Notes on the Text

1. ushered in a new era — возвестило новую эру

2. To call for — требовать; нуждаться

3. Half-life — период полураспада

4. To dispense with — обходиться без тв xt. Radioactivity

The discovery of natural radioactivity by the French re­searcher Henri Becquerel ushered in a new era in science and technology. This phenomenon is based on the principle that substances occurring in nature, such as uranium and radium, are transformed into other chemical elements, independently of influences from outside, emitting different kinds of radia­tions which blacken a photographic plate as this is done by the rays of light.

In the decades following this discovery thousands of sci­entists in many countries of the world have systematically investigated the essence and the application of radioactivity and of the radiation emitted by radioactive nuclides.

The basic practical and theoretical work done by the Cu­ries, the work by E. Rutherford who achieved an artificial nuclear transformation, the development of apparatus for the detection of radioactive nuclides by Geiger and Muller, the discovery of neutron by the English physicist J. Chad­wick, the discovery of the artificial radioactivity by the Cu­ries and; the discoveries of some other scientists are the mile­stones in the history of radioactivity.

The field of application of radioactive nuclides in chem­istry, physics, biology, agriculture, medicine and industry has rapidly expanded.

One of the most interesting fields of applications of radio­activity is the determination of the age of carbonaceous ma­terials, that is materials containing carbon, by measurement of their radioactivity due to carbon 14.

This technique of radiocarbon dating permits the dating of samples containing carbon with an accuracy of around 200 years.

At the present time the method involved can be applied to materials that are about 25,000 years old.

Today the range of application of radioactive nuclides comprises all branches of research work. Thus, for example, certain medical examinations call for short lived radioactive nuclides in oirder that the human organism should not be ex­posed too long a period of time to radiation, whereas a radio­active nuclide which excites the luminescent material should have a long half-life.

Investigations into the reaction mechanisms in chemistry, researches in the field of physics, the explanation of vital processes in plants, animals and man, diagnostics of diseases of the human body, the testing of metallic and ceramic ma­terials are but a few fields of science and technology which today, 91 years after the discovery of radioactivity, cannot dispense with radioactive nuclides and the radiation emitted by them.

It should be added that a considerable number of research problems has only become soluble by the use of radioactive nuclides.

natural

to occur

independently

influence

outside

to emit

plate

ray

essence

detection milestone to expand carbon accuracy to comprise for example certain

to expose wr to call for , whereas '■ -

to excite half-life explanation vital to test a few

considerable

Remember the following words and word combinations;

Ex. 14. Answer the following questions:

1. Who discovered the phenomenon of radioactivity? 2. What is the phenomenon of radioactivity based on? 3. What are the milestones in the history of radioactivity? 4. Where can radioactivity be applied? 5. What is the most interesting

field of applications of radioactivity? 6. Where are radioac- tive nuclides applied now?

Ex. 15. Open the brackets choosing the correct forms of the Participles. Translate the sentences into Russian:

1. Much could be (writing, written) about the application of nuclides. 2. Many experiments have been (carrying out, carried out) in the field of radioactivity. 3. The work (doing, done) by the scientists was of great significance. 4. Many of the above-mentioned applications of radioactive nuclides or of the radiation (emitting, emitted) by them are directly or indirectly connected with industry. 5. A mechanical meth­od was (substituting, substituted) by a new one. 6. This type of radiation consists of a current of positively (charged, charging) particles. 7. This discovery (following, followed) by many experiments was of great use to chemists. 8. The two substances (investigating, investigated) were homogeneous.

9. The man (speaking, spoken of) was the first to discover this phenomenon.

Ex. 16. Find the pairs of antonyms and remember them:

long-lived, artificial, dependent, slow, natural, indepen­dent, outside, discovered, inside, undiscovered, short-lived, rapid.

Ex. 17. Translate the following words of the same root:

1. to consider, consideration, considerable, considerably;

2. to produce, production, productivity, product; 3. to de­pend, dependence, dependent, dependently, independent; 4. to use, use, useful, useless, usefulness; 5. to increase, in­crease, increasingly; 6. to measure, measurement, measurable;

6. to add, addition, additional; 8. to discover, discovery, discovered.

Ex. 18. Read the text fluently and answer the questions that follow:

Half-Life

The discovery of radioactivity raised a number of ques­tions. In the beginning research-workers tried in vain to influ­ence the phenomena of radioactivity by pressure and increased or reduced temperatures. They understood that the forces involved could not be controlled by the means available at the time.

Further they have found that certain elements were trans­formed into other elements completely uninfluenced by meas­ures taken.

The first clue that could lead to the formulation of some laws was the half-life which is defined as the time required for disintegration of one half of the atoms of a sample of an ra­dioactive element,