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53

Nobody really knows. Using the naive Bohr model of the atom, we run into trouble around $Z=137$ as the innermost electrons would have to be moving above the speed of light. This result is because the Bohr model doesn't take into account relativity. Solving the Dirac equation, which comes from relativistic quantum mechanics, and taking into account that the ...


13

For all radioactive decay (or other nuclear reaction) of a nuclide into other nuclides, the atomic number $Z$ and mass number $A$ need to be conserved. $$\ce{_{Z_1}^{A_1}X -> _{Z_2}^{A_2}Q + _{Z_3}^{A_3}R }$$ $$Z_1 = Z_2 + Z_3$$ $$A_1 = A_2 + A_3$$ Additionally, the charges must be conserved. If $\ce{_{Z_3}^{A_3}R }$ is an alpha particle $\ce{_2^2\...


10

Light can pass through a gold foil though, it just has to be thin enough. Pure gold is a very malleable substance and can be beaten with a hammer into foils of around 100 nm thickness. Sources suggest the gold foil used in the Geiger–Marsden experiment (known more commonly as the Rutherford gold foil experiment) was about 86 nm thick. Somewhere around this ...


9

There are fewer decays because there are fewer atoms to decay The simple reason why the number of decays (strictly, the number of decays per unit time) decreases in simple radioactive decay is because there are fewer atoms left to decay. Nuclear decay is probabilistic. The probability of any given unstable atom decaying is constant (independent of time or ...


7

Some of the electrons will react with positrons formed during the fusion processes; they annihilate each other and give off high-energy radiation (also called gamma rays): Source But this process happens at the core, and there is no way that those electrons get out to the surface. So my best guess is that the electrons which don't get annihilated just ...


7

By beta decay in the nucleus of the atom a neutron decays into a proton, an electron, and an electron antineutrino and a lot of energy. It will lose a little mass, since $E = mc^2$, so the decay energy is coming from the mass we lose. The electron (or beta particle) has a high energy and leaves the atom. $$\ce{_0^1n -> _1^1p+ + _{0}^0e- + \overline{\nu_{...


6

To clear up what are becoming confusing comments. An atom is a nucleus of protons and neutrons surrounded by electrons. An atom can decay by fission to make two or more atoms with a smaller number of protons and neutrons in each new atom. The electrons get distributed between them. Now in physics we'd normally describe this as a nuclear decay, rather ...


6

There is no theory, nor is there a need for one. To put in in other words: yes, there is a theory, and that's the one you are already familiar with. Antimatter elements are precisely the same as ordinary matter elements, only the other way around. There "are" (read: "could be", though some were actually detected) antihydrogen, antihelium (all with the same ...


5

We do not know. Physicists THINK that there ought to be a fundamental limit in scale for space-time that occurs near $10^{-33}$ centimeters and $10^{-43}$ seconds; often called the Planck Scale. There is also a unit of mass associated with this scale which is about $10^{-5}$ GRAMS or $10^{19}$ Billion Electron Volts (BeV or GeV). It is a simple matter to ...


5

Naively, the nuclear electric field at Z ~ 137 or greater, reciprocal of the Fine Structure constant, would "spark the vacuum." Vacuum would be torn into electron-positron pairs. The electrons go in to convert protons to neutrons plus neutrinos. As stated above, non-classical treatment suggests we'll never get near a cold nucleus that sparks the vacuum. ...


5

Here's a list of types of radioactive decay. The most notable types of decay that are not among the classic three involve the direct emission of a free proton or a neutron, the emission of atomic clusters other than helium nuclei (alpha particles), the absorption of one of the innermost shell electrons into the nucleus, or spontaneous fission of the unstable ...


5

An ion is created. Usually this is not noted down in the nuclear reaction because while talking of nuclear reactions we only concern ourselves about nuclei, not the entire atom. The reaction is to be read as "A 14-$\ce{C}$ nucleus decays into a 14-$\ce{N}$, an electron, and an antineutrino." Also, note that the neutrino has no charge.


5

The nuclear shell model is a useful "first approach" to determining nuclear spin. It doesn't always work, but it is a relatively simple way to make a first attempt. Here is a nuclear shell energy diagram. As you can see it is somewhat analogous to an electron orbital energy diagram. A set of shells are filled by neutrons and a separate set is filled by ...


5

Nuclear fission involves the splitting of a heavy nucleus into two lighter fragments plus the release of energy. As an example here is one route by which $\ce{^235U}$, a fissile material, can split apart. $$\ce{^{235}_{92}U + ^{1}_{0}n -> ^{141}_{56}Ba + ^{92}_{36}Kr + 3^{1}_{0}n + 200 MeV}$$ Note the 3 neutrons generated in the fission process, they ...


5

Fusion is an increase in the number of protons in the nucleus by fusing two nuclei. You know fusing means joining together, right? So that can help you remember which is which. "Confusion" comes from the same root word, and happens when you mix things up together in your mind - the "fusion" in "confusion" is the bringing things together. Fission is a ...


5

This is really a physics question but I will answer it anyway. I'm not sure how much subatomic physics you know so I will give two different versions. Simply put, a neutron decays to form a proton and electron. $$\ce{n -> p+ + e-}$$ This explains why the proton number increases by one to form Xenon. More properly a down quark inside a neutron decays to ...


5

Since the gravitational force between two protons is negligible there must be another force holding the nucleus together. This is the strong nuclear force, which as the name suggests is extremely strong but it is also extremely short range and so it's effects are only felt on the scale of nuclei and baryons. As you can see in the graph, if two protons ...


5

I have heard that electrons absorb or eject photons when transitioning from one orbital to another. Is this correct? Not exactly. The atom as a whole emits or absorbs the photon. There is no reason to single out the electron versus the nucleus in such transitions. Can atomic nuclei eject photons? Yes there are two ways a nucleus in particular (as ...


5

Reflect means to bounce back, as in a ball bouncing off a wall. The average density of an atom is very low, so the observed reflection was startling... like throwing many billiard balls at a mass of fluffy cotton candy and every now and then a ball comes bouncing back! The explanation offered was that there must be some "hard", dense object inside ...


5

Consider that to get diffraction effects you generally need the wavelength of the diffracting particle to be related to a length scale of importance in your sample. For the moment, take it to be something on the order of an inter-atomic spacing, roughly an Angstrom ($\pu{\mathring A}$). Taking an alpha particle at $\pu{3MeV}$ (the ones originally used were ...


5

Neutrinos come from the elementary nuclear reactions: $$n^0\to p^++e^-+\overline\nu$$ or $$p^+\to n^0+e^++\nu$$ Not sure what do you mean by collision, since beta decay normally does not include any collision (unless there is an electron capture, of course; but neutrino emission occurs anyway, capture or no capture). As for the purpose, they have none, much ...


5

It is a general principle, not limited to nuclear chemistry, but is common for many areas, e.g. for the reaction kinetic of the 1st order. All processes, where the value time rate is proportional to the value, have value time evolution in the form of the exponential function. $$\frac {\mathrm{d}x}{\mathrm{d}t}= -k \cdot x$$ leads to $$x= x_0 \cdot \exp {...


4

Since this thread seems to have been bumped by @Community a better answer is in order. Physicists don't typically make a distinction between rest mass $m_0$ and moving mass $m$ but rather consider mass to be the invariant of the energy-momentum $4$-vector: $mc^2=\sqrt{E^2-\boldsymbol{p}^2c^2}$ where $m$ is the invariant mass of the system, $E$ its total ...


4

Further to @ManishEarth's answer, note that the distinction is important in doing mass-energy calculations. In the above example, you can find the energy released by subtracting the tabulated mass of a $N^{14}$ atom from the tabulated mass of the $C^{14}$ atom, and ignore the electron mass. Why? Because the actual Nitrogen atom produced only has 6 orbital ...


4

The real thing is that we do NOT know for sure. Accepting Quantum Mechanics, we have some parts of the answer, but we can not know the rest until we test it. Curiously, the higher Z is, the more relativistic the atom is. So, relativistic quantum mechanics do matter in the Periodic Table. Option 1. Something avoids to allow elements with Z>118. That is quite ...


4

No, as hey answered, neutrons are made of two down quarks and an up quark. Protons are made of two up quarks and a down quark. It is the conversion of a down quark into an up quark that results in the neutron --> proton conversion. Read here for more information about this reaction. The confusion with this probably comes from the fact that net reaction ...


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