Low-energy proton accelerators - Istituto Nazionale di ...radprot/index_htm_files/Low-energy...

L. Moritz Erice, October 2-9, 2001 1

TRIUMF

Radiation Protection at Low-energy Proton Accelerators

Radiation Protection at Low-energy Proton Accelerators

Lutz Moritz, TRIUMF4004 Wesbrook Mall

Vancouver, B.C. Canada V6T 2A3

E-mail: [email protected]

(Work supported by a grant from the National Research Council of Canada)


TRIUMF

Overview• Introduction• Generation of prompt radiation

– Interaction of protons with matter– Nuclear interactions– Characteristics of prompt radiation field– Attenuation of the prompt radiation field

• Induced radioactivity production– Magnitude of induced radioactivity– Prediction of residual radiation field

• Environmental Impact– Neutron skyshine– Some aspects of emission of radioactive

effluents• Summary


TRIUMF

Introduction

LowHigh

1MeV 1GeV 1TeV0.1GeV 0.1TeVIntermediate

10MeV 10GeV 10TeV

Energy scale for proton accelerators:


TRIUMF

DTL

Many acceleration schemes are available:

Cyclotron

RFQ

Cyclotron

Van de Graaff

Ballista

Cyclotron

Cyclotron


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Many applications:• Research• Radiotherapy

– protons– neutrons – heavy ions – π-mesons

• Industrial and medical radioisotope production• Waste transmutation• Contraband detection


TRIUMF

Example: Contraband detector:

‘Contraband’ detector:

13C(p,γ)14N reaction produces gamma rays precisely tuned for absorption by nitrogen


TRIUMF

Generation of prompt radiation• Interactions of protons with matter

– Low energies: energy loss by ionization– Higher energies: energy loss by nuclear interactions

• Nuclear Interactions– Direct interactions– Pre-equilibrium– Equilibrium → evaporation

• Characteristics of the prompt radiation field


TRIUMF

Interaction of protons with matter

Range in iron:6.13101.1 pER −×=

For other materials:

Fe

FeFe A

ARRρ

ρ= 0.01

0.1

1

10

100

10 100 1000

Proton energy (MeV)

Prot

on ra

nge

in ir

on (c

m)

Low-energy protons have a definite range, however, at high energies “range” not meaningful


TRIUMF

Nuclear interaction probability fn(Ep)

0

0.2

0.4

0.6

0.8

1

1.2

0 0.25 0.5 0.75 1

Proton energy (GeV)

Prob

abili

ty o

f int

erac

tion

BeCAlFeCuPb

At high energies every proton undergoes nuclear interaction if target thick enoughAt high energies every proton undergoes nuclear interaction if target thick enough

At high energies attenuation characterized by nuclear interaction length

At high energies attenuation characterized by nuclear interaction length


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Interaction of protons with matter

Specific ionization is greatest for low-energy protons:

Bragg peakat the end of proton range

Application to Proton therapy


TRIUMF

Proton therapy facilities


TRIUMF

Proton therapy facilitiesRange shifter: This wedge shaped piece is adjusted to shift the Bragg peak to match the depth of the tumour within the body.

Range modulator: Used in conjunction with the Range Shifter to target the tumour. This extends the Bragg peak so as to match the overall depth of the tumour.


TRIUMF

Proton therapy (TRIUMF)


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Proton therapy (PSI)


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+

+/-

+/-

Neutrons

Protons

Pions

Muons

Secondary ParticlesProduced:

Neutrinos

Gamma rays

Electrons+/-

Characteristics of prompt radiation field

Above pion threshold (~430 MeV):


TRIUMF

Nuclear interactions

E

dEddΩ

σ2Directreactions

Evaporation

Schematic spectrum of emitted particlesSchematic spectrum of emitted particles

Direct reactions:•ΔA=0

Elastic scatteringInelastic scatteringCharge exchange reaction

•ΔA≠0Transfer reactionsKnockout reactions

Direct reactions:•ΔA=0

Elastic scatteringInelastic scatteringCharge exchange reaction

•ΔA≠0Transfer reactionsKnockout reactions


TRIUMF

Multi-step description of nuclear interactions

P0

P1 P2 P3 P4

Q1 Q2 Q3 Q4

Greater complexity

Multi-step direct

Multi-step compound

Initial State

Equilibrium


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Angular distribution of emitted particles

Multi-step direct: “memory” of initial direction is preserved

Anisotropic angular distribution

Multi-step compound: phase relations preserved

Angular distribution not symmetric about 90o

Evaporation: all memory of initial direction destroyed Isotropic angular distribution


TRIUMF

Energy spectrum of evaporated particles

nnn

n dEEEEd ⎟⎠⎞

⎜⎝⎛

ΘΘ∝ exp)( 2φ

Θ is the “nuclear temperature”

0.0001

0.001

0.01

0.1

1

0 10 20 30 40 50

Energy (MeV)

d/d

E

2 MeV4 MeV6 MeV8 MeV

Θ

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

0 20 40 60

Proton energy (MeV)

Tota

l neu

tron

yiel

d (p

er p

roto

n)

CAlFePb


TRIUMF

Interaction of prompt radiation with matter

ONLY nuclear reactionsONLY nuclear reactions

Energy loss by ionization,Coulomb scattering andnuclear reactions, decay

Energy loss by ionization,Coulomb scattering andnuclear reactions, decay

+

+/-

+/-

+/-Energy loss by ionizationEnergy loss by ionization

Practically no interactionPractically no interaction

Energy loss by photo-electric, Compton scattering & pair production

Energy loss by photo-electric, Compton scattering & pair production


TRIUMF

At low and intermediate energies ONLY high-energy neutrons can penetrate great thickness of concrete

At low and intermediate energies ONLY high-energy neutrons can penetrate great thickness of concrete

Charged particles are ‘ranged out’

Neutron

Proton

Pion

Muon

Interaction of prompt radiation with matter


TRIUMF

Most complete description of interactions available in simulation codes

• MCNP• LAHET• FLUKA• MARS• Etc.

Will be discussed in a separate lecture


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One example: 30 MeV radioisotope production cyclotron target caves


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Example: neutron dose rate in TR30 target maze

• Simulation code correctly accounts for all paths of radiation leakage

• Simple model underestimates dose rate

1.E-08

1.E-06

1.E-04

1.E-02

1.E+00

1.E+02

0 10 20 30

Distance along maze (m)

Neut

ron

dose

rate

(Sv

h-1)

Tesch recipe FLUKA

)(4)(1

21

2

∏=

=n

iii rf

raaHH

3.1

3.1

022.0135.2

exp022.045.0

exp)(

A

rAr

rf

ii

ii +

⎟⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛

=


TRIUMF

Need for simple point source, line-of-sight shielding calculations

• Even simple MC calculation still has ‘turn-around’ time of ~1 day

• Quick check to get order of magnitude estimate

• Independent confirmation QA


TRIUMF

target

proton beamθ

dΩ

r

d(θ)

H fieldfield

sourcesource

shieldshield

Geometry for generalized shielding problem

20 /])(/exp[),()/,,( rdEHdEH pp θλθλθ −=Would like:


TRIUMF

Restricted, lateral shielding problem

target

proton beam

r

HmaxHπ/2 H

θmθ

d(θ)

fieldfield

sourcesource

shieldshield

2/)/exp()2/( rdHH casc λπ −=Tesch:


TRIUMF

Values of parameters Hcasc , ρλh (concrete)

1.0E-18

1.0E-17

1.0E-16

1.0E-15

1.0E-14

1.0E-13

10 100 1000Proton energy (MeV)

Hca

sc(9

0o , @1m

)/p (S

v)

0

250

500

750

1000

1250

1500

0 200 400 600

Proton energy (MeV)

Dos

e at

tenu

atio

n le

ngth

(kg

m2 )

O'BrienCarterBraidBanAlsmiller

Based on neutron yield with En>8 MeVBased on neutron yield with En>8 MeV


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Neutron tenth-value layer, ρλ10 , in concrete (NCRP Report No. 51)

0

50

100

150

0 20 40 60

Incident particle energy (MeV)

Tent

h va

lue

laye

r (g

cm-2

)

(p,n)(He-3,n)(d,n)


TRIUMF

Equivalent formulations of dose attenuation

102 ///

0

102 λλλ dddeHH −−− ===

λ = attenuation lengthλ2 = half-value layerλ10 = tenth-value layer

30.210ln693.02ln101022 λλλλλ ====


TRIUMF

Dose attenuation length ρλh (concrete)

0

250

500

750

1000

1250

1500

1 10 100 1000

Proton energy (MeV)

Dos

e at

tenu

atio

n le

ngth

(kg

m-2

)

NCRP No. 51O'BrienCarterBraidBanAlsmiller


TRIUMF

Neutron attenuation length, ρλn (concrete)

0

500

1000

1500

1 10 100 1000

Neutron energy (MeV)

Atte

nuat

ion

leng

th (k

g m

-2)

High energy limit

Concrete ρ = 2400 kg m-3


TRIUMF

Thick target neutron yield per incidentproton (En>100 MeV) (FLUKA)

0.1

1

10

100

0.1 1 10

Proton Energy (GeV)

Neu

tron

yie

ld p

er p

roto

n

BeCAlFeCuNbPb


TRIUMF

Nuclear interaction probability fn(Ep)

0

0.2

0.4

0.6

0.8

1

1.2

0 0.2 0.4 0.6 0.8 1 1.2

Proton energy (GeV)

Prob

abili

ty o

f int

erac

tion

BeCAlFeCuPb

At high energies every proton undergoes nuclear interaction if target thick enoughAt high energies every proton undergoes nuclear interaction if target thick enough


TRIUMF

0.1

1

10

100

0.1 1 10

Proton Energy (GeV)

Neu

tron

yie

ld p

er p

roto

n BeCAlFeCuNbPb

Thick target neutron yield per interactingproton (En>100 MeV)


TRIUMF

High-energy neutron yield per interactingproton (En>100 MeV)

0.82 ± 0.030.46 ± 0.03Pb

0.80 ± 0.020.46 ± 0.02Nb

0.76 ± 0.020.44 ± 0.02Cu

0.76 ± 0.020.46 ± 0.02Fe

0.76 ± 0.010.58 ± 0.01Al

0.73 ± 0.020.59 ± 0.02C

0.71 ± 0.010.66 ± 0.02Be

mn0Material

mp

p EE

nEn ⎟⎟⎠

⎞⎜⎜⎝

⎛=

00)(

(E0=1 GeV)


TRIUMF

Angular distribution of neutrons with En>100 MeV (FLUKA)

Aluminium

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

60 80 100 120

Angle (θ )

Neu

tron

yie

ld (n

ste

rad-1

) 0.2 GeV0.3 GeV0.4 GeV0.5 GeV0.6 GeV0.7 GeV0.8 GeV0.9 GeV1.0 GeV

Copper

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

60 80 100 120

Angle (θ )

Neu

tron

yie

ld (n

ste

rad-1


Lead

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

60 80 100 120

Angle (θ )

Neu

tron

yie

ld (n

ste

rad-1



TRIUMF

High-energy (En>100 MeV) neutron angular distributionφ (En>0.1) = φ0 exp(-βθ )

0

1

2

3

4

5

6

0 200 400 600 800 1000

Proton energy (MeV)

Angu

lar r

elax

atio

n pa

ram

eter

β

AlCuPb‘Moyer’ value


TRIUMF

Obtain h0 and λ from FLUKA simulation

1.0E-11

1.0E-09

1.0E-07

1.0E-05

1.0E-03

0 1 2 3 4 5Depth in concrete shield (m)

Dos

e eq

uiva

lent

rate

(pSv

per

pr

oton

)

FLUKABest fit

λ

h0=hint×25

5 m

500 MeV


TRIUMF

Source term & attenuation length

0.00

0.50

1.00

1.50

2.00

0 500 1000

Incident proton energy (MeV)

h 0 (p

Sv m

2 )

800

900

1000

1100

1200

0 500 1000

Incident proton energy (MeV)A

ttenu

atio

n le

ngth

(kg

m-2

)

‘Moyer’ value


TRIUMF

Point source, line-of-sight attenuation of prompt radiation field

2

00 /)/exp()exp()()/,,( rd

EE

hEfdEHm

ppnp λβθλθ −−⎟⎟

⎠

⎞⎜⎜⎝

⎛=

Nuclear interaction probability

Nuclear interaction probability

High-energy neutron yield

High-energy neutron yield

Angular dependenceAngular dependence

Exponential AttenuationExponential Attenuation

Geometry factorGeometry factor


TRIUMF

Comparison (dose equivalent at θ = π/2)500 MeV

1.0E-11

1.0E-09

1.0E-07

1.0E-05

1.0E-03

0 1 2 3 4 5

Depth in concrete shield (m)D

ose

equi

vale

nt ra

te (p

Sv p

er p

roto

n)

FLUKAThis paperTesch

200 MeV

1.0E-12

1.0E-10

1.0E-08

1.0E-06

1.0E-04

0 1 2 3 4 5Depth in concrete shield (m)

Dos

e eq

uiva

lent

(pS

v pe

r pro

ton)

FLUKAThis paperTesch


TRIUMF

Example: 500 MeV proton beam stop

Beam line 2A test (graphite target)

1.0E-08

1.0E-07

1.0E-06

1.0E-05

-10 -5 0 5 10

Horizontal distance (m)

Dos

e eq

uiva

lent

(pSv

per

pro

ton)

This paperSnoopyFLUKA

1.8 m2.9 m

x


TRIUMF

Attenuation of neutrons in iron

0.0010.01

0.11

10100

1000

0.01 0.1Neutron energy (MeV)

Cro

ss s

ectio

n (b

arns

)

7.1069.015615611

22

==⋅⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛

+−

−=⋅⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛

+−

−=Δ nnnn EEEmMmME

Max. energy loss in elastic collision:

keV

ΔEn insufficient to cross “gap” Build-up of low-energy neutrons

0.001

0.01

0.1

1

10

100

1000

1.0E-06 1.0E-04 1.0E-02 1.0E+00 1.0E+02


Cro

ss s

ectio

n (b

arns

)


TRIUMF

Interaction of neutrons with hydrogen

0.01

0.1

1

10

100

1.E-111.E-091.E-071.E-051.E-031.E-011.E+011.E+03


Cro

ss s

ectio

n (b

arns

)

TotalElastic


TRIUMF

Example: ISAC Target/ion Source Shielding (Plan)

Steel

Concrete(low Na) Ion beam

SlitsCu Beam dumpTarget

Proton beam

Concrete

Steel shielding always followed by concrete

Steel shielding always followed by concrete


TRIUMF

Radioactivity induced in targets and structures


TRIUMF

Induced total radioactivity production in perspective

Asat ~ 6 TBq/kWAsat ~ 6 TBq/kW

2000 MW

Rule of thumb:

Asat ~ 50 TBq/kWAsat ~ 50 TBq/kW

Accelerator

Fission reactorRule of thumb:

0.1 – 1.0 MW 103-104 TBq103-104 TBq

108 TBq108 TBq


TRIUMF

Residual fields of components (targets)Total radioactivity produced in thin targets of medium A per unit proton beam current Ip (μA):

AS ≈ 1.5 × 109 Ip Bq per g cm-2

≈ 3×10-4 Ip Sv h-1 @ 1m per g cm-2

= 3×10-2 Ip Sv h-1 @ 1m per 100 g cm-2

AS ≈ 1.5 × 109 Ip Bq per g cm-2

≈ 3×10-4 Ip Sv h-1 @ 1m per g cm-2

= 3×10-2 Ip Sv h-1 @ 1m per 100 g cm-2

For Ip > 1-10 μA~ Remote handling


TRIUMF

Determining induced radiation fields (I)

Activity from Silberberg and Tsao

Cross Sections

Activity from Silberberg and Tsao

Cross Sections

Input target elementor compound

Input target elementor compound

Select possible productSelect possible product

Look up gamma-raylibrary

Look up gamma-raylibrary

Flux to dose conversion algorithm

Flux to dose conversion algorithm

Add dose contributionAdd dose contribution

Last product?No

Yes

Total dose rate &‘Danger Parameter’Total dose rate &

‘Danger Parameter’

Method due to Barbier, using semi-empirical cross sections


TRIUMF

Mass distribution of products (Silberberg & Tsao)

(bombardment by 500 MeV protons)

0.01

0.1

1

10

100

1000

0 50 100 150 200 250

Atomic mass of product (summed over Z)

Cro

ss s

ectio

n (m

b)

CuFeAl

0.01

0.1

1

10

100

1000

0 50 100 150 200 250

Atomic mass of product (summer over Z)

Cro

ss s

ectio

n (m

b)

PbU-238


TRIUMF

Bombardment of U-238 with 500 MeV protons

0.01

0.1

1

10

100

1000

0 50 100 150 200 250


Cro

ss se

ctio

n (m

b)

LAHET Code SystemSilberberg & Tsao

fragmentation fission

spallation

peripheral

Can also calculate cross sections using MC codes


TRIUMF

Can explore variation of production cross sections with proton energy

Bombardment of Pb

0.01

0.1

1

10

100

1000

0 50 100 150 200 250


Cros

s se

ctio

n (m

b)

0.1 GeV0.5 GeV1.0 GeV10 GeV

At low energies production dominated by peripheral reactions

At low energies production dominated by peripheral reactions

At high energies production more or less equal for all product masses (10-20 mb)

At high energies production more or less equal for all product masses (10-20 mb)


TRIUMF

Determining induced radiation fields (II)

FLUKAFLUKA

‘Star’ density‘Star’ density

‘ω factors’‘ω factors’

Induced radiation field at 1 mfrom selected materials

Induced radiation field at 1 mfrom selected materials

CERN ‘ω factors’(not validated at low-intermediate energies)

Density of high-energy nuclear reactions


TRIUMF

Determining induced radiation fields (III)Ion chamber

HPGe

Total dose rateTotal dose rate

Gamma-ray spectrumGamma-ray spectrum

Determine partial dose ratesfor each isotope

Determine partial dose ratesfor each isotope

Determine saturation valuesper unit beam current for

each isotope

Determine saturation valuesper unit beam current for

each isotope

Allows calculation of induced radiation fields for arbitrary

irradiation history

Allows calculation of induced radiation fields for arbitrary

irradiation history

Irradiation history

Collimator

Normalize


TRIUMF

Determining induced radiation fields (III)

Useful for:

Shutdown and maintenance planning

Decommissioning planning


TRIUMF

Example: build-up and decay of induced radiation field in a 500 MeV cyclotron

0

0.5

1

1.5

0 100 200 300 400 500 600 700 800

Time in days since Jan. 1, 1999

H (m

Gy

h-1)

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700 800

Time in days since Jan. 1, 1999

Beam

cur

rent

( A

)


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Environmental Impact

Skyshine

Release of effluents

Air

Water


TRIUMF

Skyshine

r

Source

Receptor


TRIUMF

Neutron interactions with air

0.001

0.01

0.1

1

10

100

0.01 0.1 1 10 100


Cro

ss s

ectio

n (b

arns

)

N-14(n, elastic)O-16(n, elastic)N-14(n, inelastic)O-16(n, inelastic)

mfp ≈ 80 m


TRIUMF

Maximum energy loss of neutron by elastic scattering

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛

+−

−=Δ 2

1mMmM

EE

n

n

24.01141141

2

=⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛

+−

−=

22.01161161

2

=⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎠⎞

⎜⎝⎛

+−

−=

Many collisions

Nitrogen:

Oxygen:


TRIUMF

Skyshine

24 rQH

π=

High-energy neutrons

Low-energy neutrons r

First approximation (geometric effect only):


TRIUMF

Some attenuation for large distances

)/exp(4

)( 2 λπ

rr

QrH −=

With λ of order a few hundred m


TRIUMF

Effect of attenuation in air

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

10 100 1000

Distance from source (m)

Rel

ativ

e do

se ra

te

No attenuation200 m400 m600 m

Attenuation length


TRIUMF

Spectrum hardens with distance

Dominated by low-energy neutrons

Dominated by high-energy neutrons


TRIUMF

Importance functions(Alsmiller et al.)

∫= θθθ dEdrEIESrH ),cos,()cos,()( rr

θ

15 mS(E,cosθ)

rDetector

Source


TRIUMF

Composite neutron leakage energy spectrum(Stapleton et al.)

1.0E-08

1.0E-04

1.0E+00

1.0E+04

1.0E+08

1.E-08 1.E-05 1.E-02 1.E+01 1.E+04


d φ/d

E (M

eV-1

)

72 10,exp −≤⎟

⎠⎞

⎜⎝⎛ −

= ETE

TAE

dEdφ

20010, 7 ≤<= − EEB

dEdφ

1000200,2 ≤<= EEC

dEdφ

max3 1000, EEED

dEd

≤<=φ


TRIUMF

Equivalent dose as a function of distance(using importance functions & composite spectrum)

1E-18

1E-17

1E-16

1E-15

1E-14

0 200 400 600 800 1000 1200


Dos

e ra

te [(

r+b)

2 H] (

Sv m

2 per

ne

utro

n)

1.1 MeV4.5 MeV12.2 MeV45 MeV125 MeV400 MeV1 GeV


TRIUMF

Stapleton et al.

2)()](/exp[

)(rb

ErarH c

+−

=λ

rbVirtual source


TRIUMF

Skyshine parameters

13.2467 ± 3347.1 ± 4.52.24 ± 0.27400

49.1 ± 3.72.41 ± 0.29Mean402Stapleton et al.

14.7617 ± 5746.4 ± 4.42.22 ± 0.2630 000

14.7604 ± 4946.8 ± 4.02.23 ± 0.2410 00014.6597 ± 3646.8 ± 3.12.23 ± 0.18500014.1532 ± 2847.3 ± 3.02.24 ± 0.181000

11.3355 ± 749.2 ± 1.82.44 ± 0.111259.6267 ± 453.1 ± 2.12.81 ± 0.14457.4213 ± 354.2 ± 2.22.94 ± 0.1512.25.7183 ± 253.1 ± 2.52.78 ± 0.164.54.0142 ± 447.1 ± 5.41.96 ± 0.281.1

g (fSv m2) λ (m)b (m)a (fSv m2)EC(MeV)


TRIUMF

Effective attenuation length in air

0

200

400

600

800

1 10 100 1000 10000 100000

Maximum neutron energy (MeV)

Atte

nuat

ion

leng

th (m

)


TRIUMF

Effect of “virtual source”

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

10 100 1000


H(r)

/Q (m

-2)

2)()](/exp[

)(rb

ErarH c

+−

=λ

)/exp(4

)( 2 λπ

rr

QrH −=

1.1 MeV

1 GeV


TRIUMF

Emission of radioactive effluents

Air: difficult to hold up except for vacuum system exhaust, but higher release limits

Water: easier to control (re-circulation, hold-up)


TRIUMF

Typical active cooling water systems

VacuumPumps Etc.

Target/collimator

ALCW

HALCW

IonExchange

CoolingTower

RawWater

BeamlineMagnets

Heat Exchanger

48V56Co

54Mn65Zn

7Be3H

Evaporation

ALCW: Active, Low-Conductivity WaterHALCW: High-Active, Low-Conductivity Water

RF Cavities

Containment

Closed Sump


TRIUMF

Design of typical drainage system

Central active sump

Localsump

Ground watersump

To storm sewer (continuously)

To sanitary sewer(as required)

Sub-surfacedrains

Always sampledbefore release

Monitored continuouslySampled periodically

Level alarms


TRIUMF

Hold-up of vacuum exhaust (RIB facilities, e.g. ISOLDE, ISAC)

primary vacuum

secondary vacuum

operating storage (high, short-lived gamma fields)

long term storage, low level, high radio-toxicity

to filtered exhaust

Charcoal filter


TRIUMF

Design of typical ventilation system

Roughing Filter

HEPA Filter

Operating Fan

Stand-by Fan

Radioactive Air

7Be

11C 41Ar3H

RadioactivityMonitor

Low pressureLeakage

Dampers

Leakage


TRIUMF

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25

Ventilation rate

Act

ivity

in ro

om

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25

Ventilation rate

Activ

ity e

xhau

sted

Effect of ventilation rate

Number of air changes per half-life

Saturation Activity

Higher ventilation rates reduce the radioactivity level in the irradiation room but increase the amount of radioactivity exhausted

Higher ventilation rates reduce the radioactivity level in the irradiation room but increase the amount of radioactivity exhausted


TRIUMF

Dose From Effluents ReleasedImmersion P(e)19Inhalation P(i)19

SourceSource

AtmosphereAtmosphere

Surfacewater

Surfacewater

Vegetatedsoil

Vegetatedsoil

CropsCrops

Aquaticanimals

Aquaticanimals

Aquaticplants

Aquaticplants

Criticalgroup

Criticalgroup

P01

External P79

External P39

P27

P26

P14

P13

P12

P69

P49

P034

Immersion P(e)29

P02

Ingestion P(i)29

0

2

1

3

4

6

7

9Sv/Bq


TRIUMF

Screening Models(NCRP Report No. 123)

Source Concentration in medium

Screening factor

Dose

Transport models

Pre-calculated committed effective dose per unit concentration

× =


TRIUMF

Three levels of screening:

Level I: assume radionuclide concentration at point of emission

Level I: assume radionuclide concentration at point of emission

Level II: dispersion in atmosphere or surface water

Level II: dispersion in atmosphere or surface water

Level III: more definitive pathway analysis (air only)

Level III: more definitive pathway analysis (air only)

if Dose < Dose Limit then no further calculation

if Dose < Dose Limit then no further calculation

Increasing sophistication


TRIUMF

Atmospheric dispersion

⎟⎟⎠

⎞⎜⎜⎝

⎛ −= 2

2

01 2exp

zzy

hU

fPσσπσ

hσz

U

x

xx

y 0001.0108.0

+=σ

xx

z 0025.0106.0

+=σ

Diffusion parameters


TRIUMF

Effect of downdraft near exhaust point

Plume:

Downdraft:

U

W0(1-ET)X0(1-ET)X0

ETX0ETX0

5.10.1;58.158.2 00 ≤≤⎟⎠⎞

⎜⎝⎛−=

UWfor

UWET

0.55.1;06.030.0 00 ≤≤⎟⎠⎞

⎜⎝⎛−=

UWfor

UWET

ET


TRIUMF

Effect of “entrainment”

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

10 100 1000 10000 100000Downwind distance (m)

Dilu

tion

fact

or P

01/f

(s m

-3)

W0/U=1.0W0/U=1.5W0/U=5.0

U = 2 m s-1

h = 15 m


TRIUMF

Summary

• Some specific application: – proton therapy

• Generation of prompt radiation– direct interactions, evaporation

• Need for point-source, line-of-sight models– models at intermediate energies

• Generation of induced radioactivity– semi-empirical recipes, measurements

• Environmental impact– skyshine, emission of radioactive effluents

Have described:

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