Uranium Materials
Miscellaneous
- Family: Other
- Region: None
- Mined At: Unspecified
- Raw Mineral: No
- Generic: No
Notes
This subject is covered in detail in discussions on clayart during late 2003 and early 2004. The dialog was started because someone submitted an old glaze containing uranium.
The following material comes from a source that we have now lost, if you know who wrote it please contact.
WHAT IS "DEPLETED" URANIUM?
Uranium is an element which has isotopes, that is, varieties that have different molecular weights. Uranium's three natural isotopes are: U-238, U-235, and U-234. Only U-235 has the right weight for atomic reactions. "Depleted" uranium is uranium from which U-235 has been removed.
In the 1970s and 1980s, some potters, teachers and ceramic chemical suppliers incorrectly assumed that "depleted" uranium was not radioactive. This misinformation found its way into many books and publications. While depleted uranium is less radioactive, it is still a significant hazard because all isotopes of uranium are radioactive.
THE NUCLEAR REGULATORY COMMISSION (NRC)
In a 1980, the NRC clearly said that the use of uranium glazes
should not be allowed ("Environmental Assessment of Consumer
Products Containing Radioactive Material," Nuclear Regulatory
Commission (NUREG/CR-1775), October 1980). However, NRC decided
not to waste its time banning uranium glazes because their
investigation showed that there were no known commercial
producers of uranium-glazed ware in 1980.
The NRC also "investigated" uranium use in art pottery and
enamels. They talked to "the art department of a major
university", a "spokesperson for an enamelists guild," and the
"purchasing agent for one of the ten largest public school
districts in the U.S." These people all denied using or buying
any uranium. Yeah, right.
As late as 1985, pottery catalogs still listed uranium. To this
day, I still occasionally find uranium oxide in university
ceramics departments.
In 1984, NRC banned uranium-containing enamels after a lot of
radioactive jewelry was imported into the US. This also meant
that domestic uranium enamels such as Thompson's Burnt Orange #
153 and Forsythia # 108 were taken off the market. I still find
stockpiles of these enamels in schools.
Even without a ban, the fact that the NRC is on record saying
that uranium glazes should not be allowed puts uranium-users at a
moral and ethical disadvantage. And just imagine explaining it to
your customers!
RADON
Uranium emits both radiation and a cancer-causing radioactive gas
called "radon." Uranium-containing fossils and rocks in museum
collections have been shown to require special ventilation to
control radon from these specimens. Radon also is emitted from
uranium oxide chemicals or even large stocks of uranium-glazed
ware.
Radon, of course, also could be present in basement pottery
studios from radioactive minerals in the soil or in cement. EPA
recommends that all home owners test for radon. Combining
basement pottery with a radon problem with use of uranium glazes
could really boost your total exposure.
TOXICITY
Unrelated to its radioactivity, uranium is also toxic to the
kidneys and can cause blood disorders. Soluble uranium from
ceramic ware, ingestion of small amounts of glaze or enamel dust
from lung clearing mechanisms, or absorption of soluble compounds
by the lungs would be potential sources for this kind of
toxicity.
To protect workers from the toxicity of uranium dusts, OSHA
assigned a permissible exposure limit of 0.2 milligrams per cubic
meter (mg/m3) in air for insoluble compounds and 0.05 mg/m3 for
soluble ones.
Inhalation of very small insoluble dust particles into the
alveoli where there are no lung clearing mechanisms effectively
places an emitting radioactive particle in intimate contact with
lung tissues.
HOW TO DISPOSE OF IT.
If you still have a uranium-containing material tucked away, get
rid of it. Most communities have a toxic waste program where you
can take it on certain days each year. This service is usually
free if you are an ordinary householder. In some cases, these
programs have refused to take uranium oxide.
However, if the materials you wish to discard are related to your
"business," you are supposed call a commercial company and pay
for disposal.
BRIEF ADVICE FOR URANIUM USERS:
1. You are a jerk if you listen to those who tell you using
uranium only raises your exposure to radiation a little over
background. It's more, but even a little is dumb when it is
totally unnecessary.
2. Remember that inhaling the fine dust can put an emitting
particle in intimate contact with lung (alveolar) tissue.
3. The stuff is also highly toxic especially to the kidneys.
4. Your customers have a right to know that you use uranium in
your glazes. And tell them while you are at it, that the Nuclear
Regulatory Commission says that uranium should not be allowed on
pottery. However, you are vastly more informed about ionizing
radiation than the NRC.
Marshall is probably referring to the famous orange Fiesta Ware that
obtained it's colour from a uranium bearing glaze. This stuff will cause a
geiger counter to read off-scale (I don't want to imply any particular level
of health hazard or lack there of). So given my other posts about uranium
being an alpha emitter which is not measured by geiger counters, what gives?
When uranium decays it produces radioactive daughter products. Most of
these are gamma and beta emitters which are detectable if there is enough
present. Go back to the formation of the earth. A certain amount of
uranium-238 and uranium-235 was present in the cosmic goo which became the
earth (appologies to the astro-physicists out there). Most of that has
decayed away and the amount we have now is just the remains. Now when the
uranium decays it produces a whole chain of radioactive daughter products.
Some of those have very short half-lives and you essentially don't see them.
Some have longer half-lives and build up to significant levels. I could
spend some time explaining this but this whole paragraph is a bit of
overkill. The point is that over geologic time uranium deposits end up full
of uranium and daughter radionuclides. It takes a very long time but after
a while the rock ends up quite radioactive due to these daughter isotopes.
Still with me? Here's where the speculation comes in. I don't think that
purified uranium oxide could have been used in Fiesta ware. If that was the
case the daughter radionuclides would have been removed and the glaze would
not be a beta/gamma emitter. Remember this stuff was made before the 1940s
and uranium chemistry was not as well known as now.
Some of the materials we use in glazes are nearly pure chemicals processed
from ores -- cobalt oxide, copper oxide, etc. But some are simply mined,
ground up and separated out as minerals. If you take the uranium minerals
directly from a mine, you will have uranium and all the daughter isotopes
the have built up since the mineral was formed. I think there is very good
reason to believe that the uranium used in Fiesta Ware was not separated
from the daughters. I mean why bother if you can get by with less costly
and less processed material? Just mine and separate out the mineral and use
that.
What this means is that you can't compare the risks of using a glaze
formulated with uranium oxide with a glaze formulated with a mineral which
contained both uranium and uranium daughters. That would be like comparing
the risk of smoking cigarettes with the risk of wearing a nicotine patch.
(Not the best analogy but you get the idea.)
BTW the advice that the WA Department of Health gives to anyone who owns
some of that Fiesta Ware is that it is fine to keep on display in your house
but recommends against using it for food.
-- Evan in Eastern Washington who's cat wants him to stop typing at least
with one hand
From: Evan Dresel
Subject: Re: Uranium in Glazes
----------------------------Original message----------------------------
There seems to be a lack of understanding of basic radiation physics here.
Uranium is an alpha emitter. I don't know how the lab measured the
radiation from the beads either -- around here they often use a device
called a PAM (Portable Alpha Monitor I think) which is actually quite
difficult to use unless you are dealing with something screaming hot because
.... Alpha particles have very poor penetration properties. You can stop
them with a piece of paper. You can stop almost all of them with the dead
layer of your epidermis. You can stop them with your clothes. You can stop
them with latex gloves. You don't want an internal dose of alpha particles
particularly in the sensitive tissues of your lungs.
Then if you are dealing with pure uranium you are dealing with three
isotopes (four if you are thinking of the mostly spent fuel from a nuclear
reactor which I think we don't need to worry about here). All three
isotopes have very long half-lives. Very long half-life means very few
atoms decay in any period of time. That means there is not much radiation
to detect. If you want to detect it the easiest way is to dissolve up the
material and put it in a liquid scintillation cocktail. That's a special
liquid which emits light when it absorbs those alpha particles. Then you
measure the light given off with very sensitive photomultipliers. The
trouble with trying to measure the radioactivity of the solid is that nearly
all of the radiation is absorbed before it even reaches the surface. Even
more so when measuring the alpha radiation from a small amount of uranium in
a glaze -- It's going to be really difficult to detect.
Ok for those of you who have read all this, what's my point? My point is
that I am not surprised at all that the beads didn't read above background.
We could get into a really esoteric discussion of what "background" is, but
I don't think it is worth it. At the risk of annoying Monona (it has been
known to happen :-() if you consider a single alpha particle more than would
be present if the material wasn't there then she is right: it will be above
background (impossible to measure because the background radiation is
fluctuating constantly with time). But that's not exactly a reasonable test
and is not generally accepted in the scientific community.
Subject: Re: Uranium in Glazes
----------------------------Original message----------------------------
Hi all,
Defining the emissions of ionizing radiation from a sample can be tricky.
In the case of a small object like a bead, if you simply put it close to a
counter and count, you may well decide that it emits no significant amount
above background, if the area of the counter is large, or a number of other
conditions. This does not mean that the bead is safe to place next to
skin. It simply means that if you live next to the bead (in the same room,
for example) you won't be absorbing any significant dose of radiation.
This is the same effect as being in a room with an incandescent bulb vs.
touching the bulb with your skin. The first is not unpleasant, but the
second is distinctly unsettling. If you wish to try the experiment, you
will find that there is a distance beyond which you cannot feel the heat
from the bulb, but as you move closer you feel it more and more until at a
certain point you begin to feel pain. Exposure to a radioactive source is
like that, only the damage to tissue becomes significant long before you
can feel it because we have no direct sensors to ionizing radiation.
The most damaging radiation for mucosa (lungs, mouth, digestive tract) are
alphas and disintigration products. Alphas may not even penetrate skin,
and they may not penetrate the glaze coat, especially if there is a clear
coat over the colour.
The most damaging radiation for close contact to skin, especially if the
source is buried in a glaze, is beta (electron) or gamma (photon)
radiation. This has the power to penetrate several millimeters of skin. It
will also penetrate a clear glaze coat over the colour.
Uranium emits alphas, betas, gammas, neutrons and fission products. If you
want to know if a bead is safe to place next to skin, you must read the
total activity of the bead and consider that as a skin contact source.
There are standard methods of doing this. The U of Alta test was probably
a simple matter of placing the bead in front of a survey counter for a few
seconds, and judging if the count rate increased significantly, perhaps
more than half again as much as background. This is not a sufficient test
to determine safety in skin contact. I won't go into the correct methods
for testing such a source, since they are somewhat involved, and are the
province of experts. They require sensitive and well shielded counters
sensitive to the appropriate particles, etc.
I would like to emphasize that unless you know what you are doing and take
sufficient precautions, any uranium salt or product is a potential if not
an actual hazard to health, even though no prompt symptoms may be detected.
People who do handle uranium do so under strict protocols regarding
shielding and protective procedures, and with constant supervision of the
level of inhaled particles and body exposure. Under such conditions, it is
possible to handle the metal and even the salt powders safely. In past,
these substances were not handled properly, and many health and safety
problems have resulted. Those who are unclear about the large scale
problems that can result should look into the situation at Rocky Flats.
Another caution: Radioactivity was not discovered until the turn of the
last century. Up until about WW2, the dangers were not appreciated, and
safety protocols were rarely instituted. It is dangerous to use prewar
practice as examples of proper usage, since our understanding has increase
considerably since then. Indeed, most of today's regulations come from the
experience of the Japanese population exposed during the bombing of
Hiroshima and Nagasaki. The legacy of this is that our data is for high
exposures, while what we are discussing is low exposures. There is a
current debate about whether the extrapolated high exposure data is
suitable for the low exposure. This will not be resolved for some time.
It is prudent to continue to regard low level exposures as somewhat
hazardous. Certainly, dust particle exposures in lung tissue are hazardous.
Gavin
From: Evan Dresel
Subject: Re: Uranium in Glazes (was- Re: A little reminder)
----------------------------Original message----------------------------
Sigh, uranium again. All isotopes of uranium are radioactive. The three
isotopes which make up the bulk of natural uranium are uranium-234,
uranium-235 and uranium-238. Nearly all the uranium **by mass** is
uranium-238. However, approximately half of the radioactivity is from
uranium-238 and half from uranium-234. That's because uranium-238 decays to
uranium-234 and uranium-234 has a shorter half life. After a certain amount
of time the decay chain reaches steady state and the uranium-234 is decaying
at the same rate it is being produced. Uranium-235 produces very little of
the radioactivity because there is little of it present (it is however very
important to those in the massive eistruction business). In depleted
uranium some of the uranium-235 has been removed. Almost certainly an even
greater proportion of the uranium-234 has also been removed. How much, I
don't know. All of the uranium isotopes are alpha emitters. That means the
radioactivity can be stopped by a piece of paper or the dead-layer of your
skin. Alpha particles however, can be quite destructive once in your body
-- particularly if inhaled into your lungs. Here's the catch -- all the
isotopes of uranium have extremely long half-lives. What that means is that
there isn't much radiation unless you have a whole lot of the stuff. The
proposed drinking water standard for uranium in the US is set mainly by it's
possible chemical effect on the kidneys, not on its radioactivity. My
suspicion is that uranium is fairly benign in glazes but haven't done enough
research. I strongly disagree with the answer, "It's radioactive, it will
kill you and your customers."
If you don't want to use radioactive materials in your pottery, you better
stop using potash-feldspar and probably nearly every clay. Potassium-40 is
present in all potassium containing materials and is quite radioactive. You
can measure the radioactivity from the potassium in fertilizer using a
simple hand-held geiger counter.
Linked Articles
L'URANIUM et la CÉRAMIQUE - Edouard Bastarache
L'URANIUM et la CÉRAMIQUE - Edouard BastaracheURANIUM and CERAMICS by Edouard Bastarache
URANIUM and CERAMICS by Edouard Bastarache
URLs
- Clayart archives, see Dec 2003, Jan 2004 - http://lsv.ceramics.org/archivedata/clayart.html
Authors
- Tony Hansen (Owner)
XML
<?xml version="1.0" encoding="UTF-8"?>
<material name="Uranium Materials" descrip="" generic="0" rawmineral="0" searchkey="" loi="0.00">
<families>
<family name="Other"/>
</families>
<notes>
<note>This subject is covered in detail in discussions on clayart during late 2003 and early 2004. The dialog was started because someone submitted an old glaze containing uranium.
The following material comes from a source that we have now lost, if you know who wrote it please contact.
WHAT IS "DEPLETED" URANIUM?
Uranium is an element which has isotopes, that is, varieties that have different molecular weights. Uranium\'s three natural isotopes are: U-238, U-235, and U-234. Only U-235 has the right weight for atomic reactions. "Depleted" uranium is uranium from which U-235 has been removed.
In the 1970s and 1980s, some potters, teachers and ceramic chemical suppliers incorrectly assumed that "depleted" uranium was not radioactive. This misinformation found its way into many books and publications. While depleted uranium is less radioactive, it is still a significant hazard because all isotopes of uranium are radioactive.
THE NUCLEAR REGULATORY COMMISSION (NRC)
In a 1980, the NRC clearly said that the use of uranium glazes
should not be allowed ("Environmental Assessment of Consumer
Products Containing Radioactive Material," Nuclear Regulatory
Commission (NUREG/CR-1775), October 1980). However, NRC decided
not to waste its time banning uranium glazes because their
investigation showed that there were no known commercial
producers of uranium-glazed ware in 1980.
The NRC also "investigated" uranium use in art pottery and
enamels. They talked to "the art department of a major
university", a "spokesperson for an enamelists guild," and the
"purchasing agent for one of the ten largest public school
districts in the U.S." These people all denied using or buying
any uranium. Yeah, right.
As late as 1985, pottery catalogs still listed uranium. To this
day, I still occasionally find uranium oxide in university
ceramics departments.
In 1984, NRC banned uranium-containing enamels after a lot of
radioactive jewelry was imported into the US. This also meant
that domestic uranium enamels such as Thompson\'s Burnt Orange #
153 and Forsythia # 108 were taken off the market. I still find
stockpiles of these enamels in schools.
Even without a ban, the fact that the NRC is on record saying
that uranium glazes should not be allowed puts uranium-users at a
moral and ethical disadvantage. And just imagine explaining it to
your customers!
RADON
Uranium emits both radiation and a cancer-causing radioactive gas
called "radon." Uranium-containing fossils and rocks in museum
collections have been shown to require special ventilation to
control radon from these specimens. Radon also is emitted from
uranium oxide chemicals or even large stocks of uranium-glazed
ware.
Radon, of course, also could be present in basement pottery
studios from radioactive minerals in the soil or in cement. EPA
recommends that all home owners test for radon. Combining
basement pottery with a radon problem with use of uranium glazes
could really boost your total exposure.
TOXICITY
Unrelated to its radioactivity, uranium is also toxic to the
kidneys and can cause blood disorders. Soluble uranium from
ceramic ware, ingestion of small amounts of glaze or enamel dust
from lung clearing mechanisms, or absorption of soluble compounds
by the lungs would be potential sources for this kind of
toxicity.
To protect workers from the toxicity of uranium dusts, OSHA
assigned a permissible exposure limit of 0.2 milligrams per cubic
meter (mg/m3) in air for insoluble compounds and 0.05 mg/m3 for
soluble ones.
Inhalation of very small insoluble dust particles into the
alveoli where there are no lung clearing mechanisms effectively
places an emitting radioactive particle in intimate contact with
lung tissues.
HOW TO DISPOSE OF IT.
If you still have a uranium-containing material tucked away, get
rid of it. Most communities have a toxic waste program where you
can take it on certain days each year. This service is usually
free if you are an ordinary householder. In some cases, these
programs have refused to take uranium oxide.
However, if the materials you wish to discard are related to your
"business," you are supposed call a commercial company and pay
for disposal.
BRIEF ADVICE FOR URANIUM USERS:
1. You are a jerk if you listen to those who tell you using
uranium only raises your exposure to radiation a little over
background. It\'s more, but even a little is dumb when it is
totally unnecessary.
2. Remember that inhaling the fine dust can put an emitting
particle in intimate contact with lung (alveolar) tissue.
3. The stuff is also highly toxic especially to the kidneys.
4. Your customers have a right to know that you use uranium in
your glazes. And tell them while you are at it, that the Nuclear
Regulatory Commission says that uranium should not be allowed on
pottery. However, you are vastly more informed about ionizing
radiation than the NRC.
Marshall is probably referring to the famous orange Fiesta Ware that
obtained it\'s colour from a uranium bearing glaze. This stuff will cause a
geiger counter to read off-scale (I don\'t want to imply any particular level
of health hazard or lack there of). So given my other posts about uranium
being an alpha emitter which is not measured by geiger counters, what gives?
When uranium decays it produces radioactive daughter products. Most of
these are gamma and beta emitters which are detectable if there is enough
present. Go back to the formation of the earth. A certain amount of
uranium-238 and uranium-235 was present in the cosmic goo which became the
earth (appologies to the astro-physicists out there). Most of that has
decayed away and the amount we have now is just the remains. Now when the
uranium decays it produces a whole chain of radioactive daughter products.
Some of those have very short half-lives and you essentially don\'t see them.
Some have longer half-lives and build up to significant levels. I could
spend some time explaining this but this whole paragraph is a bit of
overkill. The point is that over geologic time uranium deposits end up full
of uranium and daughter radionuclides. It takes a very long time but after
a while the rock ends up quite radioactive due to these daughter isotopes.
Still with me? Here\'s where the speculation comes in. I don\'t think that
purified uranium oxide could have been used in Fiesta ware. If that was the
case the daughter radionuclides would have been removed and the glaze would
not be a beta/gamma emitter. Remember this stuff was made before the 1940s
and uranium chemistry was not as well known as now.
Some of the materials we use in glazes are nearly pure chemicals processed
from ores -- cobalt oxide, copper oxide, etc. But some are simply mined,
ground up and separated out as minerals. If you take the uranium minerals
directly from a mine, you will have uranium and all the daughter isotopes
the have built up since the mineral was formed. I think there is very good
reason to believe that the uranium used in Fiesta Ware was not separated
from the daughters. I mean why bother if you can get by with less costly
and less processed material? Just mine and separate out the mineral and use
that.
What this means is that you can\'t compare the risks of using a glaze
formulated with uranium oxide with a glaze formulated with a mineral which
contained both uranium and uranium daughters. That would be like comparing
the risk of smoking cigarettes with the risk of wearing a nicotine patch.
(Not the best analogy but you get the idea.)
BTW the advice that the WA Department of Health gives to anyone who owns
some of that Fiesta Ware is that it is fine to keep on display in your house
but recommends against using it for food.
-- Evan in Eastern Washington who\'s cat wants him to stop typing at least
with one hand
From: Evan Dresel <pedresel@revolution.3-cities.com>
Subject: Re: Uranium in Glazes
----------------------------Original message----------------------------
There seems to be a lack of understanding of basic radiation physics here.
Uranium is an alpha emitter. I don\'t know how the lab measured the
radiation from the beads either -- around here they often use a device
called a PAM (Portable Alpha Monitor I think) which is actually quite
difficult to use unless you are dealing with something screaming hot because
.... Alpha particles have very poor penetration properties. You can stop
them with a piece of paper. You can stop almost all of them with the dead
layer of your epidermis. You can stop them with your clothes. You can stop
them with latex gloves. You don\'t want an internal dose of alpha particles
particularly in the sensitive tissues of your lungs.
Then if you are dealing with pure uranium you are dealing with three
isotopes (four if you are thinking of the mostly spent fuel from a nuclear
reactor which I think we don\'t need to worry about here). All three
isotopes have very long half-lives. Very long half-life means very few
atoms decay in any period of time. That means there is not much radiation
to detect. If you want to detect it the easiest way is to dissolve up the
material and put it in a liquid scintillation cocktail. That\'s a special
liquid which emits light when it absorbs those alpha particles. Then you
measure the light given off with very sensitive photomultipliers. The
trouble with trying to measure the radioactivity of the solid is that nearly
all of the radiation is absorbed before it even reaches the surface. Even
more so when measuring the alpha radiation from a small amount of uranium in
a glaze -- It\'s going to be really difficult to detect.
Ok for those of you who have read all this, what\'s my point? My point is
that I am not surprised at all that the beads didn\'t read above background.
We could get into a really esoteric discussion of what "background" is, but
I don\'t think it is worth it. At the risk of annoying Monona (it has been
known to happen :-() if you consider a single alpha particle more than would
be present if the material wasn\'t there then she is right: it will be above
background (impossible to measure because the background radiation is
fluctuating constantly with time). But that\'s not exactly a reasonable test
and is not generally accepted in the scientific community.
Subject: Re: Uranium in Glazes
----------------------------Original message----------------------------
Hi all,
Defining the emissions of ionizing radiation from a sample can be tricky.
In the case of a small object like a bead, if you simply put it close to a
counter and count, you may well decide that it emits no significant amount
above background, if the area of the counter is large, or a number of other
conditions. This does not mean that the bead is safe to place next to
skin. It simply means that if you live next to the bead (in the same room,
for example) you won\'t be absorbing any significant dose of radiation.
This is the same effect as being in a room with an incandescent bulb vs.
touching the bulb with your skin. The first is not unpleasant, but the
second is distinctly unsettling. If you wish to try the experiment, you
will find that there is a distance beyond which you cannot feel the heat
from the bulb, but as you move closer you feel it more and more until at a
certain point you begin to feel pain. Exposure to a radioactive source is
like that, only the damage to tissue becomes significant long before you
can feel it because we have no direct sensors to ionizing radiation.
The most damaging radiation for mucosa (lungs, mouth, digestive tract) are
alphas and disintigration products. Alphas may not even penetrate skin,
and they may not penetrate the glaze coat, especially if there is a clear
coat over the colour.
The most damaging radiation for close contact to skin, especially if the
source is buried in a glaze, is beta (electron) or gamma (photon)
radiation. This has the power to penetrate several millimeters of skin. It
will also penetrate a clear glaze coat over the colour.
Uranium emits alphas, betas, gammas, neutrons and fission products. If you
want to know if a bead is safe to place next to skin, you must read the
total activity of the bead and consider that as a skin contact source.
There are standard methods of doing this. The U of Alta test was probably
a simple matter of placing the bead in front of a survey counter for a few
seconds, and judging if the count rate increased significantly, perhaps
more than half again as much as background. This is not a sufficient test
to determine safety in skin contact. I won\'t go into the correct methods
for testing such a source, since they are somewhat involved, and are the
province of experts. They require sensitive and well shielded counters
sensitive to the appropriate particles, etc.
I would like to emphasize that unless you know what you are doing and take
sufficient precautions, any uranium salt or product is a potential if not
an actual hazard to health, even though no prompt symptoms may be detected.
People who do handle uranium do so under strict protocols regarding
shielding and protective procedures, and with constant supervision of the
level of inhaled particles and body exposure. Under such conditions, it is
possible to handle the metal and even the salt powders safely. In past,
these substances were not handled properly, and many health and safety
problems have resulted. Those who are unclear about the large scale
problems that can result should look into the situation at Rocky Flats.
Another caution: Radioactivity was not discovered until the turn of the
last century. Up until about WW2, the dangers were not appreciated, and
safety protocols were rarely instituted. It is dangerous to use prewar
practice as examples of proper usage, since our understanding has increase
considerably since then. Indeed, most of today\'s regulations come from the
experience of the Japanese population exposed during the bombing of
Hiroshima and Nagasaki. The legacy of this is that our data is for high
exposures, while what we are discussing is low exposures. There is a
current debate about whether the extrapolated high exposure data is
suitable for the low exposure. This will not be resolved for some time.
It is prudent to continue to regard low level exposures as somewhat
hazardous. Certainly, dust particle exposures in lung tissue are hazardous.
Gavin
From: Evan Dresel <pedresel@revolution.3-cities.com>
Subject: Re: Uranium in Glazes (was- Re: A little reminder)
----------------------------Original message----------------------------
Sigh, uranium again. All isotopes of uranium are radioactive. The three
isotopes which make up the bulk of natural uranium are uranium-234,
uranium-235 and uranium-238. Nearly all the uranium **by mass** is
uranium-238. However, approximately half of the radioactivity is from
uranium-238 and half from uranium-234. That\'s because uranium-238 decays to
uranium-234 and uranium-234 has a shorter half life. After a certain amount
of time the decay chain reaches steady state and the uranium-234 is decaying
at the same rate it is being produced. Uranium-235 produces very little of
the radioactivity because there is little of it present (it is however very
important to those in the massive eistruction business). In depleted
uranium some of the uranium-235 has been removed. Almost certainly an even
greater proportion of the uranium-234 has also been removed. How much, I
don\'t know. All of the uranium isotopes are alpha emitters. That means the
radioactivity can be stopped by a piece of paper or the dead-layer of your
skin. Alpha particles however, can be quite destructive once in your body
-- particularly if inhaled into your lungs. Here\'s the catch -- all the
isotopes of uranium have extremely long half-lives. What that means is that
there isn\'t much radiation unless you have a whole lot of the stuff. The
proposed drinking water standard for uranium in the US is set mainly by it\'s
possible chemical effect on the kidneys, not on its radioactivity. My
suspicion is that uranium is fairly benign in glazes but haven\'t done enough
research. I strongly disagree with the answer, "It\'s radioactive, it will
kill you and your customers."
If you don\'t want to use radioactive materials in your pottery, you better
stop using potash-feldspar and probably nearly every clay. Potassium-40 is
present in all potassium containing materials and is quite radioactive. You
can measure the radioactivity from the potassium in fertilizer using a
simple hand-held geiger counter.</note>
</notes>
</material>
Much more information with complete interlinking to many related Copyright 2003 http://digitalfire.com, All Rights Reserved Please support http://ceramicmaterials.info to improve this library |  |
INSIGHT is ceramic chemistry |