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NUCLEI — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsNUCLEI2 Marks
Question
Briefly explain the discovery of neutrons.
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Answer

→Neutron was discovered by a scientist named Chadwick.
→Chadwick observed emission of neutral radiation when beryllium nuclei were bombarded with $\alpha$-particle. ( $\alpha$-particle is made up of a helium nucleus)
→In addition he observed that this neutral radiation could knock out protons from light nuclei such as those of helium, carbon and nitrogen.
→The only neutral radiation known at that time was photons. (electromagnetic radiation)
→Application of the principles of conservation of energy and momentum showed that if the neutral radiation consisted of photons, the energy of photons would have to be much higher than is available from the bombardment of beryllium nuclei with $\alpha$-particles.
→From conservation of energy and momentum, the mass of new particle (neutron) was found to be as very nearly the same as mass of proton.
→ Currently, the mass of neutron
$m_n=1.00866 u=1.6749 \times 10^{-27} kg$
→Chadwick was awarded the 1935 Nobel prize in physics.
→A free neutron, unlike a free proton is unstable.

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