Question

A free neutron decays to a proton but a free proton does not decay to a neutron. This is because (a) neutron is a composite particle made of a proton and an electron whereas proton is a fundamental particle (b) neutron is a uncharged particle whereas proton is a charged particle (c) neutron has larger rest mass than a proton (d) weak forces can operate in a neutron but not in a proton

Short answer

A free neutron decays to a proton because the neutron has a larger rest mass than the proton, making such decay energetically possible. The correct option is (c) neutron has larger rest mass than a proton.

Step-by-step solution

Understand Particle Decay

Particle decay happens when one particle is converted into other particles. In this context, it's important to recognize that a particle will only decay if such a process is energetically favorable and allowed by conservation laws, such as conservation of energy, charge, and baryon number.

Assess the Mass of Neutron and Proton

In the decay process, the combined rest mass of the products must be less than or equal to the rest mass of the original particle. A free neutron decays into a proton, an electron, and an antineutrino. Since the rest mass of the neutron is greater than the rest mass of the proton, this decay is energetically possible.

Compare the Possibility of Reverse Transition

Conversely, for a proton to decay into a neutron, an energetically favorable condition must exist. However, a proton has a lower rest mass than a neutron. Therefore, without additional energy, such a decay would violate the conservation of energy and is not observed to occur in nature.

Explain the Role of Weak Force

The weak nuclear force is responsible for the decay of a neutron into a proton, which is a type of beta decay. The force can change the flavor of quarks, which allows a neutron (made up of one up quark and two down quarks) to decay into a proton (made up of two up quarks and one down quark).

Choose the Correct Option

Considering the above steps, we can determine that the correct option is that a neutron can decay to a proton because it has a larger rest mass, which makes the decay process energetically possible, and allows for the conservation laws to be respected.

Key concepts

Conservation Laws in Particle Decay

In the realm of physical chemistry, understanding the principles governing the transformation of particles is essential. One of the cornerstones of these transformations, known as particle decay, is the suite of conservation laws. These laws are among the most fundamental principles in physics and dictate that certain properties of an isolated system remain constant over time, even as the components within that system may change.

For instance, during particle decay, the total energy before and after the process must remain the same, adhering to the conservation of energy. Similarly, conservation of charge ensures that the sum of electric charge is unchanged from initial particle to final products. Furthermore, the conservation of baryon number stipulates that the total number of baryons (particles such as protons and neutrons) is also conserved.

This has direct implications for our example of neutron decay. A free neutron can decay into a proton, electron, and antineutrino, because the process obeys these conservation laws—the sum of the charges, energy, and baryon numbers before and after the decay are equal. Thus, understanding these laws is like holding a blueprint to the possibilities of particle transformations.

Neutron to Proton Decay

Neutron to proton decay is an observable phenomenon explained by the differences in rest mass and the role of fundamental forces. Simply put, a free neutron can decay into a proton because it is heavier; it has more rest mass. This additional mass can be converted into energy and other particles during the decay process.

Let's detail this concept: a neutron, which is neutral, decays into a proton, an electron (which carries a negative charge), and an antineutrino (which effectively has no charge). The proton that results from this decay is positively charged, ensuring the conservation of electric charge. The mass of the neutron, larger than that of the proton, is pivotal because it provides the excess energy needed to create the other particles and thus drive the decay process, respecting the principles of conservation of energy.

The understanding of this decay is crucial not just for academic purposes but also for its applications in fields like nuclear chemistry and astrophysics, where such transformations are key to the events that shape the universe.

Weak Nuclear Force

One of the four fundamental forces of nature, the weak nuclear force, or weak interaction, has a pivotal role in the transmutation of particles. This force is peculiar because it is the only one capable of changing the type, or 'flavor,' of quarks, the building blocks of particles like protons and neutrons.

The action of the weak force is most noticeable in beta decay, which is the process we observe when a neutron transforms into a proton. Here's a closer look: a neutron, which consists of one up quark and two down quarks, transforms through the weak nuclear force. This force converts one of the down quarks into an up quark, which consequently changes the neutron into a proton that contains two up quarks and one down quark. This transmutation comes with the emission of an electron and an antineutrino, and it is crucial to understand that without the weak force, such a change in particle identity would not be possible.

Thus, the weak nuclear force is not just about providing the means for change; it's the essential ingredient that allows particles to evolve and the universe, as we know, to engage in complex chemical and physical processes.