Tungsten Calorimeter Model Calculations and

Radiation Issues

Pavel Degtiarenko

Radiation Control Group, Jefferson Lab

• Modeling electromagnetic cascades using Monte Carlo methods: EGS4, GEANT3, MARS, FLUKA, Geant4, others…

• JLab specifics: 0.5-12 GeV energy range, neutron production and other hadronic reactions in electronuclear interactions are significant in solving shielding problems

• Modified version of GEANT3 developed in 1995 including electro-, and photonuclear reactions, GEANT/DINREG – P. Degtyarenko,

M. Kossov

• Used in many shielding and background calculations at JLab. E-M cascade calculations agreed with EGS4 to 5-10%. Hadronic production has been compared with several experimental results, and agreed with experimental measurements with accuracy 30-50%

• GEANT/DINREG has been used in the present Calorimeter calculations

• Silver calorimeter (diameter 15 by length 24 cm) model calculation results:

• Little dependence on beam energy in 0.5 – 12 GeV range

• E-M loss = 1.1± 0.2%, Hadronic loss = 0.34 ± 0.17%

• Electromagnetic part of the losses can be decreased significantly by using outer layer of the cylinder made of Tungsten

• Silver can be replaced by Tungsten completely as the thermal conductivity and melting temperature combination for Tungsten is acceptable

• Tungsten advantages are better energy confinement and smaller radiation fields, both prompt and due to activation

• ALARA principle at JLab: as low radiation production as reasonably achievable

• Tungsten solution minimizes energy losses while keeping heating/cooling times acceptable

• Cylinder geometry diameter 16 by length 16 cm

• Entrance hole diameter 1 by length 1 – 5 cm

• Optimal entrance hole length ~ 2.5 cm

• Cut corners 1 by 2 cm at the entrance face and 4 by 5 cm at the exit face: decrease heating and equilibration time, but increase cooling time, while keeping losses practically unchanged

• Bottom flat surface: shave 1 cm thick layer

• Result: 0.46 ± 0.20 % losses in the beam energy range 0.7 – 12 GeV, with the hadronic losses contributing 0.3 ± 0.15 %.

• E-M losses decreased 10 times, hadronic losses roughly remained the same as in the Silver Calorimeter variant

• Power density distribution in Tungsten calorimeter calculated for beam power = 5 kW at energies from 0.75 to 12 GeV

• Conservative steady-state evaluation of temperature distribution inside the calorimeter showed maximum temperature at the center not exceeding 1000 °C when average temperature of the block is approx. 50 °C

• At 5 kW beam power, maximum local power density and local temperature will be reached at low beam energies

Calorimeter Operation, Radiation Issues• High levels of prompt radiation around the device

• dose rates of the order of 10 krad/h at 1 meter

• Activation of the calorimeter

• self-shielding

• cool-off periods may be required before handling

• additional local shielding may be needed

• Environmental radiation

• dose rate at CEBAF boundary will be 10-20 times the “average design limit”

• Calorimeter operation must be included in the Radiation Budget for a particular experiment

Conclusion• Tungsten Calorimeter 16 cm length by 16 cm diameter provides better beam energy confinement and lower emitted radiation as compared with 24 by 15 cm Silver Calorimeter

• Prompt dose rates around the calorimeter are expected of the order of 10 krad/h at 1 meter, special shielding should be used to protect sensitive electronic equipment in its vicinity

• Dose rates at CEBAF boundary during the operation of the calorimeter will be high, but manageable taking into account small cumulative operation times for the device. Operation of the device must be accounted for in the JLab Radiation Budgeting procedures

• Off-line handling of the device will require special technical and administrative controls by the JLab Radiation Control Group