According to geologists, if there were no heat source, Earth should have cooled to its present temperature in no more than 1 billion years. Yet, Earth is more than 4 billion years old. Why is Earth cooling so slowly? The answer is nuclear radioactivity, that is, high-energy particles produced in radioactive decays heat Earth from the inside (
[link] ).
Earth is heated by nuclear reactions (alpha, beta, and gamma decays). Without these reactions, Earth’s surface would be much cooler than it is now.
Candidate nuclei for this heating model are
, which possess half-lives similar to or longer than the age of Earth. The energy produced by these decays (per second per cubic meter) is small, but the energy cannot escape easily, so Earth’s core is very hot. Thermal energy in Earth’s core is transferred to Earth’s surface and away from it through the processes of convection, conduction, and radiation.
Summary
The three types of nuclear radiation are alpha (
) rays, beta (
) rays, and gamma (
) rays.
We represent
decay symbolically by
. There are two types of
decay: either an electron (
) or a positron (
) is emitted by a nucleus.
decay is represented symbolically by
.
When a heavy nucleus decays to a lighter one, the lighter daughter nucleus can become the parent nucleus for the next decay, and so on, producing a decay series.
Conceptual questions
What is the key difference and the key similarity between beta (
)
decay and alpha decay?
What is the difference between
rays and characteristic X-rays and visible light?
Gamma (
γ ) rays are produced by nuclear interactions and X-rays and light are produced by atomic interactions. Gamma rays are typically shorter wavelength than X-rays, and X-rays are shorter wavelength than light.
Consider
[link] . If the magnetic field is replaced by an electric field pointed in toward the page, in which directions will the
-,
-, and
rays bend?
Assume a rectangular coordinate system with an
xy -plane that corresponds to the plane of the paper.
bends into the page (trajectory parabolic in the
xz -plane);
bends into the page (trajectory parabolic in the
xz -plane); and
is unbent.
(a) Calculate the energy released in the
decay of
. (b) What fraction of the mass of a single
is destroyed in the decay? The mass of
is 234.043593 u. (c) Although the fractional mass loss is large for a single nucleus, it is difficult to observe for an entire macroscopic sample of uranium. Why is this?
a. 4.273 MeV; b.
; c. Since
is a slowly decaying substance, only a very small number of nuclei decay on human timescales; therefore, although those nuclei that decay lose a noticeable fraction of their mass, the change in the total mass of the sample is not detectable for a macroscopic sample.
The
particles emitted in the decay of
(tritium) interact with matter to create light in a glow-in-the-dark exit sign. At the time of manufacture, such a sign contains 15.0 Ci of
. (a) What is the mass of the tritium? (b) What is its activity 5.00 y after manufacture?
Write a nuclear
decay reaction that produces the
nucleus. (
Hint: The parent nuclide is a major waste product of reactors and has chemistry similar to calcium, so that it is concentrated in bones if ingested.)
Write the complete decay equation in the complete
notation for the beta (
) decay of
(tritium), a manufactured isotope of hydrogen used in some digital watch displays, and manufactured primarily for use in hydrogen bombs.
If a 1.50-cm-thick piece of lead can absorb
of the rays from a radioactive source, how many centimeters of lead are needed to absorb all but
of the rays?
A rare decay mode has been observed in which
emits a
nucleus. (a) The decay equation is
. Identify the nuclide
. (b) Find the energy emitted in the decay. The mass of
is 222.015353 u.
Astronomy (from Ancient Greek ἀστρονομία (astronomía) 'science that studies the laws of the stars') is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution.
Rafael
vjuvu
Elgoog
what is big bang theory?
Rosemary
what type of activity astronomer do?
Rosemary
No
Richard
the big bang theory is a theory which states that all matter was compressed together in one place the matter got so unstable it exploded releasing All its contents in the form of hydrogen
according to the theory of astronomers why the moon is always appear in an elliptical orbit?
Gatjuol
hi !!! I am new in astronomy....
I have so many questions in mind ....
all of scientists of the word they just give opinion only.
but they never think true or false ...
i respect all of them...
I believes whole universe depending
on true ...থিউরি
Govinda
hello
Jackson
hi
Elyana
we're all stars and galaxies a part of sun. how can science prove thx with respect old ancient times picture or books..or anything with respect to present time .but we r a part of that universe
there many theory to born universe but what is the reality of big bang theory to born universe
Asmit
what is the exact value of π?
Nagalakshmi
by big bang
universal
there are many theories regarding this it's on you believe any theory that you think is true ex. eternal inflation theory, oscillation model theory, multiple universe theory the big bang theory etc.
Aarya
I think after Big Bang!
Michele
from where on earth could u observe all the stars during the during the course of an year
is that so. the question was in the end of this chapter
Karuna
in theory, you could see them all from the equator (though over the course of a year, not at pne time). stars are measured in "declination", which is how far N or S of the equator (90* to -90*). Polaris is the North star, and is ALMOST 90* (+89*).
So it would just barely creep over the horizon.
Christopher
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