Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: X-ray Hazard
Date: Mar 07, 9:15 pm
Poster: Don Estes

On Mar 07, 9:15 pm, Don Estes wrote:

I had spoken with Richard Hull about X-ray hazard in the fusors, who said don't worry about it below 15 KV or so, start to worry at 25-30KV, and get REAL worried above 50 KV. However, since it's not just me but my son who will be working with this device when we get it doing I thought I might dig a bit. An old friend of mine from MIT is now a professor of radiology at UC Irvine, so I sent him and email and, to make a long story short, I ended up talking with a Professor Werner Roeck who is the senior physicist in the Medical Radiology department there. He has 35 years experience with X-rays, and was very helpful.

Some highlights of our conversation (I will post more when I get some of the info he promised). First, the physics:

Below 11 KV, it just ain't an issue, pretty much as Richard said. However, between 11 KV and about 35 or so X-rays are actually MORE of a hazard than at higher voltages, because at lower energy they are absorbed entirely in the body and at higher energy a significant fraction just pass on through.

Second, scatter is not much of an issue below about 25 or 35 KV, so if we just aimed our viewport at the ceiling it would be fine (but illegal). Above that, scattering will start to bathe the room with X-rays, which is why early X-ray pioneers developed various cancers and died young. He gave me a couple of horror stories.

On yes, at lower voltages the X-rays are line of sight, so if you can't see the inner grid the X-rays can't getcha. Higher voltages the scattering may in fact get you after all.

Now, legal stuff: we apparently need a certified health physicist to review our specs and give us a letter on what is safe and what isn't. Several mm of lead is recommended, or its equivalent (which the healthy physicist must look up and certify).

Yes, the nanny state is alive and well in America. On the other hand, when it's my son, I have a tendency to be real, REAL paranoid. It's just my nature, and he doesn't like it one bit (he's 16, but then he'll get over that eventually).

When I get more info than a 10 minute call over my cell phone when I couldn't take notes I'll post more. Don't rely on the above figures since my recollection of the conversation could be faulty.

Bottom line: X-rays at 15 KV could be more than a sunburn. Also, as my radiologist friend reminds me, a sunburn IS a radiation burn.