Courses
Courses for Kids
Free study material
Offline Centres
More

Neutron Mass

ffImage
Last updated date: 01st Mar 2024
Total views: 393k
Views today: 7.93k
hightlight icon
highlight icon
highlight icon
share icon
copy icon

Introduction

Neutrons are subatomic particles with no electrical charge. They are found in the nucleus (center) of atoms, together with protons.


The word neutron comes from the Greek word νέος ( neutrós ), meaning “neutral”  since they have no charge and hence interact weakly with other particles.


Neutrons have a mass of 940.6 MeV/c² or approximately 1.6749 × 10−27 kg on the atomic mass unit (u) scale. By contrast, protons have a rest mass of 0.93887 u.


Formation

The neutrons in the cosmos are formed by fusion in the core of stars.


When a very high-energy cosmic ray proton collides with an atomic nucleus, it can produce a neutron and a hydrogen nucleus (H) in a reaction that may be written as follows:


proton + atomic nucleus → neutron + H


There is another reaction, the opposite one, where a high-energy neutron collides with an atomic nucleus, producing a proton, an electron (e) and an anti-neutrino (ν):


neutron + atomic nucleus → proton + e + anti-neutrino


These newly created particles are on their own, typically moving at great speed. This makes it very hard to capture these particles due to their high kinetic energy.


How were Neutrons discovered?

Until 1930, it was presumed that two fundamental particles were proton and electron.


In 1932, a physicist named James Chadwick discovered neutrons.


He performed an experiment where he found that on bombarding beryllium with the alpha particles, some neutral radiations were emitted. Such bombardment led to extremely powerful penetrations that could not be deflected by electric or magnetic fields.


According to the application of conservation of energy and momentum, he found that they are not protons because protons are charged particles and can be deflected on a curving path towards the negative plate. It means there is something that has no charge. It is the neutron. 


Thus, neutrons are subatomic particles carrying no charge.


Neutron Mass

The mass of the neutron is slightly lesser than the mass of the proton. 


The mass of a proton is 1.6726231 x 10⁻²⁷ kg whereas the mass of the neutron, mn = 1.6726231 x 10⁻²⁷ kg

       

Mass of Neutron in Grams

We know the mass of neutron in kg is 1.6726231 x 10⁻²⁷ Kg.


We also know that 1 kg = 10³ g


So, mass of neutron in grams = 1.6726231 x 10⁻²⁷ x 10³


mn= 1.6726231 x 10⁻²⁴ g


Mass of Neutron in Amu

The rest mass of the neutron that we have calculated above is in the unit of kg.


In amu or atomic mass unit, the mass of neutron is calculated as,


Since 1 kg = 6.0229552894949E+26 amu


So, 1.6749286 x 10⁻²⁷kg = 1.6749286 x 10⁻²⁷ x 6.0229552894949E + 26 

                                 

mn  (amu) = 1.008664904(14)  amu


Rest Mass of Neutron

The concept of rest mass is very simple. We generally think of mass as being a constant quantity for an object. However, the theory of relativity tells us that energy and mass are interchangeable. It means that the mass of a body increases with the increase in its velocity relative to the observer.


Energy gets affected by increasing an object's mass. So, the minimum mass of an object is when it is stationary. Rest Mass is the mass of a body as measured when it is at rest relative to an observer, given by,


The same value as the mass of a neutron.


\[m=\frac{m_{0}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}\]


 Where mo is the rest mass, v = velocity and c = speed of light. 


Putting the value of m = 1.6749286  x 10⁻²⁷ kg, v = 2.19 km/s = 2190 m/s, c = 3 x 10⁸ m/s


 1.6749286  x 10⁻²⁷  =\[\frac{m_{0}}{\sqrt{1-\frac{2190^{2}}{(3\times 10^{8})^{2}}}}\]


=\[\frac{m_{0}}{\sqrt{(3\times 10)^{2}-\frac{2190^{2}}{(3\times 10^{8})^{2}}}}\]


=\[m_{0}\times \frac{(3\times 10^{8})}{\sqrt{(9\times 10)^{16}}}-(4796100)\]   

     

=\[m_{0}\times \frac{(3\times 10^{8})}{\sqrt{(9\times 10)^{16}}}\]


=\[m_{0}\times \frac{(3\times 10^{8})}{(3\times 10^{8})}\]


Cancelling out the common terms, we get m0 x 1


 1.6749286  x 10⁻²⁷ equivalent to m0


So, we get the value as mo   = 1.6749286 x 10⁻²⁷Kg


Mass of One Neutron 

The mass of a free neutron is 1.6749286 x 10⁻²⁷ kg or 939,565,346 eV/c².


In common particle physics, units of mass and energy are interchangeable.


Here, eV stands for electron-volt which is equivalent to 1.6 x 10⁻¹⁹ J.


c = speed of light = 3 x 10⁸ m/s.


Since 1 kg = 5.6095883571872E+35 eV


So, 1.6749286 x 10⁻²⁷kg = (5.6095883571872E+35) x (1.6749286 x 10⁻²⁷) 


Mass of one neutron, mn = 939,565,413.3 eV


So, regarding mega-electron volt


1 MeV = 10,00,000 eV


Mass of neutron, mn = 939.565346 MeV/c².


Relative Mass of Neutron

An atom contains three subatomic particles, namely proton, electron, and neutron.

The proton and neutron are found inside the nucleus at the centre of an atom.


The nucleus is smaller than the size of an atom as a whole, and the electrons are arranged in shells around them.


(ImagewillbeUploadedSoon)


(ImagewillbeUploadedSoon)


Since protons are about 99.86% as massive as neutrons and electrons are about 0.054% as massive as neutrons.


The relative mass of each particle of an atom is in kilograms.


So, the relative mass of a neutron is 1.


Relative Charge on a Neutron

Neutrons do not hold any charge.


In an experiment conducted by James Chadwick in 1932, he observed that this subatomic particle didn't get deflected by electric and magnetic fields.


That's why the relative charge on a neutron is also 0.


Conclusion

The mass of the neutron is slightly lesser than that of a proton. The rest mass of a neutron is calculated as 1.6749286 x 10⁻²⁷ kg. In common particle physics, units of mass and energy are interchangeable. Here, eV stands for electron-volt, which is equivalent to 1 Neutron that does not hold any charge. The relative mass of a neutron is 1, and the relative charge on a neutron is 0. Students who understand this concept can also go through other related topics like mass of an electron, mass of a proton, mass of an atom, mass of a relative object, mass between two particles and relative charge on two particles. This will give students ample practice to understand the topic better. Vedantu offers online tuition for Science classes. Take Online Tests, participate in Live Discussions and get free assignment help on Vedantu.

FAQs on Neutron Mass

1: What is the Approximate Mass of a Neutron?

A neutron is a subatomic particle that forms a part of the nucleus. The mass of a neutron is equivalent to that of the mass of a proton. It weighs 1 amu which approximately equals a bit less than 1 u. Students who understand this concept can also go through other related topics like mass of an electron, mass of a proton, mass of an atom, mass of a relative object, mass between two particles and relative charge on two particles. This will give students ample practice to understand the topic better. Understanding these topics are very important for any student to get through their exams. If you need any help with the topic or the concept, do contact us through Vedantu.com. We provide online tutors for Science classes and help students with various concepts.

2. Do all neutrons have the same mass?

The rest mass of a neutron is a constant value. Therefore, all the neutrons have the same masses. The mass of each neutron is slightly lesser than the proton. Students who have a better understanding of this concept can even go through other related topics like Mass, Mass of an Object, Relative Mass between Two Particles and Relative Charge on Two Particles. One can also get through various models that are given for solving question papers by Vedantu. The best thing about Vedantu is that it offers Live Classes, and an expert can solve your doubts directly. You are not at all required to wait for the answers until other students reply. Get answers to your doubts anytime, anywhere!

3. What is MeV/c2?

MeV/c2 stands for million electron volts upon charge square. The rest energy of a particle can be calculated in units of MeV by multiplying its rest mass in units of MeV/c2 by c2.


The rest energy of a particle is the minimum amount of energy it contains, and this is always a positive quantity. Yet because the value of c2 in MeV/c2 is so large, the units needed to measure this energy are correspondingly tiny: 1 eV/c2 = 1.602176487x10-19 J. Students who understand this concept can also go through other related topics like the mass of an Object MeV/c2. This will give students ample practice to understand the topic better. Understanding these topics are very important for any student to get through their exams. If you need any help with the topic or the concept, do contact us, our online tutors for Science classes and help students with various concepts.

4. How do you find a neutron?

The mass number of an atom is the sum of the number of protons and neutrons in the nucleus, and the atomic number is equal to the number of protons.

For example, Carbon, 6C14 , here no of protons = 6, mass number = 14

So, mass number (A) = no of neutrons + no of protons

 14 = X + 6

We get number of neutrons (X) = 8

One should use the mass number of an atom to find out a neutron. This way, one can find out a neutron in an atomic structure. Students are advised to go through other related topics, including Atomic Number Atomic Mass Relative Atomic Mass Another Topic of the Week, Atomic Radius Every topic of this article is described in great detail. Students must go through all the points made in this article and practise sessions at home to improve their understanding of concepts. If you have any doubts, ask your teachers, or you can also post your queries at Vedantu. Our students' community will help you out by providing appropriate solutions.

5. Do neutrons exist alone?

No, neutrons cannot exist alone because the half-life of neutrons is about 10 minutes. After that, they decay into protons, electrons, and anti-electron neutrinos. Neutrons are stable in the nucleus of an atom. The atom has around 6.02E+24 neutrons at any time in the nucleus. One should note that only the unstable free neutrons decay and their life is about 10 minutes. Students who are pursuing their education in Physics can go through other related materials like Introduction to Electricity and Magnetism. This will give them deeper knowledge about the topic. By studying from a wide range of topics, students can get a better understanding of important concepts. Vedantu offers online tuition for Physics classes. Take Online Tests, participate in Live Discussions and get free assignment help on Vedantu.

Students Also Read