Posted by: hikermor

Radiation - 02/20/19 08:34 PM


This is a followup article on an unusual situation at Grand Canyon National Park, where the park safety officer states that workers and visitors in one o the park buildings were exposed to dangerous levels of radiation from three buckets of uranium ore kept in the building.

The article cited above gives the response o experts who dispute, on various grounds, the dangers to which people were exposed. note that one of those quoted says that gamma rays pose insignificant dangers since they are stopped by almost anything.

This didn't agree with what I remembered from my long ago high school physics class so the quote below from Wikipedia:

"Gamma rays are ionizing radiation and are thus biologically hazardous. Due to their high penetration power, they can damage bone marrow and internal organs. Unlike alpha and beta rays, they pass easily through the body and thus pose a formidable radiation protection challenge, requiring shielding made from dense materials such as lead or concrete."

So something is screwed up. It is best to take a lot of breaking stories with a grain of salt (non-iodizing)....
Posted by: Phaedrus

Re: Radiation - 02/20/19 11:54 PM

Why did they have three buckets of uranium ore?!?!
Posted by: Russ

Re: Radiation - 02/21/19 12:10 AM

Alpha particles “are not, in general, dangerous to life unless the source is ingested or inhaled”.
Alpha particles are commonly emitted by all of the larger radioactive nuclei such as uranium, thorium, actinium, and radium, as well as the transuranic elements.

OTOH, Gamma radiation “is a penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei.”

So the question in my mind is, are they confused about the type of radiation or do they really think that gamma radiation can’t penetrate. Someone is confused.
Posted by: chaosmagnet

Re: Radiation - 02/21/19 01:58 AM

I’m not an expert by any means, but hikermor and Russ are right. Alpha radiation (aka Alpha particles) can’t penetrate the skin, so as long as you don’t ingest an Alpha emitter it mostly can’t hurt you. Beta radiation can hurt or kill you, and Gamma radiation is more dangerous.
Posted by: hikermor

Re: Radiation - 02/21/19 03:13 AM

Since the buckets were in a curatorial facility, presumably they were geological samples, probably from the Orphan Mine, situated on the South Rim not far away, and now no longer active. It was a critically important mine in the 1950s.

I dealt extensively with curatorial issues during my career in the NPS and I can guarantee that simply putting samples in a bucket is not the proper way to handle any museum specimen, even if not radioactive. It is feasible to properly store and care for radioactive items, but care is required - special packaging for sure.
Posted by: Russ

Re: Radiation - 02/21/19 02:04 PM

I’m not an expert either, but I can read. The Uranium ore which was stored in the buckets is typically something like 99% Uranium-238 (U-238 or 238U) which is common in nature. The ore is radioactive, but the type of radiation is significant.

I found the following section of the U-238 page interesting because it describes how U-238 is used for shielding. From that description, it’s fairly easy to discern that Uranium ore emits Alpha radiation (which was probably absorbed by the plastic buckets), but would not be a source of Gamma radiation as U-238 is used as shielding from Gamma radiation.
Radiation shielding
238U is also used as a radiation shield – its alpha radiation is easily stopped by the non-radioactive casing of the shielding and the uranium's high atomic weight and high number of electrons are highly effective in absorbing gamma rays and x-rays. It is not as effective as ordinary water for stopping fast neutrons. Both metallic depleted uranium and depleted uranium dioxide are used for radiation shielding. Uranium is about five times better as a gamma ray shield than lead, so a shield with the same effectiveness can be packed into a thinner layer.

Grand Canyon tourists exposed to radiation, safety manager says
“The report indicated radiation levels at "13.9 mR/hr" where the buckets were stored, and "800 mR/hr" on contact with the ore. Just 5 feet from the buckets, there was a zero reading.”
Scary if you don’t ask, milli-roentgen’s of what?

What does it all mean? I for one wouldn’t be concerned about the ore itself. I would be concerned about going public before all the facts and exposure data are in, possibly needlessly causing a scare. OTOH, why store multiple buckets of Uranium ore in a museum where some toddler could stick something in his mouth? That was just dumb.

Again, I’m not an expert on Uranium radiation, but this seems to be hype to make a point about a “cover-up”; sometimes you really don’t want to watch sausage being made.
Posted by: hikermor

Re: Radiation - 02/21/19 04:05 PM

" OTOH, why store multiple buckets of Uranium ore in a museum where some toddler could stick something in his mouth? That was just dumb. "

Correct. It's called sloppy curatorial procedures...

Curation is often the orphaned stepchild of science - not a whole lot of fun and excitement, but in the long run, very significant.
Posted by: EMPnotImplyNuclear

Re: Radiation - 02/22/19 07:11 AM

Originally Posted By: Russ
OTOH, why store multiple buckets of Uranium ore in a museum where some toddler could stick something in his mouth? That was just dumb.

Heh, who leaves a toddler next to buckets?