SHIELDING for a HIGH ENERGY SHIELDING for a HIGH ENERGY DIGITAL RADIOGRAPHY BAYDIGITAL RADIOGRAPHY BAY

P.Berry, P. Heintz, S.K.VelardeP.Berry, P. Heintz, S.K.VelardeLos Alamos National LaboratoryLos Alamos National Laboratory

University of New Mexico Medical University of New Mexico Medical SchoolSchool

Three Rivers Technical Conference Three Rivers Technical Conference 20102010

Rogers, MNRogers, MN

Unclassified per T. N. Claytor, ADC 3/15/10

WE’RE GOING HIGH ENERGY

OBJECTIVESOBJECTIVES

• Identify key personnel needed to build a Identify key personnel needed to build a radiography facilityradiography facility

• Know the elements and requirements in Know the elements and requirements in the buildingthe building

• Know the basic elements in performing Know the basic elements in performing shielding calculationsshielding calculations

• Follow the project after the planning phase Follow the project after the planning phase through completionthrough completion

PLANNING COMMITTEEPLANNING COMMITTEE

• Management Representative Management Representative (budget)(budget)

• Radiographers Levels II and IIIRadiographers Levels II and III

• Radiological PhysicistRadiological Physicist

• ArchitectArchitect

• Construction RepresentativeConstruction Representative

• Equipment VendorEquipment Vendor

KEY to SUCCESSKEY to SUCCESS

COMMUNICATIONCOMMUNICATION

And perhaps cooperation and consensus

Some Issues to be Some Issues to be AddressedAddressed

• What accelerator to purchase?What accelerator to purchase?

• What objects will be radiographed?What objects will be radiographed?

• What modalities will be used (DR ,CT)?What modalities will be used (DR ,CT)?

• Any other activities in the facility?Any other activities in the facility?

• Types of doors (sliding or swinging)?Types of doors (sliding or swinging)?

• Handling and storing of radioactive material?Handling and storing of radioactive material?

• Future use of area around the facility?Future use of area around the facility?

Some Issues to be Some Issues to be AddressedAddressed

• Density of the concrete has to be specifiedDensity of the concrete has to be specified

• Mechanical penetrations have to be Mechanical penetrations have to be planned in advanceplanned in advance

• Plan for HVACPlan for HVAC

• If any changes are made to the original If any changes are made to the original plan NOTIFY the physicist IMMEDIATELYplan NOTIFY the physicist IMMEDIATELY

• Ensue proper concrete pouring techniquesEnsue proper concrete pouring techniques

door

D-primaryD-leakage

Description of the Environment Description of the Environment Outside of the BayOutside of the Bay

• Parking Lot to the left of the bay.Parking Lot to the left of the bay.

• Grassy area in the direction of the primary beamGrassy area in the direction of the primary beam

• New office building will be constructed 100 ft in New office building will be constructed 100 ft in the direction of the primary beam.the direction of the primary beam.

• Radiography bay will be inside of a larger Radiography bay will be inside of a larger building.building.

• 8 foot wide hallway separating the bay and office 8 foot wide hallway separating the bay and office space.space.

PRODUCTION OF RADIATION TYPES IN PRODUCTION OF RADIATION TYPES IN A LINACA LINAC

electrons photonselectrons photonsBREMSSTRAHLUNGBREMSSTRAHLUNG

Photo-neutronsproduction

Radioactive nucleus

Pair-production

positron

electron

Radioactivenucleus

Neutron capture

ACCELERATOR HEAD > 10 MeV

Photoneutron Photoneutron ProductionProduction• Interaction of photon beam with heavy metal Interaction of photon beam with heavy metal

accelerator components results in neutron accelerator components results in neutron production.production.

• For all practical purposes neutron production For all practical purposes neutron production threshold is 8-10 MeV.threshold is 8-10 MeV.

• Neutrons are emitted isotropically and scattered Neutrons are emitted isotropically and scattered many timesmany times

• Photoneutrons are produced mainly from the Photoneutrons are produced mainly from the target, and collimators– exiting through the target, and collimators– exiting through the collimatorcollimator

Threshold for Photoneutron Threshold for Photoneutron ProductionProduction

ElementElement Atomic Atomic NumberNumber

(A)(A)

Abundance Abundance (%)(%)

Threshold Threshold Energy (MeV)Energy (MeV)

DD 22 .02.02 2.232.23

BeBe 99 100100 1.671.67

Cu Cu

6363 69.269.2 10.8510.85

CuCu 6565 30.830.8 9.919.91

W W 182182 26.326.3 8.068.06

WW 184184 30.630.6 7.417.41

PbPb 208208 52.452.4 7.377.37

DefinitionsDefinitions

• Control AreaControl Area: limited access area with the occupational : limited access area with the occupational exposure controlled by the radiation supervisorexposure controlled by the radiation supervisor

• Uncontrolled area: any space not meeting the definition Uncontrolled area: any space not meeting the definition of a controlled area (general public)of a controlled area (general public)

• Shielding design goals (P): effective dose values Shielding design goals (P): effective dose values recommended by NCRP-2004 for controlled and recommended by NCRP-2004 for controlled and uncontrolled areasuncontrolled areas

• Primary BarrierPrimary Barrier: a wall, ceiling, or floor designed to : a wall, ceiling, or floor designed to attenuate the useful beam to the required degreeattenuate the useful beam to the required degree

• Primary radiation: radiation emitted directly from the Primary radiation: radiation emitted directly from the source that is intended to be used for industrial imaging source that is intended to be used for industrial imaging

DefinitionsDefinitions

• Occupancy factor (T): the fraction of time that the Occupancy factor (T): the fraction of time that the maximally exposed person is present in an area maximally exposed person is present in an area while the beam is on. (always 1.0 for radiation while the beam is on. (always 1.0 for radiation workers) workers)

• WorkloadWorkload (W): the average dose of radiation (W): the average dose of radiation produced by a source over a specified time (most produced by a source over a specified time (most often a week) at a specific location. If there is no often a week) at a specific location. If there is no dependable information, assume 8 hours per dependable information, assume 8 hours per day , 5 days a week for a total of 40 hours per day , 5 days a week for a total of 40 hours per week. If this is to be exceeded, NCRP 51 page 42 week. If this is to be exceeded, NCRP 51 page 42 gives the guidelines for this problem.gives the guidelines for this problem.

Definitions Definitions

• Secondary Barrier: A wall, ceiling, floor designed Secondary Barrier: A wall, ceiling, floor designed to attenuate leakage and scattered radiation to to attenuate leakage and scattered radiation to the required goal.the required goal.

• Secondary radiation: All radiation produced by Secondary radiation: All radiation produced by scattering off of objects, or leakage through the scattering off of objects, or leakage through the protective source housing –all radiation in the bay protective source housing –all radiation in the bay except for the primary beamexcept for the primary beam

• Leakage radiationLeakage radiation: All radiation , except the : All radiation , except the useful beam, coming from within the accelerator useful beam, coming from within the accelerator head and other beam-line components.head and other beam-line components.

• Use factor (U): the fraction of a primary beam Use factor (U): the fraction of a primary beam workload that is directed toward a primary barrierworkload that is directed toward a primary barrier

Shielding Design GoalsShielding Design Goals

• Controlled AreaControlled Area

0.1 mGy/wk0.1 mGy/wk

• Uncontrolled AreaUncontrolled Area

0.02 mGy/wk0.02 mGy/wk

Shielding MaterialsShielding MaterialsMaterialMaterial DensityDensity

(g/cm^3)(g/cm^3)RadiationRadiation

TypeTypeAdvantageAdvantage DisadvantageDisadvantage

ConcreteConcrete 2.352.35 Photons & Photons &

NeutronsNeutronsInexpensiveInexpensive Requires tooRequires too

Much spaceMuch space

High High DensityDensity

ConcreteConcrete

3.8-4.63.8-4.6 Photons &Photons &

NeutronsNeutronsGain spaceGain space ExpensiveExpensive

EarthEarth 1.4-1.61.4-1.6 Photons &Photons &

NeutronsNeutronsAlmost FreeAlmost Free Difficult toDifficult to

controlcontrol

BoratedBorated

polyethylenpolyethylenee

0.950.95 NeutronsNeutrons High crossHigh cross

Section forSection for

Thermal n.Thermal n.

ExpensiveExpensive

LeadLead 11.3511.35 PhotonsPhotons Save spaceSave space Produce Produce neutronsneutrons

SteelSteel 7.97.9 PhotonsPhotons Save spaceSave space Produce Produce neutronsneutrons

Assumptions for the Assumptions for the ProblemProblem• 15 MV LINAC15 MV LINAC

• Dose Rate 20,000 cGy/min@ 1 meter (200 Dose Rate 20,000 cGy/min@ 1 meter (200 Gy/min)Gy/min)

• Leakage .001%Leakage .001%

• Workload: 4.8 x 10Workload: 4.8 x 105 5 Gy/week Gy/week

• Beam width at the inner wall 8.6 feet in diameterBeam width at the inner wall 8.6 feet in diameter

• Room size: 55 feet x 30 feet x 25 feet.Room size: 55 feet x 30 feet x 25 feet.

• All calculations are 0.30 meters from the outer All calculations are 0.30 meters from the outer wall.wall.

door

D-primaryD-leakage

Sample Problem (primary Sample Problem (primary barrier)barrier)

• Equations:Equations:B = PdB = Pd22/WUT/WUTn = log (1/B)n = log (1/B)

S = TVL(1) –(n-1) TVL(2)S = TVL(1) –(n-1) TVL(2)

where “n” is the number of tenth value where “n” is the number of tenth value layers, S is the total wall thickness and layers, S is the total wall thickness and TVL(1) and TVL(2) are the tenth valuesTVL(1) and TVL(2) are the tenth values

Primary BarrierPrimary Barrier

• Distance = 14.3 meters Leakage = 1Distance = 14.3 meters Leakage = 1P = 20X10P = 20X10-6-6 (Sv/wk) (Sv/wk)U =1, T = 1/40 (this is a grassy area and U =1, T = 1/40 (this is a grassy area and rarely occupied)rarely occupied)

• TVL(1) = 44 cm; TVL(2) = 41 cmTVL(1) = 44 cm; TVL(2) = 41 cm

Wall thickness is 8.8 feetWall thickness is 8.8 feet

Secondary Barrier or Secondary Barrier or CeilingCeiling

• B = P dB = P d22/ ((Leakage) WUT)/ ((Leakage) WUT)

n = log (1/B) n = log (1/B)

S = TVL(1)- (n-1) TVL(2) S = TVL(1)- (n-1) TVL(2)

Secondary BarrierSecondary Barrier

• Distance = 6.38 meters Leakage = 0.001%Distance = 6.38 meters Leakage = 0.001%

• P = 20X10P = 20X10-6-6 (Sv/wk) (Sv/wk)U =1 T = 1/40U =1 T = 1/40

• TVL(1) = 36 cm; TVL(2) = 33 cmTVL(1) = 36 cm; TVL(2) = 33 cm

Wall thickness is 2.5 feetWall thickness is 2.5 feet

DOORDOOR

• Reduce the energy and quantity of the Reduce the energy and quantity of the neutrons reaching outside of the door.neutrons reaching outside of the door.

• Hydrogenous material reduces the neutron Hydrogenous material reduces the neutron dose equivalent to an acceptable level.dose equivalent to an acceptable level.

• Neutrons are absorbed by (n, gamma) Neutrons are absorbed by (n, gamma) reactions in the door.reactions in the door.

• The gamma rays (neutron-capture gamma The gamma rays (neutron-capture gamma rays are released in the range of a few rays are released in the range of a few MeV.MeV.

• Lead in the door is required to attenuate Lead in the door is required to attenuate the beam to an acceptable level.the beam to an acceptable level.

DIRECTED SHIELDED DIRECTED SHIELDED DOORDOOR

• Typical Sliding Door with the entire Typical Sliding Door with the entire door encased in steel.door encased in steel.

l

concrete

polystyrene

lead

X-ray beam

gap

DOOR AT THE END OF THE DOOR AT THE END OF THE MAZEMAZE INDIRECT INDIRECT• The neutron contribution as well as the The neutron contribution as well as the

photon contribution is calculated.photon contribution is calculated.• The main issue is the scattered radiation The main issue is the scattered radiation

down the maze.down the maze.• The door construction is still the same, The door construction is still the same,

lead- poly- lead with the entire door lead- poly- lead with the entire door encased in steel. This door is a swinging encased in steel. This door is a swinging door and opened and closed pneumatically.door and opened and closed pneumatically.

• EXCELLENT REFERENCE: McGinley, P, EXCELLENT REFERENCE: McGinley, P, Shielding Techniques for Radiation Shielding Techniques for Radiation Oncology Facilities,2d ed.Oncology Facilities,2d ed.

SLIDING DOORSLIDING DOOR

AFTER ALL OF THE PLANNING IS

COMPLETED

ITEMS DURING and POST ITEMS DURING and POST CONSTRUCTIONCONSTRUCTION

• Ensure that the proper shielding report is Ensure that the proper shielding report is being used.being used.

• Test the concrete for the proper density.Test the concrete for the proper density.• Ensure that all radiation protection Ensure that all radiation protection

equipment-warning lights, door interlocks, equipment-warning lights, door interlocks, emergency off buttons-have been ordered emergency off buttons-have been ordered and installed.and installed.

• Ensure that all registrations have been Ensure that all registrations have been completed.completed.

• Ensure that the final radiation survey was Ensure that the final radiation survey was conducted by an authorized expert.conducted by an authorized expert.

HELPHELP

HOW DO YOU DEFINE A DEAD PANEL?

COMING ATTRACTIONS

•My panel is dead!!!!!!!!!What does this mean physically?Please send answers to Phil Berrypberry@lanl.gov

•This will be for a project: Failure Modes of Digital DetectorsWill be to determine the dose for “My panel is dead!!!!!!!!”

Take Home PointsTake Home Points

• Did you identify key personnel needed Did you identify key personnel needed to build a radiography facilityto build a radiography facility

• Did you consider all of the main Did you consider all of the main elements and requirements in the elements and requirements in the buildingbuilding

• Be sure you understand the basic Be sure you understand the basic elements in performing shielding elements in performing shielding calculationscalculations

• Follow the project after the planning Follow the project after the planning phase through completionphase through completion

THANK YOU FOR YOUR THANK YOU FOR YOUR ATTENTIONATTENTION