Question

Identify each of the following as alpha decay, beta decay, positron emission, or gamma emission: a. \({ }_{55}^{127} \mathrm{Cs} \longrightarrow \frac{127}{54} \mathrm{Xe}+{ }_{+1}^{0} e\) b. \({ }_{38}^{90} \mathrm{Sr} \longrightarrow{ }_{39}^{90} \mathrm{Y}+{ }_{-1}^{0} e\) c. \({ }_{85}^{218} \mathrm{At} \longrightarrow{ }_{83}^{214} \mathrm{Bi}+{ }_{2}^{4} \mathrm{He}\)

Short answer

a: Positron emission, b: Beta decay, c: Alpha decay.

Step-by-step solution

Understand Types of Decay

Identify the different types of decay. Alpha decay emits an alpha particle \(^4_2 \text{He}\), beta decay emits a beta particle \(^0_{-1} e\), positron emission emits a positron \(^0_{+1} e\), and gamma emission emits a gamma ray \(^0_0 \text{γ}\).

Identify Decay Type for Part (a)

Examine the reaction: \({ }_{55}^{127} \text{Cs} \rightarrow{ }_{54}^{127} \text{Xe}+{ }_{+1}^0 e\). The presence of \({ }_{+1}^0 e\) indicates it is positron emission.

Identify Decay Type for Part (b)

Examine the reaction: \({ }_{38}^{90} \text{Sr} \rightarrow{ }_{39}^{90} \text{Y}+{ }_{-1}^0 e\). The presence of \({ }_{-1}^0 e\) indicates it is beta decay.

Identify Decay Type for Part (c)

Examine the reaction: \({ }_{85}^{218} \text{At} \rightarrow{ }_{83}^{214} \text{Bi}+{ }_{2}^4 \text{He}\). The presence of \({ }_{2}^4 \text{He}\) indicates it is alpha decay.

Key concepts

alpha decay

Alpha decay involves the emission of an alpha particle, which comprises 2 protons and 2 neutrons. This particle is symbolized as \(^4_2 \text{He}\). During alpha decay, the atomic number of the element decreases by 2 and the mass number decreases by 4. For example, in the equation \({ }_{85}^{218} \text{At} \rightarrow{ }_{83}^{214} \text{Bi}+{ }_{2}^{4} \text{He}\), astatine (At) decays into bismuth (Bi) with the release of an alpha particle. This kind of decay usually occurs in heavy elements such as uranium and radium. It reduces the mass of the original nucleus while making it more stable.
Alpha particles are relatively large and heavily charged, causing them to lose energy quickly and travel only short distances through matter. Because of this, they are generally not harmful when outside the body but can be harmful when ingested or inhaled.

beta decay

Beta decay is characterized by the emission of a beta particle, which is an electron (\(^0_{-1} e\)) from the nucleus. In this process, a neutron in the nucleus transforms into a proton and a beta particle. The atomic number increases by 1, but the mass number remains the same. For example, in the reaction \({ }_{38}^{90} \text{Sr} \rightarrow{ }_{39}^{90} \text{Y}+{ }_{-1}^{0} e\), strontium (Sr) decays into yttrium (Y) by emitting a beta particle.
Beta particles are smaller and lighter than alpha particles, allowing them to penetrate matter more deeply but with less ionizing power.
Beta decay helps to balance the neutron-to-proton ratio in unstable nuclei.

positron emission

Positron emission involves the emission of a positron, which is the antimatter counterpart of an electron and is symbolized as \(^0_{+1} e\). During positron emission, a proton converts into a neutron, releasing a positron. This decreases the atomic number by 1 but keeps the mass number unchanged. For instance, in the equation \({ }_{55}^{127} \text{Cs} \rightarrow{ }_{54}^{127} \text{Xe}+{ }_{+1}^0 e\), cesium (Cs) decays into xenon (Xe) with the release of a positron.
Positron particles can travel short distances and annihilate with electrons, producing gamma rays. This process is significant in medical imaging techniques like PET scans (Positron Emission Tomography).
Positron emission occurs in proton-rich nuclei, helping to achieve a balanced state.

gamma emission

Gamma emission involves the release of gamma rays, which are high-energy photons symbolized as \(^0_0 \text{γ}\). This type of decay usually occurs after other types of decay have left the nucleus in an excited state. The emission of gamma rays brings the nucleus back to its ground energy state without changing the number of protons or neutrons.
Gamma rays are highly penetrating and can travel through large amounts of matter. They carry no charge and have no mass, which makes them very effective at transferring energy. Because of their penetrating power, gamma rays require heavy shielding, such as lead or thick concrete, to protect against their ionizing radiation.
Gamma emission is important in diagnostic imaging and cancer treatment, due to its ability to target and destroy cells with precision.