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Chapter 42: Q 20 Exercise (page 1236)
A sample of 1.0x1010atoms that decay by alpha emission
has a half-life of 100 min. How many alpha particles are emitted
between t = 50 min and t = 200 min?
Therefore are emitted between t=50 min and t = 200 min.
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Are the following decays possible? If not, why not?
You learned in Chapter 41 that the binding energy of the electron in a hydrogen atom is .
a. By how much does the mass decrease when a hydrogen atom is formed from a proton and an electron? Give your answer both in atomic mass units and as a percentage of the mass of the hydrogen atom.
b. By how much does the mass decrease when a helium nucleus is formed from two protons and two neutrons? Give your answer both in atomic mass units and as a percentage of the mass of the helium nucleus.
c. Compare your answers to parts a and b. Why do you hear it said that mass is 鈥渓ost鈥� in nuclear reactions but not in chemical reactions?
Stars are powered by nuclear reactions that fuse hydrogen into helium. The fate of many stars, once most of the hydrogen is used up, is to collapse, under gravitational pull, into a neutron star. The force of gravity becomes so large that protons and electrons are fused into neutrons in the reaction . The entire star is then a tightly packed ball of neutrons with the density of nuclear matter.
a. Suppose the sun collapses into a neutron star. What will its radius be? Give your answer in .
b. The sun's rotation period is now 27 days. What will its rotation period be after it collapses?
Rapidly rotating neutron stars emit pulses of radio waves at the rotation frequency and are known as pulsars.
A sample contains radioactive atoms of two types, A and B. Initially there are five times as many A atoms as there are B atoms. Two hours later, the numbers of the two atoms are equal. The half-life of A is 0.50 hour. What is the half-life of B?
Use the potential-energy diagram in Figureto estimate the strength of the strong force between two nucleons separated by .
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