Understanding Nuclear Spin: Odd Proton and Neutron Counts

In summary: Beu-156 (Z=63, N=93) has Jπ = 0+ and half-life = 15.19 days.Bi-208 (Z=83, N=125) has Jπ = 5+, half-life = 3.68E+5 y.La-138 (Z=57, N=81) has remarkable stability. Jπ = 5+, half-life = 1.02E+11 y.Ta-180m (Z=73, N=107) is also remarkably stable with Jπ = 9-, half-life = > 1.2E+15 y, while the ground state, Ta-180 (Jπ = 1+) has a
  • #1
Gavroy
235
0
hi

i have a question about nuclear spin

if the number of protons and neutrons is even, then my chemistry book says, that the nuclear spin is always zero.

i guess that the reason is, that there are always 2 protons and 2 neutrons in one state with opposite spin and therefore the overall spin is zero, so that's all right for me.

but then:

if the number of protons and neutrons is odd, then my chemistry book says, that the nuclear spin is some number like 1,2,3,4 and so on.

how so?

i mean, if i have let me say 19 protons and 9 neutrons, then there are 18 protons that give me zero spin(after the first rule) and 8 neutrons that give me zero spin(also after the first rule)

therefore i would say, that this proton and neutron could give me only 1, but not 2 or more...or are these rules not correct or where am i wrong?
 
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  • #2
Gavroy, For an even-even nucleus the spin is zero, without exception. For other nuclei you need to consider not just the spin of the unmatched nucleon but its orbital angular momentum as well, and their combination j = l + s.

For an even-odd or odd-even nucleus the spin of the nucleus is equal to the j-value of the unmatched nucleon.

For an odd-odd nucleus things are not so predictable. The j-values of the unmatched neutron and proton will couple to form the nuclear spin, which must therefore be in the range |jp - jn| ≤ J ≤ jp + jn. There is a set of guidelines called the Nordheim rules that often give the correct spin, but there are exceptions.
 
  • #3
Gavroy said:
hi

i have a question about nuclear spin...

if the number of protons and neutrons is odd, then my chemistry book says, that the nuclear spin is some number like 1,2,3,4 and so on.

how so?

i mean, if i have let me say 19 protons and 9 neutrons, then there are 18 protons that give me zero spin(after the first rule) and 8 neutrons that give me zero spin(also after the first rule)

therefore i would say, that this proton and neutron could give me only 1, but not 2 or more...or are these rules not correct or where am i wrong?

First, keep in mind that almost all odd-odd nuclides are unstable. There are exactly four stable odd-odd nuclides; they are the lightest possible: [itex]^{2}_{1}H[/itex], [itex]^{6}_{3}Li[/itex], [itex]^{10}_{5}B[/itex], and [itex]^{14}_{7}N[/itex]. All four stable odd-odd nuclei have J=1. All other odd-odd nuclei are unstable.

Among the unstable odd-odd nuclides, there are a few that have J=0. Most of these have short half-lives (under a second). Thumbing through my http://www.nndc.bnl.gov/wallet/wallet05.pdf" , the longest half-life for an odd-odd nuclide with J=0 is [itex]^{170}_{71}Lu[/itex], which has a half-life right around 2 days.

As Bill K points out, these nuclides can have states with higher orbital angular momentum, so that J=1, 2, 3... are possible. But these excited states decay pretty quickly, I think...

BBB
 
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  • #4
Eu-156 (Z=63, N=93) has Jπ = 0+ and half-life = 15.19 days.

Bi-208 (Z=83, N=125) has Jπ = 5+, half-life = 3.68E+5 y.

La-138 (Z=57, N=81) has remarkable stability. Jπ = 5+, half-life = 1.02E+11 y. Either side of La-138 are two stable nuclides, Ba-138 (stable) and Ce-138 (t1/2 = ≥ 0.9E+14 y).

Ta-180m (Z=73, N=107) is also remarkably stable with Jπ = 9-, half-life = > 1.2E+15 y, while the ground state, Ta-180 (Jπ = 1+) has a short half-life of 8.154 h.

Thanks to bbbeard for pointing to the BNL pocket/wallet chart of nuclides.
 
  • #5
Ta-180m is unusual because its decay has never been observed.

V-50 has a very long half life (over 1017 years). The last time I checked, its decay had never been detected directly and its lifetime is inferred from geochemistry.
 
  • #6
Astronuc said:
Eu-156 (Z=63, N=93) has Jπ = 0+ and half-life = 15.19 days.

Ah, yes, thanks. I had missed that when skimming the wallet cards...

BBB
 

1. What is nuclear spin?

Nuclear spin is a quantum mechanical property of the nucleus of an atom. It is a measure of the angular momentum of the nucleus, and is caused by the motion of protons and neutrons within the nucleus.

2. What is an odd proton and neutron count?

An odd proton and neutron count refers to the number of protons and neutrons in the nucleus of an atom being an odd number. For example, if an atom has 9 protons and 10 neutrons, it has an odd proton and neutron count.

3. How does an odd proton and neutron count affect nuclear spin?

An odd proton and neutron count can result in a non-zero nuclear spin. This means that the nucleus has a magnetic moment and can interact with external magnetic fields.

4. What is the significance of understanding nuclear spin with odd proton and neutron counts?

Understanding nuclear spin with odd proton and neutron counts is important in many areas of science, such as nuclear physics, chemistry, and medical imaging. It can help us understand the properties and behavior of atoms and molecules, as well as develop new technologies and medical treatments.

5. How is nuclear spin measured?

Nuclear spin is measured using spectroscopy techniques, such as nuclear magnetic resonance (NMR) and electron spin resonance (ESR). These techniques involve applying a magnetic field to the nucleus and measuring the frequencies of the resulting energy transitions.

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