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