# Tag Info

14

There is an electrostatic repulsion between the protons in the nucleus. However, there is also an attraction due to another kind of force besides electromagnetism, namely the so-called "strong nuclear interaction". The strong nuclear interaction ultimately boils down to the forces between the "colorful" quarks inside the protons - and neutrons. It is ...

14

A neutron is not a proton and an electron lumped together (as your question seems to suggest you think) A hydrogen atom is a bound state of an electron and a proton (bound by the electromagnetic force) whereas a neutron is a bound state of three quarks (bound by the strong force). You might be tempted to think that a neutron is also a bound state of an ...

8

Masses and coupling between quarks are free parameters in the standard model, so there is not real explanation to that fact. About the measurment: you can have a look at this wikipedia article about Penning traps which are devices used for precision measurements for nucleus. Through the cyclotron frequency (Larmor factor) we can obtain the mass of the ...

8

The proton ($uud$) turns into a neutron ($ddu$). Up and down quarks don't have equal charges; the up is $+\frac{2}{3}e$ and the down is $-\frac{1}{3}e$. By the way, such an operation has a name - isospin symmetry transformation - corresponding to an approximate SU(2) symmetry that makes the proton and neutron have almost similar masses.

8

Great question. The electric field creates such a strong force that it would be very hard to move large amounts of just one type of charge. So astrophysical systems do generally eject equal numbers of protons and electrons. In particular, the solar wind is electrically neutral. So these cosmic rays are created in very nearly equal numbers, but by the ...

7

Blue. The proton is way smaller than a wavelength of visible light. But blue light has a shorter wavelength than any other visible color, red light is longer wavelength, blue is shorter, other colors in the middle somewhere. White light is a mixture of all the colors of light, all the wavelengths in the visible range. If you illuminate the proton ...

6

As @dmckee says the problem is complicated. It is complicated because it is not a solution of a potential describing one force, but a balance between electromagnetic forces and the strong force that is keeping the quarks within the nucleons. (In the nucleus the strong force is like a type of Van der waals potential, a higher order interaction, overflowing ...

6

Hmmm...some back-of-the-envelope calculations: The depth of the air column at sea level is $14\text{ lbs/in}^2 = 2 \times 10^5\text{ g/cm}^2$, so neglecting space-charge effects and assuming minimum ionization the whole way we get about $4 \times 10^5\text{ MeV} = 0.4\text{ TeV}$ energy loss. We are actually above minimum ionization, so we can multiply that ...

6

A neutron is a fermion, a hydrogen atom is a boson. This is related to the fact that a neutron decays into three fermions rather than two which is what you seem to think. A neutron is composed of three valence quarks, $u,d,d$, while a hydrogen atom is made out of $u,u,d,e^-$. The internal size of a neutron is about $10^{-14}$ meters while the internal size ...

6

A proton is made of two up quarks and a down quark, whereas a neutron is made of two down quarks and an up quark. The quark masses contribute very little of the actual mass of the proton and neutron, which mostly arises from energy associated with the strong interactions among the quarks. Still, they do contribute a small fraction, and the down quark is ...

6

The goal of such a treatment is to induce damages in the cells of the tumor by mean of ionizing radiation. These radiations can be X-rays (photons), electron, proton or things like carbon ions. The problem is: if you try to irradiate a tumor, you first have to go through normal tissues and the risk is to damage them also. Photons will transfer energy ...

6

Such a process is forbidden by energy conservation: the proton is the lightest baryon (that is the lightest bound state of three quarks). hawking radiation finds it's energy by reducing the energy of the black hole, but there is not lighter baryon state for the proton to go to. Baryon number violating proton decay processes are theorized, but have not been ...

5

Most proton-proton collisions will be elastic: throw in two protons and two protons will come out, deflected at some angle. But the more interesting collisions are those where individual constituents of the proton (quarks, antiquarks, or gluons) interact. For instance, all the interesting high-energy proton-proton collisions at the LHC are really collisions ...

5

Consider two independent systems, two distant atoms, for example. Each atom has is own angular momentum $J_1$ and $J_2$. If these atoms are different and distant (non interacting), then the QM variables are separated, the total wave function becomes a product of the two atomic wave functions, and the total system angular momentum is a sum of the two. The ...

5

The neutron is made of two down quarks and an up quark; the proton of two up quarks and a down quark. This leads to two effects that differentiate their masses. One is that the up and down quark themselves have different masses. The other is that the proton is charged, and so quantum corrections involving virtual photons affect its mass. The details are ...

4

The neutron decays into a proton, an electron and an antineutrino. So even the end components are different from Hydrogen which is just a proton with an electron orbiting around it. The binding forces are also different. The proton and the electron are bound by the electromagnetic force. The neutron by the strong to the rest of the nucleons in a nucleus. ...

4

Your day to day experience of the material world is governed by chemistry. This is at some level the science of atoms and groups of atoms. Things like hardness, colour, toxicity and others are all largely determined by the interaction of atoms. In particular the outer coating of atoms, the electrons. Obviously the details of why element or compound A is ...

4

Thanks to @dmckee, and the link he suggested: interactive table of the isotopes. Looking at that table, it seems to me that there is not a reliably direct relationship between number of neutrons and radioactivity. Using Calcium (Ca) as an example (assuming I'm reading the chart correctly): Ca-40: stable Ca-41: radioactive (with a relatively long ...

4

Not to worry :). The electrons that come out with rubbing are electrons that are loosely bound to the material, from the last energy level of the atoms. To get a second one out from the same atom would take a lot more energy, so it usually does not happen. Not to forget that there are a large number of atoms ( about 10^23/mole) making up any matter so ...

4

Because a proton can decay to a positron. It is an experimental fact that the proton and positron charges are very close. To conclude that they are exactly equal requires an argument. If a proton could theoretically decay to a positron and neutral stuff, this is enough. In QED, charge quantization is equivalent to the statement that the gauge group is ...

4

On the level of QED and above, the equality of the charges has no theoretical explanation. But it is extremely well established experimentally, as even small deviations would add up to huge amounts of electricity in bulk matter. On the level of the standard model, the value of the charges of the up and down quark comes from simple arithmetic from those of ...

4

When physicists say that a particle has electric charge, they mean that it is either a source or sink for electric fields, and that such a particle experiences a force when an electric field is applied to them. In a sense, a single pair of charged particles are a battery, if you arrange them correctly and can figure out how to get them to do useful work for ...

4

In $\beta$ decay a neutron turns into a proton, an electron and an electro antineutrino. So if the proton and electron charge were not the same either the neutron must originally carried a net charge or the antineutrino must carry a charge. For the neutrino current limits are reported by the particle data group as less than 10$^{-15}$ of the electron ...

3

No spin measurement of proton can give a value more or less than $\hbar/2$. But what do we mean when we say that spin of proton is $\hbar/2$ ? Spin is a 'vector' quantity (at least this is what it is classically). So one should also specify its direction. The thing is that in this case direction doesn't matter much. If you think of proton as some sphere and ...

3

A proton is a bound state of three quarks. The quarks themselves are (as far as we know) pointlike, but because you have the three of them bound together the proton has a finite size. It doesn't have a sharp edge any more than an atom has a sharp edge, but an edge is conventionally defined at a radius of 0.8768 femtometres. Protons are spherical in the same ...

3

dmckee's answer is certainly a reason why quarks can't just tunnel out of protons. However, even if they could tunnel out, the process would be different to that of Hawking radiation. HR arises because the vacuum states of two frames are different. The observer freely falling into the black hole sees no radiation, whereas the observer held stationary ...

2

If changing the protons into something else counts as "destroying" it, then yes, this is what keeps stars burning. In particular, two protons can interact and form a deuteron, a positron and an antineutrino and some energy.

2

Extremely unlikely. The beam would diffuse very rapidly. The LHC beam is condensed into a very small location by magnetic fields and it's energy is maintained through the use of an RF field which replenishes the energy each time the beam circulates while orbiting in a near perfect vacuum. In the absence of such fields the beam would first repel itself ...

2

The answer is "because". It is an experimental fact. It is among the first data that were gathered which supported the atomic theory. If they were not the same the atoms would not be neutral, there would always be left over charge and the chemistry and atomic physics data would be different, if there were chemistry and atoms at all. This fact together ...

2

Well, I will try to give you an intuitive understanding. Consider there are two forces acting on the nucleons, the strong force (attractive, short ranged and acting between all the nucleons) and the electromagnetic force (repulsive, long ranged and acting only between protons). Now if you want to keep your nucleus stable, i.e. attractive forces should be ...

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