1 Lead/Emulsion compatibility in OPERA bricks Short description of CNGS and OPERA projects What is an OPERA “brick” Alternative packaging Technical description of OPERA Emulsions Emulsion/lead compatibility: CERN Emulsion/lead compatibility: Nagoya (Japan) S. Buontempo INFN- Naples

2 The CNGS project

3 The OPERA Detector SM1 SM2 31 walls (brick walls+TT) + 1 spectrometer spectrometer 31 Walls (each containing 3328 bricks) In total there are bricks ~ 1.8 kton

4 The (light and strong) support structure for the “brick walls" Tests of full scale prototypes (Frascati and Naples) wall Tensioning from the bottom Suspension from the top Brick loading test Height ~ 6. 7 m 1 full wall contains 64x52 = 3328 bricks = ~28.5 kton

5 Brick Manipulator System (BMS) Portico study completed (total weight 5 t ) full height LAPP in 2004 Brick Manipulator System prototype used for extensive tests programming and upgrade of the automation system brick loading and safety  protective skate Brick loading system

6 What do we call a “brick” ? ECC CSS CS (one emulsion sheet covered by laminated paper) Skates Laminated paper Carton paper Pile (emulsion,lead,emulsion,…) (exploded view, not to scale) Baseline solution for packaging

7 Alternative brick packaging

8 BAM: Brick Assembly Machine bricks in one year = 1000 bricks/day = 2 bricks/min Lead palletting Piling Robot Quality Check CS + Skates gluing ECC Packaging Additional protection Emulsion palletting

9 Technical description of OPERA emulsion films When a charged particle goes trough emulsion there is an energy loss, - dE/dx  k Z 2     F    This energy excites AgBr grains along the trajectory realising the so called latent image. During developing and fixing baths excited grains are reduced to silver grains and they look like dark spots.  Avg. 30 grains/100  m Plastic base Protective gel layer 1  m Insensible gel layer 1  m Gelatine ( C, O, N...) AgBr (1g Ag / film) 42  m 200  m 42  m So all metals able to reduce Silver (Al, Fe etc...) are dangerous !!

10 Here there are some samples from CHORUS experiment...  interaction Low energy electron tracks nuclear fragments (black tracks) Fog : a random grain in this view Animation (neutrino interaction and a decay)

11 Emulsion/lead compatibility We performed several test on this purpose and results are the following for vacuum packaging. Authomatic and manual measurements gave us the result that the fog density in the case of lead contact is 10 times bigger. For packaging without vacuum, we did not found an effect so dramatic. Reference emulsion (fog density < 3 grains/(10  ) 3 ) Emulsion in contact with lead for 57 days (vacuum packaging, 20°C); fog density 27 grains/(10  ) 3. Animation

12 Emulsion/lead compatibility Summary of Tests performed in July Pb-Ca laminated with usual oil and cut with Rapid D oil First time in long term contact with emulsion (51 days) Unfortunately bad quality emulsion (fog= 10) Vacuum and mechanical packaging tested Vacuum at 20°C fog increase factor 3 Vacuum at 34°C very high fog (not measurable) Mechanical at 20°C no effect Mechanical at 34°C minor effect (20%increase)

13 Emulsion/lead compatibility Summary of Tests performed in September Pb-Ca laminated with usual oil and cut with Rapid D oil CERN pure lead Pb-Ca degassed Pb-Ca painted Medium term contact with emulsion (20 days) Unfortunately bad quality emulsion (fog = 5-10) Vacuum and mechanical packaging tested Vacuum at 20°C minor effect for any lead Vacuum at 30°C minor effect for any lead Mechanical at 20°C minor effect for any lead Mechanical at 30°C minor effect for any lead

14 Emulsion/lead compatibility Summary of Tests performed in October 1) Pb-Ca laminated and cut with usual lamination oil 2) Pb-Ca laminated and cut with usual lamination oil, “US cleaned” 3) Pb-Ca laminated with usual oil and cut with Rapid D oil 4) Pb-Ca laminated with usual oil and cut with Rapid D oil, “US cleaned” Long term contact with emulsion (40 days) Unfortunately bad quality emulsion (fog = 7) Vacuum and mechanical packaging tested Vacuum at 20°C factor 4 increase of fog with any lead Vacuum at 30°C factor 5 increase of fog with any lead Mechanical at 20°C no effect for any lead Mechanical at 30°C no effect for any lead

15 Emulsion/lead compatibility Nagoya (Japan) (Result1) The fog density decreases with the increase of the buffer space. Test1. Effect of buffer space in the package Short term contact with emulsion (14 days) High temperature 40 o C Good quality emulsion (fog = 3) Only vacuum packaging Test to understand if it is a gas effect

16 Emulsion/lead compatibility Nagoya (Japan) Test2. Effect of film numbers in the package (Result2) Fog density decreases with the increase of the number of films. These results (Test1 and Test2) are consistent with the hypothesis that the state of the matter, which increases the fog density, is a kind of gas. Probably a gas of low molecular weight because, the increase of the buffer space diluted the effect.

17 Emulsion/lead compatibility Nagoya (Japan) Tests on the origin of the gas. Out gas from lead? Contact & non-contact test (Result3) Fog increase was suppressed in the case of non-contact It can be concluded that the main part of the gas comes from the direct contact between film and lead

18 Emulsion/lead compatibility Nagoya (Japan) Attempts to inert the lead. Treatment by H 2 SO 4 (0.2N) (Result4-1) The treatment with H 2 SO 4 suppressed the effect. (Result4-2) The surface oil did not suppress the gas creation (comparing no treat and only wash samples).

19 Emulsion/lead compatibility Nagoya (Japan) Treatment by temperature and vacuum Results: Treatment (3) Treatment (4) Vacuum 100oC With OilOil removed With Oil Oil removed FD6.8+/ / / /-0.6 (3) Leave the lead in air at 100 o C for 4 days. (4) Leave the lead in vacuum (~20Torr) at 100°C for 4 days. After the treatment, the lead plates were cooled in air and vacuum-packed with films. The packed samples were kept at 40°C for 1 week. (Result4-3) Both treatment worsen the situation

20 Emulsion/lead compatibility Nagoya (Japan) Lead treatment by water. We put the lead in de-mineralized water at room temperature for 4 days. By the immersion, a lot of white precipitate (powder like) was created and the corrosion was continued until the end of immersion. After the treatment, the lead plates were dried in air for a half day and vacuum-packed with films. The packed samples were kept at 40 o C for 1 week. Result: The observed fog density is 4.1+/ No clear improvement but no extra degradation.

21 Emulsion/lead compatibility Nagoya (Japan) Why two years old Pb-Ca is safe? The surface of this sample is covered by a kind of passive state In order to check this hypothesis, the surface of the two years old Pb-Ca was removed mechanically and the contact test was repeated. Result: Fog increase was observed. FD= 5.9 +/- 0.4 after 40 o C 1week The toxic lead (Pb-Ca) and two-years-old Pb-Ca were immersed in de-mineralized water in order to check the resistivity against the water corrosion. Result: in the case of toxic lead, as described in water treatment case, a lot of white precipitate (powder like) was created and the corrosion was not stopped. On the other hand, completely no corrosion was observed in the case of two years old Pb-Ca. We can conclude that the surface of the two-years-old Pb-Ca is covered by a kind of passive state

22 Emulsion/lead compatibility Nagoya (Japan) Why only Pb-Ca shows the effect ? In Ca lead we have Ca + 2H 2 O -> Ca(OH) 2 + H 2 In pure lead we have Pb + H 2 O + 1/2O 2 -> Pb(OH) 2 Why vacuum treatment worsens the situation? This can be explained as the existence of the inverse reaction of the water reaction of calcium on the surface (need further study). Comment: ….maybe under vacuum we just extract more water from emulsion (??)

23 Conclusions in Japan First conclusions from Japan are: 1) The origin is gas. 2) The gas is dominantly created by the direct contact between emulsion film and the lead. 3) We found a method to inert the toxic lead. The method is a surface treatment with H 2 SO 4, which make a kind of passive state on the lead surface. The passive state probably prevents the reaction between emulsion film and lead. After some further discussions their advice is: There are many questions raised, especially the mechanical stability of the passive state. It should resist the expansion stress caused by temperature variation. It should resist the treatment of the BAM etc. Who will or how to prove it is OK for 12M lead plates (?) Maybe better to go to pure lead….

24 Conclusions in Europe We do not see any effect (or in the measurement error bars) on the fog in the mechanical packaging  we need solid arguments before rejecting that packaging solution We fear anyway a long term chemical aggression of the lead on emulsion  further study on Pb/Em compatibility (Pb cleaning? surface treatment?) to minimize the risk The main difference in mechanical packaging is the air tightness  need further study in H 2 atmosphere (very poisoning) All the materials used in mechanical packaging (adhesive tape, thin PE, springs, etc) must be studied in terms of degassing. Humidity tightness and stability inside the packaging should be studied for both packaging solutions.