Can meteorites be radioactive?

Meteorites have long fascinated people due to their extraterrestrial origins and scientific value. One common question is whether meteorites can be radioactive. The quick answer is yes, some meteorites are naturally radioactive. Meteorites are broken off fragments of asteroids and comets that have collided with Earth. Asteroids and comets contain varying amounts of radioactive elements, which can be carried over into meteorites. Typically, the level of radioactivity is low and not dangerous. However, precautions should still be taken when handling meteorites, especially newly fallen ones where radiation levels may be higher.

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What causes radioactivity in meteorites?

There are three naturally occurring radioactive elements that can be found in meteorites: uranium, thorium, and potassium. These elements have unstable isotopes that decay over time, giving off ionizing radiation. Here is a quick overview of each element:

Uranium – Uranium has several radioactive isotopes, the most common being uranium-238 and uranium-235. As uranium undergoes radioactive decay, it transforms into other radioactive elements like radium and radon.

Thorium – The isotope thorium-232 is radioactive and decays into radium and radon gases. Thorium is more abundant than uranium in meteorites.
Potassium – A small fraction of potassium is the radioactive isotope potassium-40. It decays to argon and calcium.

These three elements were present when asteroids and comets originally formed over 4.5 billion years ago in the solar system. As a result, meteorites broken off from these bodies can contain detectable levels of uranium, thorium, and potassium isotopes.

How much radiation do meteorites emit?

The level of radiation emitted by meteorites varies considerably depending on the type and source of the meteorite. Here are some key points on meteorite radioactivity levels:

Most stony meteorites have very low levels, often barely above the background radiation on Earth. A common measurement used for radiation dosage is millisieverts per hour (mSv/hr). The background dose from cosmic radiation is around 0.1-0.2 mSv/hr. Stony meteorites typically emit 0.003 – 0.3 mSv/hr.
Iron meteorites tend to be more radioactive, sometimes measuring 1-3 mSv/hr. This is due to higher uranium content in their minerals.

Achondrite meteorites derived from the Moon or Mars have radiation levels from 0.01 – 0.8 mSv/hr.
Fresh falls or finds have higher radiation because short-lived radon gas has not yet dissipated.
Meteorite specimens kept enclosed in a collection for years have lower radiation as the radon gas escaped.

For comparison, a transatlantic flight exposes passengers to 0.05 mSv of cosmic radiation. So handling the majority of meteorites results in only slightly increased exposure above ordinary background radiation. Exceptions are very rare meteorite types that can havedose rates up to hundreds of mSv/hr, requiring careful handling procedures.

What radioactive elements are found in meteorites?

As mentioned earlier, uranium, thorium, and potassium isotopes account for most of the radioactivity from meteorites. Here is more detail on the specific radioactive elements:

Uranium decay series

Uranium-238 and uranium-235 decay through a series of 14 radioactive elements before stabilizing into lead-206 and lead-207 respectively. Some of the prominent radioactive elements in the decay chains include:

Radium – Especially radium-226 with a half-life of 1600 years.
Radon – Radon isotopes are gaseous and can escape from meteorites. The most common are radon-222 and radon-220.
Polonium – Polonium-210 and polonium-214 are present, with polonium-210 having a 138 day half-life.

Thorium decay series

The thorium-232 decay series progresses through 12 radioactive isotopes to lead-208, including:

Radium – Radium-224 and radium-228 are common.
Radon – Radon-220 (also called thoron).

Lead – Lead-212 and lead-208.

Potassium-40

Potassium-40 decays directly to argon-40 and calcium-40 with a half-life of 1.3 billion years. The argon gas escapes from the meteorite rock over time.

Carbon-14

Carbon-14 is produced from cosmic rays interacting with elements in the meteorite. It is present in very low concentrations and is used for dating meteorites.

Are meteorite radiation levels dangerous?

For almost all meteorites, the radiation levels are not considered dangerous or a health risk. However, there are some precautions that should be taken:

Wash your hands after handling meteorites to avoid ingesting any dust particles.
Work with meteorites in a well-ventilated room to allow any radon gas to dissipate.

Limit close contact handling time for very radioactive specimens emitting over 5 mSv/hr.
Store meteorites in sealed plastic for radon buildup.
Always use a radiation monitor when handling newly fallen meteorites.

Iron, pallasite, and certain carbonaceous chondrite meteorites have higher uranium content and need cautious handling.

Following basic radiation safety guidelines is advised, especially for people who frequently work with meteorite specimens. The radiation exposure remains relatively low from briefly handling the majority of meteorites.

Could a meteorite make you sick?

It is highly unlikely that handling a meteorite could make you sick or cause observable health effects. Here are some key points:

Acute radiation sickness requires short-term doses over 100 mSv. Meteorites do not emit radiation nearly this high.
Long-term exposure risks like cancer require chronic radiation over years. Brief contact with meteorites is not a concern.
Ingesting meteorite dust particles could theoretically be hazardous if they are highly radioactive. But this risk is extremely low.

Washing hands after handling and avoiding grinding meteorites prevents ingestion of dust.
Fresh falls may release radon gas trapped in the cracks. But radon dissipates quickly into the atmosphere.
Radioactive elements like polonium and radium are not very soluble and so unlikely to enter the body from touching meteorites.

Monitoring radiation levels is recommended when preparing meteorite thin sections or powdering samples. Otherwise, casual exposure to most meteorite specimens presents a negligible health risk.

Are chondrites or iron meteorites more radioactive?

Iron meteorites are generally more radioactive than chondritic meteorites per unit of mass. Here is a comparison:

Iron meteorites – Average around 0.5 parts per million uranium. The mineral kamacite contains trace uranium.

Chondrites – Ordinary chondrites have 0.05-0.1 ppm uranium. Carbonaceous chondrites have 0.01-0.05 ppm uranium.
Achondrites – Lunar and Martian meteorites contain 0.01-0.1 ppm uranium.

However, chondrites often have much larger total mass so their overall radiation can still be significant. Other factors like radon accumulation and potassium-40 levels also contribute to radioactivity.

Iron meteorites also have higher gamma radiation since kamacite concentrate uranium decay products. Handling iron meteorite specimens requires more precautions for this reason. Chondrites emit primarily alpha and beta radiation which is only hazardous if ingested.

Are meteorite finds or falls more radioactive?

Fresh meteorite falls generally have higher radiation levels than finds due to radon gas accumulation. Here is a comparison:

Finds – Meteorites that have been on the ground for months or years have lost most of their radon gas which dissipates into the air.

Falls – Newly fallen meteorites still contain concentrated radon gas in cracks and voids which increases gamma radiation emissions.

For example, a fresh meteorite fall might measure 0.2-0.4 mSv/hr while a find of that type radiates at just 0.04 mSv/hr. The radioactivity of finds can increase slightly again when cracked open as new radon accumulates. In general, fresh falls require more handling care until measured radiation drops to safe levels through degassing.

Can meteorites set off radiation detectors?

Yes, some meteorites contain enough radioactive elements to trigger radiation alarms and detectors. Here are some examples:

Airport security – Iron or stony-iron meteorites can set off alarms due to higher gamma radiation.
Geiger counters – Measurable clicks indicating alpha, beta, and gamma radiation.
Radon detectors – New falls emit radon gas which can be picked up by sensors.

X-ray fluorescence – Detects presence of uranium and thorium.

Radioactive meteorites are perfectly natural objects not associated with any nuclear hazard. But they may require additional screening or procedures when passing through security checkpoints. Proper labeling and documentation of meteorites is recommended to avoid undue concern by inspectors.

Has anyone ever been sickened by a meteorite?

There are no documented cases of someone becoming acutely ill due solely to radiation from handling a meteorite. Sickness requires very high radiation doses over a short period which meteorites do not emit. However, theoretical risks do exist such as:

Ingesting fragments of a highly radioactive meteorite.
Extended close contact with large radioactive meteorites.
Radon gas buildup in an enclosed room full of meteorite samples.

Grinding meteorites into breathable dusty material.

Following basic radiation safety precautions and monitoring levels before processing meteorites mitigates these risks. Meteorites are generally not dangerous to briefly handle with bare hands. Their historical and scientific value outweigh the miniscule health hazards for most collectors and researchers.

Conclusion

Meteorites can definitely be radioactive due to naturally occurring uranium, thorium, and potassium isotopes. However, the radiation levels are typically low enough that brief handling does not pose a significant health risk with some basic safety measures:

Monitor radiation when preparing thin sections or powdering meteorites.
Wash hands thoroughly after handling meteorites.
Work with meteorites in a ventilated area.

Take precautions with newly fallen meteorites until degassing occurs.
Limit close contact handling time for specimens over 5 mSv/hr.
Ensure proper labeling for passing through security checkpoints.

While meteorites can trigger radiation detectors, acute effects or sickness from exposure is highly unlikely given the low doses. Common sense handling procedures allow for safe study and collection of these fascinating extraterrestrial objects.