### Category: Modern physics

Proton vs. Electron

## Introduction

Every atom in the universe consists of proton, electron and neutron. What we see around us is the combination of these particles in different pattern and amount. As far as we know, these particles are composed of basic elementary particles called quarks.

The universe that we have seen is all composed of matter except for few antimatter that we managed to produce in lab for few seconds or milliseconds. Every gram of any matter consists of million of billions of atoms and every atom has several electrons, protons and neutrons. So, our universe has uncountable numbers of these particles. Let’s look upon our topic: proton vs. electron.

## Discovery

Electron was discovered by Joseph John Thomson (J. J. Thomson) in 1897 while studying cathode rays while proton was discovered by Ernest Rutherford in 1911 by using gold foil experiment.

## Composition

Electrons are regarded as fundamental particle and are not made up of any other particles while protons are made up of quarks. The combination of two up and one down quarks forms proton. Figure showing how proton is formed by the combination of tow up quarks and one down quarks

## Symbol

Electrons are denoted by e or β while protons are denoted by p, p+, N+, or 11H+.

## Antiparticle

Antiparticle of electron is anti-electron and that of proton is anti-proton.

## Classification

Electrons fall under the Lepton group while protons fall under Hadron group and Baryon sub-group.

## Mass

Electrons are very light particles while protons are heavier ones. Mass of an electron is 9.1*10-31 kg and that of proton is 1.67*10-27 Kg.

## Charge

Electrons are negatively charged particles while protons are negatively charged ones. Charge of an electron is -1.6*10-19 C and charge of a proton is +1.6*10-19 C. Charge on a proton may be illustrated as follows:

Proton is the combination of two up and one down quarks. Each up quark has +2/3 C charge and each down quark has -1/3 C charge. So this combination gives the net charge of proton as:
+2/3 + 2/3 -1/3 = +1

Similarly, electron is the combination of one up and two down quarks. Each up quark has +2/3 C charge and each down quark has -1/3 C charge. So this combination gives the net charge of proton as:
-2/3 – 2/3 + 1/3 = -1

## Specific Charge

Specific charge the ratio of charge to its mass. We know that mass of electron is less than that of proton and both have charge of unit magnitude. Since specific charge is inversely proportional to the mass, electron has higher value of specific charge.

The value of specific charge of electron is -1.758*1011 C/Kg and the value of specific charge of proton is +9.576*107 C/Kg.

## Location

Electron is located in an orbit around the nucleus and revolving around it while proton is located inside the nucleus, bounded with neutrons and other protons.

## Existence in an Atom

Protons are located inside nucleus and are held together by strong binding energy between nucleons while electrons revolve around nucleus (according to old concept) by the help of electromagnetic force.

## Introduction

Radioactive Decay is the process of emission of radioactive radiations from a nucleus of an atom. The unstable nuclei ( generally the nuclei of atomic mass greater than 83 ) and having more number of protons than that of neutrons are unstable nuclei. These nuclei get disintegrated themselves, forming nuclei of more stable atom ( especially isotopes of lead ). The process of radioactive decay continues until the unstable nuclei is converted into stable nuclei.

Depending upon the types of particles emitted, radioactive decay can be classified into three types:

• ### Alpha decay (α-decay):

Alpha decay is the process of radioactive decay in which alpha particle is released from the nucleus of an unstable atom. During alpha decay, the atomic number of parent atom decreases by two units and mass number decreases by four units. Alpha decay is represented in the equation as:
ZXAZ-2XA-4 + 2He4
Here, X is the parent nucleus, Y is the daughter nucleus and He is alpha particle representing Helium atom.
Thus in alpha decay, atomic number of nucleus shifts two steps backwards.
Eg. If an atom of uranium (92U238) decays, it changes into Thorium atom (90Th234). Along with Thorium atom, an alpha particle(2He4) is also formed.
92U23890Th234 + 2He4
• ### Beta decay (β-decay):

Beta decay is the process of radioactive decay in which beta particle is released from the nucleus of an unstable atom. During beta decay, the atomic number of parent atom remains unchanged. Beta decay is represented in the equation as:
ZXAZ+1YA + -1e0
Here, X is the parent nucleus, Y is the daughter nucleus and e is alpha particle representing an electron.
Thus in beta decay, atomic number of nucleus shifts one steps forward.
Eg. If an atom of radium (88Ra228) decays, it changes into Actinium atom (89Ac228). Along with Actinium atom, an beta particle(-1e0) is also formed.
88Ra22889Ac228 + -1e0
During beta decay from nucleus of an atom, an electron is released. But it doesn’t mean that nucleus of atom contains electron. In fact, the neutron disintegrates to form a proton, electron and an anti-neutrino. So, elements having high neutron-proton (n/p) ratio show beta decay.
• ### Gamma Particle (γ-decay):

Gamma decay is the process of radioactive decay in which gamma ray is produced from the nucleus of an atom. During gamma decay, atomic mass and atomic number of an atom remains unchanged. So, no new element is formed. In gamma decay, the nucleus achieves the state of stability by emitting photons of suitable frequency.

Generally, during alpha and beta decay, the daughter nuclei are in the excited state. These excited nuclei return to their respective ground state by emitting gamma ray. So alpha and beta decay is followed by gamma decay.

1. Radioactive decay is a spontaneous phenomena and is unaffected by external conditions like temperature, pressure, magnetic filed, etc.
2. In all known radioactive transformations, either alpha particle or beta particle is formed. i.e. Never both or more than one of each kind is emitted by an atom.
3. The rate of disintegration of radioactive substance is directly proportional to the number of radioactive atoms present at that time.
If dN/dT be the number of disintegrations per second then,
Rate of decay ∝ Number of atoms
or, dN/dT ∝ N
or, dN/dT = -λN,
where λ is a proportionality constant called decay constant and negative sign indicates that the rate of disintegration decreases with increase in time.

## Mathematical Treatment

dN/dT = -λN
On solving this, we get
N = N0eλt
where, N0 is the initial number of radioactive atoms at t = 0.

Following are the applications of radioactive decay

It is the process of estimation of age of archeological organic materials by radioactive process. By measuring the number of N-12 and N-14 atoms present in given specimen, we can calculate the age of given specimen.
2. ### Agricultural application:

Radioactive radiations are used to produce the diseases resistance seeds. It is also used in making radio-phosphorous which is used as fertilizer.
3. ### Industrial application:

Radioisotopes are used in quality checking of some industrial products like machinery parts, lubricants, etc
4. ### Medical application:

Radioactive radiations are used to detect different diseases like brain tumor, hemorrhage (internal bleeding), etc. It is also used in the treatment of many diseases like blood cancer, bone fracture, etc.

Radiation hazard refers to the harmful effects which is caused due to over exposure of living body to radioactive radiations like alpha-particle, beta-particle, etc. When a living cell comes in contact with radiations, its normal functioning is disturbed. Similarly, whole tissue gets damaged and organ is destroyed. Radiation hazards are so intense that they even change the genetic information and produce mutation. These radiations cannot be prevented completely. However, we can control radiation hazards by minimizing the use of radioactive materials and using them far away form human inhabitation.

7 Properties of Nucleus

## 7 Properties of Nucleus

Nucleus is a positively charged spherical body present in the center of atom. By various experiments and researchs, scientists have figured out various properties of nucleus. Among many properties of an atomic nucleus, some of the properties of nucleus are described below:

• ## Composition of Nucleus:

Nucleus is composed of protons and neutrons which are collectively called nucleons. These nucleons are bounded together by a energy called as binding energy. This binding energy of nucleus is responsible for the stability of an atom.
• ## Nuclear Charge:

The nucleus comprises of protons and neutrons. Since neutrons are chargeless particles, the charge of nucleus ls equal to the number of protons in the nucleus. i.e. Nuclear charge = +Ze
where, Z is the atomic number
and e = 1.6×10-19 (electronic charge)
• ## Nuclear Mass:

The mass of the nucleus is called nuclear mass. Nuclear mass is equal to the sum of masses of protons and neutrons each of which has mass of one atomic mass unit (1 amu)
1 amu = 1.66 × 10-27 Kg.
If mp and mn are the masses of protons and neutrons respectively and N and Z be the numbers of protons and neutrons respectively, then
Nuclear mass = Nmp + Zmn
However, the experimental measurements show that real mass of nucleus is less than this theoretical mass. This difference in mass of nucleus is called mass defect.
• ## Nuclear Shape and Size:

Nucleus is supposed to be nearly spherical in shape. From the experimental observations, scientists have found that the radius of nucleus (R) is directly proportional to the one-third power of mass number (A).
i.e. R = roA1/3
where, ro = 1.15 × 10-15m.
Rutherford’s alpha particle scattering experiments showed that the radius of nucleus is in the order of 10-10m. So. volume of nucleus (V) is given by,
V = 4/3 πR3
or, V = 4/3 πro3A
• ## Nuclear Density:

Nuclear density (ρ) is given by the ratio of nuclear mass to the nuclear volume.
ρ = (nuclear mass)/(nuclear volume)
ρ = (m × A)/(4/3 πR3)
where, m is the mass of one nucleon
ρ = (3m)/(4πro3)
Putting m = 1.66 × 10-27 and ro = 1.15 × 10-15,
ρ = 2.7 × 1017 kgm-3
This shows that the density of nucleus is very high and is independent with atomic number. All the nuclei have approximately same density.
• ## Nuclear Spin or Angular Momentum:

Proton and neutron are in continuous motion in discrete quantized orbit. This orbital motion produces the nucleon with mechanical angular momentum. In addition to orbital motion, nucleons have internal angular momentum called spin. As a result, they posses angular momentum associated with orbital spin.
• ## Disintegration of Nucleus

Neutron-Proton ratio also plays important role in imparting properties of nucleus. Higher will be the neutron-proton ratio in the nucleus, more unstable will be the atom and it disintegrates. Atoms having least neutron-proton ratio are most stable one and have maximum value of binding energy ( You may refer to: Binding Energy of Nucleus). During disintegration, radioactive radiation are produced from the nucleus of atom.

So, these are the properties of the nucleus. Feel free to comment below about your opinions or suggestions…..

Properties of X-rays

## General properties of x-rays

• X-rays are the electromagnetic radiation of short wavelength ranging from 10-9 to 10-12 m and are invisible to normal human eye.
• They travel in straight line with the speed of light in vacuum (3×108 ms-1).
• They do not posses any charge i.e. X-rays are neutral.
• X-rays are not deflected by electric and magnetic field.
• They have high ionization power. They can ionize the gases through which they pass. Due to the high ionizing power of x-rays, they are used to cure cancer.
• X-rays affect photographic plate and they are even more effective than ordinary light.
• They produce fluorescence in some metals like Zinc sulphide, Bariumplatino cyanide, Cadmium tungestate, etc.
• X-rays show wave like properties like reflection, refraction, interference, diffraction and polarization similar to that of ordinary light.
• They can produce photoelectric effect and compton effect.
• Excess exposure of x-ray on living beings may cause harmful effects.
• They cannot pass through iron , lead, bone, etc and this property of x-ray is used in radiography. Absorption of x-ray increases with the increase in thickness and atomic number of the atoms in materials.
• Secondary x-rays are produced when they fall upon some metals.
• Frequency of x-ray is nearly equal to 1000 times more than that of visible light. Therefore, x-ray photons are much stronger than the photons of visible light.
• X-ray produce highly reactive OH ions in solution. So, they can carry out chemical change.
• They are produced by the collision of fast moving electrons with the metal target of high atomic mass like tungsten, platinum, etc.

## Hard x-rays and soft x-rays

• ### Hard-x-rays

The x-ray having low wavelength, high frequency and high penetrating power are hard x-rays
• ### Soft x-rays:

The x-ray having high wavelength, low frequency and low penetrating power are soft x-rays.
Binding energy of nucleus and nucleons

## Binding Energy

The nucleons are held together within a nucleus by strong attractive forces among the nucleons. One has to apply some energy in order to break the nucleus into its constituents. This energy required to decompose the nucleus into its constituents is known as binding energy of nucleus.

Experimentally, it is found that the mass of any permanently stable nucleus is less than the sum of masses of the constituent particles. The decrease in mass is known as mass defect. It is denoted by Δm.

The mass Δm disappears as an equivalent energy given by Einstein’s mass-energy relation :E=mc2 is liberated. This energy is called the binding energy of nucleus and is responsible for holding the nucleus together in the nucleus.

If M is the experimentally determined mass of a nucleus having z-protons and each of mass mp and N neutrons each of mass mn. Then mass defect is given by

Δm = (Zmp + Nmn) – M

So, B.E. = [(Zmp + Nmn) – M ]c2
The Binding energy is a measure of nuclear stability. Greater the binding energy, greater will be the stability of nucleus. A nucleus having the least possible energy equal to binding energy is said to be in the ground state. If the nucleus has energy greater than Emin, it is said to be in the excited state. If E = 0, the nucleus dissociates into its constituent particles.

## Illustration of binding energy of nucleus :

Let us take an example of the deuteron to calculate binding energy. The nucleus of deuterium is called deuteron  and is made up of a proton and a neutron. If M is the mass of deuteron nucleus and mp and mn are the masses of proton and neutrons respectively, then mass defect

Δm = [(Zmp + Nmn) – M]

= (1.0086654 + 1.0072764) – 2.0135534

= 0.0023884 a.m.u.

So, B.E. = 0.0023884 × 931

= 2.23 MeV

Thus, deuteron composes of  neutron and proton which are held together with energy equal to 2.23 MeV. In fact, when a γ – ray photon with energy 2.23 MeV or more collides with deuteron, the latter breaks down into proton and neutron. This process is known as photo disintegration.

## Binding Energy per Nucleon Table

 Element Mass Defect (amu) Total Binding Energy (MeV) Average Binding Energy(MeV) H-2 0.0024 2.23 1.12 He-4 0.0304 28.29 7.07 Li-7 0.0431 40.15 5.74 Be-9 0.0624 58.13 6.46 C-12 0.0989 92.15 7.679 O-16 0.1371 127.62 7.976 Ca-40 0.3674 342.0494 8.551 Fe-56 0.5286 492.266 8.79 Ag-107 0.9825 914.7075 8.549 Pb-206 1.7412 1261.057 7.869 U-235 1.9354 1801.857 7.667 U-238 1.9341 1800.647 7.566

## Stability of nucleus and binding energy:

Binding energy per nucleon is the average energy which is we must supply to take out a nucleon from the nucleus.

B.E. per nucleon = Total binding energy of a nucleus/The number of nucleons it contains

The stability of a nucleus depends upon binding energy per nucleon rather than the total binding energy. Hence, knowledge of binding per nucleon is more important than the total binding energy of nucleus. If we plot a graph between binding energy per nucleon and the mass number for various nuclei, we obtain the graph as follows: A few peaks are seen at low values of mass number A are for lighter nuclei He, C, O, which are comparatively stable nuclei in their neighborhoods.

## Results from B.E. vs. A graph :

1. Binding energy per nucleon for light nuclei such as 2He2 is very small. Then it increases rapidly with mass number up to A = 20 and the curve possesses peaks corresponding to nuclei 2He4, 6C12 and 8O16. Te peaks indicate that these nuclei are more stable than those in their neighborhood.
2. After A = 20, binding energy per nucleon increases gradually and for mass numbers between 40 and 120, it becomes more or less flat. For mass numbers between 40 and 120, it becomes more or less flat. For A = 56 (26O56), binding energy per nucleon is maximum and is equal to 8.8 MeV.
3. Then after binding energy per nucleon falls slowly with A, dropping to 7.6 MeV at highest mass number 240. Evidently, nuclei of intermediate mass number (40 – 120) are the most stable. This low value of binding energy per nucleon in case of heavy nuclei is unable to control over the coulomb’s repulsion between protons. This causes fission of heavy nuclei and they disintegrate emitting α particles have extra stability. some other particles like β and γ are also emitted. The process of disintegration of heavy nuclei is radioactivity.
4. Thus, binding energy per nucleon has low value for both light and very heavy nuclei. In order to obtain higher values of binding energy per nucleon, the higher nuclei may unite together to form a heavier nucleus (fusion) or heavier nucleus may split into lighter nuclei (fission). In both processes, greater the value of binding energy per nucleon results in the liberation of energy.

## Significance of binding energy curve :

1. The binding energy curve rises slowly as A increases has a peak value at the middle at A = 56 (26O56) and then falls slowly. The fact that binding energy exists at all means that the nuclei more complex than single proton of hydrogen can be stable. Such stability in turn, accounts for the existence of various elements and hence explains the reasons for the existence of different forms of matter.
2. The cause of release of energy in the fusion of light nuclei into heavier ones is explained by the the increase of binding energy per nucleon with mass number. Such a release of energy explains how sun stars get their energy.
3. On the other hand, breaking of heavier nuclei into lighter ones (fission) also releases energy. We can use it for production of electric energy in nuclear reactors.

## How to calculate total binding energy of nucleus?

Binding energy is the result of the mass defect of proton and neutrons. So, it can be calculated by subtracting the experimental mass of nucleus from its expected mass.
Let us take helium (He-4) atom as an example. Helium atom has two protons and two neutrons. Thus its expected mass (in amu) can be calculated as:
2*(mass of proton) + 2*(mass of neutron)
= 2*1.0073 + 2*1.00867
= 4.03194 amu
But from experimental results, it was found that the mass of He-4 nucleus is 4.0016 amu.
So the mass defect or binding energy of He-4 nucleus is:
exected mass – experimental mass
= 4.03194 – 4.0016
= 0.03034 amu
This gives the total binding energy for helium nucleus. To convert amu into Mev, we can multiply it by 931 ( can be calculated by using formula E=mc2. Hence the binding energy of helium nucleus in terms of Mev is 28.3 Mev.
In this way we can calculate the binding energy of any atomic nucleus

## What does binding energy measure?

Binding energy gives the amount of energy that holds the nucleons (protons + neutrons) together inside the nucleus. In other words, total binding energy gives the total energy required to break the nucleons apart.
Similarly, binding energy per nucleon gives the amount of energy hold by each nucleon. So, greater the binding per nucleon, more stable the atom will be.

Feel free to comment below ….

Cathode rays – Introduction and Properties

## Cathode Rays Introduction :

Cathode rays are the invisible rays, emerging normally form the cathode of a discharge tube kept at a presence of (10-2 to 10-3 )mm Hg and under a very high potential difference of the order  (10-15) kV, supplied from an induction coil.

OR,

When the gas pressure in a discharge tube is kept around 10-2 to 10-3 mm of Hg, and potential difference of about  10-15 kV is applied between is electrodes by means of an induction coil, then the whole tube is filled with darkness (crook’s dark space) and the wall of the tube facing the cathode is illuminated by fluorescence whole color depends upon the composition of the tube. Due to falling of a particular type of invisible rays on the glass, the fluorescence produces. The rays emerge from the cathode and are called cathode rays.

These cathode rays are independent of the nature of the gas and their propagation is independent of the position of anode.

## Properties of Cathode Rays

Here are the some of their properties:

• ## Cathode rays travel in straight line

They have rectilinear propagation as that of light and always travel in straight path.

• ## Cathode rays heat the material they fall on

If we place a platinum strip at the centre of curvature of a concave cathode, it becomes red hot. It is because the cathode rays have very high kinetic energy due to their high velocity. When they fall on platinum, their heat energy converts into kinetic energy.

• ## Cathode rays exert mechanical pressure

They have high momentum, so that they exert pressure on striking a surface. If we place a light paddle wheel of mica in their path such that rays fall on half part of the wheel, then the wheel rotates which proves that they have momentum. This fact that they possess K.E. or momentum establishes that these rays are the moving particles of mass.

• ## Cathode rays can produce physical and chemical changes

They rays affect the photographic plate and turn the color of lithium chloride into violet.

• ## Cathode rays can ionize gases

If they collide with atoms of gases, they can eject electrons from them.

• ## Cathode rays can produce x-rays

When they fall on hard metals having high melting point (e.g tungsten, platinum, molybdenum etc), they produce x-ray.

• ## Cathode rays produce fluorescence

When they fall on glass, zinc sulphide or barium platinocyanide, these substances emit coloured light. The color depends on the nature of the substance.

• ## Cathode rays penetrate through metal foils

If we place aluminium foil normally in the path of cathode rays, they can penetrate through it and rays emerge from other side.

• ## Cathode rays deflect in electric and magnetic field

If we keep two plates parallel to the path of cathode rays, inside or outside the tube, and apply potential difference between them, the rays deflect towards the positive plate.

Similarly, When we bring one end of the bar magnet near the discharge tube, the cathode rays deflect from their path. The polarity of end of magnet determines the direction of their deflection.

• ## Cathode rays carry negative charge

The direction of their deflection in electric and magnetic field show that they are bunch of negatively charged moving particles. These particles are ‘electron’.

Feel free to comment below if you have any queries, suggestions, or reviews regarding this article.