Accelerator Radiological Protection A Personal and Privileged - PowerPoint PPT Presentation

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 • Introduction—the problem with ‘history’ • The birth of ‘health physics’ • Burton J. Moyer • Shielding • Dosimetry • Skyshine • The future Ralph H. Thomas July 2003 #2

The problem with history ‘History is the witness that testifies to the passing of time; ‘History is the witness that testifies to the passing of time; it illuminates reality, vitalises memory, provides guidance it illuminates reality, vitalizes memory, provides guidance in daily life…’ in daily life…’ Marcus Tullius Cicero Marcus Tullius Cicero circa 50 BC circa 50 BC ‘History is more or less bunk’ Henry Ford By Charles Wheeler Chicago Tribune 25 May 1916 Ralph H. Thomas July 2003 #3

Outline • Introduction—the problem with ‘history’ The birth of ‘health physics’ • • Burton J. Moyer • Shielding • Dosimetry • Skyshine • The future Ralph H. Thomas July 2003 #4

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 Ralph H. Thomas July 2003 #5

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 235 • 1942 Nuclear Weapons: 75 mg U ‘Calutron’ Medical effects of transuranics Hamilton et al . Self-sustaining neutron chain Fermi et al . reaction Ralph H. Thomas July 2003 #6

The birth of health physics (continued) Cockcroft Walton Ralph H. Thomas July 2003 #7

The birth of health physics (continued) First Cyclotron Ralph H. Thomas July 2003 #8

The birth of health physics (continued) Joseph Hamilton drinking radiosodium Ralph H. Thomas July 2003 #9

The birth of health physics (continued) Edwin McMillan Ralph H. Thomas July 2003 #10

Outline • Introduction—the problem with ‘history’ • The birth of ‘health physics’ Burton J. Moyer • • Shielding • Dosimetry • Skyshine • The future Ralph H. Thomas July 2003 #11

Burton J. Moyer Ralph H. Thomas July 2003 #12

Burton J. Moyer–Influences • Shielding • Dosimetry • Environmental Impact (‘Skyshine’) Ralph H. Thomas July 2003 #13

Outline • Introduction—the problem with ‘history’ • The birth of ‘health physics’ • Burton J. Moyer Shielding • • Dosimetry • Skyshine • The future Ralph H. Thomas July 2003 #14

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 Ralph H. Thomas July 2003 #15

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) Ralph H. Thomas July 2003 #16

Shielding–Bevatron Bevatron roof shielding Ralph H. Thomas July 2003 #17

Shielding–Moyer model Moyer model Ralph H. Thomas July 2003 #18

Shielding–Moyer model (continued) E max ] ⋅ d 2 n E , θ ( ) H = 1 [ ( ) ⋅ B E , θ ( ) ⋅ exp − d θ ( ) λ E ( ) r 2 ⋅ ⋅ dE ∫ g E dEd Ω E min In cylindrical geometry: 1 ⋅ NH 0 E m ⋅ exp −βθ ( ) ( ) ⋅ exp − d cosec θ λ ≈ r 2 cosec 2 θ Ralph H. Thomas July 2003 #19

Shielding–Typical beam-stop experiment Blockhouse Ralph H. Thomas July 2003 #20

Shielding–Typical beam-stop data (a) Shielding Ralph H. Thomas July 2003 #21

Shielding–Typical beam-stop data (b) Shielding Ralph H. Thomas July 2003 #22

Shielding–A comparison of neutron attenuation length in concrete measured in beam-stop experiments 1961–1964 Proton Attenuation Energy Density Length (g/cm 3 ) (g/cm 2 ) Laboratory Year (GeV) Detector Reference CERN 1961 20 3.6 Nuclear 132 ± 10 Citron et al . Emulsion [1961] Nuclear Thomas ORN L & RL 1962 10 3.6 164 ± 20 Emulsion (Ed.) [1963] DESY, SLAC , 1962 20 3.6 Nuclear 132 ± 2 Thomas CERN Emulsion (Ed.) [1963] 11 C Smith et al . UCR L 1964 6.2 2.4 108 ± 20 activation [1964] 24 Na UCR L 1964 6.2 2.4 112 ± 20 Smith et al . activation [1964] 198 Au Smith et al . UCR L 1964 6.2 2.4 116 ± 20 activation [1964] 32 S RL 1964 6.2 2.4 123 ± 10 K. B. Shaw activation [1964] Ralph H. Thomas July 2003 #23

Shielding–BNL Lateral shielding experiment (a) BNL Isofluence Contours Ralph H. Thomas July 2003 #24

Shielding–BNL Lateral shielding experiment (b) BNL Attenuation Ralph H. Thomas July 2003 #25

Shielding–Lateral shielding experiment at CERN CERN shielding Ralph H. Thomas July 2003 #26

Shielding–Variation of neutron production with Energy Neutron production shielding Ralph H. Thomas July 2003 #27

Outline • Introduction—the problem with ‘history’ • The birth of ‘health physics’ • Burton J. Moyer • Shielding Dosimetry • • Skyshine • The future Ralph H. Thomas July 2003 #28

Dosimetry–Moyer’s philosophy • Systematic study and measurements of physical characteristics of radiation field, e.g. : — Total particle fluence, Φ — Differential energy spectra, (d φ /dE) — Irradiation geometry, G • Conversion coefficients, <g>, used to convert total fluence data, Φ , to ‘radiation protection’ quantities, H H = g Φ Ralph H. Thomas July 2003 #29

Dosimetry–Conversion coefficients H = g G Φ E max where:   ( ) d φ g G E   dE ∫   dE E min g G = E max   d φ   dE ∫   dE E min and G indicates the irradiation geometry Ralph H. Thomas July 2003 #30

Dosimetry–The stability of conversion coefficients A Comparison of Neutron Fluence to Dose Equivalent Coefficients for AP Irradiation Geometry 1.E+04 MADE, NBS 63 (1957) MADE, RHT (1965) Conversion Coefficient (pSv Cm 2 ) MADE, ICRP 21 (1971) MADE, NCRP 38 (1971) 1.E+03 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) 1.E+02 1.E+01 1.E+00 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) Ralph H. Thomas July 2003 #31

Dosimetry–The power of radiation transport calculations Values of <g> for the early Bevatron Conversion <g> (pSv • cm 2 ) Spectrum Geometry function Bevatron no roof AP 380 shield 1-MeV monoenergetic AP NBS 63 386 neutrons Hess cosmic ray AP RHT 1965 193 spectrum Bare Cu target above AP RHT 1965 142 ground Steel-shielded Cu AP RHT 1965 94 target Steel-shielded Cu ISO DSTZ 2000 43 target Ralph H. Thomas July 2003 #32

Outline • Introduction—the problem with ‘history’ • The birth of ‘health physics’ • Burton J. Moyer • Shielding • Dosimetry Skyshine • • The future Ralph H. Thomas July 2003 #33

Skyshine–Bevatron Ralph H. Thomas July 2003 #34

Skyshine–Empirical formulation (Stapleton et al .) a ( ) , ( ) = ) 2 ⋅ exp − r λ E H r ( b + r where: a = 2 × 10 − 15 m 2 Sv b = 40 m λ E = 660 m at 5 GeV Ralph H. Thomas July 2003 #35

Skyshine–Neutron spectra (Donahue et al .) Ralph H. Thomas July 2003 #36

Skyshine–Spectrum hardening (Donahue et al .) Ralph H. Thomas July 2003 #37

Apollo 13–The real deal Eye Flash Experiment Ralph H. Thomas July 2003 #38

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 Ralph H. Thomas July 2003 #39

Look before you leap Ralph H. Thomas July 2003 #40

H. Wade Patterson Ralph H. Thomas July 2003 #41