But there is no way to predict when a particular pun intended nucleus is going to decay. A nucleus consists of protons and neutrons held together by powerful forces. Certain combinations are more stable than others. Within one element—and to be careful, let's assume we are talking about one nuclide or one isotope of one element —every atom has exactly the same combination of protons and neutrons.
Every once in a long while, however, the jiggles might line up or form a resonance that sends the nucleus across the limit of its cohesion, and the nucleus splits.
Beta Particles — Electrons ejected from the nucleus of a decaying atom. Although they can be stopped by a thin sheet of aluminum, beta particles can penetrate the dead skin layer, potentially causing burns.
They can pose a serious direct or external radiation threat and can be lethal depending on the amount received. They also pose a serious internal radiation threat if beta-emitting atoms are ingested or inhaled. See also alpha particle , gamma ray , neutron , x-ray. Decay Chain Decay Series — The series of decays that certain radioisotopes go through before reaching a stable form.
For example, the decay chain that begins with uranium U ends in lead Pb , after forming isotopes, such as uranium U , thorium Th , radium Ra , and radon Rn Gamma Rays — High-energy electromagnetic radiation emitted by certain radionuclides when their nuclei transition from a higher to a lower energy state.
These rays have high energy and a short wave length. All gamma rays emitted from a given isotope have the same energy, a characteristic that enables scientists to identify which gamma emitters are present in a sample.
Gamma rays penetrate tissue farther than do beta or alpha particles , but leave a lower concentration of ions in their path to potentially cause cell damage. Gamma rays are very similar to x-rays.
See also neutron. Isotope — A nuclide of an element having the same number of protons but a different number of neutrons. Neutrons are, as the name implies, neutral in their charge. That is, they have neither a positive nor a negative charge. A neutron has about the same mass as a proton. See also alpha particle , beta particle , gamma ray , nucleon , x-ray. Radioactive Decay — Disintegration of the nucleus of an unstable atom by the release of radiation.
Radiation — Energy moving in the form of particles or waves. Familiar radiations are heat, light, radio waves, and microwaves. Ionizing radiation is a very high-energy form of electromagnetic radiation.
Let us agree that when we roll a "6", we smash the die to pieces and the game is over for that particular die. We begin rolling the die and get a "3", and then a "1" and then a "5". Next we roll a "6" and destroy the die as agreed upon. Since the die was destroyed after four rolls, we say that this particular die had an individual lifetime of four rolls.
Now we get a new die and repeat the game. For this die, we roll a "2", then a "1", then "4", "3", "1", "5", and then finally a "6".
This die therefore had an individual lifetime of seven rolls. When we repeat this game for many dice, we discover that the individual lifetime of a particular die can be anything from one roll to hundreds of rolls. However, if we average over thousands of individual lifetimes, we find that the dice consistently have an average lifetime of about six rolls. Since an individual die has no internal machinery telling it to show a "6" after a certain number of rolls, the individual lifetime of a die is completely random.
However, since the random events are governed by probabilities, we can experimentally find a fixed characteristic average lifetime of a group of dice by averaging over a large ensemble of dice. We can also mathematically find the average lifetime by calculating probabilities. Plotting the results of these demonstrations results in a curve of an exponential decay function. Showing this plot and asking them questions about the shape and changes in number of isotopes through time may help students to develop some intuition about half-life.
Although most introductory students may not be prepared for the equation for exponential decay, discussion of half-life and radioactive decay prepares entry-level students for the introduction of more mathematical discussion of exponential growth and decay in upper level classes.
So many systems, how do we choose? Most students don't really know how isotopes are used to determine age. In particular, they have a hard time understanding that different systems are appropriate for different types of radiometric dating and why.
There are several important points that can be emphasized to help avoid confusion when talking about the various systems: Geologists have a plethora of choices for calculating the age of a rock using big and complicated systems. Check out this table of isotope systems and half-lives Excel 18kB Jun24 04 ; all of these are used to date rocks or sediment!
With all these systems, how do we choose? Geologists use a number of criteria to decide which of the systems to use: Zircon, which is a useful mineral for U-Pb dating. Details Is the half-life of the system appropriate for the rock that you are trying to date? Most geologists have an idea of the age of a rock if age is less than 6 half-lives, it'll work.
Does the rock have minerals that can be used for the isotope system you want to use? You need to have minerals in your rock that contain the element s you want to use.
What event do you want to date? Some systems are very good for dating igneous events, others are very good for dating metamorphic events.
Remember, it is impossible to date sedimentary minerals because they eroded from some igneous or metamorphic rock. Together, the answers to those questions help geologists decide which system they should use.
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