NMD-25

I-131 decay

A = A0 (1/2)^{t/8.02 d}. β/γ therapy and uptake nuclide.

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RadionuclidesI-131

Governing equation

A=A_0\,(1/2)^{t/8.02\,\mathrm{d}}

$t \in \left[0, 40\right]$

where

A_0: Administered activity (MBq)
t: Time (d)
A: Remaining I-131 (MBq)

The figure, part by part

Each numbered marker wears the color of its card. Hover a card to light the marker. Tap a marker to jump to that card. The slider walks a red point along the curve; Animate drawing traces it like a pen.

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①

Governing law — red

A=A_0\,(1/2)^{t/8.02\,\mathrm{d}}

$t \in \left[0, 40\right]$

$t = 0$ $A = 3700$

Along the curve

②

Domain of the variable — blue

t_{\min} = 0,\quad t_{\max} = 40

$t \in \left[0, 40\right]$

$t = 0$ $t = 0$

Along the curve

③

Response curve — green

A=A_0\,(1/2)^{t/8.02\,\mathrm{d}}

$t \in \left[0, 40\right]$

$t = 0$ $A = 3700$

Along the curve

④

Rate of change — amber

\frac{\mathrm{d}A}{\mathrm{d}t}

$t \in \left[0, 40\right]$

$t = 0.252$ $A^{\prime} = -312.9$

Along the curve

Lecture brief

Historical brief

MIRD schema, in-vivo decay, uptake fractions and PET coincidence turned unsealed sources into organ dose. The sheets compute activity, residence and well-counter geometry. This sheet (NMD-25 — I-131 decay) is the form associated with I-131. Working symbols: $A_0$ , $t$ $\rightarrow$ $A$ . T½ 8.02 d, β Emax 606 keV, γ 364 keV (81 %). Isolation rules follow this decay and the volatile iodine.

Purpose

Purpose: compute

A

from

A_0

t

in Nuclear medicine via

A=A_0\,(1/2)^{t/8.02\,\mathrm{d}}

A = A0 (1/2)^{t/8.02 d}. β/γ therapy and uptake nuclide. Use it when a real nuclear medicine question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

A_0 = 3700.000\,\mathrm{MBq}

t = 4.000\,\mathrm{d}

, the governing relation

A=A_0\,(1/2)^{t/8.02\,\mathrm{d}}

yields

A = 2618.6\,\mathrm{MBq}

. A therapy capsule decaying over days. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Administered activity A_03700 MBqTime t4 d

Outputs

Remaining I-131 A2618.6 MBq

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Narration of this film

A therapy capsule decaying over days.

T½ 8.02 d, β Emax 606 keV, γ 364 keV (81 %). Isolation rules follow this decay and the volatile iodine.

Reading speed

Watch on YouTube