What is Alpha Radiation?

Alpha radiation is another name for the alpha particles emitted in the type of radioactive decay called alpha decay. Alpha particles are helium-4 (4He) nuclei.

Radioactivity was discovered by Becquerel, in 1896 (and one of the units of radioactivity – the becquerel – is named after him); within a few years it was discovered (Rutherford gets most of the credit, though others contributed) that there are actually three kinds of radioactivity, which were given the exciting names alpha (radiation), beta (radiation), and gamma (radiation; there are some other, rare, kinds of radioactive decay, the most important being positron, or positive beta). Rutherford (with some help) worked out that alpha radiation is actually the nuclei of helium … by allowing alpha radiation to go through the thin walls of an evacuated glass tube, and later analyzing the gas in the tube spectroscopically).

Some fun facts about alpha radiation:

* alpha radiation is the least penetrating (of alpha, beta, and gamma); typically it goes no more than a few cm in air

* like all kinds of radioactive decay, alpha decay occurs because the final state of the nucleus (the one decaying) has a lower energy than the initial one (the difference is the energy of the emitted alpha particle, both its binding energy and its kinetic energy)

* alpha decay involves both strong and electromagnetic interactions (or forces), unlike beta and gamma decay

* the key to the specifics of alpha decay is the quantum effect called tunneling; Gamow worked this out, in 1928

* only heavier nuclides can undergo alpha decay; the lightest are light isotopes of tellurium

* alpha radiation played a star role in the development of our understanding of the nature of atoms … Rutherford, in 1909, aimed a beam of alpha radiation at a piece of thin gold foil, and counted the number of particles which were deflected at each angle; from this he deduced that the atom has a very small nucleus (with all the positive charge, and nearly all its mass).

For more background on alpha radiation, check out the Jefferson Lab’s What are alpha rays? How are they produced?.

There are many ways alpha radiation can turn up in Universe Today articles; for example, in NASA May Have to Revamp Science Plans Without RTGs, alpha radiation is essential to RTGs; and in Opportunity Rover Sidelined by Charged Particle Hit, alpha radiation is what’s used to help determine the elemental composition of samples.

Nucleosynthsis: Elements from Stars and Cosmic Rays are two Astronomy Cast episodes which also cover alpha radiation.

Source: Wikipedia

Alpha Particle

An alpha particle is a particle made up of two protons and two neutrons. Since this configuration is similar to that of a helium nucleus, it’s often referred to as a helium nucleus. The term is commonly used in nuclear physics, and is one of the three particles commonly emitted during a radioactive decay, i.e., alpha, beta, and gamma particles.

Alpha particles gained prominence during the early days of particle physics when scientists used them as projectiles to bombard certain targets. One of the most widely celebrated experiments that made use of alpha particles was that of Ernest Rutherford’s that led to the discovery of the atom’s structure.

Using alpha particles as projectiles and gold foils as targets, Rutherford was able to come to the conclusion that atoms were made up of very dense positively charged cores with the much lighter negatively-charged electrons orbiting around it. His conclusion was based on the observation that the trajectories of the alpha particles were slightly deviated (as expected) at most times but in rare instances bounced off like ping-pong balls thrown against a wall.

The alpha particles went through the gold foils unhindered when they passed through the large but sparsely filled region around the nucleus. However, when, during much rarer instances, they happened to collide head on or even came close to the very dense and positively charged nucleus, they were deflected at very wide angles.

Through this information, there was no other option but for Rutherford to conclude that the atom must have a very dense nucleus which is very much smaller compared to the entire atom.

In terms of atomic proportions, alpha particles are considered very massive because of the existence of the two protons and two neutrons. Furthermore, they are also positively charged due to the protons. As such, they can easily wreak havoc to most targets. That is, they have high ionization properties.

Alpha particles are released during alpha decay processes which can happen most especially to ultra-heavy nuclei like uranium, thorium, actinium, and radium. Since they’re not as fast (due mainly to their masses) as betas and gammas, they can’t travel across large distances and can be easily stopped by a piece of paper or human skin.

However, again because of their huge masses, alpha particles can be very dangerous whenever they can somehow enter the body through inhalation or ingestion. Minus that possibility, you don’t have to worry much about this heavyweight of a particle.

Universe Today has some interesting related content that you might want to read. Want to know about how the Opportunity rover got sidelined by a charged particle hit? And here’s an article about alpha radiation.

There’s more about it at NASA. Here are a couple of sources there:

Here are two episodes at Astronomy Cast that you might want to check out as well: