| a. |
What
do you understand by absorbed dose and dose equivalent? State their respective
units. |
4
marks |
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The absorbed dose D is defined as the
energy imparted to unit mass of human body. |
|
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 |
1 |
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The unit of absorbed dose is gray which
is 1 J kg-1. It is a physical quantity. |
1 |
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The dose equivalent H is the product
of absorbed dose D and the relative biological effectiveness Q. |
|
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H = D Q
...........(2) |
1 |
|
The unit of dose equivalent is Sivert
(Sv). It depends on the ad hoc experimental results. |
1 |
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| b. |
Radon
gas is known to be a major contributor of background radiation. Discuss
the hazard due to radon gas and suggest how the hazard can be minimized. |
3
marks |
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|
|
Radon is a colorless and odorless gas that
emits a-particles: |
|
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 |
1 |
|
It poses a health hazard because, when inhaled,
it can damage the internal organs, like the lung, and causes cancer. |
1 |
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|
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Radon is found in soil and rocks. It can seep
into buildings through the foundations. To minimize the harzard, the room
should be well ventilated, with windows open at all times. |
1 |
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| c. |
Besides
background radiations, state two other contributors of the radiation dose
of people living in Hong Kong Special Administrative Region. |
2
marks |
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Contribution to radiation dose |
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Medical check up using X-rays.
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Nuclear power stations
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Cigarettes
-
TV
|
2 |
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| d. |
What
is meant by sealed source? Explain why sealed sources usually have a very
long half-life. Discuss the potential danger of sealed sources and explain
how they should be handled and stored. |
4
marks |
|
|
|
|
A sealed source is a radioactive source in the form of
a solid sealed into suitable containers. |
1 |
|
In school laboratory, sealed source is commonly used in
demonstrating the properties of radiation. Since they cannot be replaced
easily, sealed sources usually have a very long half-life. |
1 |
|
The potential danger of sealed sources is loss or fall-out
from the container. Once it is attached to the skin of human body or admitted
inside, the radiation, which are emitted continuously, would cause deterioating
effects to health. |
1 |
|
Sealed source are usually housed inside lead boxes, which
are locked inside a rigid cabinet/safe. |
0.5 |
|
The source should be checked periodically (e.g.
half-yearly) to ensure that the radioactive material does not fall out. |
0.5 |
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| e. |
State
three applications of radioactivity in a hospital. |
3
marks |
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Applications |
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Radiotherapy: Killing cancer cells by g-rays
from Co-60
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Medical tracer: Revealing the circulatory system by injecting short
half-life g-source.
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Sterilization: Killing bateria of equipment by g-rays.
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Energy source for pacemaker: Heat from the a-decay
is used to generate electricity by thermopile/set of thermocouples.
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any 3 |
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