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NOTE: This page is not meant to be a complete authority on the subject; it's just a quick primer on radiation, safety, and radioactive mineral collecting. Please read the page in its entirety.
1. What is radiation? What kinds of radiation are there?
"Radiation" in the common sense actually refers to "ionizing radiation" -
a term for invisible particles or waves that have high enough energy to strip
electrons from atoms, causing chemical changes. The three basic types of
natural radiation are alpha, beta, and gamma. There
are also X-rays and neutrons.An alpha particle is composed of two protons and two neutrons- essentially, it's a helium nucleus, an ionized helium atom (i.e., a helium atom devoid of its electrons and having a net charge of +2). Alpha particles are comparatively large and cannot penetrate much more than a sheet of paper or a few inches of air. However, they are extremely potent ionizing agents because they interact with plenty of matter in their [short] path.
A beta particle (actually, "beta-minus" particle, since it has a charge of -1) is simply a stray electron- not from the usual, orbital region of an atom, though- beta particles spring into existence directly from an atom's nucleus as the result of neutron breakdown. "Beta-plus" particles are positrons or "positive electrons", something encountered seldom in nature.
Beta radiation can be stopped by a few centimeters of wood, plastic, or glass.
A few millimeters of aluminum will also stop most beta. Do not use lead or
other highly-dense materials to shield from beta radiation, unless the materials
are very thick. See below to read why. Gamma radiation is nothing more than high-energy photons (invisible light; electromagnetic waves). It has no charge, but its high energy means that it can cause ionization. Fortunately, gamma rays move so fast and have such energy that they often pass right through matter without interacting at all.
Incidentally, gamma "rays" could technically be called "particles" in the
sense that photons are both waves and particles, but the word "rays" is normally
used for this type of radiation. Don't fret if you have trouble grasping
the wave-particle duality of light; even the great quantum physicist Niels
Bohr said that no one can truly understand this concept.X-rays (also called "Roentgen rays") are also high-energy photons, and in fact, some x-rays have high enough energy that they are essentially just gamma rays with a different name. X-rays are not really a different category from gamma radiation; they're just photons in a different energy range.
Neutrons are yet another radiation type; however, stray neutrons do not often exit the nucleus of an atom, except in cases of nuclear fission (the splitting of the nucleus). Some elements undergo spontaneous fission; the synthetic isotope californium-252 is a strong neutron emitter because it has an exceptionally high rate of spontaneous fission, while the natural isotope uranium-238 is an extremely weak neutron emitter because it undergoes spontaneous fission far less frequently. Spontaneous neutron emission by U-238 is so sparse, in fact, that ordinary detectors won't even pick it up.
2. Aren't radioactive minerals dangerous?
If stored and handled properly (see below), they are not cause for worry.
The vast majority of the radioactive content in minerals is either uranium-238
or thorium-232, both of which have extremely slow decay rates (and therefore
have low activity compared with short-lived, man-made radioactive elements).
Key points to remember when collecting radioactive minerals:1. Radiation levels taper off drastically as one moves farther away from the mineral sample. The difference between radiation at 1 cm away and radiation at 1 meter away is enormous. It is an inverse-square relationship.
2. Radioactive minerals do produce radon, but it is a very slow process. However, it is best not to store them in one's sleeping quarters. Areas where radioactive minerals are stored should have good ventilation so radon does not build up.
3. The minerals should not be carried in the pockets (especially not near the waist area), nor should they be brought near the eyes. The lens of the eye and the reproductive organs are especially vulnerable to radiation damage (although, again, brief exposure is probably not harmful; consider it this way: a CT scan exposes these organs to much more radiation than you'd get from brief handling of a mineral specimen). If you want to look at radioactive minerals with magnification, use a micro/macroscope, not an eye loupe. It's also preferable to limit yourself to micromount or thumbnail-sized specimens when using magnification. For highly radioactive specimens, consider using a microscope with a projector screen or computer monitor attachment.
4. The everyday sources of radiation that the average person encounters are more dangerous than a properly handled radioactive mineral collection. Naturally occurring potassium-40 is present in all of our cells in small amounts, but this represents more of a hazard than a chunk of radioactive ore sitting in a display case- because the radiation from K-40 is already inside us and is closer to areas where it can cause damage.
5. Generally speaking, don't horse around. Wash the hands after handling radioactive minerals. Do not crush, saw, or grind radioactive minerals so as to cause their dust to enter the air, especially indoors. Do not smoke, drink, or eat while handling radioactives.
6. ALWAYS store with proper labels and in such a way that everyone knows what they might be touching. Keep the specimens locked in a case where children and pets cannot get into them.
3. Can a radioactive mineral cause nearby objects to turn radioactive too?
The answer is no. It typically requires neutron
bombardment (as in a nuclear power plant) to make something radioactive.
The amount of "induced radioactivity" caused by natural uranium and thorium
is vanishingly small. Alpha particles from the decay of Th and U are sometimes
captured by the nuclei of lighter elements, ejecting neutrons from these
nuclei, but this is not a very efficient (or common) process.
In other words: you can store your radioactive minerals for
many, many years in a box, but they won't cause the box itself to become
radioactive. Consider a crystal of uraninite in quartz, embedded in the side
of a mountain for a billion years. If radioactive rocks could somehow "cause"
radioactivity in their surroundings, then the surrounding quartz would become
radioactive, which would then induce the surrounding rocks, and so on. Eventually
the entire earth would become highly radioactive in such a scenario! We would
never have existed on earth if such were true. 4. Is shielding necessary for radioactive mineral collections?
Generally, no... as long as you don't amass a huge pile of highly radioactive
ore and stand near it habitually. As stated before, distance is the best
form of "shielding".
When making a display cabinet, build it fairly deep so the larger radioactive
specimens can sit 1-2 feet back from the viewing glass. Then use a double
layer of glass, acrylic, or plexi as the cabinet front. This combination
will stop all of the alpha radiation and nearly all of the beta.
Thick metal or concrete will stop much of the gamma radiation, but not all.
Recall that alpha and beta are more dangerous than gamma because they are
charged and because they interact with matter more frequently. Gamma radiation
is often cited as being "the most dangerous" of the three major types, but
that's only because it's the most penetrating form of radiation.
Certain types of shielding can actually
be worse than none at all. Lead and other dense metals (e.g., tungsten) can
emit X-rays when exposed to beta particles such as those thrown out by the
natural decay products of U-238 and Th-232. This phenomenon is called bremsstrahlung.
If the lead is thick enough, the X-rays won't get out the other side of it.
Nevertheless, if you're going to use shielding for a mineral display, it's
best to make it out of wood, acrylic, or plexiglas. For a storage box, you
could use aluminum or other beta particle shielding as the inner layer, then
lead on the outside.5. Who should collect radioactive minerals?
Simply put: only responsible adults who have educated themselves on the potential
hazards should collect radioactive minerals. With proper safety precautions,
this can be a very interesting area of study.6. Just how radioactive are these minerals?
Following is a relative dose scale for comparison (see table). Radiation,
as it pertains to human health, is often measured in a dose called millisieverts
(mSv). Something that decays faster (has a shorter half-life) will give a
larger dose of radiation than the same amount of a slower-decaying material
in the same time interval (Cobalt-60 is therefore much, much more dangerous
than Uranium-238.). You would have to hold a radioactive mineral specimen
in your hand for many hours to exceed the currently accepted safe exposure
limit, even for a uranium miner. Following is a rough scale, assembled from
various sources (See Radiologyinfo.org;
Human
Health Aspects of High Level Radioactive Wastes; Nuclear Waste Management
Organization (NWMO) data; World Health Organization (WHO) data; WISE Uranium Project):| Calculated
dose from holding a ca. 5 x 10 cm chunk of rich uranium ore in your hand
for 1 hour |
0.03-0.06 mSv |
| Chest X-Ray |
0.1 mSv |
| Average background exposure for 1 year |
3 mSv |
| Lower intestinal X-Ray |
4 mSv |
| Living on the Colorado Plateau for 1 year |
4.5 mSv |
| Typical yearly dose for a uranium miner |
5-10 mSv |
| Calculated
dose from holding a ca. 5 x 10 cm chunk of solid uranium metal directly
against your skin for 1 hour |
10 mSv |
| Full-body CT scan |
10 mSv |
| Maximum allowed yearly dose for uranium miners |
20 mSv |
| Lowest dose for which there is any statistical evidence of
causing cancer |
50 mSv |
| Acute dose causing radiation sickness |
1,000 mSv |
| Acute dose typically causing death |
7,000-10,000 mSv |
| Acute dose used to destroy cancer cells |
10,000+ mSv |
| Calculated
dose from one hour of exposure to one milligram of Cesium-137 at a distance
of one millimeter from the skin |
200,000 mSv |
| Calculated
dose from one hour of exposure to one microgram of Cesium-137
at a distance 0.001 cm (less than one human cell-length away from it) |
1,000,000 mSv |
Unit conversion: 1 millisievert = 100 millirems. Thus, 0.05 mSv in one hour corresponds to 5 mR / hr.
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