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Half life graphs

A half life graph plots the activity of a radioactive source against time, and the graph builder draws it for twelve real isotopes from technetium 99m to uranium 238. Switch on the half life line and a dashed construction drops from half the starting activity to the time axis, so the class reads the half life off the graph the way the exam expects.

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MBMrs Bennet
Science graph builder
Decay: Iodine-131 (Medical Tracer) New graph
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5101520253035404550501001502002503003504004500Activity (Bq)Time (days)

A hand-built replica of the real builder page, not a screenshot. Every control shown exists in the product.

Part of the Graph builder, Velocity time graphs, IV characteristic graphs, Infrared radiation graphs and Distance time graphs pages.

Why this works in Physics

The graph above is iodine 131, a medical tracer with a starting activity of 400 Bq. The dashed lines run across from 200 Bq and down to 8 days, and a second reading from 100 Bq lands at 16 days, which is the check that tells pupils the half life is constant. The lines are drawn in the colour you choose, or hidden so the class has to construct them.

The usual slip is reading the time for the activity to reach zero, or halving the time axis instead of the activity axis. A curve that never reaches the axis makes the first mistake visible, and picking a different isotope from the list changes the units from hours to days to years while the shape stays the same, which is the point the specification wants made.

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