This decay pattern is always the same for Tm-170. The other ¾ of the atoms are beta emitters with no associated gamma emission. When Tm-170 decays, approximately ¼ of its atoms emit beta particles and an associated gamma ray. Another example of characteristic decay patterns is that of Thulium-170 (Tm-170).
Therefore, when a Co-60 source decays, each disintegration of an atom results in two gamma rays. Each of the gamma rays possess a certain energy level that is always the same. Almost immediately additional energy adjustments are made in the atom and two gamma rays are emitted. In a Cobalt-60 source (Co-60) each atom decays by emitting a beta particle.
That is, one disintegration in a radioactive source does not necessarily result in the same amount of radiation emission. This leads us to another distinction among radioactive materials. We have been talking about the activity of a radioactive material in terms of disintegration of the atoms in the material and not about the resulting radiation. How can we assess the amount of radiation coming from a source? If you want to read more about this, you can read the material below. Different radioisotopes produce different amounts of radiation as their nuclei change. Please note that the decay rate or the activity of the radioisotope does not directly relate to how much radiation is produced. The activity, in curies, of 1 gram of any radioactive source is known as its specific activity. With radioactive sources, we compare the activities of the sources in terms of gram for gram. It is fairly simple to determine the activity of a source when you know how many atoms decay per second. If you said that the activities of these two sources were 1/2 Ci and 2 Ci, you were correct. One decays at a rate of 18.5 billion atoms per second, and the other decays at a rate of 74 billion atoms per second.Ĭan you determine the activities of the values below in curies? Now let's consider two radioactive sources. Determining the activity of radioactive sources in curies This discussion will continue using curies as units, however, SI units are encouraged in most places now. One Bq is equal to one disintegration per second. The SI unit for activity is the Becquerel, Bq, named after Henri Becquerel, who shared the Nobel prize with the Curies. If the rate of decay is greater than 37 billion atoms in one second, then the source would have an activity greater than one curie, and if that source had fewer than 37 billion atoms decaying in one second, its activity would be less than one curie. (This was determined to be the radioactivity of 1 gram of radium.) Remember that we said each isotope has its own decay pattern. In scientific terms, this is expressed by the equation: 1 Ci = 3.7 X 10 10 disintegrations/sec. A quantity of radioactive material is considered to have an activity of 1 curie or 1 Ci, when 37 billion of its atoms decay (disintegrate) in one second. The basic unit of measure for describing the activity (radioactivity) of a quantity of radioactive material is the curie, named after Marie Curie. Now that we have an idea of how radioactive isotopes decay, let's look at how this is measured and apply the terms we just learned.  How do you measure the decay of radioactive isotopes? Highly unstable isotopes have half-lives measured in fractions of seconds, more stable isotopes have half-lives measured in billions of years. Some isotopes decay very rapidly and, therefore, have a  short half-life. The half-life of a radioisotope describes how long it takes for half of the atoms in a given mass to decay. The rate of decay is a fixed rate called a half-life. Not all of the atoms of a radioisotope decay at the same time, but they decay at a rate that is characteristic to the isotope. Compare two radioactive sources and determine their specific activities in curies.Explain how you measure the decay of radioactive isotopes.After this reading this section you will be able to do the following: