Neutron exposure at CERN Mitsu KIMURA 19 th July 2013
Neutron exposure at CERN
Mitsu KIMURA
19th July 2013
First trial of neutron exposure• Aim to expose the neutron with a few MeV - study radiation exposure in cancer treatment - reference signal in DM search experiment
• There is a 2.5 MeV neutron source in CERN - Maximum beam intensity : 1 x 106 n/sec in 4p sr. - X-ray background : no information
• First trial on 16 – 18 July - Measurement for neutron flux and X ray background flux
• Participants : - T. Asada (Nagoya), C. Regenfus, M. Kimura
Neutron source by DD nuclear fusion
2.5 MeV neutron -> recoil proton range is about 70 mm. A base track cannot be produced.
90 cm
Collimator No collimator
9.5 cm
32 cm
38 cm
Estimated neutron flux (in 4p)
6 – 7 x 105 n/sec
Measured by Christian
Measured by company
Electric current : 8 mA ( the amount of deuteron plasma)≒Accelerating voltage : 80 kV
Exposure condition :
Time schedule
• 1st exposure (7/16 17:40 – 7/17 14:50, 21 hr) - with collimator, - Nagoya sample (distance from production point : 45, 200 cm)
• 2nd exposure (7/17 16:20 – 7/18 12:00, 20 hr) - no collimator, - Bern + Nagoya sample (45, 200 cm)
• 3rd exposure (7/18 12:30 – 15:00, 2.7 hr) - no collimator, - Bern sample (7 cm)
• 4th exposure (7/18 15:24 – 18:00, 2.6 hr) - no collimator, - Nagoya sample (7 cm)
Setup of Bern sample
7cm 45cm 200 cm
Distance from production point
Neutron
X ray with less than 80 keV
1
2
3
Distance Sample Size Exposure Shield by lead plate Exp time
1 7 cm OPERA New gel
5 x 10 cm2
2 x 2 cm2Horizontal, VerticalVertical
Cover whole area 2.7 hr
2 45 cm OPERANew gel
Full size2 x 2 cm2
Vertical ½ : OPEN, ½ : coverCover whole area
20 hr
3 200 cm OPERANew gel
Full size2 x 2 cm2
Vertical ½ : OPEN, ½ : coverCover whole area
20 hr
7 cm 45 cm 200 cm
NagoyaNagoya Bern
Bern
Failure
The sample at the 45 cm fell to the ground during beam exposure
Before exposure After exposure
Development
• Participants : A. Ehtesham, M. Kimura• OPERA film - 19th July 9:30 – 12:20• New gel - 23rd July 10:30 – 13:30 - Development for 20 min - Fix for 90 min
Conclusions
• Neutron source with a few MeV is very important for medical application and DM search experiment
• We performed neutron exposure to nuclear emulsions at CERN
• Exposure and development are completed• We plan 2nd exposure in 21 – 23 August
Recoil proton range by SRIM
0 500 1000 1500 2000 2500 30000
10000
20000
30000
40000
50000
60000
70000
80000
90000
100000
Flight Length
C
Br
He
H
Energy[keV]
Flyg
ht le
ngth
[nm
]
proton
68 mm
Neutron cross section
2.2 barn @ 2.5 MeV
JENDL 4.0
Estimated number of recoil protons
• Number of hydrogen Ntarget = r x V x e x NA / A = 2.2 x 1022 - Gel density r = 2.77 g/cc - Volume V = 10 cm x 12.5 cm x 44 mm = 0.55 cc - Mass fraction of hydrogen in OPERA gel e = 2.4% • Number of recoil protons Nevent = s x Ntarget x J (s-1) x T (s) = (2.2 x 10-24 cm-2) x (2.2 x 1022) x (7 x 105 x W) x T
Distance Number of recoil protons in 10 x 12.5 cm2
Np / view(= 0.3 x 0.3 mm2 x 44 mm)
7 cm 5.3 x 105 3.8
45 cm 9.6 x 104 0.7
200 cm 4.9 x 103 0.04
X ray in a lead plate
80 keV
Main process in material • Rayleigh scattering : absorption• Compton scattering : to generate electron track
- Absorption length l : 0.4 g/cm2 @ 80 keV- Living probability after Pb 1mm thick exp (- L / l) = exp{- (11.34 g/cc x 0.1 cm) / 0.4 g/cm2} = 0.059
Neutron in a lead plate
8 barn @ 2.5 MeV
• Cross section s = 8 barn• Number of atoms in 1 mm lead Ntarget = r x l x NA / A = 11.34 g/cc x 0.1 cm x 6.02 x 1023 x 207.2 = 3.3 x 1021
• Interaction probability Prob = s x Ntarget
= (8 x 10-24) x (3.3 x 1021) = 0.027• Living probability 1 – Prob = 0.973
JENDL 4.0
The effect of lead shieldN
eutron flux
Elec
tron
flux