1. 30.1 X-rays and radioactivity
Nature of X-rays
X-rays are a kind of electromagnetic wave of high frequency (i.e. short wavelength).
radio wave
micro- wave
infrared radiation
visible light
ultraviolet radiation
X-ray
gamma ray
increasing frequency
Electromagnetic spectrum

2. X-rays can be produced by rapid deceleration of high-speed charged particles, for example, hitting a heavy metal target with high-speed electrons.
X-ray tube

3. Low-frequency X-rays can pass through flesh but not through bones.
Depending on the frequency of the X-rays as well as the medium through which they transmit, they lose energy to different extent in transmission.
flesh
bone
low-frequency X-rays
Low-frequency X-rays can pass through flesh but not through bones.
X-rays are also a kind of ionizing radiation.
Ionization is the process in which one or more electrons are removed from an atom, which then becomes an ion.

4. Applications of X-rays
Medical use
Radiographic imaging
Computed tomography (CT) scan
An X-ray image of lungs
A CT scan image of a patient’s head

5. X-ray inspection in airports
Security use
X-ray inspection in airports
An X-ray image of luggage
An X-ray image of a passenger in an airport
Industrial use
Detecting defective products at the point of production

6. 30.3 Radiation safety Radiation dose
The amount of radiation absorbed by a unit mass of a material is the dose. Its unit is the gray (Gy) or J kg−1.
Equivalent dose describes the biological effect on a tissue or organ due to different types of radiation.
Effective dose is the weighted equivalent dose that describes the biological effect on the whole human body.
The unit of equivalent dose and effective dose is the sievert (Sv) or millisievert (mSv).

7. typical effective dose
Potential hazards
artificial source
natural source
typical effective dose
source
cosmic ray (depending on altitude)
0.25–0.35 mSv per year
food and water
0.4 mSv per year
radon in average household
2 mSv per year
X-ray diagnosis
0.4 mSv each time
1000 mile flight trip
0.01 mSv each time
cigarette smoking (1 pack per day)
15–20 mSv per year
Effective doses from various sources
Example 30.5

9. Safety precautions In radiation fields
Workers have to follow the ‘ALARA (As Low As Reasonable Achievable) principle’, which means to reduce exposure to radiation to the lowest possible level.
Workers wearing protective clothing
Handling highly radioactive materials with robot arms

10. In school laboratories
Sources should be handled with special forceps. Never use your hands to touch the radioactive source directly.
Sources should be kept away from the body, especially the eyes, and should not be pointed to anybody.
Sources should be stored in a suitable lead container and kept locked when not in use.

11. Warning signs should be labelled on both the containers and the storage room.
Wash your hands thoroughly after conducting experiments.
Report to the Radiation Board of the Department of Health immediately if the source is lost or is damaged.

12. In medicine
During a radioactive medical treatment, both the patient and the radiotherapist should be protected from over exposure to radiation.
The diagnosis room for radiotherapy is a controlled area.
The radiotherapist works behind a lead shield when the patient is undergoing treatment.