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Chapter 42: Q.53 (page 1237)
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?
Activity of a radioactive substance after a time t
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a. Is the binding energy of a nucleus with more than, less than, or equal to the binding energy of a nucleus with ? Explain.
b. Is a nucleus with more tightly bound, less tightly bound, or bound equally tightly as a nucleus with ? Explain.
The plutonium isotope 239 Pu has a half-life of 24,000 years and decays by the emission of a 5.2 MeV alpha particle. Plutonium is not especially dangerous if handled because the activity is low and the alpha radiation doesn’t penetrate the skin. However, there are serious health concerns if even the tiniest particles of plutonium are inhaled and lodge deep in the lungs. This could happen following any kind of fire or explosion that disperses plutonium as dust. Let’s determine the level of danger.
How many grays of gamma-ray photons cause the same bio-
logical damage as 30 Gy of alpha radiation?
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 p+ + e- S n + n. 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 km. 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
Consider the atoms and . Some of the following questions may have more than one answer. Give all answers that apply.
a. Which are isotopes?
b. Which are isobars?
c. Which have the same chemical properties?
d. Which have the same number of neutrons?
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