Alpha Decay: Videos & Practice Problems

Alpha decay is a type of radioactivity where an unstable nucleus emits an alpha particle, consisting of two protons and two neutrons, equivalent to a helium-4 nucleus. This process often occurs in heavy nuclei to produce a more stable atom. In balancing nuclear reactions, it's crucial to maintain equal mass numbers and atomic numbers on both sides of the equation. For instance, platinum-171 decays to form osmium-167 and an alpha particle:

${\mathrm{Pt}}^{171}\to {\mathrm{Os}}^{167}+{\alpha }^4$

Alpha particles, being large, have high ionizing power but low penetrating power, meaning they can cause significant damage to biological tissues if ingested or inhaled, despite being unable to penetrate the skin. Protective measures include clothing, paper, and even air, which can shield against these particles. Understanding the balance of nuclear reactions and the implications of alpha particle emissions is essential for safety in environments with radioactive materials.

Alpha Decay

Alpha decay is a type of radioactive decay where an unstable nucleus emits an alpha particle, which is composed of 2 protons and 2 neutrons. This means that the atomic number of the alpha particle is 2, corresponding to helium, and its mass number is 4, as it is the sum of the protons and neutrons. Therefore, an alpha particle can be represented as either He4 or the alpha symbol (α).

Alpha decay typically occurs in heavy nuclei that have an excess of protons and neutrons. The process results in the formation of a stable helium atom, specifically the helium-4 isotope. When balancing nuclear reactions, it is crucial to ensure that both the atomic number (number of protons) and the mass number (total number of protons and neutrons) are equal on both sides of the equation.

For example, consider the decay of platinum-171 (Pt₇₈) emitting an alpha particle. The mass number on the reactant side is 171, and the alpha particle contributes a mass number of 4. To maintain balance, the product side must also total 171. Thus, the remaining mass number must be 167, leading to the formation of osmium-167 (Os₇₆). The atomic number on the reactant side is 78, and since the alpha particle contributes 2 protons, the remaining number of protons must be 76, which corresponds to osmium on the periodic table.

In summary, the alpha decay of platinum-171 can be expressed as:

Pt₇₈¹⁷¹ → Os₇₆¹⁶⁷ + α

It is essential to ensure that both the mass number and the atomic number are conserved during nuclear reactions, confirming that the total counts are equal on both sides of the equation. This principle is fundamental in understanding nuclear chemistry and the behavior of radioactive isotopes.

Alpha Decay Reaction Example

In the process of alpha decay, radium-204 undergoes a transformation that results in the emission of an alpha particle, which is represented as $\text{^4_2He}$ or helium. To write a balanced nuclear reaction, it is essential to ensure that both the mass numbers and the atomic numbers are conserved on both sides of the equation.

Starting with radium-204, which has a mass number of 204 and an atomic number of 88, the decay process can be expressed as follows:

On the reactant side, we have:

$\text{^204_{88}Ra}$

During alpha decay, an alpha particle is emitted:

$\text{^4_2He}$

To maintain balance, we need to determine the resulting isotope. The total mass number on the product side must equal 204. Since the alpha particle contributes a mass number of 4, the remaining mass number must be:

$204 - 4 = 200$

Next, we consider the atomic numbers. The atomic number of radium is 88, and the alpha particle contributes 2 to the atomic number. Therefore, the new isotope must have an atomic number of:

$88 - 2 = 86$

Referring to the periodic table, the element with atomic number 86 is radon (Rn). Thus, the balanced nuclear reaction for the alpha decay of radium-204 can be written as:

$\text{^204_{88}Ra} \rightarrow \text{^200_{86}Rn} + \text{^4_2He}$

This equation illustrates that radium-204 decays into radon-200 and an alpha particle, maintaining the conservation of mass and atomic numbers throughout the reaction.

Characteristics of Alpha Particles

When discussing energetic particles, two key concepts arise: ionizing power and penetrating power. Ionizing power refers to the ability of energetic particles to ionize atoms and molecules, while penetrating power indicates how effectively these particles can pass through matter. Understanding these properties is crucial for protecting ourselves from potential harm, as ionization within our bodies can lead to serious health risks.

Focusing on alpha particles, represented by the symbol ₂He, they are the largest type of energetic particle. This size contributes to their high ionizing power, making them particularly damaging to biological tissues. However, their large size also results in low penetrating power, meaning they struggle to pass through materials such as skin, clothing, and even paper. Consequently, everyday items can effectively shield us from alpha particles, as they cannot navigate through small openings or crevices.

In terms of decay, an example of an alpha decay reaction is the transformation of platinum-171 into osmium-167. Due to their high ionizing power, alpha particles can cause significant damage if they enter the body, as they can ionize surrounding biological tissues slowly and effectively. This is particularly concerning in scenarios where alpha particles may contaminate food, leading to ingestion and subsequent health risks.

To summarize, while alpha particles are highly ionizing and potentially harmful, their low penetrating power allows for effective shielding through common materials. Awareness of these properties is essential for safety, especially in environments where exposure to such particles may occur.

Alpha Decay Example

Alpha decay is a type of radioactive decay where an unstable parent nuclide emits an alpha particle, which consists of 2 protons and 2 neutrons, effectively a helium nucleus. This process results in the loss of these particles from the original atom, leading to a decrease in both the mass number and atomic number of the nuclide. Specifically, the mass number decreases by 4, and the atomic number decreases by 2, as the emission of the alpha particle removes these nucleons from the atom.

It is important to note that alpha particles are relatively large compared to other forms of radiation, such as beta particles or gamma rays. Due to their size, alpha particles have limited penetration ability; they cannot easily penetrate the skin or cellular structures. Instead, they are more likely to be stopped by a sheet of paper or the outer layer of skin.

In summary, during alpha decay, the parent nuclide loses 2 protons and 2 neutrons, resulting in a new element with a lower atomic number and mass number. This process is a key concept in understanding nuclear reactions and the behavior of radioactive materials.

Here’s what students ask on this topic:

What is alpha decay?

Alpha decay is a type of radioactive decay in which an unstable atomic nucleus emits an alpha particle and transforms into a lighter nucleus. An alpha particle is composed of two protons and two neutrons, which is the same as a helium-4 nucleus. When an alpha particle is emitted, the original atom loses four units of mass (since the alpha particle has a mass number of 4) and two units of positive charge (since it has two protons).

This process decreases the atomic number of the original element by two, leading to the formation of a different element that is two places to the left on the periodic table. For example, if uranium-238 undergoes alpha decay, it will emit an alpha particle and become thorium-234.

Alpha decay typically occurs in the heaviest elements where the strong nuclear force is not sufficient to hold the nucleus together against the repulsive forces between protons. The emitted alpha particles have relatively low penetration power and can be stopped by a sheet of paper or even the outer layer of human skin.

Which missing item would complete this alpha decay reaction?

To complete an alpha decay reaction, you need to know that an alpha particle consists of 2 protons and 2 neutrons, which is equivalent to a helium-4 nucleus (⁴He). During alpha decay, an atomic nucleus emits an alpha particle and transforms into a new nucleus whose atomic number is reduced by 2 and mass number by 4.

The general equation for alpha decay is:

X Z A → Y Z-2 A-4 + He 2 4 Here, XZA is the parent nucleus (the original unstable nucleus), YZ-2A-4 is the daughter nucleus (the new, more stable nucleus), and He24 is the emitted alpha particle.

So, if you have an alpha decay equation with a missing item, you would identify the parent nucleus and subtract 2 from its atomic number and 4 from its mass number to find the daughter nucleus that completes the reaction.

What happens during alpha decay?

Alpha decay is a type of radioactive decay where an unstable atomic nucleus emits an alpha particle and transforms into a lighter nucleus. An alpha particle consists of two protons and two neutrons, which is essentially a helium-4 nucleus. When an atom undergoes alpha decay, its atomic number decreases by two, and its mass number decreases by four, reflecting the loss of the two protons and two neutrons.

For example, if you start with an atom of uranium-238 (which has 92 protons), after alpha decay, it will transform into an atom of thorium-234, which has 90 protons and a mass number reduced by four. This process releases energy, which is carried away by the alpha particle. Because alpha particles are relatively large and carry a double positive charge, they interact strongly with matter and have a short range. This means they can be stopped by a sheet of paper or even the outer layers of human skin and pose little hazard unless ingested or inhaled.