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Accelerator Radiological Protection A Personal and Privileged - - PowerPoint PPT Presentation

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Accelerator Radiological Protection A Personal and Privileged Odyssey G. William Morgan Lecture Health Physics Society Meeting San Diego, California Ralph H. Thomas University of California (Retired) July 2003 Outline Introductionthe

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Health Physics Society Meeting San Diego, California Ralph H. Thomas University of California (Retired) July 2003

Accelerator Radiological Protection

A Personal and Privileged Odyssey

  • G. William Morgan Lecture
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Ralph H. Thomas July 2003 #2

Outline

  • Introduction—the problem with ‘history’
  • The birth of ‘health physics’
  • Burton J. Moyer
  • Shielding
  • Dosimetry
  • Skyshine
  • The future
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Ralph H. Thomas July 2003 #3

The problem with history

Marcus Tullius Cicero circa 50 BC

‘History is the witness that testifies to the passing of time; it illuminates reality, vitalizes memory, provides guidance in daily life…’

‘History is the witness that testifies to the passing of time; it illuminates reality, vitalises memory, provides guidance in daily life…’ ‘History is more or less bunk’

Marcus Tullius Cicero circa 50 BC Henry Ford By Charles Wheeler Chicago Tribune 25 May 1916

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Ralph H. Thomas July 2003 #4

Outline

  • Introduction—the problem with ‘history’
  • Burton J. Moyer
  • Shielding
  • Dosimetry
  • Skyshine
  • The future

The birth of ‘health physics’

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SLIDE 5

Ralph H. Thomas July 2003 #5

The birth of health physics

  • 1895

Discovery of x-rays Roentgen

  • 1932

Particle Accelerators Cockcroft & Walton and Lawrence et al.

  • 1932

Discovery of the neutron James Chadwick

  • 1933

Artificial radioactivity Fermi et al.; Joliot-Curie

  • 1935

Neutron RBE ~10 John Lawrence

  • Neutron limit: 0.01 R/day

Ernest Lawrence

  • Nuclear Medicine: Radiosodium

and radiophosphorus

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Ralph H. Thomas July 2003 #6

The birth of health physics (continued)

  • 1936

Neutron Radiotherapy Stone et al. Metabolism of radionuclides Hamilton et al. Neutron Radiobiology Aebersold et al.

  • 1938

Radioactivity of Tritium Louis Alvarez

  • 1940–42 Transuranic elements:

McMillan and Seaborg Np, Pu

  • 1942

Nuclear Weapons: 75 mg U ‘Calutron’ Medical effects of transuranics Hamilton et al. Self-sustaining neutron chain Fermi et al. reaction

235

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Ralph H. Thomas July 2003 #7

The birth of health physics (continued)

Cockcroft Walton

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Ralph H. Thomas July 2003 #8

The birth of health physics (continued)

First Cyclotron

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Ralph H. Thomas July 2003 #9

The birth of health physics (continued)

Joseph Hamilton drinking radiosodium

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Ralph H. Thomas July 2003 #10

The birth of health physics (continued)

Edwin McMillan

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Ralph H. Thomas July 2003 #11

Outline

  • Introduction—the problem with ‘history’
  • The birth of ‘health physics’
  • Shielding
  • Dosimetry
  • Skyshine
  • The future

Burton J. Moyer

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Ralph H. Thomas July 2003 #12

Burton J. Moyer

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Ralph H. Thomas July 2003 #13

Burton J. Moyer–Influences

  • Shielding
  • Dosimetry
  • Environmental Impact (‘Skyshine’)
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Ralph H. Thomas July 2003 #14

Outline

  • Introduction—the problem with ‘history’
  • The birth of ‘health physics’
  • Burton J. Moyer
  • Dosimetry
  • Skyshine
  • The future

Shielding

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Ralph H. Thomas July 2003 #15

Shielding–Its importance

Shielding at the source controls all the principal exposure modes:

  • Prompt radiation
  • Release of radionuclides and noxious chemicals
  • Migration of radionuclides in soil and groundwater to water

supplies

  • Recycling of radioactive accelerator components
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Ralph H. Thomas July 2003 #16

Shielding–Methods of attack

  • Measurement (method of choice in the 60s and 70s)
  • Solution of the Boltzmann Equation (elegant but difficult)
  • Monte Carlo techniques (now extremely powerful)
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Ralph H. Thomas July 2003 #17

Shielding–Bevatron

Bevatron roof shielding

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Ralph H. Thomas July 2003 #18

Shielding–Moyer model

Moyer model

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Ralph H. Thomas July 2003 #19

Shielding–Moyer model (continued)

H = 1 r2 ⋅ Emax ∫ Emin g E

( )⋅ B E,θ ( )⋅exp −d θ ( ) λ E ( )

[ ]⋅ d2n E,θ

( )

dEdΩ ⋅dE In cylindrical geometry: ≈ 1 r2cosec2θ ⋅NH0Em ⋅exp −βθ

( )⋅exp −dcosecθ λ

( )

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Ralph H. Thomas July 2003 #20

Shielding–Typical beam-stop experiment

Blockhouse

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Ralph H. Thomas July 2003 #21

Shielding–Typical beam-stop data (a)

Shielding

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Ralph H. Thomas July 2003 #22

Shielding–Typical beam-stop data (b)

Shielding

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Ralph H. Thomas July 2003 #23

Shielding–A comparison of neutron attenuation length in concrete measured in beam-stop experiments 1961–1964

Laboratory Year Proton Energy (GeV) Density (g/cm3) Detector Attenuation Length (g/cm2) Reference

CERN 1961 20 3.6 Nuclear Emulsion 132 ± 10 Citron et al. [1961] ORN L & RL 1962 10 3.6 Nuclear Emulsion 164 ± 20 Thomas (Ed.) [1963] DESY, SLAC , CERN 1962 20 3.6 Nuclear Emulsion 132 ± 2 Thomas (Ed.) [1963] UCR L 1964 6.2 2.4

11C

activation 108 ± 20 Smith et al. [1964] UCR L 1964 6.2 2.4

24Na

activation 112 ± 20 Smith et al. [1964] UCR L 1964 6.2 2.4

198Au

activation 116 ± 20 Smith et al. [1964] RL 1964 6.2 2.4

32S

activation 123 ± 10

  • K. B. Shaw

[1964]

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Ralph H. Thomas July 2003 #24

Shielding–BNL Lateral shielding experiment (a)

BNL Isofluence Contours

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Ralph H. Thomas July 2003 #25

Shielding–BNL Lateral shielding experiment (b)

BNL Attenuation

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Ralph H. Thomas July 2003 #26

Shielding–Lateral shielding experiment at CERN

CERN shielding

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Ralph H. Thomas July 2003 #27

Shielding–Variation of neutron production with Energy

Neutron production shielding

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Ralph H. Thomas July 2003 #28

Outline

  • Introduction—the problem with ‘history’
  • The birth of ‘health physics’
  • Burton J. Moyer
  • Shielding
  • Skyshine
  • The future

Dosimetry

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Ralph H. Thomas July 2003 #29

Dosimetry–Moyer’s philosophy

  • Systematic study and measurements of physical

characteristics of radiation field, e.g.: —Total particle fluence, Φ —Differential energy spectra, (dφ/dE) —Irradiation geometry, G

  • Conversion coefficients, <g>, used to convert total fluence

data, Φ, to ‘radiation protection’ quantities, H H = g Φ

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Ralph H. Thomas July 2003 #30

Dosimetry–Conversion coefficients

H = gG Φ where: and G indicates the irradiation geometry gG = Emax gG E

( ) dφ

dE       dE ∫ Emin Emax dφ dE       dE ∫ Emin

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Ralph H. Thomas July 2003 #31

Dosimetry–The stability of conversion coefficients

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04

Neutron Energy (MeV) Conversion Coefficient (pSv Cm2)

MADE, NBS 63 (1957) MADE, RHT (1965) MADE, ICRP 21 (1971) MADE, NCRP 38 (1971) MADE & H*(10), ICRP 51 (1987) E, ICRP 74 (1995) E, Ferrari et al. (1997) E, Yoshizawa et al. (1998) E, Bozkurt et al. (2001)

A Comparison of Neutron Fluence to Dose Equivalent Coefficients for AP Irradiation Geometry

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Ralph H. Thomas July 2003 #32

Dosimetry–The power of radiation transport calculations

Values of <g> for the early Bevatron

Spectrum Geometry Conversion function <g> (pSv•cm2)

Bevatron no roof shield AP 380 1-MeV monoenergetic neutrons AP NBS 63 386 Hess cosmic ray spectrum AP RHT 1965 193 Bare Cu target above ground AP RHT 1965 142 Steel-shielded Cu target AP RHT 1965 94 Steel-shielded Cu target ISO DSTZ 2000 43

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Ralph H. Thomas July 2003 #33

Outline

  • Introduction—the problem with ‘history’
  • The birth of ‘health physics’
  • Burton J. Moyer
  • Shielding
  • Dosimetry
  • The future

Skyshine

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Ralph H. Thomas July 2003 #34

Skyshine–Bevatron

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Ralph H. Thomas July 2003 #35

Skyshine–Empirical formulation (Stapleton et al.)

H r

( ) =

a b + r

( )2 ⋅exp −r λE

( ),

where: a = 2 × 10−15m2Sv b = 40 m λE = 660 m at 5 GeV

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Ralph H. Thomas July 2003 #36

Skyshine–Neutron spectra (Donahue et al.)

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Ralph H. Thomas July 2003 #37

Skyshine–Spectrum hardening (Donahue et al.)

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Ralph H. Thomas July 2003 #38

Apollo 13–The real deal

Eye Flash Experiment

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Ralph H. Thomas July 2003 #39

The future

  • Increasing exposure to high-LET radiations (new

technologies)

  • Solid radiological basis needed for protection standards

(e.g., RBE for neutrons)

  • Stability in radiation protection standards and quantities
  • Clarity in dosimetric requirements
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Ralph H. Thomas July 2003 #40

Look before you leap

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Ralph H. Thomas July 2003 #41

  • H. Wade Patterson