CLASSE Safety Handbook

Origins of Ionizing Radiation

The electrons accelerated in the CESR bending magnets emit x-rays. Most of these x-rays are absorbed by the vacuum chamber walls, the tunnel walls, or the magnets. Higher intensity x-rays are created for CHESS in undulators and wigglers placed into the CESR ring for this purpose. X-rays can also be created in the processing of RF cavities.

Particles lost from any accelerator beam also cause radiation. Particles are lost when they collide with solid material or gas molecules or interact with another beam (as in CESR). They plow into the walls of the vacuum chamber and create a cascade of gamma rays and more electrons. Gamma rays are a higher energy cousin of x-rays. Some of the gamma rays hit atomic nuclei and knock out neutrons, most of which are stopped by thick concrete shielding. A few of the neutrons change some of the nuclei of accelerator components, such as targets and beam pipes, into radioisotopes. Radioisotopes, unlike RPE, can emit radiation after the accelerator is turned off. Fortunately, only a few locations at CLASSE have residual radioactivity at any detectable level. Areas of residual radioactivity usually include the linac, the linac snouts, the injection lines, the transfer lines, the inflector magnets, and occasionally at other places along the synchrotron or CESR. A survey for radiation is done every time the interlocks are to be turned off, and all areas above 2 mrem/hour at 30 cm are marked with signs.

In addition to x-ray radiation from accelerated electrons and lost beam particles, ionizing radiation at CLASSE can originate from several types of devices operated at high voltage. These include electrostatic separators in CESR, electron guns, and field emission equipment such as RF cavities.

Exposure to Ionizing Radiation

A key concept in radiation protection is ALARA, (As Low As Reasonably Achievable) the concept that everyone should be exposed to as little radiation as possible; Cornell's guidelines state that radiation workers should receive no more than 500 mrem annually and non-radiation workers no more than 100 mrem annually. Cornell policy is considerably stricter for radiation workers than that of the Nuclear Regulatory Commission (NRC), which requires exposure to be limited to 5000 mrem per year for radiation workers (and, like Cornell, 100 mrem per year for non-radiation workers), as shown in the table below. Notice that CLASSE has elected to establish a uniform maximum yearly occupational dose of 100 mrem per year for all personnel.

Regulator	Maximum allowed whole-body exposures
	Radiation Workers	Non-radiation workers
US Nuclear Regulatory Commission	5000 mrem per year	100 mrem per year
Cornell University	5000 mrem* per year (*quarterly notification at 10% & investigation at 25% of year-to-date, pro-rated annual limit)	100 mrem per year
CLASSE	100 mrem* per year (*500 mrem per year under rare, pre-approved circumstances)	100 mrem per year

While most personnel will never be exposed to significant doses of ionizing radiation from sources at CLASSE, keep in mind the following principles of radiation protection to minimize your exposure:

• Time: Exposure equals exposure rate multiplied by time. Spending as little time as possible in a radiation area, waiting as long as you can after radiation-producing equipment has been turned off, and planning ahead will reduce your exposure.
• Distance: Maximizing the distance between you and the radiation source will significantly reduce your exposure.
• Shielding: Use appropriate shielding to protect yourself from unnecessary radiation. Lead shielding and source containers provide extra protection.

Remember and use the concept of ALARA and the principles of time, distance, and shielding to protect yourself from radiation.

If you believe radiation is entering an occupied area, notify all people in the area, vacate the area, and notify the CESR operator and the CLASSE Safety Director.

Controlled, Uncontrolled, and Exclusion Areas

Using the Cornell EHS Radiation Safety Manual definitions, the lab is divided into uncontrolled areas, where there is little possibility of radiation exposure, and controlled areas, where there is some possibility of exposure. In uncontrolled areas, the potential radiation dose rate must be below two mrem per hour and 100 mrem per year. No precautions need to be taken, and there is no radiation danger. All offices, building entrances, and most of (but not all) the following spaces are uncontrolled: Newman Laboratory, the Physical Sciences Building third and fourth floors, and the second and third floors of Wilson Lab.

The following are the controlled areas:

• CESR control room
• CESR tunnel and cross tunnel
• CESR control room
• Linac (LS1)
• All of L0, including the pathway from East to West
• LS2 (above the linac)
• Rooms 101/102
• All CHESS hutches & caves
• G-line area just outside hutches, where signed
• The area inside the ERL shielding blocks in L0E
• The ERL control room
• Rooms 120/128/128A
• Room 180

The 3rd floor of Wilson and above have no controlled areas; the 1st floor hallway from the loading dock to CHESS is not a controlled area. There are no currently no controlled areas at Newman Laboratory or Physical Sciences Building, but you should be aware of signage for any area you enter because designations can change. If you are in a controlled area, you must wear a radiation badge (in fact, controlled areas are often called "badge areas"). Radiation badges are part of the personal radiation monitoring that helps us confirm the effectiveness of our protective measures. The large subset of the controlled areas at CLASSE that have potential for high radiation levels, designated as exclusion areas, are subject to more stringent rules: first, exclusion areas are separated from working and public areas by gates, radiation shielding, and an interlock system that prevents radiation-producing equipment from turning on. The radiation dose rate is expected to remain below two mrem per hour in CLASSE controlled areas that are not exclusion areas.

(NOTE: The cross-tunnel should not be used for casual passage to Tower Road.)

Interlock Systems

The major interlock systems at CLASSE are for CESR, ERL, and CHESS; each halts beam transport into certain areas if a perimeter is breached or certain required conditions are not met. Smaller systems can also have interlocks or "interlock chains" to guarantee proper procedures are followed prior to startup.

CESR interlock system

The CESR interlock system is an arrangement of gates and light beams that detect anyone walking into a radiation area at the wrong time. Electronic message boards near each entrance display the access and machine conditions. Signs and sounds provide information about the local environment. Before beam is injected from the linac, the CESR operator searches and resets all the interlocked area to guarantee only people with keys are inside. The keys prevent the accelerator from turning on. If you find yourself inside a radiation area when the warning sounds and the radiation area announcement comes over the PA system, do whichever of these three things is quickest (pull the crash cord, push a crash button, or break a light-beam interlock by stepping through it) to prevent beam coming on. When the machine is running, the board reads "synchrotron on" or "CESR on," and you may not enter. If you enter, you will interrupt the light beams, which sounds a loud siren and automatically shuts off CESR. If you break an interlock, go to the nearest beam phone to explain who you are and where you are to the CESR operator. The board will read "interlocks set" when the machine is ready to run. You may enter the area only if the sign also says "TAKE A KEY," and only with a key (because the key must be used to access controlled areas. Every person in a group must take a key and carry it until exiting interlocked areas, at which point it must be returned to its original location. (CESR cannot be turned on until all keys are returned. If you accidentally take a key from the building, call the CESR operator immediately and return the key to Wilson as soon as possible.) Never share keys. White keys allow access to all areas. Their storage box is located in the control room. While you have a white key in your possession, it is impossible for the linac, synchrotron, or CESR to generate or transport beams.

When taking a key, you should sign it out. If taking more than one key for a group, inform the CESR operator how many keys are being taken and write the names of the individuals receiving the keys on the sign-out sheet. If returning more than one white key, indicate the individuals for whom the keys are being returned on the sign-out sheet and inform the operator.

Colored keys available for access to specific areas are located near those areas. For example, CHESS West keys, which are yellow, allow access to CHESS West and are located in the CHESS area. To find out more about colored keys and the areas to which they allow access, speak with your supervisor or a CESR operator, or ask to see the short video (?) on the interlock system. If the sign reads "AREA SAFE," then the machine is completely off and the entire experimental area has been surveyed for residual radioactivity. Once the area has been declared safe, no keys are necessary and all experimental areas are open, but you must still wear a radiation badge (discussed later in this chapter) and pay close attention to posted warnings.

Radiation monitors outside the CESR exclusion area are interlocked to the linac and/or storage ring. If beam conditions deteriorate enough that significant radiation is leaking through (or over) the shielding walls, these monitors trip off the accelerator if the instantaneous dose rate exceeds 2 mrem/hr.

ERL Phase 1 interlock system

The ERL Phase 1 accelerator is located along the south wall of L0 (protruding slightly into L0E) behind large blue shielding blocks, and the ERL control room is in #147, adjacent to an associated laser room in #141/143. Radiation-producing equipment is located inside the shielded area, and access inside the area is prohibited while radiation can be produced. An interlock system with light beams and keys similar to that of CESR enforces the perimeter. There are three floor level entrances to ERL, each through a labyrinth of shielding blocks and protected by light beam interlocks. Similarly, access to the ERL mezzanine from the stairway or the ladder (for emergency escape only) is also protected by light beam interlocks. If the interlocks are broken, the high voltage to the gun (at the east end of the area) and power to the superconducting RF cavity are disabled, and the laser shutter is closed. Electronic message boards outside each floor-level entrance, similar in design to those at CESR entrances, indicate whether the ERL is on, if a key is needed for access, or if the area is safe for access without a key; each status indicator only applies to the ERL area. Before the ERL is turned on, the ERL area is searched by the ERL operator to ensure the absence of personnel, which then allows the setting of interlocks; only then is the gun HV enabled. Always check with the ERL operator in Room 147 and carefully read the message boards before entering the ERL area.

Radiation monitors outside the ERL exclusion area are interlocked to the ERL gun. If beam conditions deteriorate enough that significant radiation is leaking through (or over) the shielding walls, these monitors trip off the ERL gun if the instantaneous dose rate exceeds 2 mrem/hr.

Room 128 interlock system

Rooms 120/128 on the Wilson first floor at the west end house an ERL accelerator development laboratory. The control "room" is on the north side of room 128, and the accelerator runs west to east along the south wall. A laser room is located at the west end of the room. The shielded beam dump is located in Room 120. The gun high voltage cannot be enabled unless all the doors to rooms 128 and 120 are secure and interlocks are unbroken. Unauthorized access through any door while the accelerator is running will disable the gun HV and close the laser shutter immediately. Moreover, the south half of the room, including the accelerator and laser room, are protected by a light beam interlock which, if tripped, will also turn off the gun HV and close the laser shutter.

CHESS interlock system

The CHESS interlock system is described here.

Area Radiation Monitoring

Electronic monitors in experimental areas check levels of high energy gamma, low energy gamma, x-ray and neutron radiation. If any monitor detects a radiation level that is too high, the red light on the monitor blinks and an alarm sounds, and the linac and/or CESR is automatically turned off. Anyone in an experimental area such as CHESS should immediately evacuate that area until an operator is able to reset the trip.

In addition to electronic monitors, area survey radiation badges check the level of radiation both inside and outside radiation areas twenty-four hours a day. Survey badges record the amount of radiation in any given area that is monitored.

There is one Radiation Logbook for CESR/CHESS and one for ERL, which are kept in the CESR and ERL control rooms, respectively. They contain records of radiation survey results, changes in shielding, and other changes that affect exposure levels. The Radiation Safety Technician also keeps several other logs associated with radiation monitoring.

Radiation Shielding

Radiation shielding is strategically placed and monitored; no one should move any lead bricks or shielding without express permission of the CLASSE Safety Committee. Shielding effectiveness is only guaranteed up to a height of eight feet above ground, so do not stand on ladders, chairs, or tables within the experimental areas.

Request a badge

If your job entails routinely entering controlled areas, an assigned radiation badge with your name on it should be issued to you. To request a badge, fill out this online form.

Radiation Badges

Personal radiation monitors provide the final check on the effectiveness of Lab's protective measures against ionizing radiation. Each employee, student, CHESS User, or visiting researcher with a need to pass through or work near radiation will be issued a radiation badge, similar to this visitor badge. When replaced it will be stored at one of five locations, depending on where you work most; at Newman Laboratory, G-Line (staff only), or in one of the CESR, CHESS, or ERL control rooms. Visitor badges can be signed out, providing full identifying and contact information, which we are required by law to collect for CHESS Users, short-term visiting researchers, and any CLASSE personnel who have temporarily misplaced an assigned badge.

A radiation badge does not protect you from radiation or give you an immediate reading of the radiation level. Instead, it records accumulated radiation exposure over a period of one to three months, and is read out afterwards by the badge vendor. (Each employee's exposure history is confidentially maintained by CLASSE and Cornell University.) Clip your radiation badge prominently to the front of your clothing between waist and neck only if you plan to enter a controlled area (it may not record exposure correctly if placed inside a pocket).

Virtually all of our radiation badges, worn by those whose work brings them into controlled areas, register below ten mrem for each two-month wear period. The radiation exposure anyone receives at CLASSE is much smaller than that already received from from natural sources (300 mrem annual dose from rocks, cosmic rays penetrating the atmosphere, radon, and natural radioisotopes in the human body). Radiation exposures from man-made sources are: dental x-ray (25 mrem, one-time dose), abdominal radiography (150 mrem, one-time dose), medical brain scan (2400 mrem, one-time dose), and commercial air flight crew member (450 mrem, annual dose from cosmic rays unshielded by the lower atmosphere). The exposures reported by the badge vendor have already been corrected for natural radiation sources by comparing them with reference badges that are stored on-site but away from radiation; hence reported exposures will almost always be lower than the expected dose from natural sources alone in that period, and should correspond to the exposure in the workplace alone.

A second type of personal radiation monitor, one that does provide immediate visual readout of the accumulated dose, is the dosimeter. CLASSE uses both analog and digital dosimeters, as shown. Dosimeters are for use by a host or tour guide on behalf of visitors (see Giving Tours).

If you have had an assigned radiation badge at CLASSE (or elsewhere at Cornell) for more than one year, you can obtain your occupational radiation dose on record with EHS by clicking this link. Be aware that this dose is only the dose recorded by your radiation badge while you've worn it, and has already been adjusted to not include normal background radiation exposure. After you enter your NetId and password, a page with your information should appear (without the need for human intervention on the EHS end) after a short wait; with some browsers the pdf file does not appear but instead is downloaded automatically, so check your Downloads (or equivalent) folder.

Radiation Badge Mishaps

Radiation badges sometimes get lost or misplaced or mechanically damaged. Sometimes a user mistakenly wears a badge when getting a medical x-ray or traveling by air. You can mistakenly take someone else's badge from the rack or someone else can take yours. Rarely, badges report unusual readings due to damage or other malfunction (in this case, you will be informed of this after the badge has been processed). If anything unusual like this happens to your badge, please notify your supervisor or advisor if you are a Cornell staff or faculty member or student, the CHESS Operator if you are a visiting CHESS user, the CLASSE Safety Director, and the RSS immediately via the online Badge Mishap form (click on the preceding words). (If you were contacted first by someone else of a mishap, please respond via this form also.) It is essential that there be an accurate record of the circumstances and timing of the mishap to whatever specificity you can provide; it is also important that there be a record of your being informed of any problem with a badge. Where and when was the badge lost or irradiated? Do your best to reconstruct your activities on that day so that possible locations can be searched, and any exposures that may turn up later on a lost badge can be understood. If it can be agreed that a non-zero exposure on your badge was obtained while it was not on your possession, or not on the Cornell University campus, then the University's record of your occupational exposure should be corrected, and this form can be used to officially request such an action.

If for some reason the online form does not work, please cut and paste the form below into your email compose window, fill it out, and send it to the CLASSE Safety Director, the RSS, and your supervisor:

Personal Radiation Protection

If you work with radioactive materials or in radiation areas, you should be aware of some more personal safety protection devices:

• Portable survey meters: These are handheld monitors for gamma and x-ray radiation that provide instant readings. Remember to check the batteries before using one. The meters are available in the vacuum lab, the control room, the west RF transmitter, CHESS, and Newman 205. GM counters are professionally calibrated once a year. Some are used with special probes that give energy compensation and are thus highly accurate. Contact the Radiation Safety Specialist if you are unsure of which to use.
• Ring badge: Those who use intense sources to calibrate monitors, and others who demonstrate a need, can obtain ring badges from the Radiation Safety Specialist. Ring badge exposures will become part of your personal radiation records. You will be issued a set, one for each hand.
• Safety glasses and gloves: You should wear safety glasses and gloves if you are working around residual radioactivity. If you are handling sources, you may be required to wear them.

Pregnant Workers and Radiation Exposure

Because the human fetus has rapidly dividing cells and is highly sensitive to ionizing radiation, pregnant women should pay special attention to minimizing their ionizing radiation exposure. While CLASSE has developed a comprehensive Radiation Safety program of radiation monitoring, education, shielding, access controls, interlocks, and signage, it is nevertheless prudent for a pregnant worker at CLASSE to gather relevant information and understand the extra precautions available. To that end, CLASSE will provide confidential counseling and services upon request by any worker who is pregnant, or thinks she may be pregnant, and is concerned about exposure to radiation. The CLASSE Safety Director and/or the CHESS Safety Officer will generally provide these services, although, with advance notice, counseling by a qualified female staff member of University Environmental Health and Safety can be arranged.

Radioactive Source Handling

LEPP owns about forty-five sealed radioactive sources, and CHESS owns ten. All of these sources are registered or on a permit from the University. All LEPP sources are sealed so that no one can touch the radioactive material directly. They are solid, covered in a permanent casing. Sources are stored in a safe when not in use. Any improperly used or unattended sources will be immediately returned to the safe.

The Radiation Safety Specialist (RSS) keeps an inventory of all sources, updating a logbook and card file each time a source is signed in or out. In cooperation with the Department of Environmental Health and Safety, the RSS handles ordering, receiving, moving, shipping, monitoring, and disposing of radioactive sources. The RSS also does periodic source surveys to ensure that all sources checked out are attended to and stored properly.

If you are interested in using or ordering a radioactive source, see the CLASSE Sealed Source (RPH) and the RSS for a personal orientation. Use of radioactive sources is restricted to approved people and locations. Undergraduate students may only sign out sources through their advisors or supervisors. Remember to wear personal protective equipment, such as gloves, when using radioactive sources. Also remember to use the principles of time, distance, and shielding to reduce your exposure to radiation. If you believe a source may be leaking, either because it looks damaged or because radiation has been detected where it is unexpected, notify everyone in the area and seek assistance from the RSS.