Chapter 33: The Atomic Nucleus and Radioactivity

Physics Test Review

what did Roentgen discover about a cathode-ray beam striking a glass surface?

it passes through solid materials, ionize air, no refraction in glass, and was undeflected by magnetic fields

what kind of rays are X-rays?

high frequency electromagnetic waves, usually emitted by the de-excitation of the innermost orbital electrons of atoms

what did the Becquerel discover about uranium?

the radiation from the uranium was different from X-rays and could ionize air; it could be deflected by electric and magnetic fields

what two elements did Pierre and Marie Curie discover?

polonium and radium

why aren't gamma rays deflected in a magnetic field?

they have zero charge

which has the higher frequency: X-rays or gamma rays?

gamma rays

distinguish between a rad and a rem.

rad- unit of absorbed energy; rem- unit of measure for radiation dosage based on potential energy

do humans receive more radiation from artificial or from natural sources of radiation?

natural sources

is the human body radioactive? Explain.

yes, somewhat because of the potassium we ingest and little carbon-14

what is a radioactive tracer?

tracking radioactive materials from objects

name the two different nucleons.

protons and neutrons

why doesn't the repulsive electrical force of protons in the atomic nucleus cause the protons to fly apart?

it has strong significant force

why is a larger nucleus generally less stable than a smaller nucleus?

strong force is short range; protons in large nucleus are farther apart than in smaller nucleus, strong force is less effective between wide apart protons

what is the role of neutrons in the atomic nucleus?

it serves as a "nuclear cement" that holds the nucleus together; it helps stabilize it

which contains the higher percentage of neutrons: large nuclei or small nuclei?

larger nuclei

how does the rate of decay of a long-half-life material normally compare with the rate of decay of a short-half-life material?

decays slower than those with shorter half life (decays faster)

what is the half-life of Ra-226?

1620 years

what kind of trail is left when an energetic particle shoots through matter?

trail of freed elections and positively charged ions

which type of detector senses radiation by the ionization of gas in a tube?

a Geiger counter

which type of detector senses flashes of light produced by charged particles or gamma rays?

a scintillation counter

what is transmutation?

the changing of one chemical element into another

when thorium (atomic number 90) decays by emitting an alpha particle, what is the atomic number of the resulting nucleus?

88: Radium

when thorium decays by emitting a beta particle, what is the atomic number of the resulting nucleus?

91: Protactinium

what is the change in the atomic mass number for each of the reactions in the preceding two questions?

alpha: -4; beta: 0 (atomic mass goes up by 4\[?\])

what change in atomic number occurs when a nucleus emits an alpha particle? A beta particle? A gamma ray?

alpha: -2; beta: +1; gamma: no charge

what is the long-range fate of all the uranium that exists in the world?

it will turn to lead

when, and by whom, did the first successful intentional transmutation of an element occur?

1919; Ernest Rutherford

what occurs when a nitrogen nucleus captures an extra neutron?

can emit a proton and became the nucleus of a carbon isotope

which is more prevalent in the food we eat: carbon-12 or carbon-14?

carbon-14

why is lead found in all deposits of uranium ore?

the naturally occurring isotopes of uranium decay slowly and become isotopes of lead

rank these three types of radiation by their ability to penetrate this page of your book, from greatest penetration to least:

a. Alpha particle

b. Beta particle

c. Gamma ray

c, b, a

consider these three nuclei: A. Th-233; B. U-235; C. U-238. From most to least, rank them by the number of

a. protons in the nucleus.

b. neutrons in the nucleus.

c. electrons that normally surround the nucleus.

a. U-235, U-238, Th-233

b. U-238, U-235, Th-233

c. U-235, U-238, Th-233

consider the following reactions: A. uranium-238 emits an alpha particle; B. plutonium-239 emits an alpha particle; C. thorium-239 emits a beta particle.

a. Rank the resulting nucleus by atomic number, from highest to lowest.

b. Rank the resulting nucleus by the number of neutrons from most to least.

2380-92 U ***-alpha→*** 4-2 He + ^^234-90 Th^^

239-94 Pu ***-alpha→*** 4-2 He + ^^235-92 U^^

239-90 Th ***-beta→*** 0/-1 e + ^^239-91 Pa^^

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a. B, C, A

b. C, A, B -----> (mass# - atomic#)

x-rays are most similar to which of the following: alpha, beta, or gamma rays?

gamma

gamma radiation is fundamentally different from alpha and beta radiation. What is this basic difference?

they have different charges

why is a sample of radioactive material always a little warmer than its surroundings?

because it decays; radioactivity is taking process

some people say that all things are possible. Is it at all possible for a common hydrogen nucleus to emit an alpha particle? Defend your answer.

no because it doesn’t have enough particles to give off radiation

why are alpha and beta rays deflected in opposite directions in a magnetic field? Why aren't gamma rays deflected?

because gamma rays have no electric charge; alpha and beta = opposite charges

the alpha particle has twice the electric charge of the beta particle but, for the same kinetic energy, deflects less than the beta in a magnetic field. Why is this so?

alpha particle has about 8000 times the inertia, making it harder to accelerate (has more mass)

how do the paths of alpha, beta, and gamma rays compare in an electric field?

alpha will accelerate towards field, beta will accelerate the opposite way, and gamma will have no effect

which type of radiation—alpha, beta, or gamma— produces the greatest change in *mass number* when emitted by an atomic nucleus? Which produces the greatest change in *atomic number?*

alpha for both

which type of radiation—alpha, beta, or gamma— produces the least change in mass number? In atomic number?

gamma for both

which type of radiation—alpha, beta, or gamma— predominates within an enclosed elevator descending into a uranium mine?

gamma

what do all isotopes of the same element have in common? How do they differ?

they have the same protons (atomic number); different number of neutrons (atomic mass)

if an atom has 100 electrons, 157 neutrons, and 100 protons, what is its approximate atomic mass? What is the name of this element?

257 (157 neutrons + 100 protons); Rutherfordium

when a 226-88 Ra nucleus decays by emitting an alpha particle, what is the atomic number of the resulting nucleus? What is the resulting atomic mass number?

226-88 Ra ***-alpha→*** 4-2 He + ^^222-86 Rn^^

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atomic number: 86

atomic mass number: 222

1. When a nucleus of 218-84 Po emits a beta particle, it transforms into the nucleus of a different element. What are the atomic number and the atomic mass number of this "daughter" element?

218-84 Po ***-beta→*** 0/-1 e + ^^218-85 At^^

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atomic number: 85

atomic mass number: 218

when a nucleus of 218-84 Po emits an alpha particle, what are the atomic number and the atomic mass number of the resulting element?

218-84 Po ***-alpha→*** 4-2 He + ^^214-82 Pb^^

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atomic number: 82

atomic mass number: 214

which has the greater number of protons: U-235 or U-238? Which has the greater number of neutrons?

same because both are uranium; U-238

state the number of neutrons and protons in each of these nuclei: 2-1 H, 12-6 C, 56-26 Fe, 197-79 Au, 90-38 Sr, and 238-92 U.

neutrons = mass# - atomic#

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2-1 H — protons: 1; neutrons: 1

2-6 C — protons: 6; neutrons: 6

56-26 Fe — protons: 26; neutrons: 30

197-79 Au — protons: 79; neutrons: 118

90-38 Sr — protons: 38; neutrons: 52

238-92 U — protons: 92; neutrons: 146

why is carbon dating ineffective in finding the ages of dinosaur bones?

they’re too old because little carbon-14 is left

is carbon dating appropriate for measuring the age of materials that are a few years old? A few thousand years old? A few million years old?

no; yes; no

the age of the Dead Sea Scrolls was found by carbon dating. Could this technique apply if they were carved in stone tablets? Explain.

no, because stone tablets aren’t living things

197-79 Au

\
197: mass number

79: atomic number / protons

how to find neutrons:

top# - bottom# (197 - 79 = 118N)

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