Transcript Radon Measurement Operator Proficiency

RADON MEASUREMENT
OPERATORS PROFICIENCY
COURSE
IN CONCERT WITH UNIVERSITY OF
ILLINOIS AT CHICAGO AND
ILLINOIS DEPARTMENT OF
NUCLEAR SAFETY
12/3/98
Illinois Department of Nuclear Safety
1
Physics of
Radon and its Decay
Products
12/3/98
Illinois Department of Nuclear Safety
2
Introduction to Radon and
Radioactivity
12/3/98
Illinois Department of Nuclear Safety
3
Radon Characteristics
 Colorless
gas
 Odorless
gas
 Tasteless
gas
 Naturally
Occurring
 Radioactive
 Inert,
does not chemically react (Noble Gas)
4
Simple Model of an Atom
Atom comprised of:


Nucleus

Protons (+)

Neutrons (neutral)
Electrons (-)
5
The Nucleus
 Made
up of positively charged protons and neutral
neutrons.
 The number of protons and neutrons combined is
called the “mass number” (or atomic mass).
 The number of neutrons is generally more than the
number of protons.
 The number of protons is the atomic number
(which identifies the element).
 The number of electrons is normally equal to the
number of protons, so that the total atom has no
net charge.
6
Isotopes
 An
isotope is any atom with the same number of
protons as another atom, but a different number of
neutrons.
 Radon-220 (thoron) is an isotope of Radon-222,
since it also has 86 protons, but it has 134 rather
than 136 neutrons.
7
Isotope Example
1P
1P, 1N
1P, 2N
Atomic # ?
Atomic Mass?
8
A Radon - 222 Nucleus
 Protons
= 86
 Neutrons
= 136
 Atomic Mass
= 222
 Atomic Number = 86
 This isotope of radon
is further identified
by its mass number,
hence the name
radon-222
9
Periodic Table of the Elements
Rn
86
222
10
Radioactive Decay
Radon-222

Occurs spontaneously

An atom changes
identity due to change
in number of protons.
(-2)

Radiation is released in
the process.
Alpha Radiation
Gamma
Radiation
Polonium 218
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Radon Entry
Radon
Radium
Uranium
12
Abbreviated Uranium-238
Decay Series
Uranium-238 (solid)
4.47 billion years
Radium-226 (solid)
1,620 years
Radon-222 (gas)
3.8 days
 Uranium
decays to
Radium and then to
Radon.
 Uranium and Radium as
solids are trapped in soil,
but radon gas can move.
 The decay rate is
expressed by “half life”.
13
The Meaning of Half Life
100
100
90
80
70
60
50
40
30
20
10
0
Percent Remaining
 Half
Life is the
time required for
half of the atoms
to decay.
50
25
12.5
0
1
2
3
6.25
3.125
4
5
 It
is not the time
for all of the
atoms to decay.
Number of Half Lives
14
Uranium-238
a,g
Thorium-234
b,g
Protactinium-234
b,g
Uranium-234
a,g
Thorium-230
a,g
Radium-226
a,g
Radon-222
a,g
Polonium-218
Bismuth-210
b,g
Polonium-210
a,g
a,g
Lead-214
Lead-206
(Stable)
b,g
Bismuth-214
b,g
Polonium-214
a,g
Lead-210
Uranium 238
Decay Series
b,g
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Radon Decay Product Characteristics
 Source
of cell damage in lungs
 Short-lived
 Have
static charges
 Chemically
 Solid
decay products most significant
reactive
particles
 Heavy
Metals
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Fate of Indoor Radon
Airborne
Breathable
 Measurable

Radon-222
Radon Decay
Products
Plated Out
Non-Breathable
 Non-Measurable

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Alpha Radiation (a)
 Alpha
radiation is a particle released when the
nucleus kicks out 2 neutrons and 2 protons (mass
number changes by 4 and atomic number changes
by 2).
 Alpha particle
– relatively massive
– relatively slow
– total charge of +2
18
Beta Radiation (b)
P+
N
b-
 Beta
Radiation is a particle which is released
when the nucleus changes a neutron into a proton
and a beta particle (atomic mass number remains
unchanged).
 Beta particle
– Relatively small mass
– Relatively fast moving
– Total charge of -1
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Radon & Short-Lived Decay Products
b+1P
Pb
82
-2 P
-2N
+1P
Bi
83
a
Po
84
bAt
85
Rn
86
a
-2 P
-2N
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Gamma Radiation (g)
 Gamma
radiation is pure energy. It is released
from the nucleus whenever an alpha or a beta is
emitted.
 Gamma ray
– No mass
– Moves at the speed of light
– No charge
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Relative Penetrating Power
Alpha
Beta
Gamma
Paper
Concrete
22
Alpha Particles Are Strong Enough
To Pit Plastic

Plastic chip from
passive radon test
(alpha track).

Magnified only 100
times.

3 months at EPA to
Action Level of 4
pCi/L.
23
Ionization Caused by Radiation
can occur with a a, b, or g
Atom in air
Ion in air (net charge +1)
Before Collision
After Collision
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Ion
 Normally,
the number of electrons orbiting the
nucleus is equal to the number of protons inside
the nucleus, so that the net charge of the atom is
zero.
 An
ion is an atom that has either lost or gained
electrons. It has a net positive or negative charge.
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Impact of Ionization
Caused by Radiation
 Measuring
ionization allows one to detect the
presence of radiation:
– Pulsed ion chambers, Electret ion chambers, Geiger
counters
 Ionization
also contributes to overall health
effects.
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Radon Measurement Units
 One
picocurie per liter (pCi/L) is 2.22
disintegration's per minute within a liter
– This comes from the fact that one Curie is 37
billion disintegration's per second (dps) and:
One
picocurie is one trillionth of a Curie,
.037 decays per second
There are 60 seconds in a minute
60 x .037=2.22, or 1 pCi/L is 2.22 dpm
or
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International Radon Unit:
The Becquerel
Becquerel per cubic meter (Bq/m3) is one
disintegration per second within a cubic meter
Becquerel = 1 disintegration per second
1 pCi/L = 37 Bq/m3
 One
 In
other words:
– pCi/L x 37 = Bq/m3, or
– (Bq/M3)/37 = pCi/L
– 4pCi/l = 148Bq/m3
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Radon Decay Product Units:
The Working Level (WL)
1
Working Level is the total amount of energy
which would be eventually released by the alpha
particles coming from the short- lived RDPs.
1 WL is created by 100 pCi/L of radon
 1 Working Level is the amount of short-lived
radon decay products within one liter that would
ultimately come from the complete disintegration
of 100 pCi/L of radon (assuming all RDPs that
are produced are measured).
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Radon Decay Product Units:
A More Practical Definition
1
1 WL
100 pCi/L
Radon
Radon
Working Level is the
amount of short-lived radon
decay products that exist at
any one moment within one
liter if a room, or container,
is constantly maintained at
100 pCi/L (assuming all
RDPs that are produced are
measured.)
30
Secular Equilibrium
 The
condition where the short-lived Radon Decay
Products (RDPs) have each reached the same
radioactivity ( in picocuries per liter) as the radon
forming them.
 It
takes 4 hours for this to occur.
31
A Water Flow Experiment
32
At Equilibrium
Water Flows are Equal
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At Equilibrium
Water Flows are Equal
 The
waterfalls would be measured in
gallons/minute.
 Replace waterfalls with radioactive decay in
decays/minute, or picocuries.
 The volume of water in the buckets is analogous
to the number of atoms of each isotope with the
short lived isotopes having the least number of
atoms at any one time.
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At Secular Equilibrium the Decay
Rates of RDPs and Radon are Equal
Radon 222 - 3.8 days
Po 218 - 3 min.
Pb 214 - 27 min.
Bi 214 - 19.7 min.
Po 214 - .000164 sec.
Pb 210 - 19.7 years
35
Equilibrium Ratio (ER)

Plated out
RDPs
Suspended
RDPs

The equilibrium ratio
describes the fraction of
RDPs that are suspended
in the air, and therefore
measurable, to the total
RDPs created.
Measured
RDPs
ER =
Total RDPs
36
Equilibrium Ratio Example
 Assume
that you measured the RDPs suspended
in the room with a working level meter and
determined there were 0.5 WL in the room.
 Assume
that you measured the radon and
determined that there was enough radon (i.e... 100
pCi/L) to create 1 WL of RDPs.
 Therefore E.R. = 0.5 WL = 0.5
1.0 WL
37
Another Equilibrium Ratio Equation
 Since
the total RDPs can be found by measuring
the radon, the total RDPs part of the equilibrium
ratio equation can be replaced by:
Total RDPs = Radon (in pCi/L)
100 pCi/L per WL
 This provides a more useful equation:
ER = Measured RDPs (in WL)
Radon (in pCi/L)
100 pCi/L per WL
38
Equilibrium Ratio Equation
 Canceling
units and moving the “100” gives:
RDPs (in WL) x 100
ER = Radon ( in pCi/L)
 This
equation allows one to determine an
equilibrium ratio, and to convert from Radon to
Working Levels, or vice versa.
39
Equilibrium Ratio Calculation
Example
 Simultaneous
measurements of radon and radon
decay products indicate 4.0 pCi/L and .02 WL
respectively. What is the equilibrium ratio?
.02
x
100
2
ER =
= = 0.5
4
4
This could also be expressed as a percent by
multiplying by 100, or 0.5 x 100 = 50%
40
Factors Affecting
Equilibrium Ratio
 Air
circulation
– Increases plate-out, thereby decreasing ER
 Electronic
air filters
– Decreases RDPs attached to dust particles, thereby
decreasing ER
 Suspended
dust, smoke
– Increases sites for RDPs so fewer plate-out
 Recent
ventilation
– Inadequate time for RDPs to have been formed
 0.3
< ER < 0.7 in homes.
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The Equilibrium Ratio Assumption
EPA and IDNS often assumes that, if nothing else
is known about the home, an ER of 0.5 (50%) is a
reasonable assumption.
 Remember that the ER can be different, not only
from house to house, but also within the same
house.
 Equilibrium ratios in homes range from 0.3 to 0.7

42
Other Versions of the
Equilibrium Equation

WL
x
100
ER =
pCi/L

WL
x
100
pCi/L =
ER

ER
x
pCi/L
WL =
100
WL x 100
ER
pCi/L
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Dynamic Equilibrium

Measurable Radioactivity
12 Hours
Rn
WL
House
Open
Time

House Closed
Once the radon entry
rate into a building has
been altered, time is
needed for radon and
RDP levels to stabilize.
12 hours is normally
sufficient for dynamic
equilibrium to occur in
a home.
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