I'm allowed to ask questions right? I need help with this:
Magnetic resonance imaging (MRI) is a noninvasive technique for visualising the living human body. It depends on a phenomenon called nuclear magnetic resonance (NMR) which occurs when certain atoms are place in very strong magnetic fields. All nuclei that have odd mass numbers exhibit NMR as do all nuclei that have even mass numbers but odd atomic numbers. Nuclei having both even mass numbers and even atomic numbers do not exhibit NMR.
The number of neutrons in the nucleus of an atom in which NMR occurs is always
A odd
B even
C odd if the number of protons is even
D even if the number of protons is odd
Also explain why
Awesome question (we looked at this in nuclear physics).
So a nucleon such as a proton or a neutron has a spin of +/- 1/2. Let's first look at a proton which can take two quantum states (+/- 1/2), now let's say we have two hydrogen atoms together where one proton is -1/2 and the other is +1/2. Now if I put in a magnetic field the -1/2 proton gains energy by being anti-aligned with the magnetic field, whilst the other drops to a lower energy level and this energy difference can be used to find the resonant frequency.
Sorry for the digression to physics, but it is a physics forum.
Now basically as long as you have either an odd number of neutrons or protons or both, you get NMR.
e.g. C-11(p-spin,n-spin) could be C-11(-,-1/2) & C-11(-,+1/2).
So the answer is C, why?
C says that the number of neutrons must be odd if Z is even.
NMR occurs for,
odd n & even p, odd n & odd p and even n & odd p, but it doesn't happen if even n & even p. C basically states this.
A is wrong since NMR can occur if n is even (iff p is odd)
B is wrong since NMR can't occur if n is even and p is even
D is wrong since NMR can occur if n is odd and p is odd.