2. roentgen also revealed that these x-rays could pass through solid matter and expose in x-ray film. this discovery led immediately to the use of x-rays in medicine, a use we are familiar with. 3. although roentgen discovered the properties of x-rays he did not know what the rays were. he therefore called them x-rays, the x standing for their unknown nature. today scientists know x-rays to be electromagnetic radiation of extremely high frequency and therefore of extremely short wave length. x-rays are considered to be produced whenever rapidly moving electrons bombard any solid material. the greater the atomic weight of the material, the more plentiful the x-rays, the greater the speed of the electrons the higher the frequency of the x-rays. 4. as mentioned above x-rays were in a wide use for diagnostic purposes in medicine since their discovery. industrial radiology has been discovered later particularly for inspecting welds and castings in the automobile and airplane industries. flaws and cracks inside the metal are readily revealed due to the use of x-ray techniques. famous paintings are often x-rayed to determine whether they are the originals or forgeries. 5. using x-rays- irradiation the scientists have learnt to change structures of well-known materials such as metals, ceramics, etc. they could obtain materials, of greater strength with higher melting point and particular electrical properties. 6. radiation is known to be a mutagenic agent. in microbiology mutations are increased by irradiation. when a large-scale production of penicillin was introduced the best strain yielded 100-200 units of penicillin. being irradiated with x-rays, the same strain produced more than 1.000 units. many new uses have been found for this treatment, in agriculture. 5. прочтите 6-й абзац текста и вопрос к нему. из вариантов ответа укажите номер предложения, содержащего правильный ответ на поставленный вопрос. what increase was obtained in the productivity of penicillin being irradiated with x-rays?

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