(a) (i) Explain why x-rays can be used to produce photographs of fractures in bones.
(ii) List four uses of x-rays other than in medicine.
(b) State the energy transformations which takes place during the operation of an x-ray tube.
(c) (i) Explain three named dangers to which human beings may be exposed when subjected to large doses of x-rays.
(ii) State two precautions that must be taken by persons working with x-rays.
(d) In an x-ray tube, an electron is accelerated from rest towards a tungsten target biased at a potential of 33 kV. Calculate, for the electron, the
(i) kinetic energy;
(ii) velocity. [h = 6.6 x 10\(^{-14}\) Js; Me = 9.1 x10\(^{-31}\) kg; c = 3.0 x 10\(^4\) ms\(^{-1}\); e = 1.6 x 10\(^{-19}\) C.]
(a)(i) Why X-rays can photograph bone fractures
X-rays are highly penetrating. They pass easily through soft tissue (flesh) but are strongly absorbed by the denser bone. When X-rays are directed through a limb onto a photographic film or detector, the bones cast dark shadows while the flesh lets the rays through. A break or crack in a bone shows up as a discontinuity (a line or gap) in the bone shadow, so fractures can be seen.
(a)(ii) Four uses of X-rays other than in medicine
- Detecting flaws, cracks and cavities in metal castings and welds (industrial radiography).
- Studying the arrangement of atoms in crystals (X-ray crystallography/diffraction).
- Screening luggage and cargo for hidden or dangerous objects at airports and borders.
- Checking the authenticity of paintings and examining the internal structure of sealed goods.
(b) Energy transformations in an X-ray tube
Electrical energy is converted into the kinetic energy of the fast-moving electrons; when these electrons strike the target, their kinetic energy is converted mainly into heat (about 99%) and a small part into X-ray (electromagnetic) energy.
(c)(i) Three dangers of large doses of X-rays
- They destroy or damage living body cells and tissues, causing radiation burns.
- They can cause cancer, for example leukaemia.
- They can damage reproductive cells, causing genetic mutations or sterility (and can damage the eyes).
(c)(ii) Two precautions
- Shield the body with lead aprons and work behind lead-lined walls/screens.
- Limit the exposure time and dose, and wear a film badge (dosimeter) to monitor the radiation received.
(d)(i) Kinetic energy of the electron
\[ KE = eV = (1.6 \times 10^{-19}) \times (33 \times 10^{3}) = 5.28 \times 10^{-15}\,\text{J} \]
(d)(ii) Velocity of the electron
Using \( \tfrac{1}{2}m v^2 = KE \):
\[ v = \sqrt{\frac{2\,KE}{m}} = \sqrt{\frac{2 \times 5.28 \times 10^{-15}}{9.1 \times 10^{-31}}} \]
\[ v = \sqrt{1.16 \times 10^{16}} \approx 1.08 \times 10^{8}\,\text{m s}^{-1} \]
The electron reaches about \( 1.08 \times 10^{8}\,\text{m s}^{-1} \).
(a)(i) Why X-rays can photograph bone fractures
X-rays are highly penetrating. They pass easily through soft tissue (flesh) but are strongly absorbed by the denser bone. When X-rays are directed through a limb onto a photographic film or detector, the bones cast dark shadows while the flesh lets the rays through. A break or crack in a bone shows up as a discontinuity (a line or gap) in the bone shadow, so fractures can be seen.
(a)(ii) Four uses of X-rays other than in medicine
- Detecting flaws, cracks and cavities in metal castings and welds (industrial radiography).
- Studying the arrangement of atoms in crystals (X-ray crystallography/diffraction).
- Screening luggage and cargo for hidden or dangerous objects at airports and borders.
- Checking the authenticity of paintings and examining the internal structure of sealed goods.
(b) Energy transformations in an X-ray tube
Electrical energy is converted into the kinetic energy of the fast-moving electrons; when these electrons strike the target, their kinetic energy is converted mainly into heat (about 99%) and a small part into X-ray (electromagnetic) energy.
(c)(i) Three dangers of large doses of X-rays
- They destroy or damage living body cells and tissues, causing radiation burns.
- They can cause cancer, for example leukaemia.
- They can damage reproductive cells, causing genetic mutations or sterility (and can damage the eyes).
(c)(ii) Two precautions
- Shield the body with lead aprons and work behind lead-lined walls/screens.
- Limit the exposure time and dose, and wear a film badge (dosimeter) to monitor the radiation received.
(d)(i) Kinetic energy of the electron
\[ KE = eV = (1.6 \times 10^{-19}) \times (33 \times 10^{3}) = 5.28 \times 10^{-15}\,\text{J} \]
(d)(ii) Velocity of the electron
Using \( \tfrac{1}{2}m v^2 = KE \):
\[ v = \sqrt{\frac{2\,KE}{m}} = \sqrt{\frac{2 \times 5.28 \times 10^{-15}}{9.1 \times 10^{-31}}} \]
\[ v = \sqrt{1.16 \times 10^{16}} \approx 1.08 \times 10^{8}\,\text{m s}^{-1} \]
The electron reaches about \( 1.08 \times 10^{8}\,\text{m s}^{-1} \).
