Both Questions are worth 8 marks each Questions are from a course called \"Clini

Question

Both Questions are worth 8 marks each

Questions are from a course called "Clinical Applications of Physics in Medicine". In field of medical physics and radiation.

Sorry its my first time posting, so im not sure if this is how you format properly. Thanks in advance.

1. My research group at McMaster that measures fluorine in bone. We use the 1'F(n,y)20F reaction which has a thermal neutron cross section, o, of 0.096b.20F has a half-life of 11.2 seconds. The neutrons are produced using the 'Li(p.n)7Be reaction The McMaster irradiation protocol is that we irradiate the bone for 30 seconds with neutrons using a current of 500 uA on the Li target A colleague recently called to tell me he had installed a new accelerator at his university where he could irradiate a Li target with 1 mA of protons using the same energy of protons, same type of Li target. However, the cooling protocol on this new machine means that it can only irradiate in short bursts of 10 seconds of current on target How much more activation of fluoride can I expect in the hand using this new machine if I move the McMaster hand irradiation cavity and detection system to my colleague's university? If neutron flux is directly proportional to dose, how do the relative doses compare? We sometimes use a Figure-of-Merit (FOM) to compare devices which is activity/Ndose. How do the FOM compare? As incentive, he tells me he has a "Li enriched target. At McMaster, we use a natural Li target, where 7Li is 92.4% of the naturally abundant target. He has a target which is 96.3% 7Li abundance. How does this change the relative activation, dose and FOM? (8 marks)

Explanation / Answer

1.This is a neutron activation technique and the activity (area under the flourine peak in the output spectrum)of Flourine will be roughly given by

Activity =Neutron flux. cross-section.concentration of flourine in bone

As the accelerator Lithium target is enriched, it yeilds higher neutron flux and as half life of 20F is 11.2 seconds, 10second irradiation time(comparable to one half life ) is good enough to generate a measurable activity.As such the accelerator facility gives better dose, activity and has better figure of merit than the former facility.

2. The activity can be measured as

A=Flux. cross-section of reaction.number of Co/K atoms

number of Co/K=( (Abundance in natural element.weight of the sample)/Atomic mass). Avogadro no.

To take the time of irradiation, time of cooling and time of counting into account we can use

Activity=Neutron flux.cross-section of reaction.(1-e-LT)(e-Lta-e-Ltb). (no.of Co/K atoms)

where L is decay constant, T, ta and tb are time of irradiation, cooling and counting

Related Questions

Navigate

• Browse (All)
• Browse B
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.