MSimon wrote:Because I'm a nuclear engineer.
Yes, and? I'm an engineer too! An aerospace engineer. Whenever I raise an issue that fall under my education and outside of yours (like SSTO, ground-side aircraft operations, or rocket science) you treat me and my views like filth. So tell me, Mr Fellow Engineer, why should I not copy your example?
Though I must regret that I did misphrase the question. The intent was not about neutron energy or activation cross sections, but rather 'how do you know the neutron flux (using whatever mechanism you chose) will not degrade critical materials inside the reactor shielding'? Specifically referring to the super conductors (which may have minimal or zero shielding) what degradation rate would you calculate? And since you are a nuclear engineer, I’ll ask you to show your working.
Activation is merely one way that can happen. What happens when the 2MeV (not to mention the occasional 16MeV) neutron hits an atomic nuclei? There are also Frenkel defects, Wigner effects, neutron-induced swelling, and the creation of dislocations and voids; all of which can alter material properties; which is usually a bad thing.
You knew that didn’t you?
Many people (who are also nuclear engineers) seem to share the view that neutron damage (of all types) will be severe enough to be measurable in the ITER reactor. So much so that shielding in ITER is not only useful to model a full scale reactor, but also necessary. If that is run at it's maximum capacity and power once a day, it will produce 200GJ of neutrons. Run continuously at equivalent fusion output, a p11B polywell will produce 43GJ over the same day; and may spread that neutron flux over a smaller area. Now 1/5th of the flux (before area effects) will produce (presumably) 1/5th the effect. Are you saying this will have effectively zero effect on all new materials in the ploywell reactor; again, specifically materials which you likely may not have worked with?
It is notable that while Mr Bussard has said he can make a working reactor for only $150M, not a working reactor free from operational issues.
Your point of view seems contrary to logic to me; though I am aware that would not be the first time such a contradiction has existed in atomic physics. Though if you can prove it, please do so to help fill in some of the gaps in information surrounding the polywell proposal.
Do you know the difference in absorption cross sections between 2 Mev neutrons and thermal neutrons? Is it typically a 10% difference or more like 2X to 10X difference?
In layman's terms it's like a large fast moving asteroid moving through earth's gravity well; it's going too fast to be captured. To be captured it would have to fly much closer to the earth where the potential well is stronger, or hit it directly, which is less likely. I lack easy access to the precise mathematics, but yes I do understand the basic concepts.
Any superconductors used in a Polywell will have to be cooled in the 20K range (or lower depending on the material) because of the magnetic field requirements. There are no 77K high mag field superconductors. You knew that didn't you?
I hadn't read that before no. And having spent a few days looking about the internet, I've been unable to find confirmation of it either. I’ll continue to look. I like learning new things. Though as I’m sure you’re aware there is a deplorable lack of easily accessible information on this subject available online. Can you make any useful suggestions for further information?
I have found a few papers discussing the exciting possibilities of YBCO and >100T fields. From what I can gather there are no commercially available HSC materials, but that's not the same as saying they're fundamentally impossible.
http://www.iop.org/EJ/article/1367-2630 ... j226629bib
http://www.iop.org/EJ/ref/-prog=article ... /9/3/047/6
And just to be clear, this is not a matter of believing you or not believing you, it's a matter of you providing no evidence for your statements.
(how much hydrogen do you contain?)
Based upon water composition of the human body, roughly 5kg; give or take. It not that difficult to work ou for the average human bodyt. You're sure you're a fully qualified engineer? As an engineer you might be aware of the legion of problems NASA has experienced with the stuff.
B10/B11 has a low high energy neutron cross section. You knew that didn't you?
You're proposing using boron for shielding in a nuclear reactor which uses boron as a fuel? That sounds like building a fire-wall out of gunpowder. You know this would sound
a little strange didn't you?
You seem very ignorant on the subject.
You seem more concerned with using your knowledge as a high horse to belittle people, rather than as a tool to educate people curious about the details. I'd be rather be ignorant than think like that.
You ask why I believe capture cross sections are lower for 2 Mev neutrons than thermal neutrons.
Actually no I didn't.
It is simple really. I looked it up.
Translation: Misread the question, losing your rag, and posted something not particularly relevant while failing to give any evidence.
Some light reading material: Half Way To Anywhere, The Rocket Company, Space Technology, The High Fronter, Of Wolves And Men, Light On Shattered Water, The Ultimate Weapon, any Janes Guide, GURPS Bio-Tech, ALIENS Technical Manual, The God Delusion.
I met a lot of Navy guys, and one roommate went into geology so he could stay on dry land for the rest of his life! 6 months under water at a time is a bit much.