By Ron B. Davis Jr., Georgetown University
The phenomenon of nuclear radiation was documented in samples of uranium ore in 1896 by Henri Becquerel. In the 20th century, scientists sought out quantitative ways to measure radiation. An electrical technique of measuring radioactivity allowed scientists to detect radiation and determine its energy. The type of radiation combined with its energy creates a fingerprint for each radioactive decay process.
Thorium and the Theory of Transmutation
The notion that radiation might actually be atoms shedding a portion of themselves was first proposed by Ernest Rutherford in 1902 when he and Frederick Soddy published a theory of transmutation that arose from their experiments with the element thorium.
Using new electrical techniques, Rutherford noted that radiation of more than one energy was being emitted. What’s more, it was being emitted by a substance that when isolated and tested had vastly different chemical properties than thorium itself. Not sure what to make of the discovery, he named the newly discovered radiation-emitting substance ‘thorium-X’.
Possibly even more interesting is that thorium and thorium-X samples seemed to emanate a short-lived gas with its own unique radioactive properties. It was referred to as ‘thoron’ gas, and, over the next two decades, it was the discovery of the atomic nucleus and the subatomic particles that comprise it that would finally reveal that thorium-X and thoron gas were not really thorium at all!
With the ability to measure the intensity and nature of radiation more precisely, Rutherford also determined that the radioactivity of a given sample is reduced by one-half over a fixed interval of time. In 1909, he introduced the concept of a half-life. It certainly seemed like emitting radiation somehow depleted the radioactive element.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Alpha and Beta Radiations
There are three different types of radiations. Two of which can transmute elements into others, and a third of which often accompanies that transmutation. Let’s start with alpha nuclear radiation, which is the loss of a helium nucleus. Let’s consider the element thorium. Thorium has no stable isotopes. However, thorium-232 is a very common primordial isotope in our environment.
And, thorium-232 can undergo an alpha decay in which its nucleus ejects a helium-4 nucleus, that’s two protons and two neutrons leaving the nucleus. So, here’s our alpha particle, and here’s our remaining radium-228, element number 88 that results from this alpha decay. In running this alpha decay, we have caused our element to take two steps to the left on the periodic table, a transmutation.
Now, the 2nd form of nuclear radiation that can transmute elements is beta radiation. So, let’s take that radium-228 and consider how it might decay. Radium-228 can release an electron from its nucleus, and in doing so convert a neutron in that nucleus into a proton. Thus, we get the emission of a beta particle with a unit of a negative charge, but virtually no mass.
So, while the mass of my isotope hasn’t changed, the identity of my isotope has. I’ve taken one step to the right on the table to make actinium-228 through beta decay.
The Decay Chain
Now, we can often string these kinds of decay processes along to create what we call a decay chain. Consider thorium-232’s full decay chain. It’s going to lose four units of mass, two protons, to become radium-228 in an alpha decay, which then undergoes beta decay to actinium-228, and then a second beta decay to thorium-228.
This isotope of thorium then undergoes a series of alpha decay getting us to lead-212, which actually can take a couple of different routes to the final stable isotope. Going through bismuth, either through a beta, then an alpha decay to get to lead-208, or going through alpha and then a beta decay to reach the same stable isotope.
And within this decay chain, we can see those elements that Rutherford called thorium and thorium-X. Thorium-X would be the radon that forms during the decay chain. And that thorium gas that he thought he had made was actually radon.
There was one additional form of nuclear radiation that often accompanies alpha and beta radiation, and that’s called gamma radiation. So, let’s go back to our radium-228 isotope. Now, as it undergoes that beta decay, remember, it loses high-energy electrons from the nucleus that gives us our proton that transmutes the element.
But, this element now has a different number of protons and neutrons, which often need to shift and rearrange themselves to find their most stable configuration within the nucleus. And as they do that, oftentimes a high-energy photon of light is ejected. Now, this light is a photon with no charge and virtually no mass, but it does carry a very high amount of energy.
The Uses of Alpha, Beta, and Gamma Radiation
In the decades since being discovered, alpha, beta, and gamma radiation have found many uses. Alpha radiation is employed in many smoke detectors. Beta particles have limited penetrating power, and can be used to measure the thickness of surfaces in manufacturing.
Gamma rays, with their very high energy, are useful as well, not for turning unsuspecting scientists into superheroes, but rather in imaging deep within metal surfaces to scan for deformities and cracks.
And although they can be dangerous to healthy cells, alpha, beta, and gamma radiation can—when properly focused or localized—and each is used to kill targeted cancer cells in the human body or discourage the growth of other tissues that may lead to other health problems.
Common Questions about Nuclear Radiation and Its Different Types
There are three distinctive types of nuclear radiation: alpha radiation, beta radiation, and gamma radiation.
Several decades after nuclear radiation had first been observed, the theories needed to identify ‘Thorium-X’ and ‘thoron’ gas were finally available. These were not new and exotic forms of thorium. They were isotopes of other elements—radium and radon gas—forming from the decay chain of thorium, then decaying again themselves on their way to becoming the stable element, lead-208.
Nuclear radiation can be extremely dangerous and destructive. Yet, when harnessed, it can have many uses. Alpha radiation can be used to detect smoke in smoke detectors. Beta radiation is practical for measuring the thinness of different surfaces. And gamma nuclear radiation is used for imaging metal surfaces. These radiations are used in medical technologies as well.