Don't panic, but your avocado is radioactive—study eyes background radiation of everyday objects

October 7, 2016 by Robert Hayes, North Carolina State University
Credit: arsheffield/Flickr

Most people assume all radioactive materials are dangerous, if not deadly. But a new study on the radiation emitted by everyday objects highlights the fact that we interact with radioactive materials every day. The goal of the work is to give people a frame of reference for understanding news stories or other information about radiation and nuclear safety.

"We did this study because understanding how much radiation comes off of common household items helps place radiation readings in context – it puts things in perspective," says Robert Hayes, an associate professor of nuclear engineering at North Carolina State University. "If people understand what trace levels of radiation mean, that understanding may help prevent panic."

The researchers used a portable meter to measure the external gamma radiation emitted in a North Carolina home. The radiation was measured in microgray per hour (μGy/hr).

Avocados, for example, gave off 0.16 μGy/hr of gamma radiation – slightly less than the 0.17 μGy/hr emitted by a banana. Bricks gave off 0.15 μGy/hr, while smoke detectors (with their americium components) gave off 0.16. By way of comparison, natural uranium ore measured 1.57 μGy/hr.

"If you're surprised that your fruit is emitting gamma radiation, don't panic," Hayes says. "The regulatory level for workers – which is safe – is exposure to 50,000 μGy per year. The levels we're talking about in your household are incredibly low."

Explore further: Transition radiation detectors work in record-high energy fields

More information: Richard D. Milvenan et al. Contributions of Various Radiological Sources to Background in a Suburban Environment, Health Physics (2016). DOI: 10.1097/HP.0000000000000564

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katesisco
3 / 5 (2) Oct 07, 2016
Hmmmmmmm........So a tad more wont hurt? That's the reasoning behind chlorine, fluoride, lead, mercury, etc? This is just short of the making a overwhelming amount of something a blessing. If you cant alter it call it an advantage.
xstos
1 / 5 (1) Oct 07, 2016
I'd be more interested in the risk factors as compared to the low levels of big pharma drugs permeating most industrialized water supplies, VOCs, and all sorts of nasty industrial chemical carcinogens, not to mention the pesticides in/outside the fruit. If I ate bananas or avocados for every meal for the rest of my life, would I die one or two days early from cancer or would it be decades? These articles always stir the sensationalism pot but never actually give any indication on what to do with their tidbits of information. Golly gee bricks are radioactive. Facts are pretty much useless without contextual statistics to make it actionable.
antialias_physorg
not rated yet Oct 07, 2016
So a tad more wont hurt? That's the reasoning behind chlorine, fluoride, lead, mercury, etc?

That's not what they're saying. But the point is to understand that if an additional radaition source is far below the natural exposure variability then you shouldn't immediately freak out.

A better way to measure these things is not in Gray (or Gray per hour) but in Sievert - which is the biological relevant dose (called 'equivalent dose' or - if including different sensitivities of different body regions - the 'effective dose').

Gray only measures how much energy is deposited in your body. But there are different types of radiation that differ greatly in how dangerous they are.
E.g. being exposed to an equivalent *energy* amount of alpha and gamma radiation (equal Gray value) can have orders of magnitude difference in how likely they are to cause cancer (Sievert).

In short: Sievert are a good unit to judge the risk of getting cancer. Gray gives you the energy emitted.
Gigel
not rated yet Oct 07, 2016
AND to put it in perspective for practical reasons, 50 000 uGy/year = 5.7 uGy/hr.

The study is done where it's not much the case. I challenge the authors to do this study: 1) for mountain mushrooms (mushrooms accumulate heavy metals and mountains retain them), and 2) in mountain areas contaminated by a nuclear accident, like the Chernobyl accident.

This was studied before and the findings indicated that mushrooms from contaminated areas have way too much radioactivity. But I say redo it.
Gigel
not rated yet Oct 07, 2016
Golly gee bricks are radioactive. Facts are pretty much useless without contextual statistics to make it actionable.

Rocks like granite are more radioactive. Concrete is radioactive and it emits radon, which could cause lung cancer. But then humans lived in caves, which are also radioactive, so probably we are resistant to radiation.
thingumbobesquire
not rated yet Oct 08, 2016
For what it's worth: My 90 year old father tells of an interesting time after he returned from serving in the army in the Pacific theater. He worked at a chemical plant in Niagara Falls that was part of the Manhattan project. He says that there was an open atomic pile in the yard that workers walked by daily. I am 63 years old and grew up adjacent to the Love Canal. I used to play almost daily during summer recess on a baseball diamond constructed on top of the buried chemical drums there. I am in excellent health. My grandmother lived to be 101, my mother is now 93. Hmm...
Gigel
not rated yet Oct 08, 2016
@thingumbobesquire: Your family may be carrying some genes that predispose you to live longer than the average people. Maybe they also protect against radiation damage.
jackofshadows
not rated yet Oct 08, 2016
The nuetron flux from brick is far, far more dangerous than the gamma-ray emissions. My preferred unit of exposure is the REM (Roentgen Equivalent Man) as it is weighted by type of exposure /damage to tissue due to damage. Not that it matters here, already terminal for another reason (cervical spine). Eventually, I expect, we'll switch to "safer" materials for economic reasons having nothing to do with the radioactivity.
Eikka
not rated yet Oct 09, 2016
E.g. being exposed to an equivalent *energy* amount of alpha and gamma radiation (equal Gray value) can have orders of magnitude difference in how likely they are to cause cancer (Sievert).


And gamma is the worst.

Sievert is used for stochastic effects of low levels of radiation, and 1 Sv (1000 mSv) carries with it a 5.5% chance of eventually developing cancer based on the linear no-threshold model.

The problem is that the linear-no-treshold model is inaccurate at doses lower than 100 mSv and over-estimates the risk of cancer by ignoring biological mechanisms for radiation tolerance and cell repair, so using them for low level background radiation is a bit iffy.

The conversion factor between Gray and Sievert at low levels of radiation is more or less guesswork, and workplace safety limits like 20 mSv/y are just arbitrary numbers pulled out of a hat some 50 years ago when nobody knew any better.
antialias_physorg
not rated yet Oct 09, 2016
[qAnd gamma is the worst.
Depends. If you ingest an alpha (or beta) emitter that is far worse than a gamma emitter of the same Gray value. Outside the body an alpha emitter isn't much of an issue because alphas will be blocked by almost anything (e.g. the outer layer of dead skin cells) pretty effectively. Betas are somewhere in between. If you have skin contact with beta emitters then they are trouble.

Radiation and biology is tricky business to understand. It depends so much on what type of emitter and how someone is exposed to them (internally, externally, from afar, in contact, through accretion in foodstuffs, ...)
That's why giving the public Becquerel or Gray values when talking about nuclear accidents isn't particularly useful.
Eikka
not rated yet Oct 09, 2016
The idea behind the Sievert radiation limits is that if you work 50 years under a radiation level of 20 mSv you get a 5.5% chance of cancer in your lifetime, which is deemed "acceptable".

But that has never actually been measured. The Sievert as a measurement is based on people and lab animals who have recieved much more than 1000 mSv in a short order of time, such as over the course of a single day, and the accumulated exposure was then extrapolated downwards in amount and upwards in time.

Which is like observing that a hit on the head with a lead pipe leads to skull fractures - the more likely the harder it hits - so it is extrapolated that getting enough raindrops on your head will eventually fracture your skull the same. This assumption was based on the idea that the radiation accumulates in the body and the genetic and tissue damage done is never repaired or eliminated otherwise.
Eikka
not rated yet Oct 09, 2016
Radiation and biology is tricky business to understand. It depends so much on what type of emitter and how someone is exposed to them (internally, externally, from afar, in contact, through accretion in foodstuffs, ...)
That's why giving the public Becquerel or Gray values when talking about nuclear accidents isn't particularly useful.


It's far more useful than someone's Stetson-Harrison estimates from 50 years ago, because at least it is based on something that is objectively measurable and relateable, and comparable.

Depends. If you ingest an alpha (or beta) emitter that is far worse than a gamma emitter of the same Gray value.


A weak beta emitter ingested is not more harmful than a strong gamma emitter externally, because the individual particles or radiation don't necessarily carry enough energy to harm tissue. I.e. a bunch of low-energy electrons vs. a single high-energy gamma photon of equal total energy are not going to have the same effect.
Eikka
not rated yet Oct 09, 2016
That's why giving the public Becquerel or Gray values when talking about nuclear accidents isn't particularly useful.

Actually, it is the same thing because there's a direct conversion factor between Gray and Sievert for various cases.

You can't actually measure Sieverts, because the figure is based on the assumed effects of radiation exposure. You first measure radiation in Gray or Bequerel or any other absolute figure, and then convert it to Sievert based on what you assume the radiation is, and what you assume the effects will be. It is simpy assumed that the effect is linear and cumulative because otherwise the conversion becomes practically impossible.

If you have a dosimeter showing mSV, it is actually measuring Gray and the scale is simply re-labeled.

Reporting exposure in Sieverts is problematic because it's a second-hand interpretation of the situation. It's saying "this is how much cancer we estimate it will cause", which will be factually wrong.
TheGhostofOtto1923
not rated yet Oct 09, 2016
As always, I like to cite.

"... you eat the gamma cookie, put the alpha in your pocket, and the beta in the box.

"Gamma radiation is much more penetrating than the other two, so more of it will escape your body without being absorbed. Alpha radiation is most dangerous inside your body because of the high energy and ionization of individual alpha particles. However, the particles have very short range, and so would be blocked by the cloth of your pocket, and mostly harmless. Beta radiation is more penetrating than alpha, so put it in the box and it will all be blocked."

-which is the standard answer given by profs in classes.

But once again thanks for all the guessing, posturing, confronting, and wasted spacetime.

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