Radioactivity in pills - Part 1

Hello there, it's been a while. The first attempt of keeping this blog alive has failed. Badly. But then yesterday I was driving with the Blues Brothers soundtrack to keep me company (virtually every decision of my life has been made at 2 AM with good music and in my car) and, during Rawhide, an idea: what if I use the blog to refresh my engineering knowledge by posting about random stuff? Best idea I've had in a while. By doing this I hope I can make people interested and/or help them understand things that can be obscure sometimes, and at the same time I will benefit of this effort because it's like preparing a lecture! So everybody wins! The first topic is nuclear radiations (aka radioactive decay aka radioactivity). I will try to explain in the best way I can what they are, how they are detected and measured and all the terminology that is often used but never explained.

Today we will focus on what radiations are.

Looking on Wikipedia for "nuclear radiation" we are redirected to the page of "Radioactive decay" and the definition states: "Radioactive decay, also known as nuclear decay or radioactivity, is the process by which a nucleus of an unstable atom loses energy by emitting particles of ionizing radiation. A material that spontaneously emits this kind of radiation - which includes the emission of energetic alpha particles, beta particles, and gamma rays - is considered radioactive".

As you certainly noticed, some words are in red. These are the terms that, in my opinion, need some clarification, because their meaning is probably not 100% clear sometimes.

Let's get started!

Unstable atom

The nucleus of an atom is formed by protons (particles with positive charge) and neutrons (particles without charge). As everybody will certainly know from high school, particles with charges of the same sign tend to repel each other. This is due to the electrostatic force. Hence, when two protons are put close to each other, they will drive each other apart, right? Not quite. This is true unless the two protons are brought close enough to each other for the strong nuclear force to "kick in" and overcome the electrostatic force. This can be seen in the figure below (taken from here):

The strong nuclear force is attractive and independent from the sign of the charge. It works between neutron and proton, proton and proton, neutron and neutron.

The curve shows the potential energy of a proton as a function of distance from the centre of a nucleus. The repulsive force is zero at great distances and increases as the proton approaches the nucleus. Two outcomes are possible: if the approaching proton is not very energetic (low energy proton) it will slow down, stop and reverse its trajectory or be deflected. On the other hand, if the energy possessed by the proton is enough to overcome the repulsion until it reaches the surface of the nucleus, the strong nuclear force will attract and try to bind the proton to the nucleus. 

This boring introduction was needed to understand the concept of unstable atom. Now imagine if our atom was composed by protons only. Locally the strong nuclear force would still be working, but the repulsive electromagnetic force would be pushing away the protons which are further from the kick-in threshold of the strong nuclear force. The heavier the atom, the more protons in its nucleus, hence, the bigger the repulsive electromagnetic force. This is why, for an atom to be stable, a certain number of neutrons is needed to balance out the repulsive electromagnetic force. But exactly, how many neutrons are needed? It depends on how big the atom is. The bigger the atom, the bigger will be the number of neutrons needed, as shown in the chart of the nuclides below (source: http://www.geigercounter.org/):

When the number of protons is higher than 83 (Bismuth), the neutrons in excess are not able to "supply" sufficient nuclear force to produce a stable nucleus. In fact, all atoms with atomic number bigger than 83 are radioactive. On the x axis we have the number of neutrons present in the nucleus, while on the y axis we have the number of protons. The legend shows the type of decay that each isotope undertakes. The black boxes represent the stable isotopes, which have the same number of neutrons and protons for light atoms, and more neutrons than protons for heavier atoms. The diagonal line is a help to visualise the fact that stable isotopes don't have the same number of protons and neutrons. We will discuss the different types of radiation decay in the next posts. 

In the end, an unstable atom is nothing more than an atom that has an excess of neutrons or protons compared to its stable isotope.

Properties of unstable atoms

• Unstable atoms tend to spontaneously transform in stable isotopes through different decay processes.
• Most of the times the nucleus of the new produced atom is in an excited state. Successive transitions to less excited states or to the ground state are accompanied by gamma radiation emission.
• The decay process consists in the emission of charged particles or capture of an atomic electron. This results in a change of the nucleus charge, giving birth to an isotope of a different chemical element.
• The nucleus produced by a spontaneous decay always has total energy less than the "mother" nucleus. This difference is the energy of the emitted radiation.

This is the end of this first post, I wouldn't want it to be too long, it might get more boring than it already is! If you made it this far, thanks a lot. If you have any comments on anything, if something is not correct or imprecise, feel free to give me a shout in the comment section, constructive criticism is always very much appreciated. I hope I can make a second post by the end of January. Happy new year everybody!


Sources:

• http://www.geigercounter.org/
• http://www.opencourse.info/astronomy/introduction/12.sun_interior/
• Shultis, J. K., Faw R. E., Fundamentals of nuclear science and engineering, 2nd edition, CRC press, 2008

Resources:

Interactive Nuclide Chart
http://www.nndc.bnl.gov/chart/

3,2,1 we're airing!

Hello there, readers. I hope you would follow this new blog in large number, and i hope not to bore you with my posts. I used to have a blog when MSN was at his peak and i loved it, acid green and shocking pink theme colored, great memories. It's a shame that windows live spaces service has been shut down. I really hope i could be posting here with the same regularity i used to have back then.

But for now just let me introduce myself: I'm Antonello (Neil if you prefer), 24 years old, and my new house is the city of London, in which I will be studying for at least three more years. I came here after a six-year academic journey in an university located in the most beautiful city in the world. Which city am I talking about? The eternal city, the city where all the roads lead, "L'Urbe", the "Caput Mundi", Rome. I wasn't born in Rome, didn't live there either, i used to commute every day of those six years, sometimes even in the weekends, but it was worth the effort. Every single moment, sad or happy, spent in that city has its own meaning, its own flavour, it's a piece of me, my personality and my life. I was literally keeping the tears from coming out of my eyes on that Tuesday, 18th of September. Tears of love for a city that is impossible not to love, even with all the things that don't work down there. It was Rome, on that sunny day of September, that made me understand what true love is. Not a girl. 

Rome, a piece of my heart.