[Boogie (OP)]

Is there any safe way to produce a collumated high energy neutron flux?

If there is, I have an idea for a specialized gold metal detector.

Imagine if you will, a gold metal detector designed to find only gold using radiation. This gold metal detector would not use a standard search coil such as used in normal metal detectors. Instead, the search coil would be replaced with a device that could produce safe, local, collumated high energy neutron flux that could penetrate the ground and transmutate natural gold into radioactive Au198, which could then be detected with a standard radiation detector using a discriminator window around the Au198 energy level. Au198 has a short half life of about 2 and a half days, so it wouldn't take long for the radioactive gold to become safe enough to market. The nice thing about this gold detector would be that it would not detect anything but gold. No more digging up aluminum beer cans, hot rocks and pull tabs. NORM may be a problem if Au198 energy level is similar in strength to Thorium, Potassium or natural Uranium but these might be rejected through the use of clever analysis of multiple discriminator windows.

Sadly, the only way I'm aware of to produce such a neutron flux also produces a deadly massive fireball.

Any thoughts?

[CliffordK]

There are a few problems with your plan.

Large particles (alpha, beta, neutron) don't penetrate into the ground very far.  You would need a very powerful gun to penetrate more than a few inches. 

Would you get fusion? 

You would likely get a mess of radioactive materials, not just selective for gold. 

¹⁹⁸Au --> ¹⁹⁸Hg (stable) + β^-

One may not desire to contaminate one's gold with mercury, although presumably it would separate out easily enough. 

The beta radiation given off would likely only be detectable to less than an inch from the source.

[Boogie (OP)]

There are a few problems with your plan.

I like problems as long as they can be solved 

Large particles (alpha, beta, neutron) don't penetrate into the ground very far.  You would need a very powerful gun to penetrate more than a few inches, or perhaps a few feet. 

Correct me if I'm wrong, but don't moisture density gauges work using neutron? I thought they used neutron in moisture density gauges because they can penetrate several meters. A simple AmBe source probably isn't enough to transmutate natural gold, but I'm talking about an extremely high energy neutron flux like you would get from a nuke (but without the harsh effects). Lots of moisture in the ground might be a problem by over moderating the neutrons.

Would you get fusion? 

That would make for a bad day of prospecting.

You would likely get a mess of radioactive materials, not just selective for gold. 

That is where multiple discriminator windows come in handy.

¹⁹⁸Au --> ¹⁹⁸Hg (stable) + β^-

One may not desire to contaminate one's gold with mercury, although presumably it would separate out easily enough. 

The old timer prospectors did it on purpose back in the day. Careful retort can solve this problem.

The beta radiation given off would likely only be detectable to less than an inch from the source.

Beta? Doesn't Au198 produce a 414 keV gamma? You should be able to detect that easily.

If my comments are in error, please correct me. The biggest problem with my plan is obtaining a device that would produce a safe beam of neutrons. I think.

There are probably serious unpleasent ramifications such as transmutating other minerals into radioactive isotopes with a much longer half life than Au198 using this device. It would not be nice to leave a trail of hazardous waste everywhere this device was used. I wonder if some sort of filtering of the neutron beam using Cadmium, Copper or other material could prevent this, or maybe it wouldn't be an issue?

Edit : corrected double negative "It wouldn't not be nice"

[CliffordK]

You're right.

Beta + Gamma from ¹⁹⁸Au
According to this, mainly 411.8 KeV, but close enough, along with a few other energies.

I'll have to read more about the depth of penetration of neutrons.  I hadn't realized that they penetrate deeper than electrons, but perhaps they interact less with normal matter than the charged particles.

"Noise", of course, is one issue with contamination.  The other issue is just the radioactive contamination itself.  How much radiation would you have to shoot into the ground to get a noticeable effect?

[Boogie (OP)]

Intrestingly, fast neutrons are produced when Be is bombarded by alpha.

Cesium-137(Cs-137) and Americium-241/Beryllium (Am241Be) as used in portable
moisture/density gauges produce all four types of radiation. The alpha radiation will be
stopped by the stainless steel capsule in which the sources are enclosed. We need only be
concerned with the external neutron and gamma type radiation.
In the process of decaying to Barium-137 (Ba-137), the Cs-137 releases beta particles
which will be stopped by the capsule wall. Most of the Ba-137 is in an active state; in going
to a stable state it releases gamma energy at 0.662Mev. This gamma energy will be used
to determine the density of the measured material.
The Am-241 decays to Neptunium-237 (Np-237). In the process it releases 0.06Mev
gamma energy and alpha particles. This additional source of low level gamma energy would
confuse our density measurement so it is shielded out by a 1/8 inch thick cup of carbide or
lead. The alpha particles will not leave the capsule. However, by mixing the Am-241 with
Beryllium-9 (Be-9), the alpha particles then bombard the Beryllium which results in the
emission of free neutrons. These free neutrons, also known as fast neutrons will have an
average energy of 4.5 Mev. When these fast neutrons collide with an average of 19
Hydrogen atoms they become thermal neutrons with a reduced energy of around 0.025
Ev. It is these thermal neutrons that the gauge counts to determine the moisture content of
a material.

ref pdf : http://www.dot.il.gov/materials/radiationsafetyS34.pdf

If you are refering to electronic noise, unless designed poorly, most radiation detection systems can easily reject noise a little below the 60keV level of Am.

How much of a neutron flux is required to transmutate gold is a very good question.

[Bored chemist]

It wouldn't work, but that's not the biggest problem.

Dear Santa Claus.
Please send me a powerful neutron source for Christmas.
I promise to use it for searching for gold.
I will not, for example, use it to irradiate people I don't like. And I have not even considered using it to produce radioisotopes that I can poison people with.
Your Faithfully
A terrorist.
P.S. I have been really good this year.

[Boogie (OP)]

It wouldn't work, but that's not the biggest problem.

Dear Santa Claus.
Please send me a powerful neutron source for Christmas.
I promise to use it for searching for gold.
I will not, for example, use it to irradiate people I don't like. And I have not even considered using it to produce radioisotopes that I can poison people with.
Your Faithfully
A terrorist.
P.S. I have been really good this year.

I'm taking offense to this comment. How many times have I mentioned "SAFE"? A terrorist would not be concerned with safety.

Was this comment really nessesary?

I already posted that it "wouldn't be nice to leave a trail of hazardous waste", and asked about possible filters to prevent that. Do you not read everything or do you just go around trolling.

I do not appreciate being called a terrorist.

[CliffordK]

I think BC's point is that you will need radioactive material to generate the neutrons.  If you were making assaying equipment, you might be able to get away with a weak source.  But, if you're planning to penetrate deep into the ground, perhaps in a cone around your detector, you will likely need a fairly powerful source. 
While it may not be high enough purity for fission, it would be enough that it could be used as a poison.

Have you read about the ²¹⁰Po poisoning of Alexander Litvinenko?  Of course, you would be using a different radioactive material, but it would have an equal toxic potential.

With proper shielding, your device should be safe enough to use...  as long as it was directed into the ground.  But, care would have to be exercised with it.  Keeping it from leaking, or pointing at anybody.

[evan_au]

A nuclear fission reactor produces neutrons (plus a variety of highly radioactive isotopes, producing all flavours of radiation), but a critical mass of uranium is not very portable.

The neutrons don't interact with electrons, and the nucleus of an atom makes up such a small fraction of the atom's cross-section that most neutrons go straight through, allowing them to penetrate a long way into matter. This requires rather thick shielding.

The neutrons get emitted in all directions, and so to produce a collimated beam, you just leave a small hole in the thick shielding.

At least with the Beryllium neutron generator, it is easy to produce a collimated beam of alpha particles - but it is important to know if the neutrons are released in the same direction as the alpha particle (allowing a colimated beam), or in a random direction (dangerous). The reaction is illustrated here: http://en.wikipedia.org/wiki/Beryllium#Nuclear_properties

Note: Radiating earthworms, cockroaches & bacteria is probably not a good idea.

[Boogie (OP)]

Thanks Clifford and evan_au.

Hopefully we can continue this discussion without further sarcastic, useless and insulting comments from he whom I have lost respect. BC's comment was unjustified and unprofessional to say the least.

Anyway, how about cold fussion neutrons, which are supposedly safer? I wonder if they would do the job? Probably not without the same sort of problems or no transmutation is possible eh?

Well, maybe someday someone will figure out how to transmutate Au without disturbing other minerals by the use of filters or something. I do not wish to harm anyone, I just want to build an awesome gold detector.

[Bored chemist]

Do you no realise that any system, no matter how it created the neutrons, would be a very dangerous item indeed?

The whole idea is fundamentally misguided.
I wasn't calling you a terrorist, I was pointing out that the idea was absurdly dangerous.

Since there is little or no evidence that cold fusion exists and, a neutron is a neutron, no matter where it came from, I'm afraid that "how about cold fussion neutrons, which are supposedly safer? " is also a non-starter.

Incidentally, since I'm not being paid for this I have no call to be professional.
I think my comment was justified as a way of pointing out the fact that any such system would be so dangerous that it would be a terrorists dream come true.

Even if you could somehow "magically" tune it to only affect gold, plenty of people have gold teeth etc. and they would't thank you for making them radioactive.

Neutrons are readily scattered, particularly by hydrogen atoms in things like wet soil, so any "collimated" beam wouldn't stay that way. The operator would get a significant dose from the back scattered neutrons.
The same strong interaction with hydrogen (the commonest atom in the body) is why neutrons are particularly harmful to biological tissues like us.

This idea is far too dangerous to take seriously- so I didn't.

[Mazurka]

The idea sounds like an advancement on the "Nucelar Density Gauge".  This is a tool most often used for measuring density (i.e. compaction/ stabillity) in civil engineering projects such as roads and landfill for quality control purposes. Using a Radium source it can also be used for deep ground investigation such as to identify voids (old mines/ caves) or low density rock up to 300m depth.

Neutron Density Tools are also commonly used in the Hydrocarbon / Mineral industry as part of "wire line logging" arrays dropped down boreholes.

In the UK the HSE has issued guidance setting out the risks relating to these devices. As the sources (typically Cesium or Americium/Beryllium for shallow detectors) are regulated under the Radioactive Substances Act (and other legilsation) it sets out some of the risks - to operators, in transporting and damage to shielding (fire/ physical damage) etc. - easy enought to google if you are interested.

I guess that the device you are proposing would have to have a significantly stronger source to transmute sufficent gold to detect - which would probably have to be vehicle mounted to accomodate sufficent shielding.  I have no idea how big the detector array would need to be either - which if vehicle mounted would also add cost/ inconveinence...   Althought I like the idea of a discriminating detector - which particularly in wire line applications could be the next step.

(Personally I do not think that commercially it would offer many advantages over more "traditional" geochemistry based surveys (either borehole core / mud sampling or direct sampling from "ditchwitch" type trenches) or petrographic analysis aimed at pathfinder minerals from drill core etc.)   

[Boogie (OP)]

Ok then, I guess I'll put my nuke powered metal detector on the back burner until more advancements are made in safer neutron generating machines.

From now on, BC, I would appreciate it if you let me write my own letters to Santa. I don't like the way you word things! If all I get is a lump of coal this year, I'm going to be so p***ed at you!

If anyone figures out a way to use X-ray, microwaves, radio waves or some sort of filtered cold brewed neutron beam to accomplish what I'm after, let me know.

[Bored chemist]

Boogie,
I was writing my letter to Santa.
A safe cheap neutron source would be a seriously cool toy.
Unfortunately I suspect that the consumer safety people would want it covered in a layer of safety warnings about a mile thick (and liberally sprinkled with boron) , and the real pig is that I'd agree with them if anyone else wanted one.

[majorminor]

First of all,  credit to boogie for an inventive try at modern pan-handling .
I did have a good laugh when Mr boogie thought Mr chemist was calling him a terrorist. The idea of a terrorist trying to make a terrifying weapon under the guise of a gold detector made me smile.