Definition

1. Noun:
   • A unit of plane angle: In geometry, a rad (short for radian) is the standard unit of angular measure in the International System of Units (SI). It is defined as the angle subtended at the center of a circle by an arc whose length is equal to the circle's radius.
   • A unit of absorbed dose of ionizing radiation: In physics, a rad is a unit measuring the amount of energy deposited by ionizing radiation in a given mass of material. One rad is equal to 100 ergs of energy absorbed per gram of irradiated matter.

Usage Examples

• Noun (Angle):
  • A full circle contains 2π rad.
  • Convert the angle from degrees to rad for the calculation.
• Noun (Radiation):
  • The patient received a dose of 50 rad during the treatment.
  • The safety limit for occupational exposure is measured in rad per year.

Advanced Usage

• The term is a standardized abbreviation. In scientific writing, especially for the angular unit, the full term radian is often preferred for clarity.
• In the SI system, the radian () is a dimensionless derived unit, as it is defined as a ratio of two lengths (arc length / radius).

Variants and Related Words

• Radian (n): The full, formal name for the angular unit .
• Millirad (mrad) (n): A unit equal to one thousandth of a rad, used for smaller angles or radiation doses.
• Gray (Gy) (n): The SI unit for absorbed radiation dose, where 1 Gy = 100 rad. The gray has largely replaced the rad in modern scientific contexts.

Synonyms

• (For angle): There is no direct synonym, as it is a specific unit. It can be described as "the SI unit of plane angle."
• (For radiation): There is no direct synonym, as it is a specific unit. It can be described as "a unit of absorbed radiation dose."

Related Phrases

• Rad per second (rad/s): A unit of angular velocity (rotational speed).
• Absorbed dose: The measured quantity for which the is a unit.

Noun

1. the unit of plane angle adopted under the Systeme International d'Unites; equal to the angle at the center of a circle subtended by an arc equal in length to the radius (approximately 57.295 degrees)
2. a unit of absorbed ionizing radiation equal to 100 ergs per gram of irradiated material