Radioactive Decay

09202019, 01:57 PM
Post: #1




Radioactive Decay
The Journal of Nuclear Medicine {vol 19, num 11} pgs. 12701271
Calculation of Radioactive Decay with a Pocket Calculator JAMES S. ROBERTSON Mayo Clinic Rochester, Minnesota "Radioactive decay is customarily expressed by the equation (1) A = A₀ e^(λt) where t = time; λ = decay constant in t⁻¹ units; A = activity, usually μCi or mCi; A₀ activity at t = 0; and e = 2.718 …, the natural logarithm base. However, the decay parameter most readily available is not λ, but the halflife, T. Therefore, the relationship λT = ln(2) = 0.693 … is invoked and the decay equation becomes (2) A = A₀ e^(0.693t/T) From this it would appear that the way to calculate A, given A₀, t and T, is first to determine x = 0.693 t/T and then to obtain A/A₀ from e^(x). However, a simplifying feature that is overlooked in this procedure is that e^(0.693) = …½, and the decay equation may therefore be expressed as (3) A = A₀ ½^(t/T) Thus, if a pocket calculator having a y^x function is used, A/A₀ may be calculated simply by entering 0.5 as y, calculating t/T as x, and calling y^x. This saves several steps when compared with using Eq. 2. For negative values of t, the same procedure works, but alternatively the number 2 may be entered as y and the absolute value of t used. These procedures are similar to the sliderule method of setting T against 0.5 or 2.0 on a loglog scale and reading A/A₀ against t, a method now in danger of being forgotten with the proliferation of inexpensive pocket calculators." 'Ahh, memories' BEST! SlideRule 

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Radioactive Decay  SlideRule  09202019 01:57 PM
RE: Radioactive Decay  Albert Chan  09202019, 02:40 PM

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