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Fallout Deposition In Hiroshima Where Gamma-Ray Thermoluminescence Measurements Exceed the Dosimetry System (DS02) Doses. Stephen D. Egbert Science Applications International Corporation Presentation at Health Physics Meeting – Sacramento, Calif. - July 24, 2012

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slide1

Fallout Deposition In Hiroshima

WhereGamma-RayThermoluminescence Measurements Exceed the Dosimetry System (DS02) Doses

Stephen D. EgbertScience Applications International Corporation

Presentation at Health Physics Meeting – Sacramento, Calif. - July 24, 2012

Department of Energy Special Session on Atomic Bomb Survivor Dosimetry –

Residual Radiation Exposure

slide2

Residual Radiation at Hiroshima

  • Since 1945, we believed Hiroshima residual radiation
      • Hypocenter neutron ground activation (out to 0.5 km)
      • Koi-Takasu area fission products (WSW 3-4 km)
      • Possibly in “black rain” area fission products (NW 1-10 km)
  • Shizuma (1996) finds a pattern of 137Cs, but very little
  • Imanaka (2011) finds original MED survey readings
      • Pattern like 137Cs; But higher dose especially NNE at ~2 km
      • Slow drop off in south until ~1 km where measurements end
  • Egbert and Kerr (2012) finds four high TLD dose areas
      • Nishitera temples (NNW 1 km) ~500-900 mGy
      • Hiroshima University area (south 1.5 km) ~200 mGy
      • Miyosen Temple (east 1.9 km) ~100 mGy
      • Hiramoto House (west 2.1 km) ~100 mGy
  • TLD pattern is similar to survey and 137Cs, but one and two orders-of-magnitude higher, respectively

MED – Manhattan Engineering District

TLD – Thermoluminescence Dosimetry

slide3

DS02 γ Dose Summary

  • Measured γ doses were obtained in ceramic tiles by thermoluminescence dosimetry (TLD) and compared with discrete ordinate and Monte Carlo calculations
  • In DS02 Report Executive Summary for γ dose
      • For Hiroshima “there remain some indications of measured values exceeding calculated values at longer distances”
      • For Nagasaki “the measured values tend to be somewhat less than calculated values, at least out to about 800 meters from the hypocenter”
  • Average weighted γ dose M/C ratio was 1.06 at Hiroshima and 0.80 at Nagasaki

DS02 – Dosimetry System 2002

M/C – Measurement to Calculation

slide4

Click for animation

Hiroshima TLD Measurements to Calculation Ratio

Nagasaki TLD Measurements to Calculation Ratio

(After adjustment for unaccounted shielding)

TLD – Thermoluminescence Dosimetry

slide5

Excess TLD Doses in 20 Nagasaki Neighborhoods Used in the DS02 Report

TLD – Thermoluminescence Dosimetry

DS02 – Dosimetry System 2002

slide6

Excess TLD Doses in 29 Hiroshima Neighborhoods Used in the DS02 Report

TLD – Thermoluminescence Dosimetry

DS02 – Dosimetry System 2002

slide7

0.01

0.02

0.03

0.1

0.03

MED Survey Map Over Hiroshima Excess TLD Measurements

  • Survey contours from measurements made during October 3-7, 1945
  • (in milliroentgen per hour)
  • TLD locations identified
  • Excess TLD dose locations labeled in italic red (>0.04 Gy) and underlined (>0.4 Gy) or blue (not observed)
  • Shading indicates confidence
  • TLD samples, with small black labels, are too close to hypocenter

MED – Manhattan Engineering District

TLD – Thermoluminescence Dosimetry

slide8

Map of 137Cs and Rain Amount Over Hiroshima Excess TLD Measurements

  • Shizuma 137Cs measurements indicated by relative radius of circles. Red circle is scaled down by a factor of 20 in order to fit on page (~0.04 Gy)
  • TLD locations identified
  • Excess TLD dose locations labeled in italic red (>0.04 Gy) and underlined (>0.4 Gy) or blue (not observed)
  • Shading indicates confidence
  • TLD samples, too close to hypocenter, are not shown

TLD – Thermoluminescence Dosimetry

slide9

0.1

0.2

0.5

0.8

Nishiyama

Reservoir

0.9

1.0

0.03

0.02

0.005

MED Survey Map Over Nagasaki TLD Measurements

  • Survey contours from measurements made during September 21 to October 4, 1945
  • (in milliroentgen per hour)
  • TLD locations identified
  • Excess TLD dose locations labeled in italic red (>0.04 Gy) and underlined (>0.4 Gy) or blue (not observed)
  • Shading indicates confidence
  • TLD samples, with small black labels, are too close to hypocenter

MED – Manhattan Engineering District

TLD – Thermoluminescence Dosimetry

slide10

Discussion About

Excess TLD Dose Method

  • Advantages of Excess TLD Dose Method
      • Excess TLD dose and residual dose to survivors may be from same isotope(s), absorbed in same period (first days)
      • Location TLD dose received is stationary and known
      • Few TLD weathering effects - No rain following weeks
      • TLD may allow proxy measurements of both skin and deep dose using ceramic as surrogate
  • Disadvantages
      • Cannot discern excess TLD dose closer than 1 km from hypocenter, where initial radiation gamma-ray dose is high
      • Uncertainty of ceramic TLD background may cause significant uncertainty in estimate of excess TLD dose

TLD – Thermoluminescence Dosimetry

slide11

Conclusions

  • TLD measurements and DS02 calculations are consistent, except in certain Hiroshima neighborhoods beyond 1 km
  • TLD measurements in excess of DS02 calculations may be from fallout deposited on or near a measured ceramic sample
  • It may be possible to make TLD measurements using different layers of the same sample to obtain data on the β, γ and bremsstrahlung doses from fallout
  • Obtaining a more complete set of TLD measurements (beyond 1 km) is a method to distinguish which suburbs and neighborhoods did and did not receive fallout
  • It may be possible to use excess TLD dose to estimate fallout deposition to provide a basis for calculating fallout doses to distal as well as proximal Japanese survivors
  • Other physical dosimetry and biological effects for survivors, such as epilation, should be reexamined to see if similar patterns are observed as indicated by the excess TLD doses

TLD – Thermoluminescence Dosimetry

DS02 – Dosimetry System 2002