Q.1: Explain how you would test whether the radiation from a radioactive source is α, β or Gamma radiation?
Ans: When radiations are allowed to pass through a magnetic field, the α and β particles are deflected while γ-rays pass through undeflected. This technique helps to identify the radiation.
Q.2: A particle which produces more ionization is less penetrating. Why?
Ans: When a particle ionizes an atom, it loses a part of its energy. Since the greater the ionizing power, the greater is the loss of energy; and hence, the smaller is its penetrating power.
Q.3: It is said that α or β particles carry an atom without colliding with its electrons. How can each do so?
Ans: An α-particle is positively charged and a β particle is negatively charged. So an α particle ionizes an atom by attraction while a β particle ionizes an atom by repulsion.
Q.4: In how many ways can Gamma rays produce ionization of the atom?
Ans: Gamma rays only ionize an atom by collision. Being a high-energy photon, it can produce ionization in three ways:
i. it may lose all its energy in a single collision with the electron of an atom (photoelectric effect);
ii. it may lose only a part of its energy in a collision (Compton effect);
iii. it may be stopped by a heavy nucleus giving rise to electron-position pair (materialization of energy).
Q.5: In what way does a neutron produce ionization of an atom?
Ans: A neutron collides with a substance containing a large number of hydrogen atoms and knocks out a proton. In this way, it causes ionization.
Q.6: Name different electromagnetic radiations that are capable of producing ionization of atoms. By what process do they ionize?
Ans:
i. Ultraviolet rays
ii. X-rays
iii. Gamma rays
The rays interact with matter inelastically. They remove electrons from the atoms of the target material.
Q.7: Why is lead a better shield against α, β, and gamma radiations than an equal thickness of a water column?
Ans: α and β particles do not travel far enough in water due to intense ionization they produce. Reduction of gamma rays' beam intensity is a measure of its range, which is considerably more. However, materials having large numbers of electrons per unit volume are more effective absorbers of gamma radiations. When gamma rays are incident on lead, then, because of the photoelectric effect, they lose their energy in a single encounter and travel only a small distance. But as water has fewer electrons than lead, so gamma rays lose less energy and penetrate through a larger distance in water. Hence, lead is a better shield against gamma rays than water.
Q.8: Lead is heavier and denser than water. Yet water is more effective as a shield against neutrons?
Ans: To be stopped or slowed down, a neutron must undergo a direct collision (elastic) with a nucleus or some other particle that has a mass comparable to that of the neutron. Water contains hydrogen. Thus nuclear protons of hydrogen atoms, after collision, move; while the neutron is slowed down. But when neutrons collide with the nucleus of lead, it bounces neutrons back almost with the same speed. Hence, water is a better shield against neutrons than lead.
Q.9: In an X-ray photograph, bones show up very clearly, but the fleshy part shows very faintly. Why?
Ans: X-rays can be stopped by bones, but they can penetrate flesh.
Q.10: In a cloud chamber photograph, the path of an α particle is a thick and continuous line, whereas that of a β particle is a thin and broken line. Why?
Ans: An α-particle is highly ionizing than a β-particle.
Q.11: Why do gamma rays not give line tracks in the cloud chamber photograph?
Ans: Gamma rays do not produce ionization directly. They interact with atoms to eject electrons. These electrons, like β particles, produce irregular cloud tracks of their own, which branch out from the direction of gamma rays.
Q.12: A neutron can produce little ionization. Is there any sure chance of getting a cloud chamber track for it to count in the Geiger counter?
Ans: Neutrons are unable to ionize a gas. However, ionization is only produced when a neutron strikes directly a nucleus or a hydrogenous material, e.g., body tissues. The knocked-out proton produces ionization in the Geiger counter.
Q.13: A cloud chamber track of an α particle sometimes shows an abrupt bend accompanied by a small branched track. What could possibly be the cause of this forked track?
Ans: When an α-particle strikes a nucleus, the recoiling nucleus leaves a track. This is the cause of a forked track.
Q.14: Why is the recommended maximum dose for radiation a bit higher for women beyond the childbearing age than for young women?
Ans: It has been found that ovary and grown follicular cells are most sensitive cells for radiation. But primordial follicles and oocytes are more radiation repellent, and they grow even after irradiation. Also, the fertility of ovary is much affected when the whole body is irradiated by a specific dose of radiation (e.g., 200 RAD) than when ovary alone is irradiated by the same dose.
Q.15: It is possible for a man to burn his hand with x- or γ-rays so seriously that he must have it amputated and yet may suffer no other consequence. However, a whole-body x- or γ-ray overexposure so slight as to cause no detectable damage might cause birth deformity in one of its subsequent children. Explain. Why?
Ans: The damage to body cells, caused by very high doses of radiation, can be as serious as to stop them from working and multiplying. Widespread damage of cells may kill people. Delayed effects, such as cancer, leukemia, deformity, and mental retardation in children and grandchildren, may take place due to genetic syndromes.
Q.16: Which of α, β, and γ rays would you advise for the treatment of (i) skin cancer (ii) the cancer of flesh just under the skin (iii) a cancerous tumor deep inside the body?
Ans:
i. For the treatment of skin cancer, we use α-particles, as their penetration is small.
ii. For the treatment of cancer of flesh just under the skin, β-particles should be used because of their medium penetration power.
iii. For the treatment of deep infection in the body, γ rays should be used, as they are highly penetrating.
Q.17: Two radioisotopes of an element are available: one of long half-life and the other of short half-life. Which isotope is advisable for the treatment of a patient and why?
Ans: For the treatment, radioisotopes of short half-life should be used so that any material remaining in the body quickly decays away.
Q.18: Why are many artificially prepared radioisotopes of elements rare in nature?
Ans: Many artificially prepared radioisotopes of elements are rare in nature because of their extremely small half-life.
Q.19: Can radiocarbon dating be used to measure the age of stone walls of ancient civilizations?
Ans: No, radiocarbon dating cannot be used to measure the age of stone walls. "Carbon-14 clock" can be used for organic archaeological samples (i.e., matter that was once living). However, a "uranium clock" can be used for this purpose.
Q.20: How can a radioisotope be used to determine the effectiveness of a fertilizer?
Ans: When P-32 is given to a plant mixed with water, the amount of the chemical absorbed by various parts of the plant is checked by a G.M. counter. This technique helps to find the exact amount of the fertilizer required.
