

high grade explosives

Comp C and HMX appear to be relatively easy to get in the arms market. I've made my own PETN, nitroglycerin, and trinitrotoluene (and that was when I was in high school). With a little care and a little knowledge, some combinations of those (or mixtures of those) can be used to generate a spherical wave. If you know what you're doing, you can get consistently uniform and pure material.

Right, but one little slip up in the machining process can severly effect the implossion. All of the explosive have to have a near perfect shaped compression with exactly the same force all around, one of the charges being either under or over balance will deform the pit and cause the reaction to fizzle (which can still be powerful, but not as powerful as you might be looking for).

Bah, it only takes C-4, photo strobes and a metal salad bowl. I saw it in a movie!

That movie scared the crap out of me. There were a few errors, but they came damned close (too damn close) to getting it right.

--Pete

What should scare you more is that there are magazines out there with actual schematics and such on how to do it. I've seen a few and that's far more scarey that these magazines are accessible by going to a local library and getting them then in how close a movie got.

[eppie]

What should scare you more is that there are magazines out there with actual schematics and such on how to do it. I've seen a few and that's far more scarey that these magazines are accessible by going to a local library and getting them then in how close a movie got.

But what should scare you less is that, unlike what governments tell us, there are not so many people that want to blow us up.
Here we are talking abut explosives but there are much more ways of making victims....also for weird loners that are angry at the world and for terrorist that are organized.
The fact is just that luckily most people are sane enough not to want to do this.

[kandrathe]

On a (slightly) unrelated note, just how dense does the shielding have to be to impart Bremsstrahlung from Nitrogen-16 decay? I mean, just how energetic is that beta particle event?

From Wolfram|Alpha... Nitrogen 16. During its decay back to O16, it gives off 5-7 MeV high energy gamma radiation. From Wiki, "Condensate from the condenser is typically retained for 10 minutes to allow for decay of the 16N. This eliminates the need to shield and restrict access to any of the feed water piping or pumps."

Errr...there's no gamma with the decay, just a beta. Given, you have an electron moving at relativistic speeds, but it's just an electron which will be stopped by your skin if the decay happens external to your body. If the N16 decays in your lungs however, there is definite damage potential.

Ah, well then, the Wikipedia is wrong about that as well.

"Radioisotope N16 is the dominant radionuclide in the coolant of pressurized water reactors or boiling water reactors during normal operation. It is produced from O16 (in water) via (n,p) reaction. It has a short half-life of about 7.1 s, but during its decay back to O16 produces high-energy gamma radiation (5 to 7 MeV)."

For gamma / neutron radiation, here is source for computing necessary shielding.

And you'll note that there are given thicknesses required to stop any gamma or neutrons. It's well known that you need 7+ thicknesses to cut the radiation to near 0 levels and it's going to depend on how powerful a gamma or neutron source is (case in point, when I was at the University of Arizona, we had a 5 Cu Co60 source. We had a couple feet of lead to act as shielding, but even still, when the source was raised to irradiate a sample, you could still measure a slight rise in radiation outside the room where the source was stored (when placing samples in the irradiation chamber while the source was lowered, we were required to wear finger dosimeters and we had to make sure that when we reached in, we had to do so that the lead shielding blocked our body and head). Given the amount of lead we needed for just a 5 Cu source, the amount of lead/uranium/other dense material for a reactor, even a small one, would be considerable.

It appears to me that Co60 is as energetic, if not more so. I also wonder if the shielding requirement would be unique to that isotope since the release of gamma radiation happens as a secondary product from the decay to nickel-60. Therefore, Lead is less effective than depleted Uranium to stop gamma radiation, and there are better dense barriers. Lead and huge walls of concrete are cheaper than using depleted Uranium, or alloys of Osmium and other dense rare materials. Most decisions regarding shielding favor excessive cheap mass, rather than super dense expensive materials.

The problem isn't better engineering, we're designing reactors now that are passively safe, it takes an act of sabotage to make them meltdown now. The problem still remains, depending on your source strength, you're going to need a certain amount of shielding and that shielding can weigh a lot.

Another aspect is this, the Russians have created suitcase and hand gernade size nukes, we know minaturization is possible, the problem is the shielding and it always will be. You can't use coulombic forces to stop a neutron or a gamma like you can with a beta or an alpha, so the only way to really stop them is material that will increase the chance of interaction and potentially back scatter to the source till the harm said radiation is nil.

Yes, but... There is very little research into crafting a solution and the ones that have been built rely on the same technologies as were available in the 1940's. There are some advances due to the use of radiation in medicine. My link to the Toshiba 4S reactor was to show that you can scale down a TMI facility from 800MW to a Toshiba 10S at 10MW. It is incrementally more difficult to shrink it further, and as Pete suggested, a small part of their safety is housing the core at the bottom of a thirty foot shaft. However, they could not allow the soil under the house to become irradiated, so the shielding provided within the 6 foot diameter shaft must be sufficient to block the large bulk of the excess radiation. There may also be ways of containing rogue energetic particles using field effects to force their interactions into smaller spaces with less weight.

And... There is a difference in engineering required to create a safe 30-50 year sustained reaction, as opposed to releasing it in a fraction of a second. Well, now we get back to my original suggestion. Once you conceive it is in the realm of physical possibility, it is our fear of misuse that squelches further consideration.

One of my main beliefs of our age is that our process of educating people crushes out their ability to imagine the impossible, and then make it a reality. Consider the mobile devices we carry in our pockets... portable communicators, super computers, GPS...

Then consider the reasoned advice of some people without imagination.

"I think there is a world market for maybe five computers."
-- Thomas Watson, chairman of IBM, 1943

"There is no reason anyone would want a computer in their home."
-- Ken Olson, president, chairman and founder of Digital Equipment Corp., 1977

"640K ought to be enough for anybody."
-- Bill Gates, 1981

"Heavier-than-air flying machines are impossible."
-- Lord Kelvin, president, Royal Society, 1895.

[--Pete]

Hi,

Right, but one little slip up in the machining process can severly effect the implossion.

Yes. Hence castable molds, density measurements, and x-rays.

What should scare you more is that there are magazines out there with actual schematics and such on how to do it.

That is quite scary.

But what should scare you less is that, unlike what governments tell us, there are not so many people that want to blow us up.

While that is true, there are some. Consider what a handful did with three (almost four) airliners. Now imagine what a small group (maybe 5 or 6) could do with a nuclear weapon in a major financial center (New York, Geneva, Hong Kong, Tokyo). When terrorism consisted of one anarchist with a pistol shooting an unpopular archduke, what you say might have been true (but consider the events generated by that small cause).

Here we are talking abut explosives but there are much more ways of making victims....also for weird loners that are angry at the world and for terrorist that are organized.

We're talking about nuclear weapons. A bit more than what comes to mind when someone mentions explosives. The only thing I can think of more dangerous would be a perfect* biological weapon. While a nuke can potentially kill millions, a biological could kill billions.

* By perfect biological weapon, I mean one that has the following characteristics:
1) It must be transmittable as an aerosol (spray, cough, sneeze) as well as contact.
2) It must have a reasonable (5 minutes or more) lifespan outside the human body.
3) It must be resistant to antiseptics and antibiotics.
4) There should be a few days of mild symptoms, including a cough or sneezing, before severe effects are noticed.
5) During those days of mild symptoms, the infected party should be contagious.
6) After the symptoms become severe, death should follow rapidly -- preferably in a few hours.

Imagine a single container of such an agent released into the crowd of check in or security scan passengers at a major international airport. Before anyone even noticed, there would be a world wide epidemic. Before any effective measures could be taken, most of the population could be dead.

Now, I know that each of those six points are possible, indeed, exist. AFAIK they don't exist in a single organism, but then again the governments that deny doing experiments in biological warfare would hardly publish the results of those experiments.

The fact is just that luckily most people are sane enough not to want to do this.

Ah, but it only takes one, or perhaps a small group, to do vast amounts of damage.

--Pete

[--Pete]

Hi,

Once you conceive it is in the realm of physical possibility, ...

You should try working in a patent library for a few months. You'd be amazed at how many ideas are conceived that violate the conservation of energy (much less the change in entropy). And people have been conceiving flying horses for millenia, but the square-cube law stays in place.

One of my main beliefs of our age is that our process of educating people crushes out their ability to imagine the impossible, and then make it a reality.

But it also fails to educate them on how to evaluate the products of their imagination. I think this is the root cause of the shift from science fiction (which should at least be plausible) to fantasy. And the inability to distinguish fantasy from reality ... never mind.

"Heavier-than-air flying machines are impossible."
-- Lord Kelvin, president, Royal Society, 1895.

Nope, that's a canard.

--Pete

[eppie]

Ah, but it only takes one, or perhaps a small group, to do vast amounts of damage.

--Pete

Although I agree with what you wrote it wasn't directed to what I meant.

Nuclear weapons and biological weapons sophisticated enough to 'kill billions' are indeed luckily not easy to make for anyone with an internet connection.

I think potential terrorists would not wait with their attack until a nuke becomes available. They would probably use something more low-tech.
So although I share your concern about 'it only takes 1 or 2 people to create disaster' I think we could better use large part of our anti-terrorist resources for other things (like telling the 90% of people with a drivers license that can't drive safely to stay at home for example).

[Lissa]

For gamma / neutron radiation, here is source for computing necessary shielding.

And you'll note that there are given thicknesses required to stop any gamma or neutrons. It's well known that you need 7+ thicknesses to cut the radiation to near 0 levels and it's going to depend on how powerful a gamma or neutron source is (case in point, when I was at the University of Arizona, we had a 5 Cu Co60 source. We had a couple feet of lead to act as shielding, but even still, when the source was raised to irradiate a sample, you could still measure a slight rise in radiation outside the room where the source was stored (when placing samples in the irradiation chamber while the source was lowered, we were required to wear finger dosimeters and we had to make sure that when we reached in, we had to do so that the lead shielding blocked our body and head). Given the amount of lead we needed for just a 5 Cu source, the amount of lead/uranium/other dense material for a reactor, even a small one, would be considerable.

It appears to me that Co60 is as energetic, if not more so. I also wonder if the shielding requirement would be unique to that isotope since the release of gamma radiation happens as a secondary product from the decay to nickel-60. Therefore, Lead is less effective than depleted Uranium to stop gamma radiation, and there are better dense barriers. Lead and huge walls of concrete are cheaper than using depleted Uranium, or alloys of Osmium and other dense rare materials. Most decisions regarding shielding favor excessive cheap mass, rather than super dense expensive materials.

Lead is cheap and dense. Uranium 238 is one of the densest materials known to man, but it's also difficult to get in quantity, especially for an institution that does nuclear research. It also has some nasty, non-radioactive qualities to it as well. Because it's expensive to get and difficult to obtain even if you have the money people don't use it for shielding on irradiators. The other aspect is lead is a lot easier to mold and work with than Uranium 238.

And no, concrete is not a good choice for shielding a gamma source as it's not that dense and you need a dense material to adequately shield against gammas. You would have to have a similar amount of weight of concrete to get the same stopping power as lead (and it's worse if you can actually use Uranium). You have to have a lot between you and the radiation source and concrete just as too many voids between the atoms to do much good.

If you look at densitys of common materials, the best gamma shielding you could get is Pt (which will cost you a lot), Tungsten is slightly better than Uranium (19.6 Mg/cubic m vs. 18.9 Mg/cubic m), with lead coming in at a respectable 12.6 Mg/cubic m, and concrete coming in at a pitiful (in comparison to the above) of 1.75 to 2.4 Mg/ cubic m. So, in order to stop as effectively as lead, you would need about 5 times as much concrete than lead to shield a similar source.

The problem isn't better engineering, we're designing reactors now that are passively safe, it takes an act of sabotage to make them meltdown now. The problem still remains, depending on your source strength, you're going to need a certain amount of shielding and that shielding can weigh a lot.

Another aspect is this, the Russians have created suitcase and hand gernade size nukes, we know minaturization is possible, the problem is the shielding and it always will be. You can't use coulombic forces to stop a neutron or a gamma like you can with a beta or an alpha, so the only way to really stop them is material that will increase the chance of interaction and potentially back scatter to the source till the harm said radiation is nil.

Yes, but... There is very little research into crafting a solution and the ones that have been built rely on the same technologies as were available in the 1940's. There are some advances due to the use of radiation in medicine. My link to the Toshiba 4S reactor was to show that you can scale down a TMI facility from 800MW to a Toshiba 10S at 10MW. It is incrementally more difficult to shrink it further, and as Pete suggested, a small part of their safety is housing the core at the bottom of a thirty foot shaft. However, they could not allow the soil under the house to become irradiated, so the shielding provided within the 6 foot diameter shaft must be sufficient to block the large bulk of the excess radiation. There may also be ways of containing rogue energetic particles using field effects to force their interactions into smaller spaces with less weight.

And... There is a difference in engineering required to create a safe 30-50 year sustained reaction, as opposed to releasing it in a fraction of a second. Well, now we get back to my original suggestion. Once you conceive it is in the realm of physical possibility, it is our fear of misuse that squelches further consideration.

One of my main beliefs of our age is that our process of educating people crushes out their ability to imagine the impossible, and then make it a reality. Consider the mobile devices we carry in our pockets... portable communicators, super computers, GPS...

Then consider the reasoned advice of some people without imagination.

"I think there is a world market for maybe five computers."
-- Thomas Watson, chairman of IBM, 1943

"There is no reason anyone would want a computer in their home."
-- Ken Olson, president, chairman and founder of Digital Equipment Corp., 1977

"640K ought to be enough for anybody."
-- Bill Gates, 1981

"Heavier-than-air flying machines are impossible."
-- Lord Kelvin, president, Royal Society, 1895.

Once again, you continue to negliect that you must have a certain amount of material between you and the radiation source, this is something you cannot work around. Neither gammas nor neturons can be effected by coulombic forces to stop them (which is why it's easy to shield against alphas and betas since they're charged particles). The only way to stop gammas and neutrons is to have them interact with an atom and you have to have them transfer their energy to those atoms through scattering or absorbtion (and absorbtion could potentially lead to more neturons with a heavy enough atom as you could get a fission event or you may get a decay event that leads to a neutron release as well). This is the only way to shield against these two forms of radiation, there's no way around not putting materials between you and the gamma or neutron source.

---

Ah, but it only takes one, or perhaps a small group, to do vast amounts of damage.

--Pete

Although I agree with what you wrote it wasn't directed to what I meant.

Nuclear weapons and biological weapons sophisticated enough to 'kill billions' are indeed luckily not easy to make for anyone with an internet connection.

If they have the materials, it's actually a bit easier to make them if you have an internet connection as the information is available and in the public domain if you know how and where to look.

I think potential terrorists would not wait with their attack until a nuke becomes available. They would probably use something more low-tech.
So although I share your concern about 'it only takes 1 or 2 people to create disaster' I think we could better use large part of our anti-terrorist resources for other things (like telling the 90% of people with a drivers license that can't drive safely to stay at home for example).

Terrorist are looking to cause as much terror as possible. Conventional means we desencitize a population eventually (look at the Israelis for this). A WMD, be it a nuclear, chemical, or biological weapon, will cause no end of terror and, depending on who it's used upon, cause said population to lash out wildly causing a greater catastrophe (if you ask anyone in the military how you respond to having a WMD use upon you, you will see that almost universally they will tell you, you respond in kind with a WMD of your own). This is why using a WMD can be devestating to the world because the populous it's used upon will likely lash out (the Japanese were actually smart when we used the two atomic bombs on them, Bushido required them to fight to the end, but the atomic bombs gave them a way out to save face as you can't really fight an enemy like that although there were some still in the Japanese military that wanted to fight it out to the bitter end, but Hirohito won over the majority of Japanese and was able to end the war while retaining some face as demanded by Bushido).