Magnetic Moments

[Dr Who]

I was wondering, how come the magnetic moment of some isotopes are unknown? This cannot be related to the isotope's half life, as nickel-59 has an unknown magnetic moment, but a half life of 100,000 years. Also, I cannot believe that it is the case, that they have not been measured yet.

 

Thanks in advance.

[Enthalpy]

There page 18, reference from 1974.

http://www.nndc.bnl.gov/nndc/stone_moments/nuclear-moments.pdf

It was a Web illusion: 1000 sites copy their data from a single one, so your data was absent from 1000 sites.

[Dr Who]

There page 18, reference from 1974.

http://www.nndc.bnl....ear-moments.pdf

It was a Web illusion: 1000 sites copy their data from a single one, so your data was absent from 1000 sites.

 

Thanks Enthalpy for the reference, however it doesn't really answer the question, of why the magnetic moments of some isotopes are unknown? Nickel-59 was given just as an example. In fact your reference does not give a magnetic moment for nickel-59 in its ground state. Other isotopes (close to the stable isotopes for each element) with unknown magnetic moments are: H4 (hydrogen-4), He5, Be7, Be11, B9, N16, F18, Mg27, Al29, Si31, P30, P33, S37, Cl39, Ar41, Ca49, Ti51, V52, V53, Cr55, Mn57, Fe53, Fe55, Co61, Ni59, Ni63, Cu67, Zn69, Zn71, Ga70, Ga73, Ge77, As73, As77, Se81, Se83, Br83, Y88, Zr93, Zr97, Nb91, Nb92, Nb94, Mo91, Mo93, Mo101, Tc97, Tc98, Tc100, Rh101, Rh104, Pd103, Pd107, Pd109, Pd11, Cd117, Te121, I128, La136, La141, Ce135, Pr139, Pr140, Nd151, Pm146, Sm155, Gd161, Ho 167, Yb177, Lu178, Hf173, Hf181, Ta180, W179, W181, W185, Re189, Os185, Ir195, Pt199.

 

Enthalpy's reference, does give the magnetic moment for some of these isotopes, but not in their ground states. It is also interesting to note that some of these isotopes have been missed out in the reference, for example it gives the magnetic moment for Si30 and Si32, but not Si31.

 

I hope this has helped to clarify my question and I'm grateful for any answers or comments.

 

Thanks

[swansont]

It could be that nobody has measured them. You need funding to do the research, and if the isotope is difficult to obtain and/or has a short half-life, that makes it difficult.

 

For example, Si-31 has a half-life of a few hours. Producing and extracting it, delivering it and preparing a sample probably takes longer than a few hours.

[Dr Who]

It could be that nobody has measured them. You need funding to do the research, and if the isotope is difficult to obtain and/or has a short half-life, that makes it difficult.

 

For example, Si-31 has a half-life of a few hours. Producing and extracting it, delivering it and preparing a sample probably takes longer than a few hours.

 

It could be that nobody has measured them, but this argument seems a little flawed to me. Firstly the magnetic moments of a vast number of isotopes (many of which are unstable) have been measured. Plus the isotopes that I have previously mentioned are only 1 or 2 neutrons few or too many from being a stable, so we are not talking extremely exotic isotopes. Secondly, the magnetic moment for a good number of the isotopes are known only when they are in an excited state and thus more than half the work has already been done at some point in the past. Thirdly, some of these isotopes have very long half life, e.g. nickel-59 (which is one of the isotopes where a magnetic moment is known for one of its excited states) which has a half life of 100,000 years. Moreover, we could compare this isotope with isotopes that have a known magnetic moment, but short half lives, e.g. carbon-15 (half life of 2.5 seconds) or boron-8 (half life of 770 milliseconds).

 

Do you think the fact that these isotopes have an unknown magnetic moment, might relate some how to their nuclear structure, e.g. they have two different configurations that produce the same radioactive decay, but each of them has a different magnetic moment?

[swansont]

It could be that nobody has measured them, but this argument seems a little flawed to me. Firstly the magnetic moments of a vast number of isotopes (many of which are unstable) have been measured. Plus the isotopes that I have previously mentioned are only 1 or 2 neutrons few or too many from being a stable, so we are not talking extremely exotic isotopes. Secondly, the magnetic moment for a good number of the isotopes are known only when they are in an excited state and thus more than half the work has already been done at some point in the past. Thirdly, some of these isotopes have very long half life, e.g. nickel-59 (which is one of the isotopes where a magnetic moment is known for one of its excited states) which has a half life of 100,000 years. Moreover, we could compare this isotope with isotopes that have a known magnetic moment, but short half lives, e.g. carbon-15 (half life of 2.5 seconds) or boron-8 (half life of 770 milliseconds).

 

Do you think the fact that these isotopes have an unknown magnetic moment, might relate some how to their nuclear structure, e.g. they have two different configurations that produce the same radioactive decay, but each of them has a different magnetic moment?

 

"Exotic" is more than neutron excess or deficiency. It's a matter of how easy it is to produce, and in a circumstance where you can do the measurement. Excited states are relatively easy to produce; all you have to do is bombard them with gammas — you can probably do that in situ — or you can get them from the decay of a parent. The angular correlations of the gammas in the de-excitation give you multiple moment information, but only for the excited state. I'm also guessing that there are other technical issues with making a measurement. The table I looked at showed dozens of different methods used. For example, one method was a beta asymmetry measurement. Ni-59 decays by electron capture, and thus wouldn't be a candidate. So it may be that exclusions are present because they simply aren't candidates for the available methods.

[Dr Who]

"Exotic" is more than neutron excess or deficiency. It's a matter of how easy it is to produce, and in a circumstance where you can do the measurement. Excited states are relatively easy to produce; all you have to do is bombard them with gammas — you can probably do that in situ — or you can get them from the decay of a parent. The angular correlations of the gammas in the de-excitation give you multiple moment information, but only for the excited state. I'm also guessing that there are other technical issues with making a measurement. The table I looked at showed dozens of different methods used. For example, one method was a beta asymmetry measurement. Ni-59 decays by electron capture, and thus wouldn't be a candidate. So it may be that exclusions are present because they simply aren't candidates for the available methods.

 

OK, that is a fair argument upon why the magnetic moment of some isotopes is unknown, thank you.

 

Do you think though that the magnetic moment is created by the nuclear structure?

[swansont]

Do you think though that the magnetic moment is created by the nuclear structure?

 

Yes.

[Dr Who]

Yes.

 

I take it from the short answer, that although it is the nuclear structure that creates the magnetic moment, we don't know how yet?

[swansont]

I take it from the short answer, that although it is the nuclear structure that creates the magnetic moment, we don't know how yet?

 

It's the combination of the individual contributions from spin and orbital angular momentum, which will give you dipole and quadrupole terms. But the devil is in the details. I don't know how well structure can be modeled; it seems that in any event, you need to determine the value experimentally.

[Dr Who]

It's the combination of the individual contributions from spin and orbital angular momentum, which will give you dipole and quadrupole terms. But the devil is in the details. I don't know how well structure can be modeled; it seems that in any event, you need to determine the value experimentally.

 

Thanks, you have been very helpful.