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Particle Physics is one of the divisions of Physics that focuses on the study of elementary particles. It includes the study and the interaction between the elementary particles of matter and radiation. Here, in this article, we will discuss Particle Physics in detail.
| Table of Content |
Key Terms: Particle physics, Matter particle, Elementary particles, Radiation, High-energy physics, Energetic collisions, Detectable particles
Particle Physics
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Particle Physics is a branch of physics that deals with the basic elements of matter and radiation and the interaction between them. The word particle can refer to various types of very small objects, but this branch usually investigates the irreducibly smallest detectable particles.
Particle physics is also known as high-energy physics as many elementary particles do not come under normal conditions and can only be identified during the energetic collisions of the particles.
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Elementary Particle Physics
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There are only four types of interactions that exist between the elementary particles. They are gravitational interactions, electromagnetic interactions, strong interactions and weak interactions.
1. Gravitational Interaction
- The mass of the particle causes gravitational interaction.
- The interaction range is infinite.
- Gravitational interaction is always attractive.
- The interaction of gravity between the two particles does not depend upon the median.
- Gravity interaction is characterized by the interchanging nature of the particles and the exchange of particles.
- The orientation of the object is independent of the velocity.
2. Electromagnetic Interaction
- Electromagnetic interaction relies on the object's charge.
- The interaction range is infinite.
- It's both attractive and repulsive.
- It is dependent on the medium between two particles.
- The electromagnetic interaction depends also on the object's velocity and direction.
- It also has the characteristics of the particles and the photon is the exchange particle.
3. Strong Interaction
- It is mainly involved in nuclear decay, like Beta decay. It also exchanges particle nature and particle exchange is gauge Boson.
Types of Elementary Particles
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On the basis of spin, there are two types of elementary particles. They are:
- Boson: This follows the B.E statistics. They have a symmetrical wave function along with an integer spin.
- Fermions: This follows the F.D statistics. They have an anti-symmetrical wave function along with a half-integer spin.
They can also be divided on the basis of interaction. There are two major types of elementary particles.
- Leptons
- Hadrons
Leptons and Baryons are a part of fermions, whereas masons are a part of Boson. Leptons are known for participating in weak interactions, and not strong ones. They are also known for electromagnetic interaction.
Hadrons on the other hand have strong as well as electromagnetic interactions. They, however, avoid weak interactions.
Standard Model of Particle Physics
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The standard model of particle physics was developed in the latter half of the 20th century. It was a collaborative effort of many scientists around the world. It is a theory related to the electromagnetic, nuclear interactions and also classifying the subatomic particles.
The development of the Standard Model was driven by a theoretical and experimental particle. This model consists of 61 elementary particles, 24 fundamental fermions, 12 particles, and their associated antiparticles, which are matter components.
Particle Physics Formulas
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| Quantity | Definition Equation | Symbols Used and their Meanings |
|---|---|---|
| Number Of Atoms | N0=N+ND | N is the number of atoms remaining at time t N0 is the initial number of atoms at time t ND is the number of atoms decayed at time t |
| Mass Number | A=Z + N | A = atomic mass = mass number = entirety of protons and neutrons N is the number of neutrons Z = atomic number = number of protons = number of neutrons |
| Radioactive Decay | dN/dt = - λN N = N0e-λt | N0 = first number of atoms N = number of atoms at time t t = time λ = decay constant |
Particle Physics: Conservation Laws
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There are two main types of conservation laws. They are:
- Exact Conservation laws: If these laws are violet in nature the reaction is not permitted. The laws of exact conservation include energy conservation, momentum conservation, angular conservation, charge conservation, charge parity time-reversal conversation.
- Approximate conservation laws: If these laws violate then the reaction may or may not be permitted. Isospin, the third component of isospin, strangeness, the conservation of charge parity, charge conjugation and time-reversal conservation.
Uses of Particle Physics
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There are multiple uses of Particle Physics in different fields all across science. They are:
- Particle physics is employed in the production of medical isotopes used in PET imaging and external radiation treatment of the beam.
- Helps to get the concept of superconductor.
- At CERN Institute for Particle Physics, touchscreen technology and the World Wide Web have been created.
- Other domains of application of particle physics are workforce development, medicine, industry, science and national security, etc.
Isospin
Isospin is an abstract quantity and not a physical quantity. Strong interactions are independent of charges, such as in the nucleus that neutron and proton cannot be differentiated. So, to differentiate between them, a quantity has been assigned which is called isospin. Only hadron particles are assigned by Isospin. The third component has potential values from –I to +I when 'I' is isospin. Isospin can be added as a vector and its third component can be added algebraically.
Things To Remember
- Particle Physics is a branch of physics that deals with the basic elements of matter and radiation and the interaction between them.
- It is also known as high-energy physics.
- There are only four types of interactions- gravitational interactions, electromagnetic interactions, strong interactions and weak interactions.
- Boson and Fermions are two types of elementary particles.
- In Particle Physics, two conservation laws are observed. They are- Exact Conservation Law and Approximated Conservation Law
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Sample Questions
Ques: Branch of physics that studies the basic elements of matter and radiation and the interaction between them (1 Mark)
A) Nuclear Physics
B) Particle Physics
C) Elemental Physics
D) Atom Physics
Ans: Option B: Particle Physics
Ques: Another name for Particle Physics is (1 Mark)
A) Zero Energy Physics
B)Constant Energy Physics
C) High Energy Physics
D) Low Energy Physics
Ans: Option C: High Energy Physics
Ques: Particle Physics is used in: (1 Mark)
A) External beam radiotherapy
B) Production of metal isotopes
C) Semiconductors
D) Option 1, 2 and 3
Ans: Option D: Option 1, 2 and 3
Ques: The number Of Atoms is given by: (1 Mark)
A) N0 = ND
B) N0 = N+D
C) N0 = N+ ND
D) N0 = N*D
Ans: Option C: N0 = N+ ND
Ques: What is the frequency of a photon having energy 2.1 X 10-30 J (1 Mark)
A) 3.1 X 1013 Hz
B) 2.1 X 1013 Hz
C) 4.1 X 1013 Hz
D) 5.1 X 1013 Hz
Ans: Option- C: 4.1 X 1013 Hz
Ques: The ground state energy of hydrogen atom is – 13.6 eV. What are the kinetic and potential energies of electron in this state? (All India 2014C, 2 Marks)
Ans: Given that: total ground state energy (TE) = (-13.6eV)
Kinetic energy = – TE
= -(-13.6 eV) =13.6 eV
Potential energy = 2 (TE)
= 2 x(-13.6) = -27.2 eV
Ques: How is the radius of a nucleus related to its mass number? (All India 2013, 1 Mark)
Ans: The radius ‘R’ of the nucleus and mass number ‘A’ is related as-
R = RoA1/3
Where Ro is a constant.
Ques: A nucleus undergoes β – decay. How does
(i) the mass number,
(ii) the atomic number change? (Delhi 2011C, 2 Marks)
Ans: During β – decay
(i) The mass number of the nucleus remains the same.
(ii) The atomic number of the nucleus increases by one.
Ques: Can it be concluded from beta decay that electrons exist inside the nucleus? (Delhi 2015C, 2 Marks)
Ans: No, the beta particle although an electron is actually formed at the instant of beta decay and ejected at once. The beta particle cannot exist inside the nucleus as its de-Broglie wavelength is larger than the dimensions of the nucleus.
Ques: Why do stable nuclei never have more protons than neutrons? (All India 2015, 2 Marks)
Ans: Protons are positively charged particles and repel each other electrically. This repulsion is very high in nuclei with more than 10 protons. The excess of neutron only produces attractive forces and is required for stability.
Ques: If both the number of neutrons and the number of protons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain. (All India 2016C, 3 Marks)
Ans: The binding energy of a nucleus gives no contribution to the mass of the nucleus due to the mass defect. Since proton number and neutron number are conserved in a nuclear reaction, the total mass of neutrons and protons is the same on either side of a reaction. So, the total binding energy of nuclei on the left side will not be the same as that on the right-hand side.
The difference in these binding energies appears as the energy released or absorbed in a nuclear reaction. The binding energy that contributes to mass is the difference in the total mass of nuclei on the two sides gets converted into energy or vice-versa.
Ques: Two radioactive samples, X, Y have the same number of atoms at t = 0. Their half-lives are 3 h and 4 h respectively. Compare the rates of disintegration of the two nuclei after 12 hours. (All India 2017C, 3 Marks)
Ans: Let N0 be the nuclei of X and Y at t = 0.
Given that: Tx = 3h, Ty = 4h and t = 12 h.
The number of nuclei present in X and Y after 12 hours is
N = N0 (1/2)t/T or Nx = N0(1/2)12/3 = N0/16 and
Ny = N0(1/2)12/4 = N0/8
Now rate of disintegration is
R = DN/dt = -λN = 0.693 x N/T
Now Rx/Ry = 2:3
Ques: A radioactive sample has the activity of 10,000 disintegrations per second after 20 hours. After the next 10 hours, its activity reduces to 5,000 dis. sec-1. Find out its half-life and initial activity. (Delhi 2017C, 3 Marks)
Ans: The activity reduces to half in 10 hours from 10000 dis sec-1 to 5000 dis sec-1. Therefore the half-life of the sample will be 10 years.
Using A = A0 (1/2)t/T, we get
A0 = 40000 disc. sec-1
Ques: Why is the energy of the beta particles emitted during beta decay continuous? (3 Marks)
Ans: The phenomenon of beta decay arises due to the conversion of a neutron in the nucleus into a proton, electron, and an anti-neutrino. The available energy in beta decay is shared by the electron and the anti-neutrino as they come out of the nucleus, therefore the beta ray energy spectrum is continuous in nature.
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