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Nanogray [nGy]: Measuring Extremely Low Radiation Doses

The nanogray (nGy) is a unit of absorbed radiation dose equal to 10⁻⁹ grays (Gy). Since the gray (Gy) is the SI unit that measures the amount of ionizing radiation absorbed by a substance (typically per kilogram), one nanogray represents one-billionth of a gray. This tiny unit is used in situations where radiation doses are extremely low, such as background environmental radiation, space research, or ultra-sensitive radiation detection studies. For example, scientists may use nanograys to measure the small amounts of cosmic radiation received by satellites or astronauts over long periods, or to study natural background radiation in very low-radiation areas. Although it is too small to be relevant for most medical or industrial applications—where doses are typically measured in milligrays (mGy) or grays (Gy)—the nanogray is valuable in research that focuses on long-term, low-level exposure and its possible biological effects. It allows for precise tracking and modeling of minimal energy deposits in matter. The use of the nanogray highlights the importance of accurate measurement at even the smallest scales when studying radiation’s impact on the environment, health, or sensitive equipment.

Gray [Gy]: The Standard Unit of Absorbed Radiation Dose

The gray (Gy) is the International System of Units (SI) measurement for absorbed radiation dose, defined as the absorption of one joule of ionizing radiation energy per kilogram of matter. It quantifies how much energy from radiation is deposited in a given mass, typically biological tissue or materials. The gray is widely used in medicine, radiation protection, and scientific research.

In clinical settings, the gray is essential for measuring and controlling doses in radiation therapy for cancer, where precise amounts of radiation are delivered to destroy tumor cells while minimizing damage to healthy tissue. For example, a typical therapeutic dose might be in the range of 1–2 Gy per treatment session.

Beyond medicine, the gray is also used in radiation safety to assess exposure levels, in nuclear industry applications, and in research involving radiation effects on materials.

The gray replaced the older unit “rad” (where 1 Gy = 100 rad) and provides a universal, standardized way to quantify radiation energy absorption, allowing for consistency across disciplines and countries. It is fundamental to understanding radiation interactions and their biological or physical consequences.