Date: Wed, 03 Jun 1998 10:55:39 -0700 From: Richard Hull To: Kronjaeg@stud-mailer.uni-marburg.de Subject: Fusor Safety ********************************* FUSOR SAFETY ********************************* It is extremely important to stress safety when working with a fusor as one can be killed or injured in so many ways and so very easily. The hazards are many and a moments inattention can spell tragedy! The fusor demands the would-be builder or amateur scientist to possess or acquire a number of technical skills associated with a large number of technical and scientific disciplines. It is incumbent upon the researcher ultimately to familiarize his or herself with a number of safety issues related specifically to each discipline required as the work progresses. It is impossible to foresee in this short post all of the possible danger zones where the amateur scientist might stumble into trouble, but a small effort will be made to point out the most obvious areas of caution. 1. Electrical hazards 2. Mechanical/machining hazards 3. Vacuum related hazards 4. Materials handling hazards 5. Radiation hazards 1. Electrical hazards The fusor utilizes high voltages. These are present all about the system when in operation. Please use heavily and properly insulated cables of silicone with armoured sheathing or grounded conduit in and around a fusor. Never work on or adjust a running fusor even a vacuum related adjustment can take you dangerously near the high voltage connections. The voltages are high enough so that if you use any materials which are no superior insulators, voltages can travel along the surfaces and shock or injure you. Ground the outer part of the chamber (normally the positive power supply lead. Likewise, use good electrical gounding techniques for all instruments, vacuum gauges, radiation monitoring equipment, etc. Electrocution is easy. Staying safe is not. I you are shocked, it may not be your first, but it could always be your last. THE FUSOR UTILIZES KILLING VOLTAGES! 2. Mechanical- machining hazards The construction of a fusor often demands a certain amount of tooling, machining, welding, etc. Many amateurs do this work themselves. Common workshop safety practices are a must! a. Wear safey goggles at all times when working with power tools. b. When working at a lathe a safety visor is advised. c. Welding is a special area where safety must be pursued. Never weld without eye protection Avoid seting materials on fire around the welding area. Wear protective non-flammable leather gloves and apron. 3. Vacuum related hazards The big problems with vacuum systems are mainly implosion/explosion of chambers and flying glass shards. If using a glass chamber or bell jar, make sure it is a Pyrex or Kimax boro-silcate type of glass. Flint glass or common glass bell jars are most dangerous as the fusor has an electron beam which can heat the chamber walls to near the melting point! Be ever vigilate around glass containers under vacuum. Most properly assembled glass vacuum systems provide for an implosion guard around the bell jar. This is usually a heavy stainless steel wire cage or cylinder. Be watchful of the electron beam heating the chamber walls when the fusor is in operation. If a plastic chamber is used, use only a polycarbonate plastic assembly! Other plastics can shatter like glass. All plastics are easily damaged by the electron beam. When bringing a chamber back up to atmosphere, gently allow air to leak back in and never just slam a valve open. Never, ever, use a mercury diffusion pump! Never, ever, use a mercury manometer or gauge. Mercury spills or breakage can contaminate a large area of your dwelling. All vacuum lines should be metal or glass. Hose sections should be short and made of a non-conducting red gum rubber or tygon. Never use a steel mesh reinforced hose in the system. All metal vacuum lines should be electrically grounded. Vacuum pump exhaust oil vapors should be trapped with an exhaust filter and not allowed to fill the lab area where they can be inhaled. There are many other vacuum safety tips to observe and the experimenter is advised to get a book or manual concerning good laboratory vacuum techniques and procedures. 4. Material handling hazards Deuterium gas is just hydrogen gas and IS EXPLOSIVE IN AIR!!! Never leak the gas to air. Vacuum out all lines through which deuterium will be admitted prior to hooking up the gas cylinder. (this means a valve right at the cylinder and one at the fusor chamber) When vacuuming down the fusor chamber, open the chamber's gas line valve and evacuate the entire gas line system up to the cylinder valve! When fully evacuated, you may now reclose the fusor chamber gas valve. Once this is done and the gas cylinder remains in place and the chamber valve remains closed, the line need not be re-pumped as it contains only pure deuterium. NO ONE NEEDS A GAS EXPLOSION BLOWING THE GLASS CHAMBER, METAL LINES, ETC ALL OVER THE LAB! Use good common sense and think before you ACT! Some vacuum systems may use an oil diffusion pump with a liquid nitrogen trap. Liquid nitrogen can severely COLD burn flesh. Fingers can be lost due to the frostbite that results. If you are using such a system and must handle LN2, make sure to obtain a dewar flask and cryo gloves for safe storage and handling. Always wear goggles and a face shield for double eye protection against flash boilout spalshes when admitting the liquid gas into a trap. 5. Radiation hazards The demonstration, air operated, fusor poses no real radiation hazards especially if operated below 10,000 volts. Regardless of where neutons start to be produced in a deuterium fusor, X-rays will begin after 15,000 volts applied across the chamber. The rays are very soft and will not penetrate chamber walls until above 20,000 volts. Beyond 30,000 volts the X-rays are very dangerous and are the number one radiation hazard. Lead sheeting or other dense material is suggested to protect people in the vacinity of operating fusors at high voltages. consult a book on X-ray technology for proper shielding requirements. Neutron production can begin at 15,000 volts although it will not be of any real significance until the 20-25,000 volt range. Remember we are making fast neutrons and these ae the worst kind of neutron. They must be slowed to thermal energies to protect personnel. To do this tanks of water or large, thick cast blocks of parafin are needed surrounding the chamber. In this manner, the slowed neutrons will react only with the outer layers of skin and body tissue. (minimal risk) Unshielded fast neutrons will see the human body as a nice moderator, (being a big bag of water), and penetrate deep into the body, thermalize and be totally absorbed in delicate easily damaged internal tissue and organs. The worst of this would occur in chambers operating well above 40,000 volts though. A simple parafin wall of about 8 inches thickness around a fusor will afford good protection from fast neutrons even above 100,000 volts. However, one would also need almost 15 mm thickness of lead to shield from the intense x-rays at this same voltage! parafin won't stop x-rays at all! Thus , if you are going over 30,000 volts in a deuterium fusor, be ready to shield with both lead and parafin. You must also have at the very least, an ionization chamber type of radiation survey meter (mainly for X-rays) inorder to know just how much radiation you are producing and or absorbing. Neutron counting is a complex and expensive issue requiring special equipment. The builder is referred to any number of books on radiation physics and metrology. I hoped this has helped explore some of the danger zones in making your own fusor. If one is careful and thinks before throwing a switch, opening a valve or proceeding in to a grey area, the fusor can be a very rewarding and safe project. Remember, you are not only responsible for your own safety, but that of those viewing your fusor or in the near vacinity. Richard Hull