Thermal neutrons are those whose energy is about

Options

A. 1 J
B. 0.03 eV
C. 1 MeV
D. 0.03 MeV

Answer

To solve the question regarding the energy of thermal neutrons, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Thermal Neutrons**:
- Thermal neutrons are neutrons that are in thermal equilibrium with their surroundings. This means they have energies corresponding to the temperature of the environment.

2. **Identify the Temperature**:
- At room temperature, which is approximately 300 Kelvin (or 27 degrees Celsius), we can relate the energy of thermal neutrons to this temperature.

3. **Use the Formula for Energy**:
- The average energy of a particle at thermal equilibrium can be approximated using the formula:
\[ E = \frac{3}{2} k_B T \]
where \( k_B \) is the Boltzmann constant, approximately \( 8.617 \times 10^{-5} \) eV/K, and \( T \) is the temperature in Kelvin.

4. **Calculate the Energy**:
- Plugging in the values:
\[ E = \frac{3}{2} \times (8.617 \times 10^{-5} \text{ eV/K}) \times (300 \text{ K}) \]
- This calculation gives:
\[ E \approx 0.0129 \text{ eV} \]

5. **Convert to a Common Value**:
- The energy of thermal neutrons is often rounded to a more commonly used value. The typical energy of thermal neutrons is approximately \( 0.025 \text{ eV} \).

6. **Round to the Nearest Common Value**:
- In many contexts, \( 0.025 \text{ eV} \) is rounded to \( 0.03 \text{ eV} \) for simplicity.

7. **Select the Correct Option**:
- Based on the calculations and rounding, the answer to the question is:
\[ \text{The energy of thermal neutrons is approximately } 0.03 \text{ eV.} \]

### Final Answer:
The energy of thermal neutrons is approximately **0.03 eV**.

---