neutron absorbtion

[colinheath]

hi all,
well as i start collecting my bits for a neutron producing fusor i am ever interested in the safety side of things(as i should be)
the high voltage safety im fine with and x-rays reasonably so.
but my question is this. the levels of neutrons an amateur fusor produces are small i know but when we absorb these how much are we increasing the risk factor of being struck ill by this?
also are there ways to stop the neutrons like a borax tub or something.
also will these neutrons irradiate anything else
many thanks
colin heath

[Richard Hester]

The best fusor on this list puts out a few million neutrons/sec. These are emitted isotropically. To figure out the dose rate assume that all the neutrons are coming from a shell at about 1/2 the diameter of the fusor. You will probably also want to assume a 6" or 8" diameter chamber. Divide the total neutrons by the shell area, and you have a starting value for neutron flux inside the fusor. You can then extrapolate the flux to any distance you desire. The neutron flux will fall off as the distance squared, so if you are standing a few feet from the fusor, the flux (and the total number of neutrons you will absorb) will get pretty small. Richard Hull had a post somewhere in this section regarding dangerous flux levels of fast neutrons, and you can compare your calculated numbers to that standard to estimate the danger level.
If you are really worried, a stack of jugs of saturated borax solution will absorb some neutrons, and moderate others (thermal are not as dangerous as fast neutrons). Placed close to the fusor, you will get extensive area protection from the "neutron shadow" cast by the shield. Borax-loaded paraffin may also be an option for shielding, and perhaps easier to deal with than a liquid shield. Distance is a very good shield as well.
The neutrons that don't hit you will be absorbed by the surrounding objects, walls, floor, etc. The induced radioactivity will be negligible, as the flux (and the total number of neutrons is pretty small to begin with. A power producing reactor would be another question, but we are many, many, many orders of magnitude away from that power level.
A more immediate concern are the soft X-rays generated by electrons striking the chamber walls. Soft X-rays can cause cataracts and skin cancer. A stainless steel chamber (except for the view port) provides excellent shielding up to about 40-50kV. After that you want to be thinking about supplemental lead shielding. If you are using aluminum or glass, you want to use supplemental shielding at lower voltage.This issue has also been discussed extensively in previous posts.

[davidtrimmell]

Basically the only real radiation hazard will be the x-rays, and then only when pushing 30-40KV. Sounds like some of the heavy hitters here are still only getting a few mREMs of neutrons in any "whole body" possible dose.

I have worked as a Sr. Health Physics Tech. and I will say Neutron exposure has a taboo, possibly related to the history of criticality incidents! OR, power entries (PWR) to the containment building, not a fun experience unless you like carrying a REM ball (heavy), telletector (gm meter with extension pole), Ion chamber, and then you are in PC's (protective clothing -it's contaminated in there;-)) and a SCBA (sub-atmospheric through the air-lock). Oh, about 130F while having to chase the reactor operators around...

Fun. But I miss it, more exciting than a network outage at the 911 center

David Trimmell

[Richard Hull]

Playing with atoms can be fun and educational provided the proper precautions are taken in a reasonable manner guided by wisdom from hours of reading and study. This list has some of the best data available to the amateur scientist on Radiation hazards associated with accelerators. Still, reading from several texts on radiation safety and shielding is a must.

Who knows, with Hormesis becoming a scientifically investigated issue. Giving yourself a smoothed average increase in rad dosage, may be doing yourself a favor.

Richard Hull