Neutron measurement with nuclear emulsion Mitsu KIMURA 27th Feb 2013
Motivation Proton radiotherapy induces secondary neutrons. Aim : Measure neutron field in the environment The secondary neutron profile is required in order to minimize the risk of radiation exposure. Worker : Radiation exposure Patient : Second cancer in the normal tissue
Nuclear emulsion Nuclear emulsion can record recoil proton tracks. 100 m Neutron flux number of recoil proton tracks Recoil proton energy track length Recoil proton angle track angle We tested whether it could be applied to measure neutron field.
The CERF facility at CERN Reference field of high energy neutron Mixed beam ( , p, K) 120 GeV/c ECC (Emulsion Cloud Chamber) set on the concrete roof-shield.
ECC design High energy beam ECC consists of OPERA films with plastic absorbers. Plastic contains hydrogen which is a component of human body. Neutrons … OPERA film 0.3 mm x 25 (OPERA film + plastic absorber 0.5 mm) x x 12.5 cm 2
Geometry in GEANT4 Concrete (2.4 m x 4.8 m x 0.8 m) Cu target Mixed beam 1.08 m ECC (10 x 12.5 x 8.6 cm 3 ) = 2.30 g/cm x 80 cm = 184 g/cm 2 60 cm 10 cm 2 x 10 5 particles Side view Top view Hadronization model : QGSP_BERT_HP
Neutron incident angle Z direction in ECC
Neutron momentum Momentum 400 MeV/c 65 MeV/c 200 MeV/c 65 MeV/c 200 MeV/c 400 MeV/c Neutron cross section in 16 O (Data from ENDF/B VII) Oxygen is main component in concrete shield (50 %).
Comparison with another experiment ● : Measured data from Nakao et al., NIMB.266(2008)93 Histogram : Our result
Other simulator Nakao et al., NIMB.266(2008) MeV Common routine / data base is used ?
Summary of simulation Neutron field measurement is important in cancer radiotherapy. Neutron spectrum is determined by cross section of Oxygen. MC spectrum are in good agreement with measured data by another experiment except higher energy region (E k > 100 MeV).
Application fields This technique can be widely applied to: Cancer therapy (proton radiotherapy / BNCT) - Secondary neutron induce a cancer Radiation exposure in aircraft - It is mainly by neutron with E k ~ 100 MeV - Soft error in computer memory is induced by neutron Radiation measurement at the accelerator - high energy (LHC), high luminosity (J-PARC)
Machine power Neutrons per p.o.t : 2.1 x 10 3 / 2 x 10 5 = 1.1 x Recoil protons per neutron : 1055 / 1 x 10 6 = 1.1 x (including reconstruction efficiency. Please see Tomoko’s slide.) Rate of recoil protons : 1.1 x / p.o.t Required time in my machine : 2.2 s / p.o.t recoil protons : 9.0 x 10 6 p.o.t (230 days) : 9.0 x 10 7 p.o.t (6 years) : 9.0 x 10 8 p.o.t (60 years)
Neutron cross section in 16 O JENDL 4.0 (JAEA)
Rate estimation (very rough) Living probability : e -t/ = e -80 cm/28.32 cm = nuclear collision length : cm (concrete) - concrete thickness : 80 cm Number of incident neutrons : 3.8 x / pot - fraction of solid angle (10 cm x 10 cm) : 1.5 x Multiplicity from MC : 250 n / p.o.t Neutrons per event : 2.3 x n / p.o.t This estimation take no thought of the effects of large angle scattering : - sky shine - ground shine …