Many people encounter older or unusual glass items and wonder if they might contain radioactive materials, especially if they exhibit an unusual glow. This article explores practical methods for identifying and assessing such items, along with general safety information.
Radioactive Elements in Glass
Glass can become radioactive when specific elements are intentionally added during its manufacturing process. The most well-known example is uranium, which glassmakers used to impart vibrant yellow or green hues. This type of glass is commonly referred to as uranium glass or, specifically for its translucent yellowish-green variety, Vaseline glass. The addition of uranium oxide, typically ranging from trace amounts to about 2% by weight, created a distinctive color and a fluorescent effect. Some 20th-century pieces, however, contained up to 25% uranium.
Uranium glass was popular for tableware and decorative items, especially from the 1830s through the 1930s. Its widespread production ceased significantly during World War II when uranium supplies were diverted for military purposes, although some production resumed later with depleted uranium. Beyond uranium, other elements like thorium were also incorporated into glass, primarily for specialized optical applications. Thorium dioxide was used in camera lenses from the 1940s to the 1970s to achieve high refractive indices and low dispersion, improving optical performance.
Visual Clues and UV Light Detection
One of the primary visual indicators for identifying uranium glass is its characteristic bright green fluorescence when exposed to ultraviolet (UV) light. This phenomenon occurs because the uranium atoms absorb UV radiation and then re-emit it as visible light, creating a distinct glow. To observe this, a longwave UV flashlight (often referred to as a black light) is typically effective. Under normal light, uranium glass might appear as a pale yellow, yellowish-green, or even other colors depending on additional colorants.
Under UV light, the glass transforms, emitting an intense, almost neon green glow. While this strong green fluorescence is a primary indicator of uranium content, it is not an absolute confirmation of radioactivity. Some non-radioactive glasses can also fluoresce, though typically with different colors or intensities. Conversely, not all radioactive glass, such as certain types of thorium glass, will exhibit this property.
Measuring Radiation with a Geiger Counter
To definitively confirm the presence of radiation and measure its level, a Geiger counter is the most reliable tool. This instrument detects ionizing radiation, such as alpha, beta, and gamma particles, by producing audible clicks or displaying numerical readings. When radiation passes through the counter’s detection tube, it ionizes the gas inside, creating a brief electrical pulse that the instrument registers. This allows for a quantitative measurement of radiation, typically expressed in counts per minute (CPM) or microsieverts per hour (µSv/hr).
To use a Geiger counter for testing glass, first establish the background radiation level in the testing area by taking a reading without the object present. This represents the natural radiation always present in the environment. Then, place the Geiger counter’s sensor close to the glass item. A significant increase in the reading above background indicates the presence of radioactive material within the glass. While uranium glass typically shows elevated readings, the exact level can vary based on the uranium concentration.
Safe Handling and Storage
For most collector’s pieces of uranium glass, radiation levels are generally very low and pose minimal risk with proper handling. The U.S. Nuclear Regulatory Commission reported in 2001 that uranium glass is considered safer than common household electronics. However, avoid activities that could release radioactive particles, such as grinding or breaking the glass, as ingesting or inhaling these particles could be harmful.
It is also advisable to avoid using uranium glass items for food or drink, as prolonged contact could lead to minute transfer of radioactive material. For display, keeping items in enclosed display cases can further reduce exposure. Storing them away from frequently occupied areas, especially bedrooms, is a sensible precaution. If an item shows unusually high radiation readings or if there are concerns about its safety, consult local authorities or a radiation safety expert for advice on handling or disposal.