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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The trackisreadby a microscope.Itsshapealsodepends on the etchingprocedure (etchant, etchant temperature, etchingdurationetc…)
Count the tracks
Count the tracksbyfiltering the trackswithcertainparameters (reduce background)
Calculateforanytrack the LET (discriminate the particles) and the impinging angle
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)
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 counter
high density (0.95 g·cm-3) polyethylene,
aluminum (purity 99.0%)
(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).
(xPEyAl), where x and y indicate the polyethylene (PE, mm) and the aluminum (Al, µm) thickness,respectively.
RDNS with 15 configurationswastestedboth with simulated and experimentalirradiation with a neutron Pu-Be source
From LET and θitispossibletocalculate the dose and the dose equivalent.
Ifa 1 cm PMMA radiatorisused, H is a goodapproximationofH*(10).
Thisisalmostindependentfrom the impingingparticle.
Uppsala, SE (21, 46.5, 96, 175 MeV)
Ithembalabs, ZA, 100 and 200 MeV
(results on their way)
Signalonly due toprotons
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
At 175 MeV more than 60% of the dose is due torecoilsheavierthanprotons.
The techniquemayalsobeusedtomeasurechargedfragments, ions, etc…
The majorityof the dose in acceleratorenvironmentis due toneutronsfrom 1 to a fewhunderdMeV
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
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