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Nuclear chemistry

Three types of radioactivity
from http://www.darvill.clara.net/nucrad/types.htm

All substance are made of atoms.

Atoms have electrons (e-) around the outside, and a nucleus in the middle.

The nucleus consists of protons (p) and neutrons (n),

In some types of atom, the nucleus is unstable: it will decay into a more stable atom.
Radioactive decay is completely spontaneous.

You can heat the substance up, subject it to high pressure or strong magnetic fields – do whatever you like to it – and you won’t affect the rate of decay in the slightest.

_______________

An unstable nucleus may decay in three ways. It may give off:

  • an alpha particle)

  • a beta particle)

  • a gamma ray)

Many radioactive substances emit particles and particles as well as rays.

You won’t find a pure source: Anything that gives off rays will also give off and/or too.

______________________________

Alpha particles are made of 2 protons and 2 neutrons.

This means that they have a charge of +2, and a mass of 4

Mass is measured in “atomic mass units” – each proton & neutron = 1 unit.

We can write them as , or, because they’re the same as a helium nucleus, .

Alpha particles are relatively slow and heavy.

They have a low penetrating power – you can stop them with just a sheet of paper.

Because they have a large charge, alpha particles ionise other atoms strongly.

______________________________

Beta particles have a charge of minus 1, and a mass of about 1/2000th of a proton. They are electrons.

We write them as or, because they’re the same as an electron, .

They are fast, and light.

They have a medium penetrating power – they are stopped by a sheet of aluminium or plastics such as perspex.

Beta particles ionise atoms that they pass, but not as strongly as alpha particles do.

______________________________

Gamma rays are waves of electromagnetic energy:
They are not particles
.

“You can consider gamma rays to be an “invisible” color of light
Visible light is just an electro-magnetic wave that our eyes respond to.
Everything else on the spectrum below is an electro-magnetic wave that our eyes do not respond to – but those “colors” of light are certainly real.
Too much exposure to UV rays causes skin cancer
Too much exposure to X-rays, or gamma rays, causes cancer is any part of our body that was exposed to it.”

This means that they have no mass and no charge. So we sometimes write .

Gamma rays have a high penetrating power – it takes a thick sheet of metal such as lead, or concrete to reduce them significantly.

Gamma rays do not directly ionise other atoms, although they may cause atoms to emit other particles which will then cause ionisation.

We don’t find pure gamma sources – gamma rays are emitted alongside alpha or beta particles.

Strictly speaking, gamma emission isn’t ‘radioactive decay’ because it doesn’t change the state of the nucleus, it just carries away some energy.

 

  • Alpha particles are easy to stop, gamma rays are hard to stop.

  • Particles that ionise other atoms strongly have a low penetrating power, because they lose energy each time they ionise an atom.

  • Radioactive decay is not affected by external conditions.

  • You need to know the information in this table:-

  • You need to know the information in this table:-

Type of Radiation Alpha particle Beta particle Gamma ray
Symbol or or or
(can look different,
depends on the font)
Mass (atomic mass units) 4 1/2000 0
Charge +2 -1 0
Speed slow fast very fast (speed of light)
Ionising ability high medium 0
Penetrating power low medium high
Stopped by: paper aluminium lead

 

We talk about “radioactive isotopes” – but what’s an isotope?

Just because something is called an isotope doesn’t necessarily mean it’s radioactive.
Different isotopes of an atom are lighter or heavier versions of that atom.

Consider a carbon atom.
It has 6 protons and 6 neutrons – we call it “carbon-12” because it has an atomic mass of 12 (6 plus 6).
If we add a neutron, it’s still a carbon atom, but it’s a different isotope of carbon.
One useful isotope of carbon is “carbon-14”, which has 6 protons and 8 neutrons. This is the atom we look for when we’re carbon dating an object.

So isotopes of an atom have the same number of protons, but a different number of neutrons.

________________

Seeing a nuclear reactor start up is cooler than my sci-fi dreams

Nuclear power and cancer

In theory, during an accident, radiation released from nuclear power plants can increase the background rates of cancer, perhaps dramatically. It has long been expected by opponents of nuclear power that it’s use would be highly dangerous. Yet in the 60 years of it’s use, the number of actual accidents, Soviet designed tragedies like Chernobyl (an event in a class by itself, due to deliberate malfeasance), and even Fukushima Daiichi, the tsunami-damaged nuclear reactor site, have caused far less damage and death than coal, oil and other sources of power.

Surprisingly, simply burning coal releases more radiation into the environment than running a nuclear reaction. Similarly, getting into an airplace to fly away from Fukushima Daiichi caused thousands of Japanese citizens to be exposed to even more ionizing radiation than if they had simply stayed at home – as airplane flights make one rise above most of the atmopshere, thereby increasing one’s exposire to natural background radiation from space.

There is also the intriguing phenomenon of radiation hormesis:

Radiation hormesis is the hypothesis that low doses of ionizing radiation (just above natural background levels) are beneficial. Low level radiation apparently activates repair mechanisms that protect against disease, that are not activated in absence of ionizing radiation. The reserve repair mechanisms are hypothesized to be sufficiently effective as to not only cancel the detrimental effects of ionizing radiation – but also inhibit disease not related to radiation exposure. This counter-intuitive hypothesis has captured the attention of scientists and public alike in recent years.

Radiation hormesis. (2016, December 10). In Wikipedia, The Free Encyclopedia. Retrieved 18:44, February 2, 2017
Radiation hormesis (Wikipedia)

There is no environment without some level of background radioactivity. What society needs to do is become familiar with the statistics, so it can make informed choices on how much power to generate/consume, and where this power should come from.

Coal releases more radioactivity than nuclear power

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