# Are particles lost during fusion?

1. Jul 18, 2015

### ShibbyMan1

Hi simple question here, I was wondering if matter (actual particles) are lost from the fusion process.

2. Jul 18, 2015

### ChrisVer

Do you have any such thing in mind?

3. Jul 18, 2015

### Staff: Mentor

What do you mean with "lost"?
A few fusion processes (most notably proton-proton fusion) involve the destruction of particles or the creation of new ones. Most of them (including all artificial fusion processes) are just a rearrangement of existing particles.

4. Jul 18, 2015

### ShibbyMan1

"Lost" as in actual particles being converted into energy (EM radiation). Such as proton, neutron, electron? Or in my layman terms, if the atoms were represented by legos, do we loose any lego pieces during fusion?

Last edited: Jul 18, 2015
5. Jul 18, 2015

### ChrisVer

Conversions can happen... (eg beta decays)
But there cannot be EM radiation from a fusion process that could change the particle content.
For example you might get an excited nucleus from the fusion, that transits to its ground state by emitting photons...but no particles are converted or lost when it does. (otherwise there would be some violation of symmetry, like charge).

6. Jul 18, 2015

### ShibbyMan1

Ah I see, so what is all of this I keep reading about? Such as "mass is converted into energy during fusion"
There seems to be alot of layman who believe actual particles(electrons, protons, neutrons) are lost during the fusion process.

If there is mass being lost, what is this "mass" if it it not physical particles?

Last edited: Jul 18, 2015
7. Jul 18, 2015

### ChrisVer

mass and energy are equivalent.
The thing with fusion is that the nuclei that you fuse together might have more mass than the products.
In that case you have a mass defect.
That mass defect is due to strong interactions that start appearing in the product (if you collide A and B and create C that contains them, then A,B in C are hold bound by strong interactions).

By the way, that remaining energy doesn't have to appear as photons- it can appear as kinetic energy of the products.

8. Jul 18, 2015

### Staff: Mentor

Mass of a system is not the sum of masses of its particles. Binding energy contributes to mass as well, and this binding energy changes.
As an example, a helium nucleus consists of 2 neutrons and two protons but it is lighter than two isolated neutrons plus two isolated protons together.

9. Jul 18, 2015

### mathman

The masses of nuclei in general are less than the sums of the masses of its constituents.
Example: neutron = 1.0087, H1 = 1.0078, H2 = 2.0141, while n+H1 = 2.0165. The difference is the energy created by the fusion - photon.

10. Jul 19, 2015

### ShibbyMan1

How exactly would it be lighter? If we didn't loose any physical particles, what exactly was given out or lost that makes the product "weigh less" "lighter" than the original components?

11. Jul 19, 2015

### ChrisVer

Suppose you have two particles that are not interacting (are free), let's say particle A and particle B...
If you apply an attractive force between them, then their energies will change, because they will fall into a potential well.
So there is something changing... that's why it's nonsense to speak about individual proton/neutron masses within a dynamic system like a nucleus.
In a similar way, the electron+nucleus in a stable atom is lighter than the electron+nucleus seperated... the difference in masses is due to the energy the electron would need to be separated from the nucleus (binding energy)...in a Hydrogen atom for example that's 13.6eV (the Hydrogen atom is 13.6eV lighter than the electron+proton).

12. Jul 19, 2015

### ShibbyMan1

So the "mass" that you have lost is not actually physical but just binding energy?

13. Jul 19, 2015

### ChrisVer

I don't understand what you mean...
Mass changes because the dynamics changed (from a free/isolated case you go to an interacting one).
In the second scenario where let's say the proton and neutron have been bound together, it's nonsense to speak about the proton's or neutron's mass rather than their system mass (deuterium's).
The mass that is lost is because the Deuterium is like a well where the proton+neutron can stand in.

So it is not being lost- it gets converted to energy (eg it can be given to the products as kinetic energy)... in any case mass is not something different to energy ... they are equivalent. And the mass (we are talking about) is just the energy a body has when it's seen being at rest.

14. Jul 19, 2015

### ShibbyMan1

Well usually most layman see a proton as physical mass, and kinetic energy or radiation as energy. And the common conception I see is that Fusion is similar to matter/antimatter collision in the sense that some physical mass is being converted or released as energy. Thats what I mean by "lost" is this conversion happening?

15. Jul 19, 2015

### ChrisVer

What's a physical mass?

In collisions you can also have the energy of a particle being converted to some other particle's mass... take for example the electron+positron annihilation, leading to muon+antimuon... this cannot happen if the electron/positron don't have enough kinetic energy, because the muons are about 200 times more massive than the electrons.

this=?

Last edited: Jul 19, 2015
16. Jul 19, 2015

### ShibbyMan1

My take on this is for your average everyday layman that has been taught fundamentals but nothing more.

Usually when you ask a random person on the street they will tell you that physical mass is something that is tangible, you can hold or manipulate, proton, neutron and electron. And energy like kinetic or potential isn't something that is physically tangible.

In school you are taught that a proton, neutron, electron is mass, and you are taught that energy like kinetic or EM is different from that.

What kind of energy is released through a fusion reaction? Is it literally a chunk of a proton getting converted into an energy? Is it some form of binding energy? What does it really mean to the every layman "mass is being converted into energy". When an everyday layman hears "mass converted into energy" they think of matter/anti-matter fusion, and protons, neutrons, electrons getting converted into gamma rays.

Is this an accurate definition of fusion? Turning some physical mass into energy?

17. Jul 19, 2015

### ChrisVer

That random person is actually wrong. In the case of the mass we are talking about (rest mass), the definition is making it clear that it's equivalent to energy, so I cannot see them as something different.
That's because a layman never had to deal with anything than Newtonian Mechanics, and somehow even confused the term "mass" with "object". In Newton the mass is just a proportionality constant, measuring the inertia (and you can't touch the inertia).

The energy released from fusion reaction depends on the reaction. For example in the $p+p \rightarrow ^2_1H + e^+ + \nu_e$, the energy goes to the products as kinetic energy.
No no chunk of proton is lost- the energy of the system changes.
A layman can think whatever he/she likes. There's nothing "bad" about him/her being wrong, that's why they are laymen. The annihilation of matter/antimatter can also lead to the creation of other particles, not only photons (I gave an example in a previous post with electrons and muons). The protons don't get converted except for if you have in succession a beta decay.

You convert some mass (I drop the term physical) , the mass defect, into energy.

18. Jul 19, 2015

### ShibbyMan1

So basically, Rest mass is just the total energy of something, regardless or whether it is physical or kinetic/potential etc? So when you say mass is converted into energy it could be anything and is not describing any specific thing.

19. Jul 19, 2015

### Staff: Mentor

Kinetic energy only if it is "internal", like particles moving around in a box. If the whole box moves this does not change its mass, as the energy is taken in the frame where the box is at rest.
The type of energy is not fixed here, right. For fusion reactions, photons and kinetic energy of produced particles are the most common results.

You can put helium, protons and neutrons on a scale and measure the difference - I would certainly call that "physical mass [difference]".

An interesting fact here: if you look inside the proton, it is made out of three quarks ("valence quarks") and their binding process. The combined mass of those three quarks is just 1% of the total proton mass. The other 99% come from the binding energy. The same is true for the neutron, nuclei and even atoms (the electron mass is negligible).
99% of the mass of all everyday objects is not from particle masses, but from binding energy.

20. Jul 19, 2015

### rootone

In one sense it's possible to consider a fusion process as resulting in mass/energy being 'lost'.
I am thinking of the Sun (and other stars). which as a result of fusion reactions are 'losing' through radiation some mass/energy in the form of photons and neutrinos, and to a much lesser extent even some baryonic matter gets emitted as 'solar wind' and similar ejections.

The 'lost' mass/energy is not actually 'gone' of course, the particles involved do still exist, but they are 'lost' in the sense that they no longer are a part of the star.

21. Jul 19, 2015

### Staff: Mentor

The sun is constantly losing up quarks and electrons in the fusion reactions. Those particles are really gone - they stop existing. Down quarks and neutrinos are produced in the processes.

22. Jul 20, 2015

### mathman

Much of the "lost" mass of the sun is the radiation (sunlight).

23. Jul 28, 2015

### ohwilleke

The short answer to the question you mean to ask is no, particles are not lost in nuclear fusion reactions of the kind used in nuclear fusion bombs and proposed nuclear reactors. When two heavy hydrogen atoms fuse to form one helium atom, for example, there are two protons with three quarks each, and two neutrons with three quarks each both before and after the reaction takes place. The number of electrons is likewise unchanged - two before and two after. The energy arising from nuclear fusion comes from the fact that the combined strong nuclear force binding energy in the two heavy hydrogen atoms is greater than the strong nuclear force binding energy in the helium atom that is produced.

Using the word "matter" and "particles" to mean the same thing makes your question more confusing that it needs to be. What you mean when you are saying matter in this question in that fashion is "fundamental particle rest mass", which doesn't change. But, the amount of matter-energy in the two heavy hydrogen atoms is greater than the combined matter-energy in the helium atom after the reaction (with the difference converted to energy released in the reaction).

In other words, the way the a fusion reaction generates energy is analogous to the way that an exothermic chemical reaction generates energy. A fusion reaction generates energy by reducing the strong force binding energy between the particles involved, while an exothermic chemical reaction generates energy by reducing the electromagnetic bond energy between the particles involved. But, because the strong force between atoms in an atomic nucleus is much stronger than the electromagnetic chemical bond between two atoms, the energy created and energy density involved is much greater.

The way a fusion reaction generates energy is not analogous to an annihilation of matter and antimatter such as what happens when an electron and postitron collide and converts the rest mass of fundamental particles directly into energy. It is also not analogous to the energy created in a weak force decay which changes the amount of rest mass present by changing the flavor of a particle when it emits a W boson which in turn decays to something else.

As mfb correctly notes, however, binding energy does contribute to the mass of a composite particle. So if you use the term "matter" to refer to the mass of a composite particle, rather than to the rest mass of the fundamental particles involved in the interaction, there is some mass to energy conversion. Actually, this is true in an exothermic chemical reaction as well, but the difference in mass due to electromagnetic chemical bonds is so tiny that it is generally neglected.

24. Jul 28, 2015

### newjerseyrunner

I think your problem is that you are making an analogy with legos where the lego represents something physical like a proton or a quark. Instead, think of the individual lego as energy, which has to be put in specific arrangements to make the elementary particles. The elementary building block is energy.

Remember that energy can translate to mass. A proton moving is slightly more massive than a proton that's perfectly still. A proton moving near the speed of light is way more massive than a proton that's perfectly still.

25. Jul 28, 2015

### ChrisVer

you should have avoided this comment... the proton will always have the mass of ~1GeV.
The extra energy that appears due to its motion [relative to a frame] is because of the kinetic energy [the momentum].
if you don't clear this out, then you can cause larger confusion because you allow the relativistic mass into the discussion.

You could however say that a proton in a nucleus, like deuterium, is lighter than a free proton. That also seems a bit off, because in the case of deuterium the proton is not a free particle and so it's not so "clear" to speak about its individual mass.