Nature of radioactivity:

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Nature of radioactivity
Spontaneous disintegration of atomic nuclei,
usually in nuclei that deviate from a balance of
protons neutrons.
Radiation involves release of energy either as
kinetic energy of ejected particles (electrons --
ß particles, positrons, or orbital electrons a
particles -- 2N/2P2, a He nucleus neutrons) or
as electromagnetic radiation (X- rays from
intranuclear transitions ?- rays from orbital
shifts of electrons).
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electron orbitals
Diameters of atoms 10 - 1 nm, 1 Å Diameters of
nuclei 10 - 6 nm Most of atomic volume is
empty! Nuclear strong force is intense but acts
only over short distances.
nucleus
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Properties of bulk matter, e.g., classical
mechanical behavior, is the result of statistical
averaging of the behavior of atoms. In cases
where detection looks at behavior of very few
atoms, e.g., radiation, fluorescence, MRI, some
spectral techniques, properties may derive from
quantum behavior of individual atoms, or Poisson
statistical behavior of small numbers of atoms or
molecules.
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Atomic isotopes that deviate most from PN
(ZA-Z) tend to undergo radioactive decay the
larger PN (A), the more likely a emission or
fission will occur.
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Each radioisotope undergoes spontaneous,
stochastic, decay at a characteristic rate not
affected by environmental factors. The time
needed for half a given mass of isotope to
radioactively decay is a half-life, t1/2.
The time needed for 1/2 a given mass of chemical
to undergo chemical degradation (that may be
secondary to radioactive decay) is a chemical
half-life.
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Loss, clearance, of 1/2 the mass of an atom or
molecule from a biological system into which it
is introduced is a biological half-life this may
be lt or gt t1/2 or chemical half-life.
Metabolic half-life is a chemical half-life
dependent on biochemical processes.
Circulatory half-life is loss of 1/2 the mass of
an atom or molecule from the circulatory
compartment of a biological system, regardless of
disposition due to movement, metabolism,
degradation, chemical or radioactive decay.
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B685BiomedicalTracers.htm
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The information retrieval engine (Decay) is
freeware that describes the types energies of
radiation generated by most radioisotopes. The
half-life of the isotopes other basic atomic
information are also given.
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Energy delivery is governed by the inverse square
law which describes the intensity of radiation at
distance Dx beyond the source, Ix I0/Dx2. Only
radiation that fails to interact with its
transmitting medium defies this rule.
Interactions with surroundings occurs by elastic
inelastic collisions with electronic shells or
nuclei, ion-pair formation, electron-positron
formation or annihilation, electronic excitation,
or particle path bending near nuclei.
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A discussion of the processes involved is found
in section 216-224 of the following US Army
document
http//www.mega.nu8080/nbcmans/8-9-html/part_i/ch
apter2.htm
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Ion chamber discharge Film exposure (latent image
formation) Thermoluminometer or storage
phosphor Geiger-Mueller detection Flow
counters Scintillation detection
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Film exposure (latent image formation) http//www.
e-radiography.net/radtech/l/latent_image.htm F.
C. TOY, Letters to Editor, Nature 121, 865-865
(02 June 1928) doi10.1038/121865a0 The
Mechanism of Formation of the Latent Photographic
Image Abstract In a communication to NATURE of
Sept. 24, 1927 (vol. 120, p. 441), the
preliminary results were described of experiments
made in an attempt to correlate the mechanism of
the latent image formation with that responsible
for producing changes of conductivity on
illumination. It was shown that the apparent
absence of the photo-conductivity effect in the
ultraviolet was due to two things (1) the small
penetration of that light, and (2) the use of
thick layers of the silver halide. With thinner
layers, of the order of 70µ, the ultra-violet
(?3650) effect in silver bromide was found to be
about twice as great as that produced by the blue
(?4358), thus supporting the original prediction
that in very thin layers of the order of 1-5µ the
effect at ?3650 would rise to nearer ten times
that at ?4358, which is the ratio of photographic
effects in very thin layers of slow, pure silver
bromide emulsions. It was further predicted that
in very thin layers the hump of maximum
sensitivity at ?4600 in the photo-conductivity-wav
e-length curve would disappear. How completely
these conclusions have now been verified can be
seen from the accompanying graph (Fig. 1). The
inference is that in very thin layers of silver
bromide the three curves representing (1) the
relative photo-conductivity effects, (2) the
relative photographic effects, and (3) the
relative light absorptions, each plotted against
the wave-length for equal incident intensity, are
closely the same, indicating that in all
probability the primary stage of the photographic
mechanism is intimately connected with that which
produces conductivity changes on illumination.
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Geiger-Mueller detection
http//wlap.physics.lsa.umich.edu/umich/phys/satmo
rn/2003/20030322/real/sld007.htm
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Liquid Scintillation detection
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Scintillation counting often uses a coincidence
counting circuit is subject to saturation
http//www.canberra.com/pdf/Literature/Timing20Co
in20Counting20SF.pdf
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Ion pair formation Photoelectric effect Bond
breakage Thermal damage Free radical formation
reaction Cell lysis Inadequate cellular repair
--gt mutation or apoptosis Chemical toxicity
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TDS Minimize time of exposure Maximize distance
from source Optimize shielding from source
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Examples of training programs http//www.osha.go
v/SLTC/radiationionizing/introtoionizing/ionizingh
andout.html http//www.ehso.emory.edu/radiation/R
SO/Training/train2.htm General radiation
safety http//www.uiowa.edu/hpo/radiation/rpg.pdf
Medical radiation safety http//www.uiowa.edu/h
po/manuals/mrpg/MRPG.pdf Laser
safety http//www.uiowa.edu/hpo/manuals/laserman/
lasermanual.pdf