Radioactivity — Part 1: The nucleus and radioactive decay: visual lesson, ICSE Class 10 Physics (Science Paper 1)

Lesson

Inside the atom’s core

Part 1 — the tiny nucleus holds almost all the mass of an atom. Some nuclei are unstable and break up on their own, giving out radiation.

In this lesson you will

Represent a nuclide with Z and A and count its protons and neutrons
Define isotopes with examples
Compare alpha, beta and gamma radiations
Write balanced equations for alpha and beta decay

Table of the three particles in an atom with location, charge and mass
Particle	Where	Charge	Mass (approx.)
Proton	Nucleus	+1	1 u
Neutron	Nucleus	0	1 u
Electron	Outside the nucleus	−1	1/1840 u

Concept

Atomic number, mass number and isotopes

Atomic number $Z$ : number of protons in the nucleus (also the number of electrons in a neutral atom); it decides the element. Mass number $A$ : number of protons + neutrons (nucleons). Number of neutrons $N = A - Z$ . A nuclide is written ${}^{A}_{Z}\text{X}$ , e.g. ${}^{23}_{11}\text{Na}$ : 11 protons, 12 neutrons. Isotopes: atoms of the same element (same $Z$ ) with different mass numbers (different numbers of neutrons), e.g. ${}^{1}_{1}\text{H}$ , ${}^{2}_{1}\text{H}$ , ${}^{3}_{1}\text{H}$ ; ${}^{12}_{6}\text{C}$ and ${}^{14}_{6}\text{C}$ . They have the same chemical properties.

Table of four nuclides with their protons, mass numbers and neutrons
Nuclide	Z (protons)	A	Neutrons
Sodium-23	11	23	12
Cobalt-60	27	60	33
Carbon-14	6	14	8
Radium-226	88	226	138

Check your understanding

Quick check: protons and neutrons

Count protons and neutrons in a nuclide.

Question: Multiple choice

Multiple choice1 mark

A nucleus of cobalt is written ${}^{60}_{27}\text{Co}$ . It contains:

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