Ch. 30 MisConceptual Questions

What has greater mass? a) a neutron and a proton that are far from each other (unbound) b) a neutron and a proton that are bound together in a hydrogen (deuterium) nucleus c) both the same

a) A stable nucleus or bound nucleus has less mass than the sum of the masses of its constituent particle

Technetium 9843TC has a half life of 4.2x10^6 yr. Strontium 9038Sr has a half-life of 28.79 yr. Which statements are true? a) the decay constant of Sr is greater than the decay constant of Tc b) the activity of 100g of Sr is less than the activity of 100g of Tc c) The long half-life of Tc means that it decays by alpha decay d) A Tc atom has a higher probability of decaying in 1 yr than a Sr atom e) 28.79 g of Sr has the same activity as 4.2 x 10^6 g of Tc

a) The decay constant of a nucleus gives the probability of decaying nuclei over a given period and is inversely proportional to the half-life of a radioactive sample and activity of a radioactive sample is more for lesser decay constant

Radon has a half-life of about 1600 years. The Earth is several billion years old, so why do we still find radon on this planet? a) Ice-age temperatures preserved some of it b) Heavier unstable isotopes decay into it c) it is created in lightning strikes d) It is replenished by cosmic rays e) Its half-life has increased over time f) Its half-life has decreased over time

b) Radon is one of the daughter nuclei in the decay chain of Uranium-238. All of the daughter nuclei in this series exist on Earth today because of the long half-life period (billions of years) of their parent nucleus. Radon that was existed on Earth would have disappeared long ago, but its existence on the Earth shows that it is continually replenished by the decay of heavier isotopes like Uranium-238

A nucleus has a) more energy than its component neutrons and protons have b) less energy than its component neutrons and protons have c) the same energy as its component neutrons and protons have d) more energy than its component neutrons and protons have when the nucleus is at rest but less energy than when it is moving

b) The nucleus has less energy than that of its constituent particles both protons and neutrons, according to Einstein's energy mass relation, since the total mass of a stable nucleus is always less than the sum of the masses of its constituent particles.

The half-life of a radioactive nucleus is a) half the time it takes for the entire substance to decay b) the time it takes for half of the substance to decay c) the same as the decay constant d) both a and b e) all of the above

b) half life of a radioactive nucleus can be defined as the time in which the radioactive substance becomes half of its original quantity to decay

After three half lives, what fraction of the original radioactive material is left? a) none b)1/10 c) 1/8 d) 1/4 e) 3/4 f) 7/8

c)

Which of the following will generally create a more stable nucleus? a) having more nucleons b) having more protons than neutrons c) Having a larger binding energy per nucleon d) Having the same number of electrons as protons e) Having a larger total binding energy

c) larger binding energy per nucleon represents the more stable nucleus. Thus, more amount of binding energy per nucleon will create stable nucleus a incorrect: if you add more number of nucleons, the effectiveness of the strong nuclear force will decrease, so the nucleus becomes less stable b incorrect: if you have more proton than neutron the electromagnetic force between the proton will be too big to be contained in the nucleus. Thus more protons than neutrons will not create a stable nucleus d incorrect: the element will be electrically neutral, but does not affect the stability of its nucleus. Thus, the same number of electron as proton will not create stable nucleus e) The mass has been lost when the nucleons of an atomic nucleus were put together, therefore it will be bigger as the nucleus gains nucleons, however having more number of nucleons can result in less stability.

A material having which decay constant would have the shortest half life? a) 100/sec b) 5/year c) 8/ century d) 10^9/day

d)

Carbon dating is useful only for determining the age of objects less than about ____ years old. a) 4.5 billion b) 1.2 million c) 600,000 d) 60,000 e) 6000

d)

Uranium-238 decays to lead-206 through a series of a) alpha decays b) beta decays c) gamma decays d) some combination of alpha, beta, and gamma

d)

If the half-life of a radioactive sample is 10 years, then it should take ___ years for the sample to decay completely a) 10 b) 20 c) 40 d) cannot be determined

d) In radioactive decay, the number of radioactive nuclei decreases with the time the half life of a radioactive nucleus can be defined as the time required for half the nuclei of a radioactive sample to decay. We cannot determine the exact time for the sample to decay completely, but we can determine only the probabilistic values over a given period.

How does an atom's nucleus stay together and remain stable? a) The attractive gravitational force between the proton and neutrons overcomes the repulsive electrostatic force between the protons b) Having just the right number of neutrons overcomes the electrostatic force between the protons c) a strong covalent bond develops between the neutrons and protons because they are so close to each other d) none of the above

d) The nuclear force is the strongest force among the gravitational force and the electrostatic force. The electrostatic force is stronger than the gravitational force. The nuclear force is the attraction force between the two nucleons inside a nucleus.

Elements of the periodic table are distinguished by a) the number of protons in the nucleus b) the number of neutrons in the nucleus c) the number of electrons in the atom d) Both a and b e) a, b, c

d) both a and b Periodic table is arranged based on the change in atomic number and atomic mass. Atomic number is the number of protons present in an atom of an element. Atomic mass is the number of protons and neutrons in the atom

As a radioactive sample decays, a) the half-life increases b) the half-life decreases c) the activity remains the same d) the number of radioactive nuclei increases e) None of the above

e) In radioactive decay, the number of radioactive nuclei decreases. The half-life of a radioactive nucleus can be defined as the time in which the radioactive substance becomes half of its original quantity to decay. The half-life of a particular radioactive sample is constant but its activity, decaying capability, of a nucleus decreases exponentially as it decays.

There are 82 protons in a lead nucleus. Why doesn't the lead nucleus burst apart? a) Coulomb repulsive force doesn't act inside the nucleus b) Gravity overpowers the Coulomb repulsive force inside the nucleus c) The negatively charged neutrons balance the positively charged protons d) Protons lose their positive charge inside the nucleus e) the strong nuclear force holds the nucleus together

e) The repulsion force between the protons in the nucleus increases as the atomic number of an atom increases and this increase in repulsion force ceases the nucleus leading to collapse of the atom. The neutrons in the nucleus reduce the repulsion forces that exist between the protons. If the neutron number is more, the nucleus will get more stability. The stronger the nuclear forces between proton-proton, proton-neutron, and neutron-neutron dominate the repulsion force between proton-proton and hold the nucleus together.

A sample's half life is 1 day. what fraction of the original sample will have decayed after 3 days? a) 1/8 b) 1/4 c) 1/2 d) 3/4 e)7/8 f) all of it

e) 7/8