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Discovery of Neutron - Experiment, Observation, Properties, Practise Problems and FAQ’s

Discovery of Neutron - Experiment, Observation, Properties, Practise Problems and FAQ’s

The story begins in 1920, when Ernest Rutherford, had postulated the existence of a neutral particle, with the approximate mass of a proton, that could result from the capture of an electron by a proton. This postulation stimulated a search for the particle. However, its electrical neutrality complicated the search because almost all experimental techniques of this period measured charged particles had proposed that the capture of an electron by a proton may produce a neutral particle with a mass similar to that of a proton. This hypothesis sparked a search for the particle. Since nearly all experimental methods used at the time monitored charged particles, its electrical neutrality hindered the search. So what prompted Ernest Rutherford to come up with such speculation?

Elements heavier than hydrogen had a greater atomic mass than their atomic number (the number of protons). The atomic mass of elements heavier than hydrogen was greater than their atomic number (the number of protons).

James Chadwick (in 1932) performed the beryllium bombardment experiment and interpreted the radiation to be composed of particles of mass approximately equal to that of the proton but without electrical charge—neutrons. 

That discovery provided a new tool for inducing atomic disintegration, since neutrons, being electrically uncharged, could penetrate undeflected into the atomic nucleus and led to a new model of the atomic nucleus being composed of protons and neutrons.

James Chadwick (in 1932) performed the beryllium bombardment experiment and postulated that the radiation was made up of neutrons, which are protons-sized particles without an electrical charge. Since neutrons are electrically uncharged and can enter the atomic nucleus undeflected, this discovery gave scientists a new method for causing atomic disintegration. It also inspired a new theory that the atomic nucleus is made up of protons and neutrons.

Table of contents

  • What is a neutron?
  • Experiment and observation
  • Properties of selected particles
  • Practice problems
  • Frequently asked questions-FAQs

What is a neutron?

A neutron is one of the subatomic particles that build up atoms. The neutron has no electric charge and mass equal to 1.67493 , slightly higher than that of the proton (for numerical simplicity we treat the mass of a proton is equal to the mass of a neutron but nearly 1839 times greater than that of the electron.

Experiment and observation

  • Chadwick bombarded a thin sheet of beryllium a thin beryllium sheet foil with alpha particles. Electrically neutral particles having a mass slightly greater than that of protons were emitted from beryllium foil. The beryllium foil released electrically neutral particles with a mass somewhat larger than that of protons.
  • Then, these rays passed through a slab of paraffin wax, due to collision, charged species (protons) were ejected.
  • Electrically neutral particles having a mass slightly greater than that of the protons were emitted. He named these particles neutrons. The emission of electrically neutral particles with somewhat larger masses than protons. He gave them the name neutrons.

Properties of selected particles:

Particles Electric Charge (C) Mass (kg) Atomic mass unit (u)
Electron (e) -1.602176 9.109382 0.00054
Proton (p) 1.602176 1.6726216 1.00727
Neutron (n) 0 1.674927 1.00867

Practice problems:

Question.1 Find the mass of 1 mole of neutrons?

  1. 10.057
  2. 10.057
  3.  9.65

Solution. 1 mole = 6.022 Mass of one neutron = 1.67 kg 

∴Mass of one mole neutrons = 1.67 kg 6.022  

= 10.057 kg

Question.2 Find the charge on one mole of neutrons

  1. -9.65
  2. 0
  3. 9.65
  4. Can’t be determined

Answer: (B)

Solution. 1 mole = 6.022 particles, Charge of one neutron = 0

∴Charge of one mole neutrons = 0 6.022  

= 0

Question.3 Calculate the number of neutrons which together weigh 1 gram. 

  1. 5.99
  2. 1.098
  3. 1.0
  4. None of these

 Answer: (A)

Solution: Mass of one neutron = 1.67 = 1.67

Let the number of neutrons =


Question.4 Name the element that does not contain any neutron

  1. Hydrogen
  2. Deuterium 
  3. Tritium 
  4. Helium

Answer: (A)

Solution: ; Atomic number = 1, mass number = 1

Number of neutron =

Frequently asked questions-FAQs

Question.1 Do all atoms have neutrons?

Answer: No, the hydrogen atom has only one neutron and one proton.

Question.2 Is the mass of a neutron exactly equal to the mass of a single proton?

Answer: No, the mass of a single neutron is slightly higher than the mass of a proton but for numerical simplicity, we treat the mass of a single proton is equal to the mass of a proton.

Question.3 What are the applications of neutrons?

Answer: Some of the basic applications of neutrons are:

1) In boron capture therapy and other medical applications, neutrons are highly ionised, penetrating particles. They do, however, activate the chemical and turn it radioactive when consumed.

2) It is significant in nuclear reactions (understanding the neutron’s behaviour, in particular, has aided in the creation of nuclear weapons and reactors).

3) The neutron emitter is used to find light nuclei in the environment, and the neutron activation analysis (NAA) method is used to investigate a basic sample of materials in a nuclear reactor.

Question.4 We know that nucleus of an atom contains positive particles (protons) and neutral particles (neutrons). So, which force holding them together.

Answer: Strong nuclear force holding them together and responsible for the stability of matter.

Related Topics

Electronic configuration Thomson atomic model
Discovery of electron Rutherford atomic model
Discovery of neutron Atomic number and mass number
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