What is Spin: Definition and 1000 Discussions

I would like to ask a question about MRI Spin echo sequence. after first 90 degree RF pulse, the free induction decay occurs. And 180degree refocusing pulse is given again. And echo signal is obtained at TE. My question is that is the the signal highest when the protons are back again in...

A spin quantum number can have a value of 1/2 or -1/2. I assume that the negative means that these two spins are in opposite directions. However, what does the 1/2 mean? Why 1/2, rather than a whole integer? Are there some sort of units associated with this value?

I have a linear wire that moves let's say a distance of 1 inch. I would like this wire to spin a small gear (0.25 in circumference) 90 degrees for every 1 inch it moves. How can I accomplish this without using a bigger gear? Any ideas are appreciated. Thanks in advance

I am looking for articles or books that would clearly and succinctly state the open problem of and issues with computing hadron masses and spins in QCD from first principles, preferably in relation to the open problem of confinement and the general open problem of non-perturbative QCD. Any...

Homework Statement A beam of spin ##\frac{1}{2}## particles is prepared in the state: ##|\psi> = \frac{3}{\sqrt{34}}|+> + \frac{5i}{\sqrt{34}}|->## a) What are the possible results of a measurement of the spin component ##S_z##, and with what probabilities would they occur? b) Suppose that the...

If all three quarks in a baryon have the same flavor, they all spin the same direction, causing the baryon to have 3/2 spin. In a proton, do both up-quarks spin in the same direction (with the down-quark spinning opposite)? Or can the two up-quarks spin in opposite directions?

Not sure if this is better suited for the electrical engineers or mechanical but I figured id post it up here to start. I am looking to size a motor that will spin a box which weighs about 600lbs. The motor needs to be in line with the boxes rotational axis. It needs to be able to rotate 360...

The figure below is from a textbook. It is explaining what excited states are using carbon as an example. I don't necessarily agree that the the state labeled as "example excited state 1" is really an excited state. Since the electrons in the 2p orbitals are unpaired, and in the absence of a...

Homework Statement Calculate the classical propagator for a massive spin 1 particle by inverting the equations of motion to the form $$A_\mu=\Pi_{\mu\nu}J_\nu$$ Homework EquationsThe Attempt at a Solution By solving the lagrangian for a massive spin 1 particle one gets $$(\Box +...

for compute: $$e^{\frac{iS_z\phi}{\hbar}}S_x e^{\frac{-iS_z\phi}{\hbar}}$$ so, if we use $$S_x=(\frac{\hbar}{2})[(|+><-|)+(|-><+|)]$$ $$e^{\frac{iS_z\phi}{\hbar}}(\frac{\hbar}{2})[(|+><-|)+(|-><+|)] e^{\frac{-iS_z\phi}{\hbar}}$$ so, why that is equal to...

Hi! I am kinda confused about what gets conserved in QED and what not. So the chirality is always conserved, I got that. So in the massless limit, helicity is too. Now in the massive limit. Are spin and helicity conserved? And if they are, are they at each interaction vertex, or just overall...

In practice, ESR/EPR seems to concern only unpaired electrons in the outer layers of organic radicals or complexes. But what about the free electrons of metals? Does it also give rise to a signal? I can't find any information on the web. Thanks

Homework Statement The ground state energy of 5 identical spin 1/2 particles which are subject to a one dimensional simple harkonic oscillator potential of frequency ω is (A) (15/2) ħω (B) (13/2) ħω (C) (1/2) ħω (D) 5ħω Homework Equations Energy of a simple harmonic oscillator potential is En...

Hello, I would like to ask about the process of measuring the Spin of a Dirac 4-spinor Ψ that is not in the rest frame. Note that even though there is plenty of information about what a Dirac spinor is, what reasoning lead to its discovery and how it can be expressed in terms of particle and...

There are some famous materials is determined as TI induced by SOC, like graphene and so on. But from some formula, for instance, Kane-Fu formula, they just need parities to get Z2 number. So I wonder if there is a known TI with weak soc.

Hello! I got a bit confused about the fact that the whole the description of spin (and angular momentum) is done in the z direction. So, if we are told that a system of 2 particles is in a singlet state i.e. $$\frac{\uparrow \downarrow -\downarrow \uparrow }{2}$$ does this mean that measuring...

Can somebody give me some insights related to spin chemical potential ? I searched on google but didn't get satisfied. What it means when two spin groups of electrons (group A with spin up and group B with spin down)have different spin chemical potential?

Homework Statement The Hamiltonian is given below: ##H=\frac {\mathbf p^2}{2m} -\frac {\partial^2_z}{2m} +V(z) +\gamma V'(z)(\hat{\mathbf z} \times \mathbf p)\cdot \vec{\sigma}## Where this term ## \gamma V'(z)(\hat{\mathbf z} \times \mathbf p)\cdot \vec{\sigma}## represents the spin orbit...

NMR textbooks often state that an ensemble of nuclei cannot absorb the excitation radiowaves if the spin population is "saturated" (wherein "saturated" is often described as equal spin population in all energy states, or a population inversion). But these same NMR textbooks show that a 180...

I'm having some trouble understanding some of the steps done in the uploaded paper. I'ts the 1975 paper by Sherrington where they explain the SK model for spin glass. Homework Statement and Homework Equations[/B] Up to equation 5 I understand all steps. I used J_0 = J_0 / N and J^2 = J^2 /...

This is about vehicle physics. I know how to calculate weight on each axle on a car during deceleration. Given the picture below: The weight on the front axle is calculated as: Wf=(c/L)*W-(h/L)*M*a and the weight on the rear axle is calculated as: Wr=(b/L)*W+(h/L)*M*a where c and b are the...

I just look at a rocket leaving his lunch pad. Vapor condensate spin around the rocket. at 0:40

What is the difference between parallel and antiparallel spins for a pair of nucleons? My understanding is that nucleons have a strong tendency to pair - proton with proton, neutron with neutron, proton with neutron. When they pair their spins either: cancel (spins pair antiparallel) pairing...

Protons and neutrons are nucleons. The spin of a nucleon is it’s intrinsic angular momentum. Spin has no classic analogue and does not mean the particle is spinning on its axis. It’s an intrinsic property of the nucleon. Protons and neutrons are fermions and have spin quantum numbers of 1/2...

From the book Introduction to Quantum Mechanics by Griffiths,. In the section 6.4.1 (weak field zeeman effect) Griffiths tells that the time average value of S operator is just the projection of S onto J while finding the expectation value of J+S $$S_{avg}=\frac{(S.J)J}{J^2}$$ How to prove this?

Other than Helium do Noble gases with even nuclear spin form superfluids? Is there a simple quantum mechanical explanation why the difference below of the Melting point and Boiling point of the Noble gases is roughly the same value? A yes or no would suffice. From...

If I have a single spin 1/2 particle, I know that it's total spin in any direction with unit vector can be computed by using the operator σ•n where σ_i are the pauli matrices. Suppose however I had a multiparticle system, is there a generalization of the pauli matrices (which let's call ρ_i) so...

I'm taking a course in particle physics. One of the features different from particle to particle is the spin. For example Higgs boson has spin 0, muon and electron have spin 1/2, graviton has spin 2, and so on. How is this decided upon? Does it occur in the experiments or is it based on...

Hi all. I'm trying to understand (QM) spin. I have plenty of questions but this one is quite simple. Lets say there is a tiny grain of coal (because it's black), far away from gravitational or EM fields. I take a laser, and pick photons that have spin +1 in the z-direction, it doesn't really...

The deuterium exists only with the proton and neutron of aligned spin, which suggests that the residual strong force is greated with aligned spins, i.e. the binding energy is greater if the spins are aligned. On the other hand the mass of ##\Delta^{+}## is greater than the mass of proton ##p##...

Consider the Stern Gerlach experiment, where the oven has a temperature such that the most probable velocity of the silver atoms is 750 m/s. The atoms are collimated by two slits of 0.03 mm width. The magnetic field has a strength of 1 T, a gradient of 5 T/cm, and the length of the magnet is...

Greg Bernhardt submitted a new PF Insights post Calculating the Spin of Black Hole Sagittarius A* Continue reading the Original PF Insights Post.

Here I am considering the one particle free Dirac equation. As is known the spin operator does not commute with the Hamiltonian. However, the solutions to the Dirac equation have a constant spinor term and only an overall phase factor which depends on time. So as the solution evolves in time...

Homework Statement Exact spin symmetry in the Dirac equation occurs when there is both a scalar and a vector potential, and they are equal to each other. What physical effect is absent in this case, that does exist in the Dirac solution for the hydrogen atom (vector potential = Coulomb and...

When one applies block spin scheme on Ising model, what's the value for block spin? If we set the average value for spin in a block, it should not be ±1 anymore. But if so, is the transfer matrix is still two dimensional?

Watching an old (2012) youtube video (), the narrator says (time 10:38) that if A measures the y-axis spin of an entangled pair and communicates his finding to B, then B "cannot" measure his x-axis spin, because doing so would give him knowledge of the spins along both axes, which uncertainty...

Homework Statement The stability of a spinning body may be explored by using equation (3.40), with no torque components present. It will be assumed here that the spin is about the z -axis and has a rate ωZ = S. Homework Equations $$I_{xx}\dot{ω} - (I_{yy}-I_{zz})Sω_y = 0$$ $$I_{yy}\dot{y} -...

In the Dirac equation, the wave-function is broken into four wave-functions in four entries in a column of a matrix. Since there are four separate versions of the wave-function, does each version have the spin angular momentum of h-bar/2? This seems overly simplistic. How does spin angular...

Can anyone with basic knowledge of Dicke States assist with explaining how we arrive at equation (4) in the paper 'Entanglement detection in the vicinity of arbitrary Dicke states': <Moderator's note: link fixed> $$\langle J^2_{x} \rangle_{\mu} = \sum_{i_1,i_2} \langle J_{xi_{_1}} \rangle_{\mu}...

Homework Statement Two spin ##\frac 12## particles form a composite system. Spin A is in the eigenstate ##s_z = + \frac 12## and Spin B is in the eigenstate ##s_x = + \frac 12## What is the probability that a measurement of the total spin will give the value ##0##? Homework Equations I know...

Homework Statement I'm trying to show the Eigenstate of S2 is 2ħ^2 given the matrix representations for Sx, Sy and Sz for a spin 1 particle Homework Equations Sx = ħ/√2 * \begin{pmatrix} 0 & 1 & 0 \\ 1 & 0 & 1 \\ 0 & 1 & 0 \end{pmatrix} Sy = ħ/√2 * \begin{pmatrix} 0 & -i & 0 \\ i & 0 & -i...

Theory explains magnetism in iron as a combined effect of magnetic moments of electrons. Now, what is confusing me is that valence electrons in iron are supposed to be free. The valence band and conduction band overlap. So, what kind of orbital and spin-ular momentum do these free electrons...

Hello In a paper I am working we have a two metal connected to each other, Within the ballistic approximation we adopt the Landauer approach and generate a pure spin current by applying a spin bias that is modeled as difference of spin-dependent chemical potentials across the interface. Can...

Hello! I want to make sure I understand the relation between this and rotation (mainly between SU(2) and SO(3), but also in general). Also, I am a physics major, so I apologize if my statements are not very rigorous, but I want to make sure I understand the basic underlying concepts. So SU(2) is...

Homework Statement (a) If a particle is in the spin state ## χ = 1/5 \begin{pmatrix} i \\ 3 \\ \end{pmatrix} ## , calculate the expectation value <Sy>(b) If you measured the observable Sy on the particle in spin state given in (a), what values might you get and what is the probability of...

Why is it that bosons (particles having symmetric wave functions) have integral spins and fermions (particles having antisymmetric wave functions) have half integral spins? A lot of books state this without specifying the reason. I was wondering if this is a theoretical deduction. Or is it an...

Homework Statement Find the normalised eigenspinors and eigenvalues of the spin operator Sy for a spin 1⁄2 particle If X+ and X- represent the normalised eigenspinors of the operator Sy, show that X+ and X- are orthogonal. Homework Equations det | Sy - λI | = 0 Sy = ## ħ/2 \begin{bmatrix} 0...

I tried to answer it and got 3/4 or 6/8 after using the union set operation for 4/8 or 1/2 and 3/8, based on what is being asked in the problem...

Hello! I am a bit confused about the idea of spin. Let's say we have spin ##1/2## particles. This means that the spin along a random axis is ##\pm 1/2##, right while the values of the particle spin (i.e. the module) is actually ##\sqrt{1/2(1+1/2)}##? Also I am a bit confused about combining...

I have read in the internet that "One naturally derive the dirac equation when starting from the relativistic expression of kinetic energy: ##\mathbf H^2=c^2\mathbf P^2 +m^2c^4## where ##\mathbf P## is the canonical momentum. Inclusion of electric and magnetic potentials ##\phi## and ##A## by...