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Nucleus — Physics STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 SciencePhysicsNucleus5 Marks
Question
Write four properties of $\gamma$-rays. What will be the difference between velocity of $\gamma$-ray of wavelength 0.01 Å and X-ray of wave-length 3 Å.
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Answer

Properties of $\gamma$-rays:
(1) $\gamma$-rays are not deflected by electric field and magnetic field which indicates that these are electrically neutral i.e. have no electric charge.
These rays are electromagnetic waves (or photons) like X-rays. The energy of $\gamma$-photons is much higher (in the order of million electron volt). Therefore, their wavelength is very short. For example, the wavelength of $\gamma$-photon of 1 MeV (= 106 eV) energy is :
$\lambda=\frac{12375}{10^6} Å \approx 0.01 Å$
which is $\left(\frac{1}{100}\right)$ of the wavelength of X-rays.
(2) Their velocity is equal to that of light i.e., $3 \times 10^8$ m/sec.
(3) They produce ionisation through gases but their ionisation power is very small in comparison to that of $\alpha-$ and $\beta$-particles.
(4) They produce fluorescence in barium platinocyanide etc.
(5) They are most penetrating. They can pass through 30 cm thickness of iron sheet.
(6) They are diffracted by crystals in the same way as X-rays.
(7) They affect photographic plate more than $\alpha$ - and $\beta$-particles.
(8) Though there is much similarlity between X-rays and $\gamma$-rays , yet their sources of origin are different. X-rays are produced by the transition of electrons in an atom from one energy level to another energy level, that is, it is an atomic property; whereas $\gamma$-rays are produced from the nucleus, and are emitted only after the nucleus ejects either an $\alpha$ - or $\beta$-particles , that is, it is a nuclear property.
(9) $\gamma$-rays exhibit the phenomenon of pair production in which $\gamma$-rays photon striking the nucleus of some atom is completely absorbed by the nucleus and its energy is converted into one electron and one positron. This phenomenon is represented by the following reaction :
$\underset{\text { (Photon) }}{\gamma} \longrightarrow \underset{\text { (Electron) }}{e^{-}}+\quad \underset{\text { (Positron) }}{e^{+}}$
(10) $\gamma$-rays destroy living tissues. This property is used in the treatment of cancer where $\gamma$-rays emitted only from radium are used.
Since $\gamma$-rays and X-rays both are electromagnetic waves having velocity 3 × 108 m/s. Hence there is no difference between velocities of these radiations.

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