| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
16 Sep 2005 05:40:07 AM |
| Object: |
Basic question about radiation |
Hi,
Total physics layman here, but hoping someone can spare a second to
clear up some areas that are a bit vague to me. VERY simple for you
guys :-)
What is radiation?
I know light is radiation, as are X-rays, gamma rays etc etc. These are
all part of the electromagnetic spectrum, so they are electromagnetic
radiation?
But are there other kinds of radiation?
How is heat radiated for example? Vague memories of high school physics
seem to tell me that the inside of a thermos flask is silvered to
reflect radiated heat, which would seem to indicate it is similar to
light above.
Are all kinds of radiation massless?
Hmmm, but radiative isotopes radiate particles as they decay so that
cannot be right.
Can someone help my ignorant wallowing! :-)
Thanks,
Lister
.
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| User: "CWatters" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 07:27:41 AM |
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<listerofsmeg01@hotmail.com> wrote in message
news:1126867207.706401.128670@o13g2000cwo.googlegroups.com...
Hi,
Total physics layman here, but hoping someone can spare a second to
clear up some areas that are a bit vague to me. VERY simple for you
guys :-)
What is radiation?
I know light is radiation, as are X-rays, gamma rays etc etc. These are
all part of the electromagnetic spectrum, so they are electromagnetic
radiation?
Google for "ionizing radiation" and "non-ionizing radiation"
Non-ionizing radiation
http://www.answers.com/main/ntquery?s=non-ionising+radiation
"Non-ionising radiation (or in American English non-ionizing radiation)
refers to any type of electromagnetic radiation that does not carry enough
energy to ionize living material - that is, to completely remove an electron
from an atom or molecule."
Ionizing radiation.
http://www.answers.com/main/ntquery?s=Ionizing+radiation
"High-energy radiation capable of producing ionization in substances through
which it passes. It includes nonparticulate radiation, such as x-rays, and
radiation produced by energetic charged particles, such as alpha and beta
rays, and by neutrons, as from a nuclear reaction."
More
http://www.epa.gov/radiation/students/types.html
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| User: "Steven Gray" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 05:37:29 PM |
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wrote in news:1126867207.706401.128670
@o13g2000cwo.googlegroups.com:
Hi,
Total physics layman here, but hoping someone can spare a second to
clear up some areas that are a bit vague to me. VERY simple for you
guys :-)
What is radiation?
I know light is radiation, as are X-rays, gamma rays etc etc. These are
all part of the electromagnetic spectrum, so they are electromagnetic
radiation?
Yes, they are.
But are there other kinds of radiation?
Yes.
How is heat radiated for example? Vague memories of high school physics
seem to tell me that the inside of a thermos flask is silvered to
reflect radiated heat, which would seem to indicate it is similar to
light above.
Heat is radiated as infrared light.
Are all kinds of radiation massless?
No, there is also particle radiation.
Hmmm, but radiative isotopes radiate particles as they decay so that
cannot be right.
It sounds as if you've actually got a pretty good handle on it. The term
radiation is applied both to electromagnetic radiation (photons) and to
particles emitted by radioactive materials.
--
Steve Gray
sgray2@cfl.rr.com
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| User: "Uncle Al" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 11:40:53 AM |
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wrote:
Hi,
Total physics layman here, but hoping someone can spare a second to
clear up some areas that are a bit vague to me. VERY simple for you
guys :-)
What is radiation?
I know light is radiation, as are X-rays, gamma rays etc etc. These are
all part of the electromagnetic spectrum, so they are electromagnetic
radiation?
But are there other kinds of radiation?
How is heat radiated for example? Vague memories of high school physics
seem to tell me that the inside of a thermos flask is silvered to
reflect radiated heat, which would seem to indicate it is similar to
light above.
Are all kinds of radiation massless?
Hmmm, but radiative isotopes radiate particles as they decay so that
cannot be right.
Can someone help my ignorant wallowing! :-)
http://www.fuckinggoogleit.com/
http://en.wikipedia.org/wiki/Main_Page
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
http://www.motionmountain.net
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "Sam Wormley" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 07:54:08 AM |
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wrote:
What is radiation?
See: http://en.wikipedia.org/wiki/Radiation
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| User: "PD" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 12:33:19 PM |
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wrote:
Hi,
Total physics layman here, but hoping someone can spare a second to
clear up some areas that are a bit vague to me. VERY simple for you
guys :-)
What is radiation?
I know light is radiation, as are X-rays, gamma rays etc etc. These are
all part of the electromagnetic spectrum, so they are electromagnetic
radiation?
But are there other kinds of radiation?
How is heat radiated for example? Vague memories of high school physics
seem to tell me that the inside of a thermos flask is silvered to
reflect radiated heat, which would seem to indicate it is similar to
light above.
Are all kinds of radiation massless?
Hmmm, but radiative isotopes radiate particles as they decay so that
cannot be right.
Can someone help my ignorant wallowing! :-)
Thanks,
Lister
There are three types of "radiation" associated with radioactivity,
meaning the decay of unstable nuclei:
a) beta rays - really high-speed electrons
b) alpha rays - really helium nuclei (2 protons, 2 neutrons, bound
together)
c) gamma rays - really a form of light
All three of these cause ionization in their passage through matter,
which is why you don't want to swallow radium. Alpha causes the most
damage but is also the least penetrating; gammas are the most
penetrating.
But "radiation" is more typically reserved for describing all kinds of
light, including radio waves, short waves, microwaves, infrared light
(radiated "heat"), visible light, UV light, X-rays, gamma rays, etc.
All of these are identical except for the range of wavelength they
inhabit.
Because light is the carrier of the electromagnetic interaction,
sometimes you will see the same term applied to the carriers of the
other interactions; e.g. gluons are "strong nuclear force radiation".
PD
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| User: "Izzie Boxen" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 06:27:18 PM |
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wrote:
What is radiation?
Can someone help my ignorant wallowing! :-)
Thanks,
Lister
Here is something I wrote some years ago (1995) for an introductory
course on radiation safety geared towards non-physicist hospital
personnel working with radioactive substances in labs or taking care of
patients being treated with radiation of various types. Hope it helps.
What is Radioactivity?
All matter is composed of atoms. There are 92 different types of atoms,
called elements, which occur in nature and eighteen more (as of June
1995) which can be made artificially. Some commonly known elements are
hydrogen, helium, carbon, nitrogen, oxygen, neon, aluminum, calcium,...
. Some not commonly known ones are ruthenium, rhodium, hafnium,
praseodymium, samarium, dysprosium, ytterbium, einsteinium,... . All
atoms have electrons and a nucleus.
It has been convenient in the past, at least for introductory purposes,
to consider the electrons as orbiting around the nucleus, much the same
as planets around the sun. This is the model that arose after
Rutherford's famous scattering experiments in 1911 and that most of us
were taught in school. However, this view is now considered as very
naive and does not lend itself to any advanced study of atoms or nuclei.
Whenever new concepts are encountered, it is usual to try to make sense
of them by modelling them in terms of concepts already understood. Only
with time, as the new concepts sink in and are understood on their own
terms, are the old models discarded for ones more in keeping with the
known facts. It is a basic tenet of physics that models are kept as long
as they help explain phenomena but are replaced by better ones when they
no longer serve their purpose. At the very least, a model should help
provide a logical explanation of some known facts. It should also,
ideally, make predictions that prove to be true. The view that our
planet Earth is spherical instead of flat only truly took hold once
Newton expounded his theory of gravity to explain why we do not fall off
a spherical planet. Whether matter is infinitely divisible or only
finitely so was eventually settled by the analysis of spectra and the
discovery of the electron (1897) and nucleus (1911), all of which helped
explain the structure of matter and the periodicities of Mendeleev's
periodic table. The discoveries of the proton (1919), neutron
(theoretically predicted 1920, found 1932) and neutrino (theoretically
predicted 1927, found 1956) lead to new models of the atom and the
discovery of new forces at work inside the atom, helping explain
radioactivity.
Present studies of subatomic structure have now discarded the once held
belief that space is empty. Space must be considered as a very real
entity in which a lot is going on invisible to our senses and any
testing equipment. Only in such a model can much of the phenomena of
high energy physics be explained. Much of this model is too abstruse for
most people not knowledgeable about quantum mechanics and particle
physics to grasp. For our purposes it is convenient to choose a model in
which space is something that can vibrate and support travelling waves.
These waves may be assumed to be able to interact, lock together and
then travel as compound or complex waves. How this locking together
takes place is not known at the present time, but this is not important
for our needs. In a similar vein, no one yet knows what causes mass or
gravity, but this does not prevent us from using the equations that
describe the interactions with mass and with gravity. These compound,
locked waves are the only ones that are detectable by our senses or
testing equipment. They can interact further to lock into more complex
waves or they can break each other up into separate component complexes.
For our model, we then consider these compound, locked waves to be our
well-known particles as well as what we usually consider to be purer
waves, such as the photon. Further we must accept that these compound,
locked waves have additional characteristics or behaviours that are very
different from what we are familiar with in ordinary waves. Such
compound, locked waves have behaviours that give rise to characteristics
besides amplitude and frequency, such as spin, isospin, parity, charge,
colour, various forces and others, all of which can only be understood
thus far within the context of quantum mechanics and particle physics.
One major benefit of this model is that the old boundaries between waves
and particles no longer exist within the model, so that the old
wave-particle duality conundrum which gave rise to a lot of arguments
and experiments in the recent past no longer exists.
Electrons have a negative electrical charge, called the electron charge,
and the nucleus has a positive charge. These charges result in an
attractive (electromagnetic) force between the electrons and the nucleus
of an atom holding the atom together. The nucleus, in turn, is composed
of protons, which carry the positive charges, and neutrons, which have
no net charge. There is a force, called the strong force, which attracts
protons to protons, protons to neutrons and neutrons to neutrons. This
is a force most people are unfamiliar with. Without this force the
nucleus could not stay together because the positive charges on the
protons result in a repulsive (electromagnetic) force between the
protons. In reality the strong force acts between the constituents of
protons and neutrons, the quarks, and only a residual amount of this
force acts to pull nucleons (protons and neutrons) together. This is
entirely analogous to the van der Waal's forces being residua of the
electromagnetic force. The electromagnetic force holds electrons to
nuclei, and the van der Waal's forces hold together molecules to
molecules within solids, liquids and, to some extent, in gases. Some
physicists even consider van der Waal's forces to be responsible for
holding atoms together in molecules. But such distinctions between the
electromagnetic force and its higher order effects does not introduce a
new force, only a convenient way of compartmentalizing its effects on
matter. For our purposes we will not consider such differences in any
force due only to higher order effects.
There is another force, called the weak force, also unfamiliar to most
people, which also acts between neutrons and protons, but in addition
involves electrons. This force is too complicated to be described as
simply a repulsive or attractive force, but is introduced here because
it is involved in some types of radioactivity, specifically what is
called beta-decay. Just as the strong force tends to keep nuclei from
falling apart, so the weak force tends to keep neutrons from falling
apart, but only inside the nucleus. The strong force does not have any
effect on electrons, but the weak force does.
The above forces are many orders of magnitude stronger than the force of
gravity at close range. The relative strengths of the strong,
electromagnetic, weak and gravitational forces at close range are
respectively 1, 10-2, 10-13 and 10-39 (some books give different values,
e.g. 10, 1/137, 10-7, 10-45, but the differences are due to different
definitions). Only the electromagnetic and gravitational forces have a
long range extending well beyond the size of a nucleus (in fact they
extend to infinity), and so are the only ones we can personally
experience (but we can see the effects of the weak force pushing out
matter in supernovae). All these forces contribute in keeping atoms
together, i.e. stabilizing them, and in keeping matter together in
general. Gravity holds matter together as galaxies, stars, planets and
moons within the universe; the electromagnetic force holds together
molecules to molecules, atoms to atoms and electrons to nuclei within
matter; the strong force holds together nucleon to nucleon within
nuclei; and the weak force "appears" to hold together the neutron, but
only within the nucleus (see section entitled "Neutron Decay" for more
detailed discussion of this).
None of the constituents of an atom stand perfectly still. The compound,
locked waves that are these particles are constantly vibrating, with the
component locked waves effectively moving about and through each other,
constrained in their modes of vibration by various forces and
conservation laws. Within these constraints the vibrational behaviour
appears otherwise random. This helps explain in an intuitive way the
probability interpretations in quantum mechanics. Only certain modes of
vibration satisfy the constraints and therefore can exist. This model
now makes quantum transitions from one locked mode to another the only
possible ones, and is intuitively satisfying compared to the old quantum
theory which did not consider particles as locked waves. Because only
certain locked, compound modes of vibration exit, matter is not
infinitely divisible and, it turns out, neither is space. This is
because the vibrations of space are quantized just as are vibrations of
matter. Energy and momentum transfer from space to matter or vice versa
is therefore quantized.
The vibrational modes are not stagnant, in that they are constantly and
randomly changing from one to another, with the changes allowable
constrained by the (empirical) laws (of nature). Some of these laws are
conservation of energy, momentum and charge. Other constraints are a
little less acceptable intuitively, but are present. For example,
Heisenberg's uncertainty principle (or relation), a necessary
consequence of wave behaviour, allows particles (i.e. the locked,
compound waves that are these particles) to suddenly appear "out of
nowhere", provided they disappear in a short enough time not to violate
the principle. The appearance of such "virtual" particles is, in fact,
the norm, and space is absolutely teeming with them. During this short
time these virtual particles are able to interact with what we perceive
as "real" particles, all subject to the other constraints of nature, of
course. Intuitively, some of these virtual particles may be conceived as
pieces of a locked, compound wave "budding off" and flying away to unite
with another locked, compound wave within the short time interval
allowed. This budding, at first glance, violates instantaneous
conservation of energy, but the total energy level returns to its
original value within the time allowed by the Heisenberg uncertainty
principle. These pieces, which are themselves locked, compound waves,
are "exchange particles" which transmit the force between the real
particles. Intuitively, the energy violation may be thought of as an
extra potential that the involved particles find themselves in. The
negative gradient of this extra potential is then the extra force
(strong or weak) felt by the particles.
If, during the time of existence of the exchange particles, the "debt"
incurred to satisfy the Heisenberg uncertainty principle is "paid"
before due by other interactions (e.g. in high energy scattering
experiments), then these exchange particles are free to leave and fly
off on their own as real particles. Interactions which "pay debts before
due" effectively interact with the locking force trying to pull an
exchange particle in, and thereby free the exchange particle from the
grips of this locking force. The exchange particle can then leave the
nucleus or the atom and be detected externally. Incidentally, the same
type of mechanism can be envisioned giving rise to photons, the known
transmitters of the electromagnetic force. Likewise, it can be
envisioned that some similar mechanism gives rise to the postulated
transmitters of the gravitational force, gravitons. However, gravitons
have not yet been observed (probably because they contain so little
energy compared to the other force transmitters). This lack of
observation helps explain why we know nothing yet of what causes some
particles to have mass and others not, since we have no measureable
entity to test theories on (recall that all we know of the
electromagnetic force was learned by measuring the effects of photons on
matter).
Because virtual particles and their real particle counterparts are
locked, compound waves under different constraints, it is understandable
that their vibrational modes should be different. For example, real
photons have waves that can vibrate in amplitude only in directions
perpendicular to the direction of motion, while virtual photons have
waves that can vibrate in amplitude in any direction. However, there are
also some strange differences. One very strange difference between
virtual transmitters of force and their free, real counterparts is that
their masses differ, e.g. the virtual photon has mass but the free
photon does not. There are theories to explain this, but looking at them
would carry us too far afield in this article. This and some other
differences are discussed in the article entitled "Virtual Particles".
Because the exchange particles for the strong and weak forces have a
finite and very short life-span (to satisfy the Heisenberg uncertainty
principle) their range of influence, or the range of the force they
transmit, is very limited (the speed of light being an absolute speed
limit). The strong force range is about 10-15m (about the size of a
proton), and the weak force range is about 10-18 -10-17m. The ranges of
the forces control the size of the nucleons (proton and neutron),
nucleus and also the atom. Transmitters of the nuclear forces are highly
unstable and fall apart soon after being freed from the nucleus.
Transmitters of the electromagnetic force, the photons, are stable and
can leave the atom to influence other particles at a great distance (out
to infinity).
This model also intuitively explains the existence of a minimal
greater-than-zero energy in atoms even at a temperature of zero absolute
degrees, since at zero degrees the locked space waves must still be
vibrating in some fundamental mode for the particle to exist at all, and
this vibration has energy associated with it.
The model also helps explain in an intuitive manner how electrons in an
atom can interact with the nuclear components in nuclear mode
transitions. Since the locked waves which are the electrons are locked
to or intertwined with the nuclear locked waves, the possibilities for
interaction are obvious. In the planetary model of atoms the electrons
remained within about 1 Angstrom or 10-10m from the nucleus, but well
beyond the 10-15-10-14m nuclear diameter, making it very difficult to
see how the electrons and nucleus could interact in nuclear transitions
which used these very short range nuclear forces.
The quantum mechanical phenomenon of tunnelling through barriers also is
explained intuitively since the locked waves extend into the barrier and
may extend to a significant amount beyond the other side of the barrier,
if the barrier is not too wide. The locking force holding the
penetrating portion of the particle to the remainder may be greater than
the separating force supplied by the barrier, resulting in passage of
the remainder of the particle through the barrier, despite the fact that
it did not have enough kinetic energy to hurdle the potential energy
barrier. The two different forces (locking force and the repulsive force
of the barrier) must be of significantly different magnitudes. Because
of the random vibrations of a locked, compound wave, the penetrating
portion does not always provide enough force to pull the rest through,
so tunnelling has a probability associated with it. In classical physics
waves are always partially transmitted and partially reflected at
potential barriers (wells or walls). In the subatomic world, however,
quantum physics applies. Partial transmission and partial reflection can
only occur if the partially transmitted and partially reflected locked,
compound waves are allowed modes of vibration. There must be a force
supplied to tear apart the original locked, compound wave into two other
allowed locked, compound waves. This force is supplied by the potential
barrier (force equals the negative gradient of this potential). In
tunnelling situations where the barrier potential is insufficient
(height or depth) to supply enough energy to allow two (or more)
permitted locked, compound waves to be produced from the original mode,
tunnelling is an all or none phenomenon. However, in high energy
collisions the very high potential barriers of the nucleus are
encountered, and these are of sufficient magnitude to break up single
modes into two (or more), allowing one mode through the barrier and the
other not, giving effective transmission and reflection.
The resonance interaction of vibrating waves also helps explain
Einstein's stimulated emission of radiation, a phenomenon used in the
production of lasers.
For electric neutrality, the number of protons must equal the number of
electrons since the charge on a proton is equal in magnitude to that on
an electron, but opposite in sign, and neutrons have no net charge (they
have a charge distribution which "averages" out to zero). However, the
number of neutrons for any number of protons in a nucleus (nuclide) can
vary within limits, giving what are called isotopes of the same element
(note that the word isotope refers to the atom as a whole). Only 27
elements have a single isotope. The resulting differences in forces and
differences in patterns of motion (vibrational modes) of protons and
neutrons about each other occasionally result in an unstable nuclide,
one which cannot hold itself together indefinitely. Of the approximately
3000 known nuclides, 259 combinations of neutrons and protons never fall
apart spontaneously. These are called the stable nuclides. The others
are unstable and, sooner or later, fall apart. These are called
radionuclides. The corresponding atoms are called radioisotopes. The
potential barrier of the nucleus keeps the nucleus together in
radionuclides longer than would be calculated otherwise based solely on
the freeing of exchange particles described above.
There are various pieces (locked, compound waves) of an atom that can
come flying out as the atom falls apart or decays. These projectiles may
themselves be unstable and undergo further disintegrations or decays.
Some of the projectiles are themselves nuclei, with or without the
appropriate number of electrons for electrical neutrality. Some
projectiles are neutrons, protons or electrons. Still others are more
bizarre and are familiar only to people working with them. It turns out
that the constituents of nuclei (the possible locked, compound waves and
their possible modes of vibration that can separate from the original
locked, compound wave) include entities in addition to neutrons and
protons, but these additional entities only reveal their existence if
they come flying out of the nucleus or other outside entities come
flying into the nucleus and interact. Mathematically, in describing wave
interactions, it is convenient (even necessary in order to solve the
problem) to consider a complex wave pattern as a sum of individual less
complex ones, even though these less complex individual ones do not
exist isolated from each other. This mathematical trick used in solving
problems does not mean that there are such things as electrons or
neutrinos inside the nucleus, even though these can come flying out. It
only means that in interactions concerning the nucleus the mathematical
description of the interaction treats the nucleus as if it does consist
of such individual particles.
In fact, we are now forced to correct the view implied above that the
nucleus consists of separate protons and neutrons, and even that the
atom consists of separate electrons and a nucleus. If protons and
neutrons were truly individual entities in a nucleus, then we could not
explain stable nuclides since isolated neutrons outside of a nucleus are
known to spontaneously decay to protons, electrons and (anti)neutrinos
with a half-life t1/2 (see below) of about 13 minutes. Similarly, if we
considered electrons and nuclei in an atom to be separate entities, then
we could not explain how electrons moving in an atom do not radiate
energy (photons) as required by classical physics. Furthermore, we can
no longer consider molecules (formed by covalent bonds) to be simple
collections of individual atoms held together. By considering a
covalently bonded molecule to be a single entity, a locked, compound
wave, we can now intuitively understand resonance structure or electron
sharing as occurs for example in a benzene molecule. However, it should
be emphasized that in many calculations, considering a molecule to be a
simple collection of atoms or an atom to consist of electrons and a
nucleus gives adequate answers as a first approximation. The Bohr atomic
model, a refinement of the Rutherford planetary model, gives very good
approximations for energies of x-rays (see below) emanating from the
hydrogen atom. Bohr's model explained the x-ray spectrum of the hydrogen
atom for the first time, and did this so well that Bohr won the Nobel
prize for his theory. Unfortunately, it does not give good
approximations for any other atom. Even in the hydrogen atom there is a
fine splitting of energy levels due to spin of the electron, not
accounted for in the Bohr model, and not at all explainable by classical
physics which cannot cope with a spinning point, the apparent
dimensionality of the electron. In other atoms there are further changes
in energy levels due to additional phenomena, also not explained by the
Bohr model. However, as long as a model helps explain things or allows
calculations of acceptable accuracy and precision, that model may be
used. It is only discarded in situations in which it is not helpful.
Models are essential in interpreting experimental results. Frequently,
in physics, more than one model is used at the same time to help
understanding and calculations. We will therefore occasionally allow
ourselves to use the term "particle" in the old-fashioned sense,
especially when it simplifies discussion or understanding.
Getting back to projectiles from radionuclides, some of these
projectiles are not even particles as the average person would define a
particle. These may have momentum and energy but no mass. "Light" of
different energies also comes out. If the energy is right, this appears
as visible light we are all familiar with. Higher energy light may be
ultraviolet light, and higher still x-rays or gamma rays. X-rays are
light coming from electrons changing from unstable modes of vibration
("orbits" in the old terminology) to more stable ones, while gamma rays
are light coming from nuclei changing to more stable modes or
configurations. The emission of this light is one way of reducing energy
to increase stability. There need be no projectiles other than this
light. All the projectiles form, what is generally called, radioactivity.
One measure of radioactivity is the rate of disintegration (decay) of a
collection of similar atoms. The time needed for half of the atoms to
decay is called the half-time t1/2. In two half-lives 1/4 of the
original atoms remain undecayed, in three half-lives 1/8 still remain,
and so on. Half-lives vary from tiny fractions of a second to billions
of years. However, only radioactive elements with half-lives of
convenient length are useful for purposes of medical diagnosis,
treatment or research or other work. The atoms must decay rapidly enough
to allow easy detection of radioactivity above that of natural
background radioactivity (which is all around us), but not so rapidly
that there is nothing left to measure before the phenomenon being tested
is over. As an example, in adding radioactive material to the melt of a
metal alloy to test for uniformity of mixing, the half-time must be long
enough to yield measurable (imageable) radioactivity in the solidified
and cooled alloy. But the half-time must be short enough to yield good
quality images of the distribution throughout the metal within a
convenient time, say minutes to hours. The half-time must also be short
enough so that no radioactivity of significance is left in the alloy
when it is shipped out to its destination. In general, the half-time
must be of the same order of magnitude as the time taken for the
biological process of interest or whatever work is done.
The situation described above of unstable atoms falling apart results in
spontaneous radioactivity. If an atom decays with its nucleus splitting
into two nuclei other than those of hydrogen or helium, then the
radioactive process is called fission. Disintegration can also be
induced by bombarding an atom with projectiles which interact with the
nucleus causing it to become unstable. This is called induced
radioactivity. However, the resultant target atom is usually not called
radioactive unless the t1/2 is large enough to be measurable and
certainly not if t1/2 is not greater than the time it takes for the
bombarding projectile to cross the target nucleus. If the projectile is
itself a nucleus, even just a proton, and the conditions just right,
then the two nuclei may fuse together forming a nucleus different from
the original two. This process is called fusion. Fusion always results
in unstable nuclei and subsequent emission of projectiles.
How the projectiles of radioactivity interact with matter is determined
by the nature of the projectiles and how energetic they are. The
projectiles may interact with either the electrons or the nuclei of
atoms. If one or more electrons are knocked out of the atom, then the
resultant atom is positively charged and is called an ion. The process
is called ionization, and the type of radiation causing this is called
ionizing radiation. The projectile may get trapped in the target nucleus
as well as knock some of its constituents out. The resultant nucleus may
be unstable and decay slowly enough to have a fairly long t1/2. However,
such a result requires very special conditions and is therefore
uncommon. It is easy to find or make materials that interact very
readily with most types of radiation but are not made radioactive. This
allows for shielding of radioactivity.
Some of the interactions are so weak as to not even cause any chemical
change or interaction; some interactions cause target molecules to break
apart and produce highly-reactive chemicals; still other interactions
cause target atoms to become radioactive. Since detection of radiation
is by means of detecting interactions of the projectiles, the nature and
energy of the projectiles also therefore determines what equipment is
needed to detect them, i.e. the radioactivity, and how easily they are
detected. Present equipment is capable of detecting and imaging the
location of a single radioactive atom. Compare this to chemical
detection of any matter which requires at least billions to trillions of
atoms or molecules. Finding a radioactive needle in a haystack is
child's play, using a Geiger counter. This incredible detection
sensitivity is what makes radioactivity so important in many types of
work, including quality control of metallurgy, chemistry and the
biological sciences. It is possible to use a very small number of
radioactive atoms in place of or along with non-radioactive isotopes of
the same atoms and follow physical, chemical and biological behaviour.
The damage that radioactivity can cause is what makes it so important in
treating many types of disease, including many types of cancer. The
sensitivity of detection and the ability to choose radioactive isotopes
(radioisotopes) and amounts of these radioisotopes that cause little
damage make diagnostic nuclear medicine an important part of medicine.
The important part about radioactivity is the projectile emission,
called radiation. Radiation can consist of fragments of nuclei,
electrons, protons, neutrons, photons (electromagnetic radiation:
visible light, UV rays, X-rays, gamma rays, etc.) and other constituents
of nuclei. The important thing about radiation is how it interacts with
matter, and this is determined by the particular projectile involved and
its energy. The question therefore arises whether there is any
difference between a proton, say, accelerated to 1 MeV energy or a
proton that has been emitted from a radioactive atom, also with 1 MeV.
The answer is that there is none as far as interaction with matter is
concerned. Neither is there any detectable difference between any other
projectile of a given energy produced by radioactive decay or by any
other means. All these projectiles, whether they come from radioactive
decay or not are collectively called radiation. Radiation therefore does
not necessarily come from radioactive atoms. The light that comes from
candles, light bulbs and the sun, as well as the heat that comes from a
fire or the sun is radiation. Such radiation can obviously have very
beneficial effects. In fact, were it not for the fusion reactions that
occur in the sun, there would be no life on earth. Likewise, controlling
the movement of electrons in conductors gives rise to beneficial
electricity, and controlling the flight of electrons through a (partial)
vacuum gives rise to televisions, electron microscopes, etc. Controlling
the radiation that comes from radioactive Americium-241 gives rise to
very sensitive smoke detectors. Very long-lasting batteries are made
with radioactivity as the energy source. Many other uses of
radioactivity also exist in which the non-damaging effects of radiation
are applied beneficially. As long as radioactivity is handled in a safe
manner, there is far more benefit to be gained than damage.
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| User: "Autymn D. C." |
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| Title: Re: Basic question about radiation |
17 Sep 2005 11:51:31 AM |
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Izzie, no one needed to know all that. All matter is not composed of
atoms. Nature makes elements of any arbitrarily-high number. Energy
in bosons, like the fotons, are just waves of the matter waves or
particles of the matter particles.Waal's -> Waals No, the color force
has a comparable range to the other pure forces.
Radiation is any unbound event. That is, any change that does not
reverse. Measuring it, however, binds the event somewhat and turns it
into an oscillation somewhat. Tossing a stone at someone counts as
radiation, as does shaking it loose. In the most general way of
thinking, that I've realised, all events are partial radiations and
oscillations.
-Aut
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| User: "" |
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| Title: Re: Basic question about radiation |
17 Sep 2005 05:01:25 PM |
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I'll drink to that.
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| User: "" |
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| Title: Re: Basic question about radiation |
17 Sep 2005 05:21:22 PM |
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wrote:
I'll drink to that.
Got Milk?
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| User: "the softrat" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 08:20:49 PM |
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On 16 Sep 2005 03:40:07 -0700, wrote:
But are there other kinds of radiation?
How is heat radiated for example?
Infra-red (electromagnetic)
Are all kinds of radiation massless?
No. Alpha radiation is very high speed helium nuclei and beta
radiation is very high speed electrons.
Cosmic rays are a mixed bag: largely very high speed protons (until
they hit the atmosphere, then all Hell breaks loose.).
HTH
the softrat
Unless Barad-dur is rebuilt, twice as evil as before, Frodo has triumphed!
mailto:softrat@pobox.com
--
Software isn't released. It's allowed to escape.
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| User: "" |
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| Title: Re: Basic question about radiation |
16 Sep 2005 07:06:28 AM |
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Sorry bud but no one in this group knows the answers that you
seek.However if you just want to put all this behind you,go to
"whitehouse.org" and G Dubya Bush will fill your head with all kinds
of cool *****.You will leave feeling all warm and fuzzy,and amazed
at how easy it was for them to bamboozle your *****!
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