What holds a nucleus together

A quote first :


      A scientist is an atoms way of understanding other atoms !!  🙂


    Have you ever wondered what holds the nucleus together ? The nucleus of an atom contains +ve cherged protons and neutral neutrons . Why dont the +ve charges just repel each other and break the nucleus ?


To understand this we will first have to understand something called :

Exchange Force  . Lets imagine 2 particles of one kind P1 and P2 and a different kind of particle D . Now D can be close to P1 or D can be close to P2 . ie either bound to P1 or P2 . See diagram


State 1 :   



        P1 D                                     P2



State 2 :


        P1                                        P2 D



 Now the position of D is uncertain ! if P1 and P2 are close then the particle D can flip flop between P1 and P2 ie sometimes be closer to

P1 and sometimes be close to P2 . This is a nice thing for D . This gives D more freedom . According to Pauli’s exclusion principle the system has less energy .


If P1 and P2 are very far away then D has to remain attached to either P1 pr P2 and going to the other particle is hard ( it is too far away !) D does not like this . This state is a high energy state .


So Physics prefers P1 and P2 to bew close to help D get more freedom .

So P1 and P2 attract each other . They attract each other by the

exchange of the particle D .


Similarly the Neutron and the proton attract each other by the exchange

of a particle called meson . The proton gives up a meson and becomes a

neutron . The meson is taken by the nearby neutron which becomes a

proton . So the proton and neutron try to come close to exchange more

mesons .


This attraction is very strong . In fact it is the strongest

force known in nature !! It is 10 raised to the power 41 times stronger

than gravity !!!!!!! It is called the strong nuclear force .


Does this also answer the question why nuclei have almost equal numbers

of protons and neutrons !!!???


But the problem is that is a very short distance foorce . It operates over

very short distances . If the proton and the neutron are very very

close then this force is important .


This is why heavier nuclei like uranium are so unstable . The reason is

that the nucleus is so large that the repulsion between the far off

protons beats the nucleur attraction between the far off proton – neutron

pair . So all large nuclei are unstable . Infact there cannot be a nucleus

with a Atomic number of 120 !!!! 

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