Radioactivity Practice Problems:

Question: If the half life of a radioactive sample is 10 hours, its mean life is
(a) 14.4 hours
(b) 7.2 hours
(c) 20 hours
(d) 6.93 hours

Ans. (a)

Question: Radioactive substances do not emit
(a) Electron
(b) Helium nucleus
(c) Positron
(d) Proton

Ans. (a)

Question: A radioactive element emits 200 particles per second. After three hours, 25 particles per second are emitted. The half life period of the element will be
(a) 50 minutes
(b) 60 minutes
(c) 70 minutes
(d) 80 minutes

Ans. (b)

Question: From which mineral is radium obtained —
(a) Limestone
(b) Haematitie
(c) Pitchblende
(d) Rutile

Ans. (c)

Question: Half life of a radioactive element depends upon
(a) Amount of element present
(b) Temperature
(c) Pressure
(d) Nature of element

Ans. (d)

Question: What percentage of original radioactive atoms is left after five half lives?
(a) 0.3%
(b) 1%
(c) 31%
(d) 3.125%

Ans. (d)

Question: The half-life of a radioactive substance is 48 hours. How much time will it take to disintegrate to its 1/16th part
(a) 12 h
(b) 16 h
(c) 48 h
(d) 192 h

Ans. (d)

Question: The half life period of radium is 1600 years. The fraction of a sample of radium that would remain after 6400 years is
(a) 1/4
(b) 1/2
(c) 1/8
(d) 1/16

Ans. (d)

Question: Uranium is used for the generation of /production of _____
(a) Electricity
(b) Cement
(c) Iron and Steel
(d) Paper

Ans. (a)

Question: The particle that possesses a half integral spin as
(a) Photon
(b) Pion
(c) Proton
(d) K-meson

Ans. (c)

Question: Consider two nuclei of the same radioactive nuclide. One of the nuclei was created in a supernova explosion 5 billion years ago. The other was created in a nuclear reactor 5 minutes ago. The probability of decay during the next time is
(a) Different for each nuclei
(b) Nuclei created in an explosion decays first
(c) Nuclei created in the reactor decays first
(d) Independent of the time of creation

Ans. (d)

Question: The half-life of a radioactive substance is 40 years. How long will it take to reduce to one fourth of its original amount and what is the value of decay constant
(a) 40 years, 0.9173/year
(b) 90 years, 9.017/year
(c) 80 years, 0.0173 year
(d) None of these

Ans. (c)

Ques: In a radioactive decay, neither the atomic number nor the mass number changes. Which of the following would be emitted in the decay process?
(a) Proton
(b) Neutron
(c) Electron
(d) Photon

Ans. (d)

Question: A radioactive material has a half-life of 8 years. The activity of the material will decrease to about 1/8 of its original value in
(a) 256 years
(b) 128 years
(c) 64 years
(d) 24 years

Ans. (d)

Question: C¹⁴ has a half life of 5700 years. At the end of 11400 years, the actual amount left is
(a) 0.5 of the original amount
(b) 0.25 of the original amount
(c) 0.125 of the original amount
(d) 0.0625 of the original amount

Ans. (b)

Question: The half-life of radium is about 1600 years. Of 100 g of radium existing now, 25 g will remain unchanged after
(a) 2400 years
(b) 3200 years
(c) 4800 years
(d) 6400 years

Ans. (b)

Question: The phenomenon of radioactivity is
(a) Exothermic change which increases or decreases with temperature
(b) Increases in applied pressure
(c) Nuclear process does not depend on external factors
(d) None of the above

Ans. (c)

Ques: The large scale destruction that would be caused due to the use of nuclear weapons is called
(a) Nuclear holocaust
(b) Thermo-nuclear reaction
(c) Nuclear reproduction factor
(d) None of these

Ans. (a)

Question: A sample of radioactive element has a mass of 10 gm at an instant t = 0.The approximate mass of this element in the sample after two mean lives is
(a) 2.50 gm
(b) 3.70 gm
(c) 6.30 gm
(d) 1.35 gm

Ans. (d)

Question: The half-life period of radium is 1600 years. Its average lifetime will be
(a) 3200 years
(b) 4800 years
(c) 2319 years
(d) 4217 years

Ans. (c)

Question: Radioactive nuclei that are injected into a patient collect at certain sites within its body, undergoing radioactive decay and emitting electromagnetic radiation. These radiations can then be recorded by a detector. This procedure provides an important diagnostic tool called
(a) Gamma camera
(b) CAT scan
(c) Radiotracer technique
(d) Gamma ray spectroscopy

Ans. (c)

Question: During a negative beta decay
(a) An atomic electron is ejected
(b) An electron which is already present within the nucleus is ejected
(c) A neutron in the nucleus decays, emitting an electron
(d) A part of the binding energy is converted into an electron

Ans. (c)

Ques: If the radioactive decay constant of radium is 1.07 x 10^–4 per year, then its half life period is approximately equal to
(a) 8,900 years
(b) 7,000 years
(c) 6,476 years
(d) 2,520 years

Ans. (c)

Question: The S.I. unit of radioactivity is
(a) Roentgen
(b) Rutherford
(c) Curie
(d) Becqueral

Ans. (d)

Question: Alpha rays emitted from a radioactive substance are
(a) Negatively charged particles
(b) Ionized hydrogen nuclei
(c) Doubly ionized helium atom
(d) Uncharged particles having a mass equal to a proton

Ans. (c)

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Question: Half-life is measured by
(a) Geiger-Muller counter
(b) Carbon dating
(c) Spectroscopic method
(d) Wilson-Cloud chamber

Ans. (a)

Question: Half-life of a substance is 10 years. At what time, it becomes ¼ th part of the initial amount?
(a) 5 years
(b) 10 years
(c) 20 years
(d) None of these

Ans. (c)

Question: The electron emitted in beta radiation originates from
(a) Inner orbits of atoms
(b) Free electrons exist in nuclei
(c) Decay of a neutron in a nucleus
(d) Photon escaping from the nucleus

Ans. (c)

Question: 10 gm of radioactive material of half-life 15 year is kept in store for 20 years. The disintegrated material is
(a) 12.5 g
(b) 10.5 g
(c) 6.03 g
(d) 4.03 g

Ans. (c)

Question: The half-life of radon is 3.8 days. Three fourths of a radon sample decays in
(a) 5.02 days
(b) 15.2 days
(c) 7.6 days
(d) 11.4 days

Ans. (c)

Question: A radioactive nucleus emits a beta particle. The parent and daughter nuclei are
(a) Isotopes
(b) Isotones
(c) Isomers
(d) Isobars

Ans. (d)

Question: A radio isotope has a half life of 75 years. The fraction of the atoms of this material that would decay in 150 years will be
(a) 66.6%
(b) 85.5%
(c) 62.5%
(d) 75%

Ans. (d)

Ques: Half life of a radioactive element is 10 days. The time during which quantity remains 1/10 of initial mass will be
(a) 100 days
(b) 50 days
(c) 33 days
(d) 16 days

Ans. (c)

Question: If the half-life of a radioactive atom is 2.3 days, then its decay constant would be
(a) 0.1
(b) 0.2
(c) 0.3
(d) 2.3

Ans. (c)

Question: A radioactive sample with a half life of 1 month has the label : “Activity=2 micro curies on 1.8.1991.” What will be its activity two months later?
(a) 1.0 micro curies
(b) 0.5 micro curies
(c) 4 micro curies
(d) 8 micro curies

Ans. (b)

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Question: Age of a tree is determined using radio-isotope of
(a) Carbon
(b) Cobalt
(c) Iodine
(d) Phosphorus

Ans. (a)

Ques: Which of the following is the correct statement?
(a) Beta rays are the same as cathode rays
(b) Gamma rays are high energy neutrons
(c) Alpha particles are singly ionized helium atoms
(d) Protons and neutrons have exactly the same mass

Ans. (a)

Question: The half life period of a radioactive substance is 5 min. The amount of substance decayed in 20 min will be
(a) 93.75%
(b) 75%
(c) 25%
(d) 6.25%

Ans. (a)

Question: A 16 gm sample of a radioactive element was taken from Bombay to Delhi in 2 hours and it was found that 1 gm of the element remained (undisintegrated). Half life of the element is
(a) 2 hours
(b) 1 hour
(c) 1/2 hour
(d) 1/4 hour

Ans. (c)