Unit Decay: A Clinically Oriented Perspective on Teaching Exponential Decay

Abstract

The concept of exponential phenomena can be difficult. Exponential processes in nuclear medicine can be simplified by using a new concept, the unit decay constant (UDC). The UDC is the dimensionless percentage expressed as a fraction that is found to be remaining of an initial value. V₀, after a “unit” length of measure, such as time, has elapsed. This change results in a new value, V₁ and the ratio of V₁/V₀ is the UDC. This paper demonstrates the development of this constant and its use in the clinical setting. The UDC provides a different perspective of the exponential process that is easily understood and more intuitive than exponentiation in base “e.” In addition, the UDC allows for rapid calculations of decay and attenuation using only simple multiplication in some cases.