Laboratory Safety - Modern Physics Laboratory

Read this before Week 1 and follow your institution’s approved laboratory procedures. The instructor must identify the actual equipment, source activities, safety contacts, and emergency equipment before work begins.

The experiments may involve laser light, ionizing radiation, electrical or thermal hazards, and flammable solvents. The controls below supplement the site’s training and written procedures; they do not replace them.

Lasers¶

Experiments 1, 4, 5, 7, and 8 use lasers; Experiment 2 may use a pulsed laser diode. Confirm each source’s class and wavelength from its label before use. A Class 2 visible laser can injure an eye during prolonged direct viewing; direct viewing of a Class 3R beam or a specular reflection can be hazardous. Do not rely on the blink or aversion response as a working control. See OSHA’s laser hazard guide.

Laser rules

Keep your eyes out of the beam plane. Do not bend down to look along a beam path or view it through an optical instrument.
Remove reflective jewelry and badges before working over the beam path. Check for other shiny surfaces that could produce a specular reflection.
Terminate the beam. Every beam path ends on an approved beam stop, not on a wall, a window, or a neighboring group’s bench.
Beam off while you reconfigure. Block or switch off the source before moving a mirror, inserting an optic, or changing a mount.
Never aim a beam out of the laboratory, and keep the door closed while a Class 3R source is on.
Report any suspected eye exposure immediately. Stop work and follow the institution’s procedure for prompt medical evaluation; do not wait for an afterimage or other symptom.

Use protective eyewear when the site’s laser safety assessment requires it. It must be rated for the laser’s wavelength and optical density; ordinary safety glasses are not a substitute. Beam enclosure, beam stops, and safe alignment procedures remain essential even when eyewear is worn.

Radioactive sources¶

Experiments 3 and 13 may use sealed check sources such as $^{90}$ Sr, $^{137}$ Cs, or $^{60}$ Co. A $^{137}$ Cs/ $^{137m}$ Ba generator, if used, produces unsealed radioactive material and needs a separate approved procedure. Source activity, shielding, handling, monitoring, and disposal depend on the actual equipment and the institution’s authorization. Do not infer a safe dose from the examples in this manual. The NRC’s radiation protection guide explains the principles of time, distance, shielding, and containment.

Source rules

Account for every source. Follow the instructor’s sign-out, storage, and return procedure. Report a missing source immediately.
Handle sources only as trained. Use the holder or tools specified for the approved source, and never touch its active window.
Increase distance and use the specified shielding. Exposure generally decreases with distance; an exact inverse-square calculation is not valid for every source geometry or near-field setup.
Minimize time outside storage. Return a source to its designated shielded container when the measurement is complete.
Never eat, drink, or apply cosmetics in the laboratory. Wash your hands when you leave. A damaged sealed source may present contamination as well as external-exposure hazards.
Treat any $^{137m}$ Ba eluate as unsealed radioactive material. Only use it under the institution’s approved procedure, with the required containment, contamination checks, and waste controls. Its short half-life does not by itself establish that the tray or waste is safe to handle or discard.

If a source is dropped, damaged, or cannot be found, stop work, keep others away, and notify the instructor and radiation safety contact. Do not touch the source or improvise a search or cleanup.

Electrical and thermal¶

The tungsten lamp in Experiment 6 becomes a burn hazard. Its envelope can remain hot after power-off. Let it cool on a heat-resistant mat or tile before handling it, and use the lamp’s rated electrical limits.
High-voltage supplies for GM tubes may operate at hundreds of volts. Do not assume a supply is safe because its nominal output current is low. Power down and follow the instrument’s discharge procedure before changing connections; do not touch exposed conductors.
Do not float an oscilloscope ground. The BNC shield on a conventional mains-powered bench scope is earthed. Connecting a probe’s ground lead to a live point can create a short circuit and shock hazard. For a floating measurement, use an appropriately rated differential probe or isolated input instrument under the instructor’s direction; see Tektronix’s floating-measurement guide.
Microcontroller inputs have specified voltage limits. Verify the board’s ratings and the interface circuit before connecting an external signal. Never feed a GM tube’s raw high-voltage pulse into a GPIO pin.

Chemical¶

Experiment 12 uses ethanol or isopropanol as a solvent for the fluorophore (fluorescein, rhodamine, quinine from tonic water, or a chlorophyll extract). These solvents are flammable: keep them away from the hot lamp and ignition sources. Follow the safety data sheet and local ventilation, glove, storage, and waste procedures for the actual solvent and dye. No food or drink belongs on the bench.

What to do if¶

Situation	Action
Suspected laser eye exposure	Stop, tell the instructor, and follow the site’s procedure for prompt medical evaluation even if no symptom is apparent.
Dropped or damaged radioactive source	Stop, keep others back, notify the instructor and radiation safety contact. Do not pick it up.
Burn from the lamp or a soldering iron	Move away from the heat source. Cool the burn under cool running water for 20 minutes; do not use ice. Report it and seek medical advice as directed by the site. See NHS burn first aid.
Smell of burning from an instrument	Switch off at the bench, unplug, tell the instructor.
Chemical spill	Stop work, keep others away, and tell the instructor. Follow the site’s spill procedure; do not clean up an unknown or radioactive spill yourself.

Before the first experiment, locate the actual first-aid kit, eyewash, fire extinguisher, exits, and emergency contact instructions in your lab.