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physics paper 1
atomic structure
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radius of an atom
1
⋅
1
0
−
10
m
1\cdot\ 10^{-10\ }m
1
⋅
1
0
−
10
m
radius of an nucleus
less than 1/10000
of the
radius
of an
atom
nucleus is where
most
of the
mass
is
concentrated
energy
levels
futher
away
from the
nucleus
have
alot
of
energy
when
electrons absorbs electromagnetic radiation
(eg.
light
)
electrons move
to a
higher energy level
when an atom
emits
electromagnetic radiation the electrons return back and move to a
lower
energy
level
radioactive decay
happens when an
isotope
with an
unstable nucleus emits radiation
to become
stable
carbon 14
is an example of a
radioactive isotope
radioactive decay is a
random
process
ACTIVITY
activity
is the rate at which an
unstable nucleus decays
it is measured in
bequerels
1Bq
=
1 decay per second
activity can be measured using a
geiger-muller tube
count rate
is the number of
decays
recorded each second by a
detector
alpha
particles (
α
\alpha
α
)
same as a
helium nucleus
2
protons
2
electrons
beta particles (
β
\beta
β
)
electron
ejected from the
nucleus
at
high speeds
formed whena
neutron
turns into a
proton
then an
electron
gamma ray
(
γ
\gamma
γ
)
electromagnetic radiation
another example of a type radiation emitted are
neutrons
beta particle:
travels
15cm
in air
stopped by a mm of
aluminium
quite
strongly ionising
gamma rays:
travels
several
metres
stopped by
several
cm
of
lead
weakly
ionising
alpha decay
loses
H
e
2
4
He^4_2
H
e
2
4
mass
number
decreases
by
4
atomic
number
decreases
by
2
beta decay
emits
e
−
1
0
e^0_{-1}
e
−
1
0
mass
number stays the
same
atomic number
increases
by
1
half-life
time taken for number of
nuclei
to
halve
time taken for
coun rate
(or
activity
) to
halve
radiation can be
ionising
this can
increase
the risk of
cancer
precautions of ionising radiation
for alpha radiation wear
gloves
for
beta
and
gamma
radiation wear a
lead apron
using a
moniter
to see how much radiation is being
recieved
contamination
alpha
particles are
highly
ionising but easily stopped from entering by your
skin
cells
however it is very
dangerous
when
inhaled
or
swallowed
beta
particles are
less
ionising but
highly
penetrating
gamma
rays are
weakly
ionising
and pass
in
and
out
the body
peer review:
scientists
explore
the
effects
of radiation
they
publish
and share their findings
the findings are then
checked
by other scientists
geiger-muller
tubes can detect
back round
radiation
natural sources of backround radiation:
certain
rocks
such as
granite
cosmic
rays from
space
man-made sources of backround radiation:
nuclear
weapons testing
nuclear
accidents
medecine
doses of radiation is measured by
sieverts
(
Sv
)
exploring internal organs using a
tracer
:
eg. to check the
thyroid glands
which absorb
iodine
patients drink
radioactive iodine
which emit gamma rays
too much or too little absorption will indicate an illness
you can even do a
bone scan
using
tracers
to find
tumours
a
controlled
chain
reaction
is used in
nucleus
reactors
uncontrolled
chain
reactions
are used in
nuclear
explosions
nuclear fusion
2
light nuclei
(hygdrogen) join to form a
heavier nuclei
some of the
mass
is converted into
energy
which is released as
radiation
this is the process that
releases
energy
in
stars
like the
sun
this is not a
chain
reaction
what effects exposure:
occupation
-
cabin crew
exposed to
cosmic rays
location
-
cornwall
irradiation
irradiation is when an object is
exposed
to radiation
the object does not become
radioactive
irradiation is used to
sterilise
medical equipment if it cant be
heated
up
issues with tracers:
they must emit
radiation
that can pass in and out the
body
must not be
highly
ionising
must not
decay
into another
radioactive
isotope
must have a
short
half life
contamination
contamination is when
unwanted radioactive isotopes
end up on other
materials
this is
hazardous
and will
decay
leading to
ionising
radiation
radiotherapy:
destroy
cancers
gamma
rays destroy
cancers
! - healthy
tissues
may be
damaged
radioactive
rods
inserted will cause
less
damage to healthy
tissues
alpha particles:
travels only
5cm
in the air
stopped by
paper
highly
ionising
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