Page 311 Answers
1. Radioactive decay and artificial radioactivity both involve changes in the
structures (or energy levels) of atomic nuclei and emission of radiation
(in the form of alpha particles, beta particles, and gamma rays).
Radioactive decay occurs spontaneously, because the atomic nuclei
involved are unstable. Artificial radioactivity involves the production of a
radioactive isotope by bombarding a stable nucleus with subatomic
particles.
4. A neutron can penetrate a nucleus easier than an alpha particle
because: (1) a neutron is smaller than an alpha particle; and (2) a
neutron is uncharged, but an alpha particle is positively charged and
therefore repelled by the positive charge on the nucleus.
5. Because of their much higher mass, alpha particles can damage DNA
molecules more readily than beta particles or gamma rays. Alpha
particles are particularly dangerous if ingested or inhaled, but they are
less dangerous when outside the human body, because they are
stopped by the skin.
6. If the source of alpha radiation is outside the human body, internal
organs are unlikely to be affected by it because alpha particles are
stopped by the skin. The skin, however, is one organ that could be
easily affected by the radiation.
7. Natural background radiation is produced by different sources in nature
and is ordinarily present in our environment and in our bodies. Sources
of this radiation include:
(1) cosmic radiation from the Sun and other sources in space;
(2) rocks and soil;
(3) water;
(4) food; and
(5) air.
8. Absorbed dose of radiation is measured in grays (1 gray _ 1 joule per
kilogram) and represents the amount of energy (in joules) absorbed by
one kilogram of tissue. However, for a given absorbed dose, different
types of radiation can damage living tissue to different extents.
Therefore, to compare different types of radiation based on the amount
of damage they cause, scientists express dosage in terms of equivalent
dose, measured in sieverts (Sv).
9. I would receive one-fourth the radiation.
10. For equal amounts of radiation, it is better to be exposed to lowintensity radiation over a long time than to be exposed to high-intensity
radiation over a short time. In the former case, the body will have a
chance to repair damaged cells, but in the latter case, the damage may
be too great for the body to repair.
11. For protection from nuclear radiation, good shields are made of lead or
concrete. The thickness needed depends on the type of radiation.
Gamma radiation, which is the most penetrating type of radiation, is
stopped by a shield of lead that is a few centimetres thick. Because
concrete is less dense, a concrete shield would need to be thicker than
the lead shield.
12. A dose of 100 mSv is about 33 times as high as the average yearly
dose from natural sources.
13. In the equation E _ mc2, E is the energy (in joules), m is the mass (in
kilograms), and c is the speed of light in a vacuum (in metres per
second).
14. If 10 kg of a substance were entirely converted into energy, it would
produce 9.0 _ 1017 J of energy.
15. (a) Mosquito’s mass = 2 mg = 2 x 10-6 kg.
Equivalent energy =(2 x 10-6)(3.0 _ 108)2 J = 18 x 1010 J.
(b) The energy in a mosquito of mass 2 mg is 5 200 times the energy
produced by burning 1 litre of gasoline!!!!