Question

The process that releases neutrons from the nucleus is

• A. \(\alpha\) - decay
• B. \(\beta\) - decay
• C. nuclear fusion
• D. pair production
• E. nuclear fission

Hint:

The release of neutrons in fission allows for a chain reaction, which is the basis for nuclear reactors and atomic bombs.

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
The question asks to identify the nuclear process characterized by the release of free neutrons from a nucleus. We need to analyze the products of each listed nuclear reaction.
Step 2: Detailed Explanation:
Let's examine each option:
(A) \(\alpha\) - decay: A heavy, unstable nucleus emits an alpha particle, which is a helium nucleus (\({^4_2}\text{He}\)). This particle consists of two protons and two neutrons bound together. No free neutrons are released.
Example: \({^{238}_{92}}\text{U} \rightarrow {^{234}_{90}}\text{Th} + {^4_2}\alpha\)
(B) \(\beta\) - decay: In \(\beta^-\) decay, a neutron within the nucleus is converted into a proton, and an electron (\({^0_{-1}}e\)) and an antineutrino are emitted. In \(\beta^+\) decay, a proton is converted into a neutron, and a positron (\({^0_{+1}}e\)) and a neutrino are emitted. In either case, free neutrons are not released from the nucleus.
Example (\(\beta^-\)): \({^{14}_{6}}\text{C} \rightarrow {^{14}_{7}}\text{N} + {^0_{-1}}e + \bar{\nu}_e\)
(C) Nuclear fusion: Two or more light nuclei combine to form a heavier nucleus. While some fusion reactions can release a neutron (e.g., Deuterium-Tritium fusion), it is not the defining characteristic of fusion in general. Many fusion reactions release protons or just energy.
Example: \({^2_1}\text{H} + {^3_1}\text{H} \rightarrow {^4_2}\text{He} + {^1_0}\text{n}\) (releases a neutron).
Example: \({^2_1}\text{H} + {^2_1}\text{H} \rightarrow {^3_2}\text{He} + {^1_0}\text{n}\) (releases a neutron).
Example: \({^2_1}\text{H} + {^1_1}\text{H} \rightarrow {^3_2}\text{He} + \gamma\) (no neutron released).
(D) Pair production: A high-energy photon (gamma ray) passing near a nucleus transforms into an electron-positron pair. No nucleons are involved or released.
(E) Nuclear fission: A heavy nucleus, typically after absorbing a neutron, splits into two or more smaller nuclei (fission fragments). This process releases a very large amount of energy and, crucially, several free neutrons (usually 2 or 3). The release of these neutrons is a key feature, as they can go on to trigger further fission events, leading to a self-sustaining chain reaction.
Example: \({^1_0}\text{n} + {^{235}_{92}}\text{U} \rightarrow {^{236}_{92}}\text{U}^* \rightarrow {^{141}_{56}}\text{Ba} + {^{92}_{36}}\text{Kr} + 3({^1_0}\text{n})\)
Step 3: Final Answer:
Among the given options, nuclear fission is the process fundamentally characterized by the splitting of a heavy nucleus and the release of free neutrons. This corresponds to option (E).