Samacheer Class 10 Science - Nuclear Physics

Alpha rays, beta rays, gamma rays, cosmic rays
(i) gamma rays
(ii) beta rays
(iii) Alpha rays
(iv) cosmic rays

Nuclear reactor, radioactivity, artificial radioactivity, discovery of radium.
(i) radioactivity .
(ii) discovery of radium
(iii) artificial radio activity
(iv) Nuclear reactor

$1 Curie = 3.7 x 1010$
Becquerel disintegrations per second
$75.6 millicurie = 75.6 x 10-3 x 1 Curie.$
$75.6 x 10-3 x 3.7 x 1010 = 279.7 x 107Bq$

Reason: U - 235 is a fissile material.
Answer: a) Both the assertion and the reason are true and the reason is the correct explanation of the assertion.
Explanation: Being a "fissile material" is the exact scientific explanation for why Uranium-235 splits apart when bombarded by a neutron.
$2. Assertion: In a \beta - decay, the neutron num-ber decreases by one.$
$Reason: In \beta - decay atomic number in-creases by one.$
Answer: (d) Assertion is false, but the reason is true.

Reason: In a nuclear fusion, the nuclei of the reactants combine releasing high energy.
Answer: (c) Assertion is true, but the reason is false.

Reason: Control rods are used to perform sustained nuclear fission reaction
Answer: (d) Assertion is false, but the reason is true.

Henri Becquerel.

Uranium.

Alpha particle & neutro.

Gamma ray.

106A263 \rightarrow 104Rf259 + 2He4.
Atomic number: 106
Mass number: 263

Refer to textbook.

Refer to textbook.

Gamma.

600R.

1942, Chicago, USA.

Becquerel (Bq).

Lead.
X. Answer the following questions in few sentences.

Natural radioactivity

Refer to textbook.

Refer to textbook.

Artificial radioactivity

Refer to textbook.

Refer to textbook.

Refer to textbook.

The minimum mass of fissile material necessary to sustain chain reaction is called "critical mass(mc)". It depends on the nature, density and the size of fissile material.

One Roentgen is defined as the quantity of radioactivity substance which produces a charge of 2.58 x 10-4 coulomb in 1 kg of air under standard conditions of pressure, temperature and humidity.

Soddy and Fajan’s displacement laws :
(i) When a radioactive element emits an alpha particle, a daughter nucleus is formed whose mass number is less by 4 units and the atomic number is less by 2 units, than the mass number and atomic number of the parent nucleus.
(ii) When a radioactive element emits a beta particle, a daughter nucleus is formed whose mass number is the same and the atomic number is more by 1 unit, than the atomic number of the parent nucleus.

Control rod : Control rods are used to control the number of neutrons in order to have sustained chain reaction. Mostly boron or cadmium rods are used as control rods.

In Japan two atom bombs were exploded in 1945. This explosion emitted hazardous radiation like \gamma rays, which adversely affects new born children with congenital diseases.

Ramu can use a pocket Dosimeter that measures exposure to ionizing radiation.

Fusion reaction that takes place in the cores of sun and other stars results in an enormous amount of energy which is called as "stellar energy".

(i) To kill the insects and parasites and prevent the wastage of agricultural products.
(ii) To keep fresh beyond their normal life enhancing the storage time prevent sprouting and spoilage of onions, potatoes and gram.
XI. Answer the following questions in detail.

(a) Controlled chain reaction : In the controlled chain reaction the number of neutrons released is maintained to be one. This is achieved by absorbing the extra neutrons with a neutron absorber leaving only one neutron to produce further fission. Thus, the reaction is sustained in a controlled manner. The energy released due to controlled chain reaction can be utilized for constructive purpose. Controlled chain reaction is used in a nuclear reactor to produce energy in a sustained and controlled manner.
(b) Uncontrolled chain reaction : In the uncontrolled chain reaction the number of neutrons multiplies indefinitely and cause fission in a large amount of fissile material. This results in the release of huge amount of energy within a fraction of second. This kind of chain reaction is used in atom bombs to produce explosion.

What are they?
$\alpha rays: Helium nucleus (2He4) consisting of two protons and two neutrons.$
$\beta rays: They are electrons (1e0), basic elementary particle of all atoms.$
$\gamma rays: They are electromagnetic waves consisting of photons.$
Charge
$\alpha rays: Positively charged particles. Charge of each alpha particle +2e$
$\beta rays: Negatively charged particles. Charge of each beta particle = -e$
$\gamma rays: Neutral particles. Charge of each gamma particle = zero$
Ionising power
$\alpha rays: 100 time greater than \beta rays and 10,000 times greater than \gamma rays$
$\beta rays: Comparatively low$
$\gamma rays: Very less ionization power$
Penetrating power
$\alpha rays: Low penetrating power (even stopped by a thick paper)$
$\beta rays: Penetrating power is greater than that of \alpha rays. They can penetrate through thin metal foil.$
\gamma rays: They have a very high penetrating power greater than that of \beta rays. They can penetrate through thick metal blocks.
Effect of electric and magnetic field
$\alpha rays: Deflected by both the fields. (in accordance with Fleming's left hand rule)$
\beta rays: Deflected by both the fields; but the direction of deflection is opposite to alpha rays. (in accordance with Fleming's left hand rule)
$\gamma rays: They are not deflected by both the fields.$
Speed
$\alpha rays: Their speed ranges from 1/10 to 1/20 times the speed of light$
$\beta rays: Their speed can go up to 9/10 times the speed of light.$
$\gamma rays:They travel with the speed of light.$

A Nuclear reactor is a device in which the nuclear fission reaction takes place in a self - sustained and controlled manner to produce electricity.
The essential components of a nuclear reactor are (i) fuel, (ii) moderator, (iii) control rod, (iv) coolant and (v) protection wall.
(i) Fuel: A fissile material is used as fuel. The commonly used fuel material is uranium.
(ii) Moderator: A moderator is used to slow down the high energy neutrons to get slow neutrons. Graphite and heavy water are the commonly used moderators.
(iii) Control rod: Control rods are used to control the number of neutrons in order to have sustained chain reaction. Mostly boron or cadmium rods are used as control rods.
(iv) Coolant: A coolant is used to remove the heat produced in the reactor core to produce steam. This steam is used to run a turbine to produce electricity Water, air and helium are some of the coolant materials
(v) Protection wall: A thick concrete lead wall is built around the nuclear reactor in order to prevent the harmful radiations from escaping into the environment
XII. HOT Questions:

90X232 \rightarrow 82Y208 + 6 2He4 + 4 -1e0
Solution:

Since each alpha decay reduces the mass number by 4: Number of alpha decays = 24 / 4 = 6 alpha decays.

Refer to textbook.

Number of beta decays needed = 82 - 78 = 4 beta decays.
Answer: 6 Alpha decays and 4 Beta decays.

X- rays are radiations that can penetrate deep into your body. Over exposure of X-ray may lead to the damage of some sensitive organs present inside our body. It is better to wear lead aprons while taking X-ray films.

Cellphone towers emit high frequency radio waves or microwaves which are dangerous to humans. These electro magnetic radiations can cause health problems like Cancer, Birth defects, low sperm count, memory loss etc. So it is better to place cell phone towers far away from residential areas.
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