Page 42 - index

2019 ‫מועד סתיו‬ - 41 - ‫ פרק ראשון‬- ‫אנגלית‬

Text II (Questions 18-22)

(1) Thermoluminescence – the process by which certain substances emit light when
they are heated – was first observed by scientists several hundred years ago. Materials
such as glass, gemstones, rocks, clay, and sand, which contain crystalline minerals,
absorb low doses of radiation when heated or exposed to sunlight. Some of this energy

(5) is trapped inside the substances and released in the form of light if they are reheated.

One of the first scientific references to thermoluminescence was made in 1663,
when Irish physicist and chemist Robert Boyle addressed the Royal Society of London.

Boyle described several experiments, including one in which he had exposed a diamond
to the heat of his own body, causing it to shine with "some kind of glimmering light".
(10) Though his methods may seem crude by today's scientific standards, Boyle is credited

with advancing the understanding of thermoluminescence – until then considered
inexplicable magic.

One practical application of thermoluminescence is the monitoring of how much
radiation medical staff, nuclear power station workers, and scientific researchers are
(15) exposed to in the course of their work. Such workers are issued badges that absorb

radiation – even very small doses – and emit a strong light signal when subjected to heat
testing. Regular testing of these radiation badges is a crucial safety procedure.

Thermoluminescence can also be used to date pottery. When clay objects are
heated in order to harden them – a process known as firing – all the radiation previously
(20) absorbed by the minerals in the clay is released. Firing is thus considered a "zeroing"

event in the history of the object, leaving the clay devoid of radiation. At that point, the
object begins to absorb radiation all over again. By reheating the clay years – or even
centuries – later and measuring the amount of radiation released, scientists can
determine the date of the initial firing. This technique is used to detect forgeries. While
(25) expert forgers might be able to create a clay object that looks exactly the same as the
original, they cannot "fake" the amount of radiation which corresponds to its supposed
age.

Questions

18. The main purpose of the text is to -

(1) explain how thermoluminescence was discovered
(2) discuss a scientific phenomenon and its practical applications
(3) describe the different uses of heat testing
(4) explain the process by which radiation is transformed into light

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