Radioactive question (1 Viewer)

[chickenwrap]

Hi guys! I have some questions on radioactive... those that know these please help me!

Carbon 11 is an important medical isotope. It is formed in a medical cyclotron from boron 10
b. Explain why the c-11 radioisotope is not manufactured in nuclear laboratories such as Lucas height

c. Once the C-11 enters the body of the patient, gamma cameras are used to scan the body. Explain how these gamma rays have been produced.

THANK YOU!

 

[dan964]

if I remember correctly Lucas Heights is a nuclear reactor which is used for the production of trans-uranic elements while carbon would be produced in linear accelerators which Lucas Heights is not.
that should get you a start

for the second part you need to know that gamma rays are produced with other forms of nuclear decay (alpha decay and beta decay) reactions.
possibly include the decay equation.

 

[anomalousdecay]

Hi guys! I have some questions on radioactive... those that know these please help me!

Carbon 11 is an important medical isotope. It is formed in a medical cyclotron from boron 10
b. Explain why the c-11 radioisotope is not manufactured in nuclear laboratories such as Lucas height

c. Once the C-11 enters the body of the patient, gamma cameras are used to scan the body. Explain how these gamma rays have been produced.

THANK YOU!

Those two scenarios above can happen. One will be in a linear particle accelerator (the one involving bombarding Boron 10 with a neutron) and the other in a cyclotron (the one involving bombarding Boron 10 with a proton).

Since the question doesn't specify whether it is talking about labs which use cyclotrons or nuclear reactors, this is a terrible question. It should at least specify what they are talking about. OPAL is a fission reactor. I can imagine ANSTO having a cyclotron lying about here and there (not too sure, but they aren't that large and ANSTO is pretty damn big so I wouldn't be surprised). That's why it is kinda inconclusive what the question is referring to and hence can't figure out which method is used to make Carbon 11.

After inspection by researching online, it seems that Boron 11 does not decay into Carbon 11. So to answer the question, we have to take this case as correct for here:



So what happens is that a cyclotron is used to accelerate a proton with enough speed to bombard a Boron 10 target nucleus. The reason why a cyclotron is used is due to the fact that alternating electric and magnetic fields are required to accelerate the proton. A cyclotron is circular such that it takes up a little amount of space but has a track long enough to adequately accelerate the charged particle.

Also another hint (after research though) that the cyclotron is used is the fact that Carbon 11 has a short half life and in the question it states that it must be used for medical purposes. A short lived isotope for medical purposes must be made on site (so at the hospital or medical centre in this case), then you can conclude that a cyclotron is used as a cyclotron is small enough to be used in hospitals.

Any way, for most radioisotopes when they decay they release energy in the form of gamma rays. Depending on the radioisotope, the wavelength of the gamma rays produced can vary. The equations for it are here on wiki: http://en.wikipedia.org/wiki/Isotopes_of_carbon

There is no way this question could have been done in an exam under exam questions though.

For the sake of interest, 1 MeV gives off a gamma ray with a wavelength of approximately 1.24 pm upon calculation (not expected to do this at all).

 

[Kaido]

Much of what anomalousdecay said is 'correct' but is not specifically taught in the syllabus.
A syllabus-based response would be as follows:

b) whilst nuclear laboratories facilitate the production of Carbon-11 (a radioisotope produced by Boron and a proton), the short half-life (~20mins) and urgent requirement of the isotope for use in e.g. PET scans would mean that the isotope need to be locally produced. Thus, instead of being produced in a nuclear laboratory and transported to hospitals; hospitals can facilitate and manufacture their own isotopes in compact cyclotrons.

c) (this question is ambiguous) Gamma rays are products of an unstable radioactive isotope decaying into more stable elements. (This process occurs since the neutron to proton ratio exceeds the stable ratio, hence the excited nucleus decays into alpha and/or beta then gamma)...

 

[dan964]

(c) is physics more so than chem

 

[Kaido]

the elementary particle theory

 

[anomalousdecay]

Much of what anomalousdecay said is 'correct' but is not specifically taught in the syllabus.
A syllabus-based response would be as follows:

b) whilst nuclear laboratories facilitate the production of Carbon-11 (a radioisotope produced by Boron and a proton), the short half-life (~20mins) and urgent requirement of the isotope for use in e.g. PET scans would mean that the isotope need to be locally produced. Thus, instead of being produced in a nuclear laboratory and transported to hospitals; hospitals can facilitate and manufacture their own isotopes in compact cyclotrons.

c) (this question is ambiguous) Gamma rays are products of an unstable radioactive isotope decaying into more stable elements. (This process occurs since the neutron to proton ratio exceeds the stable ratio, hence the excited nucleus decays into alpha and/or beta then gamma)...

This is pretty much all you can say within the scope of the syllabus.

 

[anomalousdecay]

Much of what anomalousdecay said is 'correct' but is not specifically taught in the syllabus.
A syllabus-based response would be as follows:

b) whilst nuclear laboratories facilitate the production of Carbon-11 (a radioisotope produced by Boron and a proton), the short half-life (~20mins) and urgent requirement of the isotope for use in e.g. PET scans would mean that the isotope need to be locally produced. Thus, instead of being produced in a nuclear laboratory and transported to hospitals; hospitals can facilitate and manufacture their own isotopes in compact cyclotrons.

c) (this question is ambiguous) Gamma rays are products of an unstable radioactive isotope decaying into more stable elements. (This process occurs since the neutron to proton ratio exceeds the stable ratio, hence the excited nucleus decays into alpha and/or beta then gamma)...

This is pretty much all you can say within the scope of the syllabus.

 

[happypeople]

b) Brief summary of how radioisotopes are produced:

Two main ways required for HSC Chemistry:
- Nuclear Reactor (such as ones in Lucas Heights)
- used for creating neutron-rich isotopes by neutron (neutral) bombardment

- Particle Accelerators (such as cyclotrons, linear particle accelerators)
- used for creating neutron-deficient isotopes by bombardment by charged particles (such as protons, which have a positive charge)
- in order for charged particles to be incorporated into elements, they must be "accelerated" in a suitable manner so that they can overcome the electrostatic repulsions brought about by the charged particles (eg. protons) already in that element

Now, to answer your question:

Carbon-11 is made from Boron-10. Now, the atomic number (i.e. number of protons) of Boron-10 is 5, and the atomic number of Carbon-11 is 6 (one more proton that Boron-10).

Remember the atomic number of an element is what makes it unique and allows us to identify what element it is.

So, to get Carbon-11 from Boron-10, we have to add an extra proton to Boron-10.

Now, protons are positively charged. And from above, we know that charged particles such as protons need to be accelerated into Boron-11 in order for it to overcome the electrostatic repulsions caused by the protons already in Boron-10.

So therefore, a particle accelerator, such as a cyclotron, and not a nuclear reactor, should be used to create Carbon-11 from Boron-10.

c)According to the zone/belt of stability used for radioisotopes, isotopes with atomic number less than 20 (such as Carbon-11, which has an atomic number of 6), should have a neutron: proton ratio of 1:1 in order for it to be stable.

View attachment 31727

However, Carbon-11 has 6 protons, and 5 neutrons {remember: the "11" in Carbon-11 is the atomic mass, which means protons PLUS neutrons, so to get the number of neutrons given that there are 6 protons in Carbon-11, just subtract 6 from 11: 11 - 6 = 5).

This gives a neutron: proton ratio of 5:6, which is not a ratio of 1:1. Therefore, Carbon-11 must radioactively decay in order to achieve a stable neutron: proton ratio.

Again, from b), we know that particle accelerators produce neutron deficient isotopes, so that means Carbon-11 is neutron deficient. Neutron deficient isotopes tend to decay through electron capture or positron emission (positrons are electrons with a positive charge) (as seen through the graph above) in order to achieve more stable neutron: proton ratio. Gamma rays may be emitted as well.

Thus, we come up with the following equations (which must be included in your answer to this question):



{NOTE: make sure to balance protons/neutrons on either side of the equation}

And since Carbon-11 can emit gamma rays when it decays into Boron-11, gamma cameras may be used to scan the body.

I hope this helps! Good luck with your studies!