Isotopes

1. Atoms which all substances made of are very complicated arrangements of still tinier particles called protons, neutrons and electrons. The difference between one substance and another lies in the electric charges carried in the centres of their atoms, for this describes how many protons they have.

2. For example, there are 6 protons in a carbon atom, but 26 in an iron atom. This means that the carbon atom also has 6 electrons to neutralize the positive charge on the 6 protons and the iron atom has 26 electrons, but we can forget about the electrons and think only of the protons in the nucleus.

3. Mixed with the protons are the neutrons which have no electric charge at all. Adding or removing one or more neutrons does not change one element into another. Lighter or heavier atoms of the same element (different varieties of the same element) are called "isotopes".

4. Many common elements which are not radioactive, such as iodine, carbon, phosphorus and sodium, have rare radioactive isotopes. These can be manufactured by "cooking" the common forms inside an atom. The heat does not affect them, but they are bombarded with myriads of protons, neutrons, electrons, gamma rays and other forms of radiation, and their atoms may either lose a few neutrons or collect a few. Different elements behave in different ways, and some lose protons as well as neutrons, and thus change from a non-radioactive isotope of one element into a radioactive isotope of a different element.

5. For example, when cobalt 59 is bombarded with neutrons its atoms seize an extra neutron each and become cobalt 60. Cobalt 60 is strongly radioactive and is used by doctors for treating cancer, instead of radium, which is much more expensive.

6. Radioactive isotopes are used in science and industry for many purposes. Some of them are employed as "tracers". For example, we know that the body needs iron, and that people who are short of it suffer from anemia. Doctors may give them a tonic containing iron, but may not be sure if it is digested or absorbed. So they include some of the radioactive isotope, iron 59, in the tonic. A few days later they can tell if the iron has found its way to the bone, where it is most needed, by means of a Geiger counter, which can detect the radiations it gives off. Naturally, only harmless amounts of radiation can be permitted, but the Geiger counter is very sensitive and can detect the arrival of a single electron.

V. Прочитайте текст и вопросы к нему

1. Which particles are substances made of?

2. How can the difference between one substance and another be explained?

3. What particles don’t have any electric charge?

4. How do different elements behave when they are bombarded with myriads of protons, neutrons, electrons, gamma rays and other forms of radiation?

5. What can radioactive isotopes be used in science and industry for?

6. What have you learned about cobalt 59?

7. What is a Geiger counter?

VI. На основе текста составьте тему"Elements and theirisotopes"

ВАРИАНТ V

I. Перепишите следующие предложения, подчеркните в каждом из них глагол-сказуемое и определите его видовременную форму и залог. Переведите предложения, обращая внимание на пассивные конструкции

1. Some people were experimenting with different unusual materials.

2. Personal computers or simply PCs are a common feature of our life.

3. The rubber solution was used for raincoat production.

4. The simplest explanation of this phenomenon is connected with the earth's magnetic field.

II. Перепишите следующие предложения, подчеркните Participle I и Participle II и укажите, являются ли они определением, обстоятельством или частью глагола-сказуемого. Переведите предложения

1. Chemistry, along with the closely related science of physics, is a fundamental branch of knowledge

2. Chemistry has two main aspects: 1) descriptive chemistry, dealing with the discovery of chemical facts; 2) theoretical chemistry, describing the formulation of theories.

3. Chemistry is concerned not only with the composition of matter, but also with the energy and energy changes associated with matter.

4. The results received were of great importance for further work.

III. Перепишите следующие предложения, подчеркните в каждом из них модальный глагол или его эквиваленты. Переведите предложения

1. You should follow all the important scientific research in your field.

2. The broad field of chemistry may also be divided in other ways. An important division of chemistry is that into the branches of organic chemistry and inorganic chemistry.

3. A chemist can interpret natural phenomena, devise experiments that will reveal the composition and structure of complex substances, study methods for improving natural processes, or, sometimes, synthesize substances unknown in nature.

4. We have to protect the metal surfaces from overheating and damage.

IV. Прочитайте и устно переведите текст

Пояснения к тексту