A positron is an anti-particle of an electron, having the same mass but opposite charge to electron. Then, the minimum energy released in annihilation of matter of a pair of an electron and a positron is nearly:
1.02 MeV
The question asks about the minimum energy released during the annihilation of an electron and a positron. This phenomenon is a direct consequence of Einstein's mass-energy equivalence principle, where mass is converted into energy.
Annihilation occurs when a particle and its corresponding antiparticle meet. In this case, we have an electron and its antiparticle, a positron.
When an electron and a positron come into contact, they annihilate, meaning they cease to exist as particles. Their entire mass is converted into energy, primarily in the form of high-energy photons (gamma rays). The minimum energy released corresponds to the conversion of their combined rest mass into energy.
The energy released from the conversion of mass is governed by Einstein's famous equation:
\[E = mc^2\]
Where:
To determine the minimum energy released, we need to consider the total rest mass of the electron-positron pair. The rest mass of a single electron (or positron) is a known fundamental constant.
Rest mass of an electron (\(m_e\)) is approximately: \(9.109 \times 10^{-31}\) kg
Since both the electron and the positron annihilate, the total mass (\(m_{total}\)) that is converted into energy is the sum of their individual rest masses:
\[m_{total} = m_{electron} + m_{positron}\]
As the mass of an electron is equal to the mass of a positron (\(m_e\)), we have:
\[m_{total} = m_e + m_e = 2m_e\]
Now, let's substitute the value of \(m_e\) into this equation:
\[m_{total} = 2 \times (9.109 \times 10^{-31} \text{ kg}) = 1.8218 \times 10^{-30} \text{ kg}\]
Next, we apply Einstein's mass-energy equivalence formula:
\[E = m_{total} c^2\]
\[E = (1.8218 \times 10^{-30} \text{ kg}) \times (3.00 \times 10^8 \text{ m/s})^2\]
\[E = (1.8218 \times 10^{-30}) \times (9.00 \times 10^{16}) \text{ J}\]
\[E = 16.3962 \times 10^{-14} \text{ J}\]
The options provided are in Mega-electron Volts (MeV), so we need to convert the energy from Joules to MeV. The necessary conversion factors are:
First, convert the energy from Joules to electron-volts:
\[E \text{ (eV)} = \frac{16.3962 \times 10^{-14} \text{ J}}{1.602 \times 10^{-19} \text{ J/eV}}\]
\[E \text{ (eV)} \approx 10.234 \times 10^5 \text{ eV}\]
Now, convert electron-volts to Mega-electron-volts:
\[E \text{ (MeV)} = \frac{10.234 \times 10^5 \text{ eV}}{10^6 \text{ eV/MeV}}\]
\[E \text{ (MeV)} \approx 1.0234 \text{ MeV}\]
Rounding to two decimal places, the minimum energy released is approximately \(1.02\) MeV.
The calculation clearly shows that the minimum energy released when an electron and a positron annihilate is approximately \(1.02\) MeV. This energy is typically emitted as two gamma-ray photons, with each photon carrying about \(0.51\) MeV of energy, moving in opposite directions to conserve momentum.
The final calculated value is 1.02 MeV.
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