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Volume 10, No. 2,
2017, 1438 H
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Arabic
Articles |
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Dark
Matter:
Its
Origins
and
Chapters
In this
article,
I
present
an
extensive
review
of the
hypothesis
of dark
matter,
starting
with the
basic
observations
which
provoked
the
assumption
of
invisible
matter
in
galaxies
and
galaxy
clusters.
Then, I
go
through
the
development
of the
concept
of dark
matter
in
cosmology,
where
the
analysis
of the
fluctuations
of the
Cosmic
Microwave
Background
Radiation
(CMBR)
show the
necessity
of an
excess
of
matter
in the
universe
much
more
than the
observed
matter.
Dark
matter
is
thought
to be
non-baryonic,
interacting
only
through
gravitational
effects
which
can be
tested
by
gravitational
lensing
and
other
means.
Investigating
the
motion
of
galaxies,
specifically
the
rotation
curves,
showed
that
some
sizable
amount
of dark
matter
might
exist
mostly
in the
galactic
halo.
For this
reason,
astrophysicists
suggested
that
dark
matter
might be
composed
of
invisible
Massive
Astrophysical
Compact
Halo
Objects
(MACHO)
like
black
holes,
neutron
stars,
white
dwarfs
and
brown
dwarfs.
However,
astronomical
surveys
of the
sky
showed
less
than 20%
of the
amount
needed
to cover
the
deficit
in the
mass of
the
universe.
Cosmological
observations
of the
accelerated
expansion
of the
universe
suggested
that the
missing
mass in
the
composition
of the
universe
might be
subdivided
into
dark
matter
and dark
energy.
Analysis
of the
fluctuations
of the
cosmic
microwave
background
radiation
suggests
that the
amount
of dark
matter
is about
26.8% of
the mass
of the
whole
universe
and the
dark
energy
should
be about
68.3%.
The
remaining
amount
which is
just
about
4.9% is
the
observable
matter.
... |
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M. B.
Altaie
JJP,
2017, 10(2)
,
59-83
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Energy
Analysis
Power of
the
Nuclear
Track
Detector
PM-355
for
Alpha
Particles
When a
heavy
charged
particle
passes
through
matter,
it loses
energy
principally
by
scattering
electrons
within
the
matter
it
passes
through
it and
will
cause
extensive
ionization
of the
material
through
ionizing
the
atoms or
molecules
close to
its
path.
Thus,
the
charged
particle
gradually
loses
its
energy
and is
subjected
to a
gradual
slowing
down
that
could
make it
stop at
the end
of the
path
within
the
medium.
The
average
energy
loss of
the
particle
per unit
path
length (dE/dx)
is
called
the
linear
stopping
power
(S),
which
may be
measured
in units
of MeV/cm
or
similar.
The
stopping
power
and
hence,
the
density
of
ionization,
usually
increases
toward
the end
of the
range of
the
particle
and
reaches
a
maximum,
the
Bragg
edge,
shortly
before
the
energy
drops to
zero.
The
curve
that
describes
this is
called
the
Bragg
curve.
The
ionization
processes
can be
treated
statistically
to
derive
the
equation
of
stopping
power,
the best
known
being
the
Bethe
formula.
...
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S. H. S.
Al-Nia'emi
and
M. M. S.
Al-Jobouri
JJP,
2017, 10(2)
,
85-95
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Bulk
Etch
Rate of
CR-39
Detector
Using
NaOH/Ethanol
Etchant
The
science
of
solid-state
nuclear
track
detectors
was born
in
1958.Operation
of the
solid-state
nuclear
track
detector
is based
on the
fact
that a
heavy
charged
particle
will
cause
extensive
ionization
of the
material
when it
passes
through
a
medium.
The bulk
etch
rate VB
is the
rate of
removal
of the
undamaged
surface
of the
detector.
Due to
the
chemical
reaction
between
the
etching
solution
(etchant)
and the
detector
material,
some
molecules
of the
detector
material
are
removed.
The
final
effect
is the
removal
of the
material
from the
detector
surface.
During
etching,
the
material
is
removed
layer by
layer
and the
thickness
of the
detector
becomes
smaller
and
smaller.
The
aqueous
solutions
of NaOH
or KOH
are the
most
frequently
used
chemical
solutions
in this
regard.
... |
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Y. Y.
Kasim
JJP,
2017, 10(2)
,
97-103
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Effect
of
Etching
Solution
Concentration
on Track
Diameter
Development
in CR-39
Nuclear
Track
Detector
In this
work,
two
empirical
relations
related
to the
track
diameter
development
of alpha
particle
tracks
in CR-39
detectors
and to
the
detector
bulk
etch
rate as
a
function
of
concentration
of
etching
solution
are
suggested
and
tested.
The
first
empirical
equation
is a
further
extension
of the
equation
suggested
in
reference
[13] to
accommodate
the
relation
of the
track
diameter
to both
etching
time and
concentration
effects.
The
second
equation
describes
the bulk
etch
rate as
a
function
of
concentration
of
etching
solution.
The bulk
etch
rate is
determined
by the
measurement
of the
removed
layer
method.
In the
process
of
developing
these
two
equations,
tracks
formed
on CR-39
track
detector
by 3 MeV
alpha
particles
are
etched
at four
NaOH
etching
solution
concentrations
of 4, 6,
8, and
10 N.
The
etching
solution
temperature
is kept
constant
at 70
oC.
Digital
image
processing
method
for
diameter
and
detector
thickness
measurements
is used.
The
study of
track
sensitivity
measurements
resulted
is
estimating
that the
optimum
etching
solution
concentration
is 6 N
at 70
oC.
... |
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Mushtaq
Abed
Dawood
Al-Jubbori
JJP,
2017, 10(2)
,
105-112
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