26.7 Radioactive isotopes in use

How are Carbon-14 atoms formed in the atmosphere?

cosmic rays knock out neutrons from nuclei

neutrons collide with nitrogen to form C-14 nuclei

How can you measure the age of a tree by the amount of C-14?

living organisms take up C-14 by photosynthesis

once the they die, the amount of C-14 remains the same and decays 

Measuring activity and comparing to activity of a living organism can help find age 

How can you use argon to find the age of rocks?

Rocks trap potassium which decays into argon

How does potassium decay into argon

electron capture

How does potassium decay into calcium?

beta-minus decay

How many times more probable is beta minus emission than electron capture? 

8 

For every 1 argon nucleus,

8 calcium nuclei

What is a radioactive tracer used for?

following the path of a substance through a system

What are some properties of radioactive tracers? 

1. half-life stable enough for measurements and short enough to decay after use 

2. emit beta or gamma so that it can be detected outside object

How can the rate of wear of a piston be measured in an engine? 

fitting a ring that is radioactive 

by measuring the radioactivity of the oil, mass of radioactive metal transferred from ring can be determined and rate of wear can be calculated 

How are underground pipe leaks detected using a radioactive tracer?

radiative tracer is injected into flow

detector outside used to detect leakage 

What kind of tracer is used for detecting underground pipe leaks?

fluid containing beta/gamma emitter

What is the choice of a radioactive isotope affected by? 

1. Half life and type of radiation

2. Toxicity and biochemical suitability 

3. need for a stable product 

How is thickness of foil monitored with radioactive tracers?

A detector is used to measure how much radiation passes through the foil

What if the foil is too thick?

reading falls

signal from detector makes rollers move closer

What is foil is too thin? 

reading increases

signal from detector makes rollers further apart 

What kind of radiation is used for thickness monitoring?

beta minus with long half-life

Why is beta radiation used for thickness monitoring?

alpha would be absorbed

gamma would pass through

How can radioactive isotopes generate electricity for remote devices? 

Each time a nucleus decays, it releases energy 

thermally insulated sealed container heats up as it absorbs radiation

thermocouple attached to container generates electricity 

Equation for power generated by radioactive isotope

P= Activity x Energy per decay