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Ste-W

Understanding Atomic Radiation

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Hope this is the correct discussion to post this, I simply cannot get my head around the basic theory surrounding Atomic Radiation. I have been working near an old Nuclear Power Station in Wales, its manily de-commissioned now but radioactive waste is still insitu, and the Station will not be totally safe until 2083 apparently. MY difficulty is actually understanding how that waste , wether it be spent fuel or simple pipe fittings from the reactor buidling remains so powerfully iradiated for so long. Where did such radiactive material come from in the first place.

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Atomic radiation is the result of either naturally occurring ( but refined/separated ) unstable elements, or the irradiation of stable elements  in a nuclear reactor, which results in them capturing radiation ( usually neutrons ), and becoming unstable.

Stable elements usually follow a 'stability' curve which is related to the proton to neutron ratio in their nuclei, and the deviation will indicate the type of radiation to expect.

The activity, A, is given by   A = dN/dt = lambda*N  where N is the number of particles in the radioactive sample.
The half-life ( when half of the nuclei have undergone decay ) is then given by  t(1/2) = ln(2)/lambda = N*ln(2)/A.
And since N is extremely large, the half-life can be up to thousands of years.

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Posted (edited)

Majority of the existing isotopes are radioactive. Only a small fraction of all isotopes are stable. Uranium has two isotopes with relatively high half-life U-235 with ~ 704 mln years and U-238 with ~ 4468 mln years. Uranium is widely present in the Earth's crust (2 to 4 parts per million). During Uranium fission there are produced much faster decaying isotopes.

Some radioactive isotopes are even part of living organisms body, including you. Carbon C-14 with half-life ~5760 years and Potassium K-40. If Carbon C-14 atom is becoming part of DNA/RNA or part of living cell, decay of it may cause damage of DNA/RNA or damage of cell. The result is mutation, damage and in extremity cancer. Carbon C-14 is created day-by-day by cosmic rays in the upper region of Earth's atmosphere.

Check natural decay chain of U-235 and U-238: https://en.wikipedia.org/wiki/Decay_chain#Uranium_series

Check Uranium U-235 fission chain https://en.wikipedia.org/wiki/Uranium-235

e.g. U-235 + n0 -> Ba-141 + Kr-92 + 3 n0

Notice that free neutron is causing Uranium 235 to break apart. But new free neutrons are created by this type of reaction. So if newly produced free neutron will hit yet another Uranium U-235 atom, entire process will repeat. Situation when it happens spontaneously is called a critical mass. Different fissile isotopes require different critical mass.

https://en.wikipedia.org/wiki/Critical_mass

When free neutron is captured by otherwise stable isotope it may be converted to unstable isotope. Object becomes contaminated.

Check Uranium 235 fission products decay chains: "Ba-141 decay chain" and "Kr-92 decay chain". They (and the rest of fuels) are the so-called "nuclear reactor waste".

 

Some of them easily dissolve in water, e.g. Cesium, that a living organism can consume. Some of them are replacing Calcium in bones, e.g. Barium and Strontium, which may lead to bone cancer many years after being contaminated. 

Edited by Sensei

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(Atomic) Radiation comes in 3 types, called alpha, beta and gamma.

The lifetime of these radiations themselves is quite short as they interact with material the encounter (hit).
It is this interaction which makes them dangerous.

A piece of tissue paper will stop most alpha rays.

Beta rays are more penetrating, and are the same type that are used in electron beam welding.

Gamma rays are the most penetrating and have been used in X ray machines.

 

The point is that there is a continual production and dispersion of this radiation due to processes inside the atom.
In NW Wales, where you are (Trawsfynydd decomissioned 1919 or Wylfa decomissioned in 2015 ) are both located near natural granite rocks.
Granite (as in Cornwall) produces natural radiation by these atomic internal processes.
These processes can take many thousands of years to complete, and have been going on since the rocks were formed.
So all this time natural rocks have been generating radiation.
We call this background radiation.
However the natural background is, we hope, safe.

Mankind has sifted and concentrated the rocks  that have a high level of activity, raising the radiation levels to way above the natural abckgoround.
At these raised radiation levels the radiation can create / initiate new processes in material that is not of itself radioactive (such as concrete, pipes etc) but can become radioactive by these new processes.
These secondary radioactive sources are generally much more short lived than the ones in the original rocks, but the concentration makes them still dangerous untill they have died away.

 

Does this help ?

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2 hours ago, Ste-W said:

MY difficulty is actually understanding how that waste , wether it be spent fuel or simple pipe fittings from the reactor buidling remains so powerfully iradiated for so long.

The material has a long half-life, or there is a decay chain involved, with moderate to long half-lives.

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6 hours ago, Ste-W said:

Where did such radiactive material come from in the first place.

Most of the radioactive material come from the neutron flux of the reactor converting the reactors materials into radioactive isotopes.  Such as nickel to cobalt-60.  The reactor core and associated fission products have almost certainly been removed off site.

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Iron will become activated, but the isotopes have either shorter half-lives than Co-60, or much longer, in which case it has a low activity.

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15 hours ago, studiot said:

The point is that there is a continual production and dispersion of this radiation due to processes inside the atom.

I should also have said that there are two types of atoms.

Those which are support these processes and are 'radioactive'.
And those which are do not support these processes and are called 'stable'.

The end of all radioactive processes are stable atoms, but on the way other radioactive atoms are formed and, which in turn, eventually decay to stable atoms.

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2 hours ago, studiot said:

I should also have said that there are two types of atoms. [isotopes]

Those which are support these processes and are 'radioactive'.
And those which are do not support these processes and are called 'stable'.

I did it for you, in the post on yours.. ;)

17 hours ago, studiot said:

(Atomic) Radiation comes in 3 types, called alpha, beta and gamma.

There are also proton emission, neutron emission, electron capture, positron capture, (anti)neutrino capture etc. etc.

Cluster decay

https://en.wikipedia.org/wiki/Cluster_decay

 

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2 hours ago, Sensei said:

 

There are also proton emission, neutron emission, electron capture, positron capture, (anti)neutrino capture etc. etc.

Cluster decay

https://en.wikipedia.org/wiki/Cluster_decay

 

Types of decay ≠ types of radiation 

(e.g. electron capture is a decay, not a type of radiation)

The radiation is any energetic particle emitted as a result of decay. 

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