Biomedical Engineering Reference
In-Depth Information
-0.198
-0.594
-0.198
-0.99
-0.198
-1.386
-0.594
-0.594
-0.99
-1.781
0.198
-1.386
-1.781
-1.781
-0.99
0.99
0.198
0.594
0.594
-0.198
-1.386
-0.594
-0.594
-0.99
1.386
1.386
0.99
1.781
1.781
0.99
1.781
-0.198
0.594
0.198
0.594
1.386
0.99
0.198
0.594
0.198
Figure 12.12
Symmetric wavefunction squared
12.7 Spin
It turns out as an experimental fact that many particles have an intrinsic property called
spin
just as they have a mass, a charge and so on. If the particles concerned are electrons, then
we refer to the phenomenon as
electron spin
. Electron spin is expressed in two possible
configurations usually referred to as
spin up
and
spin down
with respect to a given axis
of quantization. I will have more to say about electron spin in a later chapter; it does not
appear from the Schrödinger treatment, just accept it as an experimental fact for the minute.
The two states are written conventionally and and authors often use the symbol
s
for the spin variable. So in the case of electrons, we might write (
s
A
) to mean that
particle A was in the spin up state and (
s
A
) to mean that particle A was in the spin down
state. In the case of two electrons we have four possibilities and we label the quantum
states individually (
s
A
), (
s
A
), (
s
B
) and (
s
B
). The combination (
s
A
)(
s
B
) describes
a situation where electron A has spin up and electron B has spin down and there are four
possible combination states
(
s
A
)(
s
B
); (
s
A
)(
s
B
);
(
s
A
)(
s
B
);
(
s
A
)(
s
B
)
