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Fig. 4.3

After recording the number of counts in consec­utive 10-second intervals over a period of a few minutes, you can then draw a graph, and use it to find the half-life of protactinium-234.

8 _____________

A radio-isotope that decays rapidly has a short half-life t ½. Its decay constant must be high, since the probability per unit time of an individual nucleus decaying must be high. Hence there is a connection between half-life and decay constant. They are inversely related by the expression

(The constant 0.693 comes in to this because , approximately.)

Thus if we know either t ½ or λ, we can calcu­late the other. For a nuclide with a very long half-life, we might not wish to sit around waiting to measure the half-life: it is easier to determine λ by measuring the activity (and using A= λ N), and then deduce t ½.

Note that the units of λ and t ½ must be compatible; for example, λ in s‾¹ and t ½ in s.

2.2. Work in pairs. Using information from the text say a few words about:

1.Geiger counter

2.Time constant

3.Decay constant

4.Exponen­tial decay

5.Half-life of a radio-isotope

2.3. Match the notions and their definitions:


1.ion a) the microwave radiation pervading the universe that exhibits a corresponding blackbody temperature of 2.7 K and that is the principal evidence supporting the big bang theory

2.ratemeter b) a form of a chemical element which sends out radiation

3.fluctuations c) a line defined by an equation so that the coordinates of its points are functions of a single independent variable or parameter

4.radio-isotope d) an instrument that indicates the counting rate of an electronic counter

5.detector e) a decrease that follows an exponential function

6.constant f) a number or quantity that does not vary

7.background radiation g) an atom or a molecule with a positive or negative electric charge caused by its losing or gaining one or more electrons

8.exponential decay h) a piece of equipment for discovering the presence of smth, such as metal, smoke, explosives or changes in pressure or temperature

9.curve i) frequent changes in size, amount, quality, etc., especially from one extreme to another

random spontaneous   environmental detecting   nuclear top count   approximate consecutive  
2.4. Match the words and verbs with prepositions to form expressions. Make your own sentences using the expressions.



rate force layer   process pattern   factor value   interval system


out out against   with in on   at from by

to average to smooth to go   to deduce sth   to interact to measure   to depend to go to stare


3.1. Before reading the text below answer the following question:

Why does the nucleus emit an entire α particle or Helium 4 nucleus, instead of simply kicking out a single proton?

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