track detector development for neutron and mixed field dosimetry michele ferrarini fondazione cnao n.
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Track detector development for neutron and mixed field dosimetry Michele Ferrarini Fondazione CNAO. Nuclear track detectors. Sensitive to high LET radiation  heavy charged particles. The damaged material is removed with Vt , the bulk material with Vb.

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track detector development for neutron and mixed field dosimetry michele ferrarini fondazione cnao
Track detector development for neutron and mixed field dosimetry Michele FerrariniFondazione CNAO
slide2

Nucleartrackdetectors

  • Sensitive to high LET radiation heavychargedparticles
slide5
The realshapeof the etchedtrackdependson a fewparameters:V=Vt(LET)/Vbθ= incidence angleLET = LET(y)
slide8

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

it is possible to
Itispossibleto:

Count the tracks

Count the tracksbyfiltering the trackswithcertainparameters (reduce background)

Calculateforanytrack the LET (discriminate the particles) and the impinging angle

neutron and mixed field dosimetry and spectrometry
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)

slide15

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) .

passive rem counters
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!
radiator degrader neutron spectrometer rdns
RadiatorDegraderNeutronSpectrometer(RDNS)

Radiator:

high density (0.95 g·cm-3) polyethylene,

Degrader:

aluminum (purity 99.0%)

detector sensitivity
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).

sensitivity experimental verification
Sensitivityexperimentalverification

Sensitivity

Sensitivity

Sensitivity

Sensitivity

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

evaluation of the unfolding capability
Evaluation of the unfoldingcapability

RDNS with 15 configurationswastestedboth with simulated and experimentalirradiation with a neutron Pu-Be source

conclusions
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
slide35

From LET and θitispossibletocalculate the dose and the dose equivalent.

Ifa 1 cm PMMA radiatorisused, H is a goodapproximationofH*(10).

Thisisalmostindependentfrom the impingingparticle.

slide36

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.
high energy quasi monoenergetic beams tested
High energy quasi monoenergeticbeamstested

Uppsala, SE (21, 46.5, 96, 175 MeV)

Ithembalabs, ZA, 100 and 200 MeV

(results on their way)

quasi monoenergetic fields
Quasi monoenergeticfields

LNL

2.0 MeV

3.3 MeV

PTB19.0 MeV

14.8 MeV

0.535 MeV

slide39

2 MeVneutrons

Signalonly due toprotons

3.3 MeVneutrons

slide40

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

slide41

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…

what is left to do
Whatisleftto do?
  • 1) Some work about the qualityofmeasurementsisstillnecessaryfor the first twoapplications, that are at a much more advanced stage.
  • Metrologicalcharacterization
slide44

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

slide45

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