Wednesday, January 14, 2015

Why I'm not Worried about Nuclear Power

Growing up in California left me with a negative impression of nuclear power without any real knowledge of it.  I remember being scared of it as a child. Especially the nuclear waste.  I used to think they should shoot it all into space.  Now such an idea seems ridiculous to me.  I can't imagine why you would need to go so far when the problem is easily manageable here on earth.   Nuclear power has moved way far down on the list of things to be afraid of.   With this article I'd like to explain why.

I'd just like to start by saying that radiation can be harmful. Everyone seems to agree with that.  What people can't always agree about is the finer details such as if harm was done, how much harm was done and how much harm could be done by any particular event or potential event.

Also, if you don't have a basic understand of radiation and radioisotopes you may wish to read this first.   

So, you may be wondering why I'm not particularly worried about nuclear power given that radiation can be harmful.  Well for starters radiation is all around us, and it always has been.

Radiation is all Around Us, and Always has Been

Radiation is constantly bombarding us from space.  It's in the oceans, the soil and the food we eat.  It's even in the air we breath.  It's a bit harder to be afraid of it when you realize it's all around us, and always has been.  The first ape that walked on two legs was being bombarded by radiation.  The first animal that crawled up out of the sea was being bombarded by radiation.  Even when the first cells came about and life as we know it began there was radiation everywhere. 

In fact even fission was happening on earth before humanity was a thing.  In the Oklo uranium deposit (located in the country of Gabon in equatorial Africa) it was discovered that a nuclear chain reaction caused by natural processes took place millions of years ago. Here is a time line.

The history of the Oklo fossil reactors spans almost the entire history of the earth. ‘Oklotime’ can be divided into four stages:
  1. U mobilization phase: Commenced ~3500 million years ago.
  2. U ore/reactor formation: Started ~2800 million years ago.
  3. Reactor operation: Commenced 2000 million years ago (for about a million years).
  4. Waste movement: The last 2000 million years.

Yet despite this nuclear reaction happening on earth uncontrolled by man, and unreported on by an media outlets, life on earth survived.  In fact there is not evidence that it was hampered in any way.  If that isn't enough for you there is something called spontaneous fission where heavy atoms undergo fission well... spontaneously.   Also, there a certain number of neutrons (around 14 neutrons/cm2/hour) constantly bombarding the earth as a result of  cosmic ray spallation.  When these neutrons encounter uranium they can induce fission just like in a nuclear reactor, but despite these two thing releasing small amounts of fission products directly into the environment since the earth began life goes on undeterred. 

Learning more About Science has Made me Less Afraid

I find learning more about science is a fun and rewarding activity.  Which is why it shocks me when I encounter articles like this one and realize that some people know almost nothing about science at all. 

All radioactivity is man-made (True/False)

Percent that got it right

It amazes me how many people don't even know about natural sources of radiation.  I'm not a scientist, I'm never going to be a scientist, but I've found certain basic information about science incredibly useful for understanding the world around me.  Without it I'm not sure how I would judge the endless barrage of claims that I encounter every day.  Let me share with you some of the things I've learned about science that have made me less afraid.

Half Lives

Half-life: Introduction to half-life

Half lives describes how long until half of any given type of radioisotope has decayed into something else.  This is important because it's during the decaying part where the radiation gets produced.   In terms of safety there are good and bad things about any half life length.  For example things with short half lives are more dangerous because they produce more radiation, but because they have short half lives they don't stick around as long which is good.  Things with long half lives stick around for a long time, but they are less dangerous because they don't produce as much radiation.  Learning about half lives made me realize that the really dangerous stuff will be gone before too long.   As for the longed lived stuff, the world is fulled of long lived radioisotopes (uranium, thorium, C-14 etc.).   It doesn't seem to hamper us much, if any.

Diffusion and Dilution 

Diffusion is a natural process where random collisions between particles in fluids or gasses cause them to travel around randomly becoming more intermingled within the medium. You can observe this process by placing a drop of red food coloring in a cup of water. Over time you can watch the red coloring spread out until the water is of uniform color. Here is a video that explains diffusion if you want to know more.

Radioisotopes mixed into air and water diffuse outward in all direction becoming diluted in the process. Picture the place where the radioisotopes starts out at as one side of the radius of a sphere and the distance they have diffused out to as the other side.  In order to better illustrate this Here is the volume of a sphere.

As you can see radius is taken to the third power.  As you can imagine this means that volume increases very quickly as radius gets bigger.  This is something called exponential growth. Exponential growth means the rate at which things grow also grows.  Here is a graph showing the growth of the volume of a sphere.

As you can see with exponential growth thing get large very quickly.  Even if things like the earth block some paths of diffusion it is still easy to see that the volume in which radioisotopes are diluted becomes large really fast, and dilution matters.  Things that are very dangerous in concentrated forums are basically harmless if diluted enough.  

You may be wondering about solid particles right now,  but if you are worried small particles like dust undergo diffusion as well although it's different than the diffusion for liquids and gasses. One difference is that dust consolidates on the ground which is two dimensional, but the area of a circle circle also grows exponentially.

Although things like wind also needs to be considered there are definitely limits to the concentration of small dust particles faraway from an accident.  As for larger particles I'm not sure what their means of locomotion would be. 


This kind of thinking might not be much consolation to people close to a serious nuclear power incident where concentrations of radioisotopes are greater, but it definitely shows that there limits to the scope of nuclear accidents, and history has shown even residents close to serious nuclear power accidents don't die from radiation poisoning.    Radioisotopes with short half lives are dangerous in concentration, but diluted over a large volume they aren't that dangerous at all, and because they have a short half life what danger they do pose will soon pass. 

The World is full of Dangerous Stuff

Another reason why I'm not particularly worried is that that life is filled with harmful and potentially harmful things.  Heck, In 2014 761 people died on commercial airlines world wide while a staggering 33,783 people died in automotive accidents in the US alone.  For me nuclear power is pretty far down on the list of things to worry about.

One example of something potentially very hazardous is water.  If inhaled the content of a single swimming pool could kill hundred if not thousands of people.  Such a situation may seem ridiculous to you, but it's no more ridiculous than arguments that single nuclear reactor can kill us all (which ignores basic laws of physics like diffusion). 

At any rate here is some information about drowning:
Every day, about ten people die from unintentional drowning. Of these, two are children aged 14 or younger. Drowning ranks fifth among the leading causes of unintentional injury death in the United States
That's quite a few people.  Certainly more then die each day from nuclear energy.   I'm sure we could cut down this number by banned all the swimming pools and putting guards around all the rivers and lakes, but people aren't willing to do that because not only would it cost to much but swimming is fun.  I wonder why we are so rational when it comes to swimming but irrational when it comes to nuclear power.  After all affordable reliable energy is more than just fun, it a necessity of modern life.

To Much Fear and Hyperbole not Enough Facts

Of the two sides the anti nuclear side is by far the largest purveyor of bull crap. I've learned to take everything they say with a grain of salt.

Hey, I call it like I see it

I tend to believe that everyone has a little bit of bull crap in them, but the anti nuclear activists often take it to the extreme.  They are given to outrage with little in the way of facts, rampant  paranoia and dismissing anything that disagrees with their preconceived notions.    One example of anti nuclear bull crap can be seen below. 

Maps like these are complete bull.  You could take a piss in the ocean and draw an equally scary map showing how your piss is slowly contaminating all the seas of the world, and it would about as meaningful as this map.  Let me give a quote that shows what they are talking about.
An estimated 538,100 terabecquerels (TBq) of iodine-131, caesium-134 and caesium-137 was released. 520,000 TBq was released into the atmosphere between 12 to 31 March 2011 and 18,100 TBq into the ocean from 26 March to 30 September 2011. 
Admittedly worse then urine, but not nearly as bad as they are making it out to be.   A think a good comparison for putting it into context would be to compare what has gone into the ocean to what was already in the ocean.
  1. The oceans have Uranium in them. In the pacific ocean the radiation from Uranium is 22 EBq or 22,000,000 trillion becquerels.
  2. The oceans have Potassium 40 in them. In the pacific ocean the radiation from Potassium 40 is 7,400 EBq or 7,400,000,000 trillion becquerels.
  3. The oceans have Carbon 14 in them. In the pacific ocean the radiation from Carbon 14 is 3 EBq or 3,000,000 trillion becquerels.
  4. The oceans have Rubidium 87 in them. In the pacific ocean the radiation from Rubidium 87 is 700 EBq or 700,000,000 trillion becquerels.
  5. The oceans have Tritium in them. In the pacific ocean the radiation from Tritium is 370 PBq or 370,000 trillion becquerels.
So we have…
Uranium                      22,000,000 trillion becquerels
Potassium-40         7,400,000,000 trillion becquerels
Carbon-14                     3,000,000 trillion becquerels
Rubidium-87            700,000,000 trillion becquerels
Tritium                              370,000 trillion becquerels
Total            8,125,370,000 trillion becquerels
So we have 8,125,370,000 trillion becquerels of radiation in the pacific ocean from natural sources and the anti nuclear activists don’t seem to care, but when the fifth most powerful earthquake ever recorded results in 18,100 TBq of radiation being released into the oceans and they start drawing scary maps and acting like we are all doomed.    The logic in this position escapes me and it only gets worse...

Uranium 238 (99.284% of natural uranium) has a half life of 4.468 billion years, and uranium 235 (0.72% of natural uranium) has a half life of 703,800,000 years, so it's going to be producing those becquerels for a long long time.   If that still isn't enough for you rivers wash more uranium into the ocean at a rate of 32,000 tons (page 165) a year, and carbon-14 is only one of the radioisotope continuously showering us as a result of cosmic rays.   Still not enough for you... There's more.  Here is the decay chain for both naturally occurring forms of uranium.


That is an awful large number of radioisotopes continuously being produced in the oceans naturally, but anti nuclear activists don't seem to know or care at all. They seem only to care about radiation has to do with their agenda against safe clean nuclear power. This has made me lose a lot of trust in them.

There  are some people who think that Fukushima should mean the end of nuclear power, but their fears seem way overblown to me.  As I learned more about the different types of energy I've come to favour nuclear power strongly.  None of the other energy sources can do what it can.  Wind and solar are intermittent, have lower power density and scaling.  Fossil fuels are increasing hard to get at, and of course there is climate change to worry about.  Nuclear power gives me hope for the future which is why I think it's worth defending

Tuesday, January 13, 2015

Is this What They Mean by Clean Energy?

Germany is destroying whole towns in order to power their country.

Wind and solar require other power sources when the wind isn't blowing or the sun isn't shining.

If those other sources are coal then they bear part of the responsibility.

Monday, January 5, 2015

Both Low EROEI and Low Power Density is a Serious Problem - Wind Addition

In my last post I talked about how having both low EROEI and low power density is a serious problem.  I used solar as an example.  In the comment section someone mentioned something about 80% of our power coming from wind, but wind isn't much better. It has a higher EROEI, but it's power density is terrible.  I'll explain below. 

If you haven't read the last article you might want to do so now.

First I'll start with the sources.

Source One - Catch 22 of energy storage.

EROEI for wind with storage is 3.9. 

Source Two - Sustainable Energy — without the hot air

The red stack (i.e. energy consumption) in figure 18.1 adds up to 195 kWh per day per person (page 103).

4,000 m^2 land per person in UK.  

Source Three - Rethinking wind power
Keith’s research has shown that the generating capacity of very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter.
Now lets think about it a little.

Lets start by talking a bit about EROEI.   The comment that inspired this post gave me a link that says EROEI is meaningless.  I disagree.  EROEI is very important when it gets close to one.  I'll explain but first let start with this definition from Wikipedia for anyone unfamiliar with the term.
In physics, energy economics and ecological energetics, energy returned on energy invested (EROEI or ERoEI); or energy return on investment (EROI), is the ratio of the amount of usable energy acquired from a particular energy resource to the amount of energy expended to obtain that energy resource.

EROEI is important because it creates a multiplier effect for other quantities.  Other quantities include things like space, different material and man power.   The closer EROEI gets to one the closer the need for those other quantities get's to infinity.

For example:

Imagine that you had a some solar panels that had a EROEI of 2. One meter square of them produces let say 5 watts average. For simplicity's sake lets stick with only this one kind of power source for now.

If you wanted to get 5 watts from these panels you would need both the one meter squared, plus another half a meter squared to maintain the one meter squared, plus another quarter meter square to maintain the half meter square and so forth.  This goes on endlessly, and when you sum up the results you get the multiplier.


Thanks to Mark44 on physics forums for this!

Now lets talk about the multiplier

The multiplier works for all quantities not just area.

For example:

if it take 5 people to maintain some generation that produces 5 watts and the multiplier is 3 then that 5 watts really needs 15 people (5 X 3 =15).

Here is the formula you need to figgure out the multiplier for any given EROEIs.

Where X = EROEI
This doesn't only apply to a one power source systems.  Any power source that with EROEI close to one would require outrageous amounts of different resources in order to contribute significantly to our total energy supply.  

Now for Wind

The multiplier for wind isn't that bad, but the power density is crap.  At between 0.5 and 1 watts per square meter even if you covered the whole of the UK with wind turbines the yield would still kind of suck.

Here's the math

4,000 m^2 is space in uk for each person.

1.34 is the multiplier for wind


4000 / 1.34 ≃ 3,000

Around 3,000 is how much possible space for wind for each person when you minus the space for wind turbines needed to maintain the system.

So between...

           (3,000 * .5 * 24)/1,000   ≃ 36  kWh per day per person

           (3,000 * 1 *  24)/1,000   ≃ 72  kWh per day per person

So maybe you can get close to 80% if you cover the whole of the UK with wind farms (assuming the EROEI doesn't drop because of diminishing returns).  Do you think people can really cover so much of the UK with renewable energy?  What about space they need for other things like energy storage.  It's really hard for me to believe, and even if you could I think it would be pretty horrible.  

Both Low EROEI and Low Power Density is a Serious Problem - Solar PV Addition

Taking information from two sources I'm going to show that a combination of low EROEI, and low power density is a huge problem.   Here is the first source which talks about EROEI with energy storage.  It's called catch 22 of energy storage.  Here is the second that talk about power density among other thing.  It's called Sustainable Energy — without the hot air.  Both of them are a good reads if you haven't read them already. 

From the First Source

The EROEI for solar pv with energy storage is listed at 1.6.

From the Second Source

If we covered 5% of the UK with 10%-efficient panels, we’d have

10% × 100 W/m2 × 200 m2 per person = 50 kWh/day/person. (page 41)

The red stack (i.e. energy consumption) in figure 18.1 adds up to 195 kWh per day per person (page 103).

Now lets think about this a little

EROEI describes the energy that is needed to be invested (i.e. used) in order to get more energy. If the EROEI is 2 then one unit (of some unit of energy) invested will get you 2 (of that unit). If solar is to become a permanent thing then maintaining any given area of it will take energy. The amount of energy is determined by it's EROEI. Lets say that the EROEI is 2. Then maintaining 1m2 of it would take 1/2m2. That 1/2m2 would need 1/4m2 and so on. The sum of all these works out to some finite number.   In order to work it out you need something called the Geometric series.

Here's the equation where X = EROEI

Using the formula I get 2.67(1/(1-(1/x))) using solar PV's EROEI. The number 2.67 is a multiplier we can use to figure out the total area needed.  That means instead of 5% of the uk's land providing 50 kWh/day/person it would take 13.3 % (5 X 2.67 = 13.3) when taking EROEI into account.   In order to get 195 kWh/day/person it would take 51.87 % (13.3 X (195/50)) or 207,480 m2 per person.

That doesn't even count the area of land used by the energy storage.  Pump hydro for the source given.   Here's a good source that talks about that.  Guess what it take a lot of space, and don't forget that there are other land uses as well. 

Source Two Page 41

And don't think you can do without most of the storage because of demand response, management, whatever you want to call it.   Solar power manufacturing facilities cost a lot.  In order to keep the prices down they need to be run 24/7, so at most you can only ration 37.5 % (1 / 2.67 = 37.5) percent of that power. 

This is simply madness, or more like a fantasy.  It's time people came to terms that they have two choices.  Fossil fuel, or nuclear power.   Fossil fuel's give us a few short years in exchange for our climate and our children's future while nuclear power gives us hope and a better life for countless millions.   I know which one I'm rooting for. 

Update:  I changed a lot.  Credit to my brother Jeremy for helping me with the math.  I also added another post that talks about the same thing for wind.

Sunday, January 4, 2015

Some Basic Information Useful for Understanding Nuclear Power Safety

When people talk about nuclear power safety they often don't explain certain basic information that you need to know in order to really understand the the subject.  This is probably for the best because repeating the same information over and over again would grow old really fast, but unfortunately this leaves people new to the subject unable to fully understand the arguments.  The goal of this article is to hopefully be helpful to anyone who doesn't understand the basics. Basically I tried to write something that I think would have been helpful to me when I was starting out. 

The Very Basic

A drawing of a Lithium atom. In the middle is the nucleus, which in this case has four neutrons (blue) and three protons (red). Orbiting it are its three electrons.
Lithium atom model
Lets start with the very basic, all the stuff on earth is made up of tiny building blocks called atoms (you can see all types on the periodic table of the elements).  Atoms are made up of three things.  Those three things are electrons, protons and neutrons.  Protons and neutron exist in the middle of the atom clumped together in what is called the nucleus.  The electrons exist around that. Atoms can form molecules (i.e. groups of atoms) by sharing electrons. 

The type of atom (i.e. the element) is determined by the number of protons in it's nucleus.  For example atoms that have one proton are hydrogen atoms, and atoms that have 92 protons are uranium atoms.

Unlike protons and neutrons, the number of electrons an atom has can change fairly easily.  The default position for atoms is having the same number of electrons as protons.  When atoms don't have an equal numbers of protons and electrons they are called ions.  Knowing what ion you're dealing is important because different ions (even of the same element) behave very differently chemically which is why they came up with Equivalent notations for writing it down.
Example of Equivalent Notations
Every proton is +1, and every electron is -1, simple subtraction tells you what ion you've got.  For example iron (Symbol Fe) has 26 protons.  If an atom of Iron has 24 electrons then its ionic state is 2+ (26 - 24 = +2), and if it has 28 electrons its ionic state 2- (26 - 28 = -2).

The number of neutrons an atom has determines what type of isotope it is.  All atoms are some type of isotope even though it's not usually that important because different isotopes of the same element (i.e. type of atom) behave the same chemically for most intents purposes and thus it is often not mentioned or thought about.

Isotopes are identified by their atomic mass.  The atomic mass includes both protons and neutrons (electrons are very light so they don't count).  So for example there are three naturally occurring isotopes of carbon on earth.  They are called carbon-12, carbon-13 and Carbon-14.  Carbon has 6 protons so Carbon-12 has 6 neutrons (12 - 6 = 6), Carbon-13 has 7 neutrons (13 - 6 = 7) and Carbon-14 has has 8 neutrons (14 - 6 = 8).

Ionizing Radiation and Radioisotopes

Not all isotopes are stable.  Unstable isotopes eventually decay into different types of atoms releasing radiation in the process.  For example Carbon-12 and Carbon-13 are stable while Cabron-14 eventually decays into Nitrogen-14 (which is stable).

The unstable isotopes are called radioisotopes (also known as radionuclide, radioactive nuclide, or radioactive isotopes), and the radiation released is know as ionizing radiation although most people just call it radiation.

When an unstable isotope decays is random while the probability of it decaying over any period time is fixed.  This probability is understood through something called a half-life.  A half-life is the time it takes for half of a given amount of a radioisotope to transmute (i.e. decay) into something else

It's a bit like rolling a dice. Every time you roll a dice the chance of getting a one is the same.  If you replace "time you roll a dice" with "fixed period of time" and "getting a one" with "a type radioisotope decaying" it's exactly the same. 

You can also use the dice analogy to understand half-lives.  Picture that you were rolling a group of six sided dice.  Every time you rolled them you remove any dice that lands on a one.  The half life of these dice would be three rolls because after three rolls half the dice should be gone.  You might be thinking to yourself that half lives aren't very precise because of the random element, but you have to remember that atoms come in large numbers.   There are something like 78,000,000,000,000,000,000 atoms in a grain of sand.  If you rolled six dice then at the end maybe half would be gone or maybe not, but if you are rolling trillions of dice pretty darn close to half of them would be gone. 

In fact half lives are so precise that people use it for dating stuff.   There is something called Radiocarbon dating that uses the half life of Carbon-14 in order to tell how old things are.  Carbon-14 is constantly being created in the earth's atmosphere by nitrogen being bombarded by cosmic radiation.  Because it's being created at a constant rate it's also being absorbed by plants at a constant rate and from plants it moves to animals.  When something dies it stop taking in Carbon-14 so by using it's half life researches can tell how long ago something died based off the amount of carbon-14 left in it's remains.   

Some radioisotopes decay into other radioisotopes.  When that happens you have what is called a decay chain.  The decay chain is used to describe how radioisotopes decay until they eventually reach a stable state.  Here is the decay chain for Thorium a common naturally occurring radioisotope. 

You may be wondering at this point where all the radioisotopes on earth come from.   Well some (34 types) are primordial (i.e. they came about before the earth was formed).  This includes Uranium, Thorium and Potassium-40.  Some of them are caused by cosmic radiation such as Carbon-14.  A small minority are created as a result of human activity, the most common of these activities involves the breaking down of larger radioisotopes into smaller radioisotopes in order to produce energy.  Here is a really good link about radioactivity in the environment if you're interested in learning more about it.

Types of Radiation 

The types of radiation produced by radioisotopes include both Electromagnetic radiation and Particle radiation.  Electromagnetic radiation plays a big part in our lives.  Depending on the frequency it has many different applications and also names.  The most familiar form is the visitable spectrum, or more commonly just called light.  It's also useful for microwaves ovens, cell phones, radio, x-rays etc.

But for our purposes we are only interested in electromagnetic radiation that is ionizing radiation. Ionizing radiation is radiation that has enough energy to knock electrons off atoms (or molecules) thus ionizing them.   This is important because as we talked about before different ions behave much differently chemically.  This can cause problems.  In most cases a few atoms (or molecules) being ionized doesn't matter much, but in some cases it does.  For example ionizing radiation can cause harm to living tissue.  You've probably noticed such harm yourself if you've ever spent too much time in the sun and got sunburned.  

Some atoms (and molecules) hold their electrons better than others so what types of radiation are ionizing isn't so clear cut, but really what we care most about is the effect of ionizing on human beings so I would say ultraviolet (sun burn) rang and higher (higher frequency that is, the higher the frequency the more energetic the more able to knock of electrons) is ionizing radiation.

Usually when we are talking about radioisotopes decaying we are talking about gamma rays (i.e. y-rays), not X-rays or ultraviolet. Lower wave length ionizing radiation can be created as secondary radiation (i.e. ionizing radiation created by other ionizing radiation) though. 

Particle radiation is simply particles that are moving very quickly.  The two types of particles that matter for what we are talking about are Alpha particles and Beta particles.

Alpha particles are helium-4 atoms without any electron.  The ones created by radioactive decay have a strong ability to ionize things, but they have little ability to penetrate shielding and can be stopped by a piece of paper or the thin layer of dead skin all of us have. 

Beta particles are electrons or sometimes positrons.  Positrons are the antimatter equivalent of electrons.  When electrons and positrons meat they destroy each other releasing some gamma rays in the process.

Metric Prefixes

Now that we've covered what radiation is and where it comes from lets talk about how it's measured.  Well before that we have to talk about something call metric prefixes.  If you spend time reading about this subject you're going to encounter these things a lot.

For Micro it's usually abbreviated μ or mc

Metric prefixes are used for writing really large or really small numbers without having to write all the zeros.  It's very similar to scientific notations in that regards.  The prefix goes before the unit abbreviation.  For example with 10 cm the c is the metric prefix (centi) and the m is the abbreviated unit types (meter). 

It's fairly easy to convert a number to a different prefix or know the number in it's entirety (i.e. what the number is without prefixes). Look at the table above to the left of prefix you want to convert from.  The number to the right of the 10 is the one we're interested in.  Take that number and subtract the number next to the 10 of the prefix you want to convert to.  If you want to convert to no prefixes then subtract zero.    If the number you get is negative move the decimal point that many spaces to left, if it's positive move the decimal point that many places to the right. 

For example 1,000 nm (-9 - (-6) = -3) = 1 µm ,  1,000 µm (-6 - (-3) = -3) = 1 mm, 1,000 mm (-3 - 0 = -3) = 1 m, and 1,000 m (0 - 3 = -3 ) = 1 km.  Where m stands for meters.

Measuring Radiation

There are a lot of different ways of measuring radiation.  I'll try and go over the most common ones.

Activity (A)

Activity measures the number of nucleus decays.  It's calculated using amounts of radioisotopes and knowledge of there half lives.  The two main units for this are Becquerel, and Curie. 

The becquerel (symbol Bq) it is the SI derived unit of radioactivity.  One Bq is defined as the activity of a quantity of radioactive material (i.e. radioisotopes) in which one nucleus decays per second. Basically it's a unit used to describe the amount of radiation produced by some amount of radioisotopes.

The curie (symbol Ci) is a non-SI unit of radioactivity, named after Marie and Pierre Curie. It is defined as 1 Ci = 3.7 × 1010 decays per second.

Conversion factors:
1 GBq = 0.027 Ci
Absorbed dose (D)

Absorbed dose measures the energy (from ionizing radiation) absorbed by a mass.  This is important because it takes energy to ionize things so knowing how much energy is going towards ionizing things help you know how much stuff is getting ionized.  This in turn can help give you some idea of the effect.  Most Geiger counters measure this. The two main unit types for this are Rad and Grey.

The SI unit for absorbed dose is the gray (Gy).  One gray is the absorption of one joule of energy, in the form of ionizing radiation, per kilogram of matter.

The other unit is called the Rad.  The rad is a non-SI CGS unit that is sometimes also used, predominantly in the USA.

Conversion factor:
1 rad = 0.01 Gy 
Dose equivalent (H)

Dose equivalent is a measure of the health effect of low levels of ionizing radiation on the human body.   The two main unit types for this are Roentgen and Sievert.  Quantities that are measured in roentgens or sieverts are intended to represent the stochastic health risk, which for radiation dose assessment is defined as the probability of cancer induction and genetic damage.  There is no way to directly measure equivalent dose.  Instead other measurements are used to arrive at equivalent dose using various conventions.  For example with X-rays and gamma rays the gray is numerically the same value when expressed as the sievert (Sv), but for alpha particles one gray is equivalent to twenty sieverts because of the radiation weighting factor that is applied.

Conversion factor:
1 rem = 0.01 Sv

Radiation Inside the Body

Internal doses can be worse than external one's (depends on amounts and other factors).   For example alpha particles can be stopped by a thin layer of dead skin making them fairly harmless outside the body, but more dangerous than other types of radiation inside it.  In fact a large part of people's average annual doses comes from alpha particles produced by the decay of Radon (symbol Rn).  Radon is an odourless, colourless, gas that exists in small amounts all around us.  Radon is constantly being created as part of the decay chain of all the naturally occurring isotopes of uranium and thorium.

At any rate predicting internal doses is important.  An important thing to remember when internal doses are concerned is that different isotopes behave the same chemically.  This can be both a good thing and a bad thing.  For example Iodine-131 is a radioactive isotope of iodine that is produced a lot in nuclear reactors.  It has a half life of about 8 days.   Like all iodine it's utilized by the thyroid which means if it gets released into the environment it can be a problem.   Luckily by taking potassium-iodide pill you can flood your body with non radioactive iodine so Iodine-131 wont get absorbed, and because it's half life is so short it will be gone in short order.  Because they behave the same chemically radioisotopes also have many beneficial uses such as Radiopharmacology a branch of medicine which uses radioisotopes for medical imaging and in therapy for many diseases (for example, brachytherapy).  Ironically Iodine-131 is also one of the radioisotope used in medicine.

Internal Dosimetry 

Internal dosimetry is the science and art of internal ionizing radiation dose assessment due to radioisotopes incorporated inside the human body.  Radioisotopes deposited within a body will irradiate tissues and organs and give rise to committed dose until they are excreted from the body or the radionuclide is completely decayed.  The internal doses for workers or members of the public exposed to the intake of radioactive particulates can be estimated using bioassay data such as lung and body counter measurements, urine or faecal radioisotope concentration, etc.

Man-Made Radiation Exposure Breakdown 

This kind of depends on what you think of as man made exposure.  For example is Radon pumped into people's houses along with natural gas man made or natural exposure?  At any rate, not counting stuff like Radon most man made radiation exposure is a result of various medical procedures (such as x-ray).  This accounts for around 20% of exposure worldwide and up to 50% of exposure in  industrialized countries.  Here is a pie chart.


Linear no threshold model

The most widely accepted model for determining harm for low doses is known as the Linear no threshold model  (LNT).  For this model it doesn't matter how much radiation you receive.  All radiation can cause harm, all radiation has an equal chance of causing harm.  Here is a nifty online calculator for it applying it. 

Organizations That Support LNT

 United States National Research Council
"The assumption that any stimulatory hormetic effects from low doses of ionizing radiation will have a significant health benefit to humans that exceeds potential detrimental effects from the radiation exposure is unwarranted at this time."
United States National Academies
"The scientific research base shows that there is no threshold of exposure below which low levels of ionizing radiation can be demonstrated to be harmless or beneficial."
 National Council on Radiation Protection and Measurements

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)
Until the [...] uncertainties on low-dose response are resolved, the Committee believes that an increase in the risk of tumour induction proportionate to the radiation dose is consistent with developing knowledge and that it remains, accordingly, the most scientifically defensible approximation of low-dose response. However, a strictly linear dose response should not be expected in all circumstances
The Controversy

Radiation can be harmful. Everyone seems to agree with that.  What people can't always agree about is the effect of very small doses of radiation.  Anyway Here is a page that does a good job of describing the controversy.  If you want to understand this subject better this is worth reading. 

Living things evolved in a world full of radiation.  Various biological defence mechanisms have come about in order to protect organisms from it and other sources of harm.  Here is a list of some of our bodies defences. 

  1. Defences against the metabolically induced reactive oxygen species (i.e. defence against things that have been ionized),  
  2. DNA repair, and  
  3. Elimination of damaged cells. 
The big disagreement is low levels of radiation, where it is difficult to show statistically what is going on.  There are several different models that describe the effects of radiation at low doses. 

Another model is the threshold model

This model says that only radiation over a certain dose is harmful.

Organizations that support this model

French Academy of Sciences (Académie des Sciences) and the National Academy of Medicine (Académie nationale de Médecine).

In conclusion, this report raises doubts on the validity of using LNT for evaluating the carcinogenic risk of low doses (< 100 mSv) and even more for very low doses (< 10 mSv). The LNT concept can be a useful pragmatic tool for assessing rules in radioprotection for doses above 10 mSv; however since it is not based on biological concepts of our current knowledge, it should not be used without precaution for assessing by extrapolation the risks associated with low and even more so, with very low doses (< 10 mSv), especially for benefit-risk assessments imposed on radiologists by the European directive 97-43.
Hormesis Model

Another model is the  is the hormesis model which postulates that a certain amount of radiation actually decreases your chance of getting cancer a little because it stimulates your body's natural defences.

What People agree About

At any rate pretty much everyone agree about larger doses so Here are a few facts I think anyone would agree with. 

  • 100 rem received in a short time can cause observable health effects from which your body will likely recover, and will increase your chances of getting cancer.
  • 1,000 rem in a short or long period of time will cause immediately observable health effects and is likely to cause death.


As for conclusions there isn't one really.  Hope this was helpful to someone.

Update:  I've made a lot of changes in order to make it more complete.  Also, changes some things to make it more balanced.

Random Idea Number One

Disclaimer:  Occasionally I get ideas about random things.  I love thinking about how to solve problems.  Even though not all my ideas are good ones, or things that I think should be done, it's still fun to share.  So I thought about it and decided it might be fun make blog posts about them.

Recently I've been reading people complaining about the low oil price, and I was thinking about why the US government doesn't buy and store it in order to keep the price at some set level.   Then I started thinking about how they might store it.  I figured the EPA might make this difficult and expensive.  Thinking about it some more what I finally came up with was abandon open pit mines.

They are already environmental problem spots so maybe people would be less against it.  Then I started thinking about how to seal them so the oil doesn't leak into the ground, and I remembered that because of China's recent policies recycled plastic prices are down.  Maybe they could be sealed with Polly Propylene or HDPE.  Then I started thinking about how to apply the plastic, and what I came up with was something like a giant heat gun that would both blow plastic chips onto the surface and melt them.   Maybe a converted jet engine would do the job.

Then I started thinking this might be useful for storing other things then oil (Such as fresh water).  Then I thought that this could be a good investment for people.  Oil went down because of a small oversupply but it's bound to come up again eventually.  People could maybe double their money in a few years.  Well that's all my thought on it.