# Nuclear Physics Mass Defect

#### Transformers

10+ Year Member
I understand in Fusion of heavy elements (i.e.- U-235) and fission of light elemetns (hydrogen) will lead to the release of energy due to the principle of mass defect. Basically, both are exothermic processes that release energy.

1.) I am confused about two things. For this mass defect which converts to energy in einsteins E=mc2, does this energy get released to the environment (as would be obvious behind the principle of nuclear reactors and atom bombs), OR does this energy go into the potential energy of the the resulting products in order to hold the protons together in the nucleus. For example, in the sun, when 4H atoms combine to form He-4, does this mass defect convert into energy to be stored in the nucleus in order to hold the protons together or is this released (which now seems less obvious because after all, there requires energy to hold the nucleus together).

2.) If the answer to #1 is that the mass defect converts into the potential energy of the resulting nucleus or nuclei (in either fusion or fission), does this also relate to the concept of the "strong nuclear force" ?

ULTIMATELY, what im trying to ask in simple terms is whether mass defect, potential energy of the nucleus, and strong nuclear force interchangeable terms?

THANKS.

#### Bernoull

10+ Year Member
7+ Year Member
Both fusion and fission release thermal energy. Nuclear reactors exploit fission to vaporize water and turn turbines while the Sun heats up Earth through fusion reactions.

I also know that the strong nuclear force results from exchange of mesons b/t nucleons and a nucleon has to have a sufficiently high velocity/energy to overcome the electrostatic barrier thus extremely high temperatures are required. The only relationship I'm aware of b/t fusion/fission and strong n. force is that a) fusion requires nucleons to be close enough so that the strong n force exceeds the electrostatic repulsive force and the nuclei fuse; b) fission occurs when the nuclei is too large such that the electrostatic repulsive force exceeds the strong n. force and the nucleus splits. The mass defects is converted to thermal energy.

OP

#### Transformers

10+ Year Member
bump, yea any other thoughts?

I mean in fission, are u sure it converts to thermal energy...?

So, if they both release ENERGY due to the mass defect, in fusion, its for PE (thus, strong nuclear force of protons), while in FISSION, its just wasted thermal energy?

#### Bernoull

10+ Year Member
7+ Year Member
Specifically the binding energy (E) is mostly converted to a high energy neutron(s) that is emitted by both fusion and fission. In fission the large nucleus is split by a relatively slow neutron called a thermal neutron. In nuclear reactors the high energy neutron that's emitted must be slowed down to the range of a thermal neutron in order to split another nucleus hence perpetuating the process. Nuclear reactors use water (moderator) to slow the high energy neutron to a thermal neutron and the water is heated in the process. Steam generated is used to electrify homes.

If you're right that binding energy becomes strong nuclear force? How do you explain the tremendous energy and heat given off by nuclear fission (think bombs and reactors) and thermonuclear fusion (think heat/light from Sun)???