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Atoms and Radioactivity

Atoms and Radioactivity

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Atoms are tiny particles that make up everything around us. They are like the building blocks of the entire universe! There are three main types of subatomic particles in atoms: protons, neutrons, and electrons. The periodic table lists all the chemical elements based on how many protons are in the nucleus of their atoms. Some atoms are radioactive, which means they are unstable and have too much energy in their nucleus. Examples of radioactive elements include Uranium, Plutonium, and Thorium. Over time, these atoms will undergo a process called radioactive decay to become more stable.

Atoms and radioactive relationships

Measuring radioactivity

To measure the activity of radioactive sources, we use a Geiger-Muller tube attached to a counter. We measure radioactivity using count-rate, which tells us how many decays are detected per second. The standard unit of activity is called a becquerel (Bq). For example, a source with 10 decays per second would have a count rate of 10 Bq. When a radioactive isotope decays, it sends out a radioactive product such as an alpha particle, beta particle, or gamma wave. Each time one of these products enters the Geiger-Muller tube, the counter clicks, and the count rate is shown to the operator.

Radioactive isotopes

Different radioactive nuclei will decay at different rates, even between different isotopes of the same element. One isotope might even be stable, while another isotope of the same element is radioactive. More massive elements tend to be more radioactive because their larger nuclei are more likely to have an unstable excess of internal energy.

Period Table with radioactive elements highlighted according to half-life
Period Table with radioactive elements highlighted according to half-life

Atoms and Radioactivity: Half-life

When learning about radioactive decay, it's important to understand a concept called half-life. This is the time it takes for half of the radioactive isotopes within a sample to decay. Another way to of it is the time it takes for the count-rate of the sample to be reduced to half its original level. Why is this important? Well, decay random, it's impossible to predict when an individual unstable Bismuth-210 nucleus will decay., if you have a larger sample of radioactive material, you can predict with more certainty that some isotopes will decay. For example, if it takes five days for the count rate of a 1 kg block of material containing approximately 1025 Bismuth-210 atoms to be halved, then you know that the half-life of Bismuth-210 is five days.

Decay of a radioactive substance

Based on the graph provided, we can determine the half-life of the radioactive sample by finding the point on the line where the remaining radioactivity is 50% and then determining its x-coordinate. The graph does not provide any specific information regarding the half-life of the radioactive sample, so we cannot calculate it directly.

However, we can use the example of Carbon-14 to understand the concept of half-life and its practical applications. Carbon-14 has a half-life of 5730 years, meaning that after 5730 years, half of the Carbon-14 in a sample will have decayed. By measuring the ratio of Carbon-14 to Carbon-12 in sample, we can estimate the age of the sample.

This technique, known as radiocarbon dating, is commonly used to estimate the age of archaeological artifacts and fossils. By analyzing the amount of Carbon-14 in a sample, researchers can determine how long it has been since the organism died and stopped absorbing Carbon-14 from the atmosphere.

Knowing the half-life of a radioactive element is also evaluating potential health risks associated with radioactive waste. By understanding how long it takes for a radioactive sample to decay, scientists can determine how long it will be before the sample no longer poses a threat to human health or the environment.

The structure of an atom and radioactivity

It’s actually due to radioactivity that we even understand the underlying structure of the atom at all. After the discovery of the electron in 1897 by J. J. Thomson, the most popular theory of how an atom was structured was the plum pudding model or the Thomson Model. Thomson proposed that negatively charged ‘plums’ (electrons) were surrounded by a positively charged ‘pudding’.

Scattering of alpha particles if Plum Pudding model was correct compared to the real results.

In 1905, Ernst Rutherford conducted an experiment to test the plum pudding model. He directed a beam of positively charged alpha particles at a strip of gold foil. The plum pudding model predicted that the positively charged alpha particles would pass through the evenly distributed positive 'pudding' with no deflection. However, a small number of alpha particles were deflected and even reflected back. Rutherford proposed a new model of the atom known as the Rutherford model. This model described the atom as consisting of a small, positively charged nucleus surrounded by a cloud of electrons. The experiment proved that the nucleus was incredibly small compared to the size of the atom as a whole, as the vast majority of the alpha particles passed through the atom without any deflection.

The effects of radioactivity on an atom

A radioactive atom will be changed after undergoing radioactive decay, which can happen in several different ways. Radioactive decay can occur due to an unstable nucleus emitting radiation. The most common forms of decay are alpha particles, beta particles, gamma-rays, or neutron emissions. Each type of radiation has different properties and characteristics.

Atoms and Radioactivity: Alpha radiation

When the nucleus of an atom has too few neutrons compared to protons, it will emit an alpha particle ‘α’, which is made from two protons and two neutrons. This helps to restore the balance within the nucleus and reduce the ratio of protons to neutrons.

An Americium-241 nucleus decays into Neptunium-237 and emits an alpha particle
An Americium-241 nucleus decays into Neptunium-237 and emits an alpha particle

An alpha particleis exactly the same as a helium nucleus. Therefore, alpha decay will cause the nucleus of an atom to lose a mass number of 4 and a proton number of 2. This is helpful when using nuclear equations, as we are able to determine what element the nucleus will decay into. A radium (Ra) nucleus emits an alpha particle. What element has the radium nucleus decayed into? Refer to the periodic table. Radium has a proton number of 88 and a mass number of 226: One helium nucleus is emitted in alpha decay, so subtract 4 from the mass number and 2 from the proton number of radium: Determine which element has a proton number of 86 on the periodic table. The answer is Radon, .

Atoms and Radioactivity: Beta particle

Oppositely to alpha decay, if an unstable nucleus has too many neutrons compared to protons, it will emit a beta ‘β’ particle. A neutron within the nucleus will spontaneously turn into a proton, ejecting a high-velocity electron in the process. The beta particle is literally just one electron.

A Caesium-137 nucleus decays into Barium-137 and emits a beta particle
A Caesium-137 nucleus decays into Barium-137 and emits a beta particle

Beta decay will cause an atom to change to a different element. Remember that a neutron has been converted into a proton. This will increase the proton number of the nucleus by one but keep the mass number unchanged, as an electron has virtually no mass. A beta particle can be written asorin the context of nuclear equations. The nuclear equation of beta decay of Caesium-137 into Barium-137 shown in the example above is.

Atoms and Radioactivity: Gamma-ray

After an instance of alpha or beta decay, an atomic nucleus will sometimes still have an excess of internal energy. The nucleus will emit this energy in the form of a gamma-ray ‘γ’, which is a high-energy electromagnetic wave.

Radioactive nucleus decaying by emitting a gamma-ray

Unlike alpha or beta radiation, gamma-rays are waves and not particles. Therefore, during gamma-ray emission, the proton number and mass number remain completely unchanged. It is written asin a nuclear equation. The nucleus loses some energy, but there is no change to the atomic structure.

Atoms and Radioactivity: Neutron emission

concept of radioactivity involves the behavior and properties of atoms and their subatomic particles. Atoms contain protons, neutrons, and electrons. Some nuclei are inherently unstable due to an excess of energy in the nucleus, which makes them radioactive isotopes. These isotopes will undergo a process called radioactive decay to change to a more stable form.

Radioactivity can be measured using a Geiger-Muller tube, with activity measured in count-rate using units of Becquerel (Bq). Different radioactive isotopes decay at different rates, with more massive nuclei tending to be more radioactive due to higher excess energy in their nuclei.

The half-life of a radioactive isotope is the time taken for half of the radioactive isotopes in a sample to decay. This decay is random and can be used to date materials or determine their radioactivity.

There are of radiation that can be emitted during radioactive decay. Alpha decay occurs when there are too few neutrons compared to protons, resulting in the release of an alpha particle consisting of two protons and two neutrons. Beta decay can occur when there are too many neutrons compared to protons, with a neutron spontaneously changing into a proton and ejecting a high-velocity electron. Gamma-ray emission involves the release of energy in the form of a wave, rather than a particle, and does not change the atomic structure of an atom.

In addition to these types of radiation, neutron emission can occur during theission of atomic nuclei, with multiple neutrons potentially being emitted at once. While neutron emission alone will not change the element of an atom, it can change it to a different isotope.

Frequently Asked Questions about Atoms and Radioactivity

Why do atoms go through radioactive decay?

Some atomic nuclei are unstable because of an excess or imbalance of internal energy. They undergo radioactive decay in order to change into a more stable form.

Are all atoms radioactive?

Not all atoms are radioactive. Most elements on the periodic table have at least one isotope with a completely stable nucleus.

Can radioactivity destroy atoms?

Radioactivity cannot destroy atoms. However, splitting an atom (nuclear fission) is actually a form of radioactive decay. The atom is not destroyed, but a lot of energy is released in the process.

What is the relationship between atoms and radioactivity?

Different radioactive nuclei will decay at different rates, even between different isotopes of the same element. More massive elements tend to be more radioactive.

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