Pair and magnetic resonances on fingers and their use
Good day, Habr.
In this article I want to talk about a remarkable physical phenomenon as a magnetic moment relative to the center of mass. Where does it come from, how can it be imagined and why should every self-respecting HimFak use it.
It all started with the fact that the teacher of electricity and magnetism told us that a student who “caught” the EPR (electronic paramagnetic resonance) with improvised means would receive the top five automatically. Not an automatic machine for the sake of, but only every second my group mate decided to take up this business and together we gathered a lot of information and I decided to share the most interesting.
To begin with, let us recall the structure of the nucleus of an atom: it consists of nucleons — protons and neutrons fastening all together. By the way, if you look at the periodic table of Mendeleev, you can see that the number of neutrons grows faster than the number of protons (for comparison, helium has 2 protons and 2 neutrons, while uranium has 92 and 146, respectively), since protons repel (electromagnetic interaction) and more and more “cement” is needed to stabilize the nucleus (strong interaction), and very heavy elements disintegrate themselves. Here in the form of a kernel and all business. The core is not always spherically symmetrical, but there is nothing to say about molecules at all.
Now let's remember what a dipole is. A dipole is an electrically neutral, but extended (not a point) system. The simplest example is a system of two unlike, but equal in absolute value charge, located at some distance. By the way, the neutron itself is obtained when the electron falls on the nucleus and "merge" with the proton. His dipole moment is sought, but, alas, so far without success. But there will be no dipole (does not have a dipole moment) spherically symmetrically distributed charges. With a magnetic dipole (the ancient name of systems with a magnetic moment) is the same story. The formulas describing them have one form, but unlike a dipole (electric), it creates a similar magnetic field. It is also worth noting that the magnetic moment of the nucleus is composed of the spins of the nucleons of this nucleus.
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The spin represents the moment of anything relative to the center of mass. If we talk about "elementary particles", then in classical physics spin, say, an electron, was represented as the rotation of this electron around an axis passing through the center of mass. But on closer examination it can be seen that this is not so because it turns out that the "equator" of the electron moves faster than the speed of light.
The magnetic moment is represented as a vector and an interesting picture is obtained: it turns out that if a constant magnetic field line passes through a certain angle to the magnetic moment, then this vector itself will begin to rotate around an axis parallel to the magnetic lines.
And if we add a high-frequency alternating field, but rather weakly relatively constant, then for a triple of values: [the magnitude of the constant magnetic field (B), the cyclic frequency of the alternating magnetic field (w), a certain constant (H)], a correspondence is established at which resonance occurs.
w = r * b
In fact, a very intensive absorption of electromagnetic energy begins, the magnetic moment, without ceasing to rotate (with the same frequency), becomes perpendicular to “B”, and this is called resonance for similarity in formulas.
The beauty in this “kind of constant” is that it is different for each substance and each compound, so having one microwave generator (they are usually with a constant frequency or variable in a small range, others are hard to make and do not need), a constant magnetic field (about its creation later) with the possibility of changing its size, a cardboard and foil waveguide and a detector (diode + ammeter ) you can determine the composition of almost any mixture. Almost any not all atoms and molecules have a magnetic moment, but almost everything. That is why every HimFak is not HimFak, if it does not have an installation for EPR and NMR. There are no fundamental differences between EPR (electron paramagnetic resonance) and NMR (nuclear magnetic resonance), the first uses the magnetic moment created by electrons, and the other uses the nucleus.
The scheme of the simplest setup for EPR / NMR (I apologize for Paint):
With resonant absorption of the field energy by the sample, an ammeter / galvanometer will indicate zero.
Practical tips:
It is better to create a constant magnetic field with Helmholtz rings, since The formulas for calculating the magnetic field are simple, and the most difficult to manufacture is finding a thick wire. The foil should be wound with the mirror side inside (we need to reflect it). The height and length of a square waveguide should be a multiple of half the wavelength.
Thank you very much. I will be happy to talk about other phenomena in physics, write in the comments.
In this article I want to talk about a remarkable physical phenomenon as a magnetic moment relative to the center of mass. Where does it come from, how can it be imagined and why should every self-respecting HimFak use it.
It all started with the fact that the teacher of electricity and magnetism told us that a student who “caught” the EPR (electronic paramagnetic resonance) with improvised means would receive the top five automatically. Not an automatic machine for the sake of, but only every second my group mate decided to take up this business and together we gathered a lot of information and I decided to share the most interesting.
To begin with, let us recall the structure of the nucleus of an atom: it consists of nucleons — protons and neutrons fastening all together. By the way, if you look at the periodic table of Mendeleev, you can see that the number of neutrons grows faster than the number of protons (for comparison, helium has 2 protons and 2 neutrons, while uranium has 92 and 146, respectively), since protons repel (electromagnetic interaction) and more and more “cement” is needed to stabilize the nucleus (strong interaction), and very heavy elements disintegrate themselves. Here in the form of a kernel and all business. The core is not always spherically symmetrical, but there is nothing to say about molecules at all.
Now let's remember what a dipole is. A dipole is an electrically neutral, but extended (not a point) system. The simplest example is a system of two unlike, but equal in absolute value charge, located at some distance. By the way, the neutron itself is obtained when the electron falls on the nucleus and "merge" with the proton. His dipole moment is sought, but, alas, so far without success. But there will be no dipole (does not have a dipole moment) spherically symmetrically distributed charges. With a magnetic dipole (the ancient name of systems with a magnetic moment) is the same story. The formulas describing them have one form, but unlike a dipole (electric), it creates a similar magnetic field. It is also worth noting that the magnetic moment of the nucleus is composed of the spins of the nucleons of this nucleus.
')
The spin represents the moment of anything relative to the center of mass. If we talk about "elementary particles", then in classical physics spin, say, an electron, was represented as the rotation of this electron around an axis passing through the center of mass. But on closer examination it can be seen that this is not so because it turns out that the "equator" of the electron moves faster than the speed of light.
The magnetic moment is represented as a vector and an interesting picture is obtained: it turns out that if a constant magnetic field line passes through a certain angle to the magnetic moment, then this vector itself will begin to rotate around an axis parallel to the magnetic lines.
And if we add a high-frequency alternating field, but rather weakly relatively constant, then for a triple of values: [the magnitude of the constant magnetic field (B), the cyclic frequency of the alternating magnetic field (w), a certain constant (H)], a correspondence is established at which resonance occurs.
w = r * b
In fact, a very intensive absorption of electromagnetic energy begins, the magnetic moment, without ceasing to rotate (with the same frequency), becomes perpendicular to “B”, and this is called resonance for similarity in formulas.
The beauty in this “kind of constant” is that it is different for each substance and each compound, so having one microwave generator (they are usually with a constant frequency or variable in a small range, others are hard to make and do not need), a constant magnetic field (about its creation later) with the possibility of changing its size, a cardboard and foil waveguide and a detector (diode + ammeter ) you can determine the composition of almost any mixture. Almost any not all atoms and molecules have a magnetic moment, but almost everything. That is why every HimFak is not HimFak, if it does not have an installation for EPR and NMR. There are no fundamental differences between EPR (electron paramagnetic resonance) and NMR (nuclear magnetic resonance), the first uses the magnetic moment created by electrons, and the other uses the nucleus.
The scheme of the simplest setup for EPR / NMR (I apologize for Paint):
With resonant absorption of the field energy by the sample, an ammeter / galvanometer will indicate zero.
Practical tips:
It is better to create a constant magnetic field with Helmholtz rings, since The formulas for calculating the magnetic field are simple, and the most difficult to manufacture is finding a thick wire. The foil should be wound with the mirror side inside (we need to reflect it). The height and length of a square waveguide should be a multiple of half the wavelength.
Thank you very much. I will be happy to talk about other phenomena in physics, write in the comments.
Source: https://habr.com/ru/post/159971/
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