Radon PHY0411 presentation

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RadonPHY0411 presentation

• Li Wai Chak 06692751
• Tse Hin 06831364

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Outline

• Introduction of Radon
• Origin of indoor Radon
• Radioactivity
• Harmful effects
• Testing methods
• Activated charcoal test
• Electret Passive Environmental Radon Monitors
  (E-PERMs)
• Alpha-tracks
• Ways to control
• Conclusions

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History

• Discovery of radioactive substances (Henri
  Becquerel,1896)
• Discovery of 3 isotopes of Radon (R. B. Owens, E.
  Rutherford, F. e. Dorn,1899-1901)

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History

• Proof of Radon being an inert gas (F. Soddy,1907)
• Awareness of high mortality from lung cancer of
  uranium mineworkers (P. Ludewig, E.
  Lorenser,1924)
• First measurement of indoor Radon (early 1950s)

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What is Radon?

• Rn
• Z 86
• Noble gas
• 1s22s22p63s23p63d104s24p65s24d105p64f145d106s26p6
  
• Colorless
• Melting point -71.15 C
• Boiling point -61.85 C
• Half-life 3.8235days(for Rn-222)

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Why should we study Radon?

• High average dose per person
• 10mSv(millisieverts) per person per year
• High mortality from lung cancer of uranium
  mineworkers
• second leading cause of lung cancer in the U.S.
  after cigarette smoking

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Origin of indoor Radon

• Ventilation rate
• Reduce energy use
• Raise concentrations of pollutant
• Natural convection

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Natural convection

• Temperature difference
• Buoyant
• Draws air from the lower part to the upper part
• Force air out the upper
• Pressure difference
• Winds
• Buoyant

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Natural convection

• Soil
• Cracks
• Drain
• Water
• Fittings
• Windows

http//geopanorama.rncan.gc.ca/ottawa/images/radon
.jpg
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Radon Concentration

• Non-stable pollutants
• Reactions and decay

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Decay series

• Isotopes can be divided into 4 types
• 4 alpha decay series
• Thorium series (A 4n)
• Neptunium series (A 4n1)
• Radium series (A 4n2)
• Actinium series (A 4n3)
• Neptunium series doesn't include Radon

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Actinium series

• U-235(7108Yr) ?Th-231(25.5h)
  ?Pa-231(3.3104Yr) ?Ac-227(21.7Yr) ?
  ?Rn-219(4s) ?
• U-235 is extremely rear
• Only gaseous element, Rn-219 is short-lived
• Not enough time to diffuse into buildings

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Thorium series

• Th-232(1.41010Yr)? Ra-228(5.8Yr)?
  Ac-228(6.25h)? Th-228(1.9Yr)?
  Ra-224(3.6d)? Rn-220(56s)? Po-216(0.15s)?
  Pb-212(10.6h)? Bi-212(61min)? (64.1)Po-212(299ns)
  or (35.94)Tl-208(3.1min)? Pb-208(stable)
• Only gaseous element, Rn-220(thoron)
• Cant be neglected

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Radium series

• Only gaseous element, Rn-222 is long-lived
• Enough time for diffusion
• Even for being breathed in

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Radium series
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Origin of decay

• Quantum tunneling through a coulomb potential
  barrier

http//hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear
/alptun2.html
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Origin of decay
Frequency of hitting the barrier,
probability for an emission per second,
http//hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear
/alptun2.html
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Origin of decay
http//hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear
/alptun2.html

• Half life 0.25 ms
• Good fit with actual half life (0.3ms)
• Sometimes more segments are needed

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Harmful effects

• breathing air with radon and its decay products
• radon is chemically inert
• Its decay products lodge in the airways of the
  lungs
• Alpha decays of the short-lived solid decay
  products
• Directly destroy the genetic materials

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Harmful effects

• 15,000-22,000 Americans die every year from
  radon-related lung cancer
• Additional 180 cancer deaths from drinking water
• Stomach cancer

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How do we measure the level of Radon?

• Three detectors available for measuring radon
  concentrations
• Charcoal canisters
• Electret Passive Environmental Radon Monitors
  (E-PERMs)
• Alpha-tracks

• Nuclear Instruments and Methods in Physics
  Research Section A Accelerators, Spectrometers,
  Detectors and Associated Equipment,Volume 518,
  Issues 1-2, 1 February 2004, Pages 452-455

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Charcoal canisters

• short-term measurements
• 24 h - 7 days
• Low cost
• Easy to use

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WHAT IS ACTIVATED CARBON?

• A material with an exceptionally high surface
  area. Just one gram of activated carbon has a
  surface area of approximately 500 m2
• Physical adsorption occurs because all molecules
  exert attractive forces, especially molecules at
  the surface of a solid (pore walls of carbon),
  and these surface molecules seek other molecules
  to adhere to. The large internal surface area of
  carbon has many attractive forces (e.g. Van der
  Waals force or London dispersion force) that
  work to attract other molecules.

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PRINCIPLE

• contains granular-activated carbon that absorbs
  the radon gas entering the canister from the
  surrounding atmosphere.
• At the end of the test period the canister is
  sealed and analyzed by a NaI spectrometer (Sodium
  iodide spectrometer) and the radon concentration
  in Bqm3 or Bq/L is reported.

• Nuclear Instruments and Methods in Physics
  Research Section A Accelerators, Spectrometers,
  Detectors and Associated Equipment,Volume 518,
  Issues 1-2, 1 February 2004, Pages 452-455

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Quantities we need to measure

• Weight of the charcoal canister (before and
  after)
• Exposure period
• Time when the measurement starts
• Gross counts
• Background counts
• Standard counts

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HOW DO WE MEASURE THE LEVEL OF RADON BY CHARCOAL
CANISTERS ?
Charcoal canisters
NaI spectrometer
Amplifier
Data Analysis System
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Procedure

• All of the canisters are weighted.
• The canisters are opened inside a room and the
  exact start times are recorded.
• After 48 hours, the canisters are removed, taped,
  and the exact time is recorded.
• The canisters are allowed to sit for at least 3
  hours to allow progeny to equilibrate with the
  radon before counting.

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WHAT IS NAI GAMMA SPECTROMETER?
multichannel analyzer
http//www.tpub.com/content/doe/h1013v2/img/h1013v
2_73_1.jpg
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HOW DOES A NAI GAMMA SPECTROMETER WORK?

• Each chemical element emits a characteristic
  gamma-ray energy/intensity, and the element can
  be identified from this gamma-ray data.
• the gamma ray enters a NaI crystal
• ? visible light/ UV will be emitted.

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NaI crystal

• When a gamma from a radioactive source interacts
  with the crystal, there are three primary methods
  by which it is absorbed.1) Photoelectric
  Effect2) Compton Interaction3) Pair Production

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Photoelectric Effect

• Gamma rays interact primarily with the bound K or
  L shell electrons from the Iodine in the crystal.
• Gamma gives all of its energy to the bound
  electron and knocks it out with an energy (Ee )
  given by where B is the binding energy of
  the electron
• Some fixed fraction of the electron energy will
  be converted to light photons which then impinge
  on the photocathode of the photomultiplier.

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COMPTON INTERACTION

• Purely a kinematic collision between the incident
  gamma photon and an electron in the crystal
• Momentum is conserved in the interaction
• The scattered photon may go in any direction and
  the electron can be scattered only in a forward
  direction with respect to the incident gammer
  ray.

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PAIR PRODUCTION

• A photon of sufficient energy gives up all of its
  energy and forms two particles, an electron and a
  positron.
• The minimum energy of pair production
• After pair production, in a few nanosecond, the
  positron interacts with an electron in a process
  called annihilation. The mass of the particles is
  changed into two photons of 0.511MeV each.

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HOW DOES A NAI GAMMA SPECTROMETER WORK?

• The photocathode ejects electrons when absorbing
  EM wave photoelectric effect
• The ejected electrons hit a dynode, which is more
  positive than the photocathode, ejects more
  electrons
• The ejected electrons hit the second dynode,
  which is more positive than the first dynode,
  ejects more electrons. . .
• The electrical signal is amplified

http//resources.emb.gov.hk/physics/articleIE/gamm
aXray/gammaXray_e.htm
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(No Transcript)
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Experimental data (Background)
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GAMMA-RAY SPECTROMETERCALIBRATION
Slope 0.0034 MeV/Channel 3.4
keV/Channel
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Experimental data (KCI)
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Data Analysis (KCI)

• KCl
• Mass 63 1g
• ROI ch 335-525
• ROI 1290582 1136 counts
• ROI (Net) 236549 1531
• Time 85918s
• Experimental radioactivity
• Expected photopeak (from data book) 1.46MeV
  (ch430)
• Experimental photopeak 1.51 MeV(ch445)

• Background
• ROI ch 335-525
• ROI 918278 958 counts
• ROI (Net) 53462 1335 counts
• Time 85262s

• Standard source (Co-60)
• 373.9 kBq 1983-7-1
• ROI 919627 959 counts
• ROI (net) 552048 1135 counts
• time 400s

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• RN radon concentration in the chamber for the
  exposure period (pCi/liter)
• Net CPM Gross CPM -background CPM for that
  detector for that day
• CF Calibration factor, radon adsorption rate (
  min-1)
• Ts exposure time of canister (min)
• E detecter efficiency for the appropriate
  detector (CPM/pCi)
• DF decay factor from the midpoint of exposure
  to the time of counting, which is calculated from
  

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Sand
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FACTORS AFFECTING THE MEASUREMENTS

• Background radiation
• Not all the radon particles emits gammer ray
• For charcoal cansister,
• variation in temperature
• humidity
• charcoal type
• air velocity during exposure

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Electret Passive Environmental Radon Monitors
(E-PERMs)

• Consists of a stable electret (electrically
  charged Teflon disc) mounted inside an
  electrically conducting chamber.
• The ions produced inside the chamber are
  collected by the electret.
• The charge reduction is measured using a battery
  operated electret reader.
• Using appropriate calibration factors and the
  exposure time, the desired parameters such as
  airborne radon concentration in air is
  calculated.

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Alpha-tracks

• One or more plastic detectors are placed in a
  holder.
• Radon gas is allowed to enter the device through
  small openings covered by a filter.
• The small particles thrown off by the radon gas
  during decay will hit the plastic detector and
  cause a tiny dent on the plastic surface.
• After the deployment period, the plastic
  detectors are removed and chemically etched to
  make the small dents easier to see under a
  microscope.
• The marks are counted and the number of marks is
  proportional to the amount of radon gas the
  device had been exposed to.

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Controlling indoor air pollution

• Entry of radon from the grounddraw air from (or
  blow air on) the soil or gravel immediately under
  the substructure of a house.
• For the reason of pressure different, we
  shouldi) increased ventilationii) air cleaning
  (reduction in indoor humidity)

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• QA

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Curies

• a unit of radioactivity
• 1 Ci 3.71010 decays per second,roughly the
  activity of 1 gram of the radium isotope 226Ra,
• SI unit
• the becquerel (Bq)one decay per second
• i.e. 1 Ci 3.71010 Bq

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Reference

• http//www.who.int/ionizing_radiation/env/radon/Ra
  don_flyer_2006.pdf
• http//en.wikipedia.org/wiki/Radon
• http//www.iaq.gov.hk/second.asp?languageenpage
  pubsubpamphletscontentdetailnumber5
• http//www.epd.gov.hk/epd/english/resources_pub/pu
  blications/files/pn99_1.pdf
• http//www.epd.gov.hk/epd/english/greenproperty/re
  f_mat/ref_mat.html
• http//www.epa.gov/radon/pdfs/402-r-03-003.pdf
• http//www.epa.gov/radon/realestate.html
• http//www.epa.gov/radon/healthrisks.html
• http//www.geocities.com/Tokyo/Bay/9229/donghei.ht
  m
• http//www.who.int/ionizing_radiation/env/radon/Ma
  r06MeetingReport.pdf
• http//www.who.int/ionizing_radiation/env/radon/Ra
  don_flyer_2006.pdf
• http//www.bsi.lv/index.php?Modproductsid44
• http//resources.emb.gov.hk/physics/articleIE/gamm
  aXray/gammaXray_c.htm
• http//www.radon.com/radon/radon_FAQ.html
• http//www.sciencedirect.com/science/journal/01689
  002
• http//hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear
  /alptun2.html
• Nuclear Instruments and Methods in Physics
  Research Section A Accelerators, Spectrometers,
  Detectors and Associated Equipment,Volume 518,
  Issues 1-2, 1 February 2004, Pages 452-455