Radiation Shielding Assessment for MuCool Experimental Enclosure

C. Johnstone1), I. Rakhno2)

1)Fermi National Accelerator Laboratory, Batavia, Illinois

2)University of Illinois at Urbana-Champaign, Urbana, Illinois

• 3D Geometry Model of the MuCool Test Area (MTA)

• Proton Beam & Target

• Calculated Dose Distributions & Neutron Energy Spectra

Elevation View of the MARS Model of the MTA

ZX

200

0

200

400

600600cm

350 0 350 700700cm

Target

Iron

Dirt

Concrete

Beamabsorber

Target hall

beamProton

Plan View

ZY

0

500

1.00e+03

1.50e+031.50e+03cm

0 500 1.00e+031.00e+03cm

Heavy concrete

Access pit

Door

Personnelentrance Beam absorberProton

beam

Target

MARS model of MuCool Test Area Lower level

Dirt

Plan View

Heavy concrete

Access pit

Door

Personnelentrance Beam absorber

Protonbeam

Target

MARS model of MuCool Test Area

Dirt

Upper level

ZY

0

800

1.60e+03

2.40e+032.40e+03cm

0 800 1.60e+03 2.40e+032.40e+03cm

Parking

Parking

Targethall

Heavy

Dirt Accesspit

Door

Rollup door

concrete

Compressorroom

Refrigeratorroom

Beam & Target

Beam: 400-MeV protons; σr = 1cm

1014 p/s or 6.7x1012 p/pulse at 15 Hz repetition rate

Proton interaction lengths, λ (cm) Targets

Target L (cm) R (cm) % of λtot

LH2 21 10.5 2

Cu 1 10 10

LH2 Al Cu

λtot 910 29 10

λinel 1110 41 16

Spallation neutron studies → full absorption (≈100%) targets of heavy & dense materials (Pb, Unat) are used.

• It is claimed that the facility can serve as a multi-purpose one for future operations.

• The 1-cm thick copper target (10% of interaction length) is considered as a generic (modest “averaged”) target.

Dose Equivalent above the Berm (normal operation)

nAttenuatioxx )//exp( 2211

nAttenuatioxx )//exp( 2211

Material(density, g/cm3)

Attenuationlength, α (cm)

Compacted soil (2.24)

39

High-density concrete (3.64)

28

Iron (7.87) 23

Dose Equivalent above the Berm (normal operation)

Calculated shielding compositions which provide the doselevel of 0.5 mrem/hr on the top of the MTA shielding.

0 5 10 15 20Dirt thickness (ft)

0

5

10

15

20

Shi

eldi

ng th

ickn

ess

(ft)

Total

Dirt

High-density concrete

0 5 10 15 20Dirt thickness (ft)

0

5

10

15

20

Shi

eldi

ng th

ickn

ess

(ft) Total

Dirt

Iron

Dose Equivalent in the Access Pit (normal operation)

Lower Level Upper Level

Dose equivalent (mrem/hr)ZY

300

600

900

1.20e+031.20e+03cm

0 300 600 900900cm

108 107 106 105 104 103 102 101 104.2e+07 3.0e08

0

Dose equivalent (mrem/hr)ZY

300

600

900

1.20e+031.20e+03cm

0 300 600 900900cm

106 105 104 103 102 101 100 101 104.9e+07 3.4e 08

2

Dose Equivalent in the Cryo Room (normal operation)

10" penetration 4" and 8" penetrations

Neutron Energy Spectra in the 10" Penetration

Near target hall Near cryo room

Conclusions• About 14' of heavy concrete is required above the MTA ceiling to provide 0.5 mrem/hr. • High dose is expected at the parking lot and access pit

(≈10 and 10-30 mrem/hr, respectively) within framework of the current design.

• Additional shielding is required in the target hall and/or cryo room.

• No access to the cryo room is permitted with the beam on.• The access pit should be fenced.

Sensitivity Study for a MICE Hydrogen Absorber

D. Errede1), I. Rakhno1), S. Striganov2)

1)University of Illinois at Urbana-Champaign, Urbana, Illinois

2)Fermi National Accelerator Laboratory, Batavia, Illinois

• Some uncertainties for emittance measurements & calculations

• Analytics & Monte Carlo results

• New multiple Coulomb scattering theory

• One of the goals of MICE is “… achieving an absolute accuracy on the measurement of emittance of 0.1% or better” n vs. H (hydrogen density variations due to temperature variations).

• dn/dz = -(Cooling/dE/dz) + (Heating/M.C.S.)

Re-evaluated heating term due to multiple scattering for muons in hydrogen.

Analytical Approach

n/n = -1/2 dE/dz z/E + … Phys. Rev. E52 (1995) 1039

-1/2 dE/dz z/E -0.065 at p = 200 MeV/c

with dE/dz from At. Data & Nucl. Data Tables 78 (2001) 183.

Monte Carlo approach

g = xx´

n = xpx /mc

xx xx xy xy xx xx xy xy yx yx yy yy yx yx yy yy

x x - x etc.

x px/mc etc.

4 det B

4 det A

ikA

Magnetic field distribution in the central hydrogen absorber(field direction, not magnitude, is shown)

Magnetic field map bfield.sfofo (Yagmur Torun)Z

Y

20

10

0

10

2020cm

20 10 0 10 2020cm

YX

20

10

0

10

2020cm

20 10 0 10 2020cm

MARS model of a hydrogen absorber 100 muon tracks

ZY

18

9

0

9

1818cm

18 9 0 9 1818cm

Al window

ZY

20

10

0

10

2020cm

20 10 0 10 2020cm

Monte Carlo results

200 MeV/c muons

0.1% in n 2% in H

Multiple Coulomb Scattering

GEANT4: “In the case of heavy charged particles (, , p) the mean free path (MFP) is calculated from the electron or positron 1 values with a “scaling” applied. This is possible because the MFP 1 depends only on the variable P, where P is the momentum, and is the velocity of the particle”.  1/k = 2na  

The cross-section describes projectile-nucleus elastic scattering AND projectile-electron scattering. As for the integrand, the “scaling” is OK. However the integration limits behave differently (by relativistic kinematics):

Mp Mt 0 projectile-nucleus

Mp Mt 0 /2 electron-electron

Mp Mt sin Mt /Mp muon-electron

1

1

))(cos(/)()](cos1[ dddPk

Multiple Coulomb Scattering

G. Moliere 1948 Z2

  H. Bethe 1953 Z2 Z(Z+1) 

U. Fano 1953 max(E), different screening for nucleus and electron, non-relativistic energies. A distribution with undefined region of applicability.……………………………………

A.Tollestrup,J. Monroe 2000 MuCool 176 Analogous to Fano + correct atomic form-factors for light elements. 

R. Fernow 2000 NuMu Note #123  

Moliere Z(Z+1) is good for heavy projectiles Measurements by G. Shen et al. PR D20 (1979) 1584 for 50 to 200 GeV/c protons. 

S. Striganov 2003 max(E), relativistic energies. A distribution for all thicknesses and defined region of applicability of Fano correction. 

Measurements by B. Gottschalk et al. NIM B74 (1993) 467 for 159 MeV protons in 14 materials and analysis for 6 other proton measurements (1 MeV to 200 GeV). It was shown that Moliere theory with Fano correction is accurate to better than 1% on the average for protons.

FH

FL

FH

FL

FH

Conclusions

• Hydrogen density variation of 2% gives rise to n variation of about 0.1%.

• New multiple Coulomb scattering theory enables to describe experimental data for protons within 1% accuracy on the average and adjust employed m.c.s. distributions to simulation step-sizes.