Nuclear track detectors

1. Track detector development for neutron and mixed field dosimetry Michele FerrariniFondazione CNAO

2. Nucleartrackdetectors • Sensitive to high LET radiation heavychargedparticles

3. The damagedmaterial isremovedwithVt, the bulk material withVb

4. Etching: the fewnmtrackisenlarged up to a fewmicrons

5. The realshapeof the etchedtrackdependson a fewparameters:V=Vt(LET)/Vbθ= incidence angleLET = LET(y)

6. CR39 – mostusedtrack detector

7. Manyformulas are availabletocalculate V(LET)

8. The trackisreadby a microscope.Itsshapealsodepends on the etchingprocedure (etchant, etchant temperature, etchingdurationetc…)

13. Itispossibleto: Count the tracks Count the tracksbyfiltering the trackswithcertainparameters (reduce background) Calculateforanytrack the LET (discriminate the particles) and the impinging angle

14. Neutron and mixedfielddosimetry and spectrometry Use the track detector coupledto a boronconverter, asthermalneutron detector (expoiting the n,αreaction on 10B). The neutronisdetectedby the 1.47 MeVαparticle. The numberoftracksisproportionalto the thermalneutonfluence (inside Bonnerspheres and Rem counters)

15. Use the recoilprotons (radiator-degradertechnique). The numberoftracksisproportionalto the fast neutronfluence. The detection efficiencydepends on the neutronenergy. Calculationofparticle LET and impinging angle. Directestimate ofthe equivalentdose bycalculating, foranyparticle the dose and the qualityfactor Q(LET) .

16. Useof CR39 asthermalneutron detector Passive REM counter

17. The numberoftracksisproportionalto the ambient dose equivalent

20. Passive REM counters: • Independentfromfieldtimestructure (e.g. pulsedfields) • Low background (fewtracks/cm2) independentfromexposuretime and high sensitivity (5 tracks/cm2 per microSievert) • Low lower detection limit (2 μSv) • Thisishow the passive neutrondosimetryisdonehere!

23. Bonnerspheres

24. Spectralresponseofvariousspheres

25. Neutronspectrum(LINAC)

26. RadiatorDegraderNeutronSpectrometer(RDNS) Radiator: high density (0.95 g·cm-3) polyethylene, Degrader: aluminum (purity 99.0%)

27. Detector sensitivity (1) Recoil protons generated inside the radiator(external radiation component). (2) Recoil protons generated inside the detector(proton self radiator). (3) Carbon and oxygen recoil nuclei generated inside the detector (ion self radiator).

28. Sensitivityexperimentalverification Sensitivity Sensitivity Sensitivity Sensitivity (xPEyAl), where x and y indicate the polyethylene (PE, mm) and the aluminum (Al, µm) thickness,respectively.

29. Evaluation of the unfoldingcapability RDNS with 15 configurationswastestedboth with simulated and experimentalirradiation with a neutron Pu-Be source

30. SpectrometriccapabilityExperimental data

31. Conclusions • Advantages • Possibility to make simultaneous measurement in several configurations because the detectors can be placed side by side without an appreciable cross scattering; • The presence of a small amount of moderating material which, produces negligible perturbation in the measured neutron field; • The small dimension allows measurements also in very narrow sites where a moderator based spectrometer cannot be used. • Disadvantages • Insensitivity to the thermal neutrons, even if this fact can be bypassed by introducing a PADC detector coupled with a boron converter. This solution has not been characterized yet; • The response functions are angular dependent. The RDNS was characterized for normal impinging neutrons only. The angular dependence has not been studied yet; • Low sensitivity when compared with moderation based fast neutron detectors. This fact is intrinsic in detectors based on protons recoil detection

32. Neutrondosimetrybased on LET spectrometry

34. Itispossibletocalculate V and θfrom the trackparameters. LET= LET (V)

35. From LET and θitispossibletocalculate the dose and the dose equivalent. Ifa 1 cm PMMA radiatorisused, H is a goodapproximationofH*(10). Thisisalmostindependentfrom the impingingparticle.

36. Anyenergy, butnotany LET or anyimpingingangle. • Thesecontributions are lost: • low LET particles (electrons, butalsoprotonswith E>10 MeV) • low energyparticles (e.g. protonsbelow 0.5 MeV) • particlesimpingingbelow the critical angle - the critical angle is a functionof LET.

37. High energy quasi monoenergeticbeamstested Uppsala, SE (21, 46.5, 96, 175 MeV) Ithembalabs, ZA, 100 and 200 MeV (results on their way)

38. Quasi monoenergeticfields LNL 2.0 MeV 3.3 MeV PTB19.0 MeV 14.8 MeV 0.535 MeV

39. 2 MeVneutrons Signalonly due toprotons 3.3 MeVneutrons

40. Foranyenergybetween 2.0 and 175 MeVneutrons the ratiobetween the measured dose and the referencevaluerangesbetween 0.6 and 0.9. The efficiencyfor 0.535 MeVneutronsdropstolessthan 0.4

41. At 3.3 MeVall the dose is due toprotons At 175 MeV more than 60% of the dose is due torecoilsheavierthanprotons. The techniquemayalsobeusedtomeasurechargedfragments, ions, etc…

42. The majorityof the dose in acceleratorenvironmentis due toneutronsfrom 1 to a fewhunderdMeV

43. Whatisleftto do? • 1) Some work about the qualityofmeasurementsisstillnecessaryfor the first twoapplications, that are at a much more advanced stage. • Metrologicalcharacterization

44. 2) Muchisleftto do for the LET spectrometrytechnique.A full Monte Carlo characterizationof the dosemetersisstillin progress (MCNPX? FLUKA?)- Angularresponsestilltobeunderstood- Metrologicalcharacterizationfor personal and environmentaldosimetry- Medicalphysicsapplication (?) : secondarydose evaluation due tofragments, withLET spectrometry

45. S. Agosteo, F. Campi, M. Caresana, M. Ferrarini, A.PortaM.Silari, (2007), Sensitivitystudyof CR39 track detector in a system ofextendedrangeBonnerspheres, Radiat. Prot. Dosimetry vol.126, No. 1-4 pp.310-313 • •M. Silari, et al. (M.Ferrarini), Intercomparisonofradiationprotectiondevices in a high-energystrayneutronfield. Part III: InstrumentresponseRadiationMeasurements 44 (2009) 673–691 • •B. Wiegel, et al (M.Ferrarini) , Intercomparisonofradiationprotectiondevices in a high-energystrayneutronfield, Part II: BonnerspherespectrometryRadiationMeasurements 44 (2009) 660–672 • •S.Agosteo, M.Caresana, M.Ferrarini, M.Silari A passive rem counterbased on CR39 SSNTD coupledwith a boronconverter (2008) ICNTS 24, Bologna, RadiationMeasurements 44 (2009) 985–987 doi:10.1016/j.radmeas.2009.10.053: • •M. Caresana, M. Ferrarini, L.Garlati, A.Parravicini, Aboutageing and fading of CR39 PADC trackdetectorsusedas air Radon concentrationmeasurementsdevices, RadiationMeasurements, (20120) DOI: 10.1016/j.radmeas.2010.01.030 • •S. Agosteo, M. Caresana, M. Ferrarini, M. Silari, A dual-detectorextendedrangerem-counter, RadiationMeasurements (2010), doi:10.1016/j.radmeas.2010.05.002 • •M. Caresana, M. Ferrarini, A. Pola, S. Agosteo, F. Campi, A. Porta, Studyof a radiatordegrader CR39 basedneutronspectrometerNucl. Instr. and Meth. A (2010), doi:10.1016/j.nima.2010.03.105 • •M. Caresana, M. Ferrarini, L. Garlati, A. Parravicini, Furtherstudies on ageing and fading of CR39 PADC trackdetectorsusedas air radon concentrationmeasurementdevices, RadiationMeasurements volume 46, issue 10, year 2011, pp. 1160 – 1167 • •M. Caresana, M. Ferrarini, A. Porta, F. Campi, Performance evaluationof a radiatordegrader CR39 basedneutronspectrometer, NuclearInstruments and Methods in PhysicsResearchSection A: Accelerators, Spectrometers, Detectors and AssociatedEquipment, Volume 680, 11 July 2012, Pages 155-160 • •M. Caresana, M. Ferrarini, M. Fuerstner, S. Mayer, Determinationof LET in PADC detectorsthrough the measurementoftrackparameters, NuclearInstruments and Methods in PhysicsResearchSection A: Accelerators, Spectrometers, Detectors and AssociatedEquipment, Volume 683, 11 August 2012, Pages 8-15 • S. Agosteo, R.Bedogni, M.Caresana, N.Charitonidis, M.Chiti, A.Esposito, M.Ferrarini, C. Severino, M.Silari, CharacterizationofextendedrangeBonnerSphereSpectrometers in the CERF high-energybroadneutronfield at CERN, NuclearInstruments and Methods in PhysicsResearchSection A: Accelerators, Spectrometers, Detectors and AssociatedEquipment, (2012) 55–68