Q. Graphite and heavy water are two common moderators used in a nuclear reactor. The function of the moderator is:

Nuclei Report Error

A

To slow down the neutrons to thermal energies

B

To absorb the neutrons and stop the chain reaction

C

To cool the reactor

D

To control the energy released in the reactor

Solution:

In a nuclear reactor moderator is used to slow down the neutrons to a level where fission can start .

Questions from Nuclei

1. A sample of $I_{51}^{131}$ as iodine ion was administered to a patient in a carrier consisting of $\text{0.10} \, mg$ of stable iodine ion. After $4$ days $67.7\%$ of initial radioactivity was detected in the thyroid gland of the patient. The percentage of stable iodine ion that had migrated to the thyroid gland, if $t_{1/2}$ for iodide ion is $8$ days is

NTA Abhyas 2020

2. A radioactive sample at any instant has its disintegration rate $5000 \, dpm$ . After $5 \, minutes$ , the rate is $1250 \, dpm$ . Then, the decay constant (per minute) is

NTA Abhyas 2020

3. A proton is bombarded on a stationary lithium nucleus. As a result of the collision two $\alpha $ -particles are produced. If the direction of motion of the $\alpha $ -particles with the initial direction of motion makes an angle $\cos ^{-1}\left(\frac{1}{4}\right)$ , then the kinetic energy of the striking proton is [Given, binding energies per nucleon of $Li^{7}=5.60 \, MeV$ and $He^{4}=7.60 \, MeV$ , $m_{proton}\approx m_{neutron}$ ]

NTA Abhyas 2020

4. Given the masses of various atomic particles $m _{ p }=1.0072 u$ , $m _{ n }=1.0087 \,u$ $m _{ e }=0.000548 u$ , $m _{\overline{ v }}=0$, $m _{ d }=2.0141 u$ where $p \equiv$ proton, $n \equiv$ neutron, $e \equiv$ electron, $\overline{ v } \equiv$ antineutrino and $d \equiv$ deuteron. Which of the following process is allowed by momentum and energy conservation ?

JEE Main 2020

5. Find the binding energy per nucleon for ${ }_{50}^{120} Sn$. Mass of proton $m _{ p }=1.00783\, U ,$ mass of neutron $m_{n}=1.00867 \,U$ and mass of tin nucleus $m _{ Sn }=119.902199 \,U $ (take $1U = 931 \,MeV)$

JEE Main 2020

Physics Most Viewed Questions

1. If $E$ and $G$ respectively denote energy and gravitational constant, then $\frac{ E }{ G }$ has the dimensions of:

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2. The de Broglie wavelength of an electron moving with kinetic energy of $144 \,eV$ is nearly

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3. A car starts from rest and accelerates at $5\, m / s ^{2}$ At $t=4\, s$, a ball is dropped out of a window by a person sitting in the car. What is the velocity and acceleration of the ball at $t =6\, s$ ? (Take $\left. g =10\, m / s ^{2}\right)$

NEET 2021 Motion in a Straight Line

4. A wheel with $20$ metallic spokes each $1\, m$ long is rotated with a speed of $120\, rpm$ in a plane perpendicular to a magnetic field of $0.4\, G$. The induced emf between the axle and rim of the wheel will be, $(1 G = 10^{-4}\, T)$

NEET 2020 Electromagnetic Induction

5. A barometer is constructed using a liquid (density $= 760 \,kg/m^{3})$ What would be the height of the liquid column, when a mercury barometer reads $76\, cm$ ?
(density of mercury $= 13600 kg/m^{3})$

NEET 2020 Mechanical Properties of Fluids

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