Nucleus

Question 1

Size of nucleus

Answer 1

R = R_oA^1/3

R_o = 1.2 x 10^-15 m
A^1/3 = mass no.

Question 2

Density of nucleus

Answer 2

2.2 x 10¹⁷ kg/m³

SAME FOR ALL NUCLEI

Question 3

1 amu - definition + relation to kg

Answer 3

1 amu is (1/12)th of the mass of a C-12 atom

1 u = 1.66 x 10^-27 kg

Question 4

Classification of nuclei

Answer 4

1. Isotopes
2. Isobars
3. Isotones

Question 5

Isotopes w examples

Answer 5

Same no. of protons (Z)
Different no. of neutrons
so A and A-Z is different

E.g. ¹H₁ , ²H₁ , ³H₁
¹⁶O₈ , ¹⁷O₈ , ¹⁸O₈

Question 6

Isobars with examples

Answer 6

Same no. of nucleons (A)
Different no. of protons/atomic no (Z)
Different no. of netrons (A-Z)

E.g.³H₁ , ³He₂

Question 7

Isotones w examples

Answer 7

Different mass no. (A)
Different no of protons/atomic no (Z)
Same no. of neutrons (A-Z)

E.g.⁷Li₃ , ⁸Be₄

Question 8

What particles are released in alpha decay

Answer 8

⁴He₂

Question 9

Particles released in Beta decay

Answer 9

β⁺ decay : ⁰β₁ (positron) + 𝜈 (neutrino)

β^- decay : ⁰β_-1 (electron) + anti-neutrino

Question 10

Gamma decay particle

Answer 10

𝜈 - neutrino

excited state to ground state

Question 11

mass defect

Answer 11

difference between mass of protons and neutrons in free state and mass of nucleus

Question 12

Δm formula

Answer 12

Δm = [Z(m_p) + (A-Z)m_n - M]

where Z= at. no.
m_p = mass of proton
A = Mass no.
m_n = mass of neutron
M = mass of nucleus

Question 13

Binding energy

Answer 13

Minimum energy required to separate the nucleons of nucleus and place them at rest at infinite distance apart

BE = Δmc²
=[Z(m_p) + (A-Z)m_n - M]c²
=[Z(m_p) + (A-Z)m_n - M] * 931.5 MeV

	 as 1u * c^2 = 931.5 MeV

Question 14

BE curve bw mass no. A = 50 to A = 80

Answer 14

1. The curve has almost a flat maximum roughly from A = 50 to A = 80 corresponding to an average binding energy / nucleon of about 8.5 MeV
2. Fe⁵⁶ has the highest BE / nucleon of 8.76 MeV

Question 15

BE curve A>80

Answer 15

1. Average BE / nucleon decreases slowly and drops to about 7.6 MeV for uranium (A = 238)
2. Unstable nuclei, beyong Bismuth (A=209), they are radioactive
3. Undergo nuclear fission to reduce mass no.

Question 16

BE curve A<50

Answer 16

1. Less stable
2. Have the tendency to fuse together because BE is less (nuclear fusion) ==> to increase mass no. so that BE increases
3. Even nuclei have larger BE than neighbouring nuclei E.g. C¹² and O¹⁶

Question 17

Nuclear fission

Answer 17

Process in which a heavy nucleus after capturing a thermal neutron splits into two lighter nuclei of comparable masses

Question 18

What is used in nuclear bombs and nuclear reactors: nuclear fusion or nuclear fission

Answer 18

Nuclear fission

Question 19

Explain chain reaction of nuclear fission

Answer 19

1. When a uranium (₉₂U²³⁵) nucleus is bombarded by a slow neutron, the nucleus is split into two nearly equal fragments along with emission of energy and two or three fast neutrons.
2. Under favourable conditions, the emitted nuetrons collide with other uranium nuclei nearby in the same manner causing further emission of energy and more neutrons
3. Thus, a chain reaction of nuclear fissions is established until the whole of the uranium is consumed
4. About 200 MeV is emitted per fission

Question 20

How can chain reaction be maintained in natural uranium despite the small concentration of ₉₂U²³⁵

Answer 20

1. With the help of moderators, by slowing down the emitted neutrons to thermal neutrons
2. The probability of these neutrons getting absorbed by ₉₂U²³⁸ and fissioning ₉₂U²³⁵ increases
3. E.g. graphite and heavy water

Question 21

Uncontrolled chain reaction

Answer 21

In an uncontrolled chain reaction, the reaction occurs rapidly so that the energy is released instantaneously and therefore, we can’t convert any of that into any useful form of energy.

E.g. nuclear bomb

Question 22

Controlled chain reaction

Answer 22

If the reaction is controlled in such a way that only one of the neutrons emitted in a fission causes another fission, so that the fission rate remains constant and the energy is released steadily.

E.g. Nuclear reactor

Question 23

Nuclear reactor + parts

Answer 23

Device in which self-sustaining controlled reaction is produced in a fissionable material.

1. Fuel
2. Moderator
3. Control rods
4. Coolant
5. Shield
6. Safety device

Question 24

Fuel- nuclear reactor

Answer 24

Fissionable material

E.g. ₉₂U²³⁵, Pu²³⁹ (Plutonium)

Question 25

Control rods

Answer 25

• Rods of cadmium or boron which are used to control the fission rate in the reactor
• Cadmium and boron are good absorbers of slow neutrons
• So when rods are pushed into the reactor, fission rate decreases and when they are pulled out, fission rate increases

Question 26

Coolant

Answer 26

Energy released inside the reactor in the form of heat is removed by coolant

E.g. air, water, CO2

Question 27

Shield

Answer 27

To protect people working near the reactor from injurious radiations, thick concrete walls are erected outside the reactor

Question 28

Safety device

Answer 28

In the case of an accident or an emergency, a special set of control rods, known as shut off rods enter the reactor automatically. Absorb the neutrons immediately.

Question 29

Critical size and mass

Answer 29

Minimum size of fissioning material for sustained fission reaction to develop

if r > 1/K — process starts
if r < 1/K — process stops

Question 30

Utilisation of energy output of nuclear reactor

Answer 30

1. Production of Neutron Beam: The fast moving neutrons emitted by fission of U²³⁵ are converged into a fine beam for artificial disintegration of other elements
2. Production of artificial radio-isotopes:
3. Generation of energy: Energy is used to produce steam which operates a turbine and turns an electrical generator

Question 31

Nuclear fusion

Answer 31

Process in which two light nuclei moving at high speeds fuse together to form a single nucleus

The mass of product nucleus is less than the masses of the individual nuclei which were fused
The lost mass is converted into energy which is released in the process

Question 32

Conditions for nuclear fusion to take place

Answer 32

• Temperature: Of the order 10⁸ K
• High kinetic energies (≅0.1 MeV)
• It is called a thermonuclear reaction because such high temperatures are required
• distance bw nuclei: 1.2 fm = 1.2 x 10^-15 m

Question 33

Stellar energy and thermonuclear energy

Answer 33

Energy obtained continuously from the stars by nuclear fusion

Question 34

T/F
energy in fusion < energy in fission

Answer 34

false

Question 35

Proton cycle rxn

Answer 35

fusion of two protons into deuterium

4₁H¹ —> ₂He⁴ + 2₁β⁰ + 2𝛎 + 2γ