A. Bâ, S. Balestra, M. Cozzi, G. Giacomelli, R. Giacomelli, M. Giorgini, A. Kumar G. Mandrioli, S. Manzoor, A.R. Margiotta, E. Medinaceli, L. Patrizii, V. Popa, I.E. Qureshi, M.A. Rana, Z. Sahnoun, G. Sirri, M. Spurio, I. Traoré, C. Valieri Bulk etch rate measurements and calibrations of plastic nuclear track detectors V. TOGO INFN - BOLOGNA Bologna, Sept 1st 2008 – 24th ICNTS

New calibrations of CR39 and Makrofol nuclear track detectors have been obtained using 158 A GeV Pb82+ and In49+ ions A new method for the bulk etch rate determination, using both cone height and base diameter measurements, was developed.

The most sensitive Nuclear track detector employed in several scientific and technological applications is CR39 We recall that more than 4000 m2 of CR39 detectors were used in the MACRO and SLIM experiments devoted to the search for new massive particles in the cosmic radiation (magnetic monopoles, nuclearites...) Makrofol and Lexan polycarbonates are also largely employed. Accurate detector calibrations are required

CR39 and MAKROFOL CR39® (PPG Industries Inc.) (C 12 H 18 O 7 ; 1.32 g/cm 3 ) Standard INTERCAST CR39: mainly used for sun glasses Improved in order to achieve: low detection threshold; (Z/  ~ 5) high sensitivity in a large range of energy losses, high quality of the post-etched surface stability of the sensitivity over long periods of time (several years) [Aging effect] uniformity of sensitivity for mass-produced sheets In order to achieve these goals, a specific scientific line of production was designed and implemented. MAKROFOL® (BAYER) (C 16 H 14 O 3 ; 1.29 g/cm 3 ) Polycarbonate films high quality transmission, high quality transmission, excellent surface uniformity excellent surface uniformity high detection threshold; (Z/ ~ 50) high detection threshold; (Z/  ~ 50)

Survived beam Fragments Target Incident beam Target 50 cm Air gapCR39 EXPOSURE SET UP Beams: ► CERN (Geneva)158 A GeV Pb 82+ & In 49+ ► CERN (Geneva) 158 A GeV Pb 82+ & In 49+

CR39 in 6 N NaOH + 1% ethyl alcohol at 70°C for 40 hMAKROFOL in 6 N KOH + 20% ethyl alcohol at 50°C for 8 h ETCHING CONDITIONS The etching was performed in a stainless steel tank equipped with internal thermo-resistances and a motorized stirring head. The temperature was stable to within ±0.1 C. In order to keep homogeneous the solution and to avoid that etched products deposit on the detector surfaces, a continuous stirring was applied during etching

BULK ETCH RATE (V B ) MEASUREMENTS Original Surface Etched Surface vBtvBt By Thickness method v B =  x /2.t Based on the measurement of the thickness of the detector after different etching times. The thickness is measured with an electronic micrometer of 1 µm accuracy in 25 positions on the detector foil.

BULK ETCH RATE (V B ) MEASUREMENTS LeLe D By D-L e method The bulk etch rate from the cone height and base diameter measurements Normally incident particle D and L e measured with a Leica optical microscope coupled to a CCD camera and a video monitor L e obtained by multiplying the measured cone height by the refractive index n of the etched detector material

BULK ETCH RATE (V B ) MEASUREMENTS LeLe D By D-L e method

CALIBRATION OF CR39 Area distribution (measurement on two faces) of 158 A GeV 49 In ions and their fragments in CR39 after 40 h etching in 6N NaOH+1 % Ethyl Alcohol (by volume) at 70 o C (a) Z/  = Z/  = 46 Z/  = 49 (b)

p versus REL for CR39 exposed to relativistic indium ions using vB evaluated with the new method. Typical statistical standard deviations are shown at Z/  = 40, 45, 49; for Z/  ≤ 37 the errors are inside the black points.

CALIBRATION OF MAKROFOL (a) (b) Z/  = 78 Z/  = 82 Z/  = Area distribution of 158 A GeV Pb ions and their fragments (measurement on two faces) in Makrofol after 8 h etching in 6N KOH + Ethyl Alcohol (80 : 20 % by volume) at 50 o C.

p versus REL for the Makrofol detector exposed to relativistic Pb ions using vB evaluated with the new method. Typical statistical standard deviations are shown at Z/  = 70, 75, 77; for Z/  ≤ 67 the errors are inside the black points.

CONCLUSIONS The ‘‘new method’’ for measuring the bulk etch rate for intermediate or high z-values yields slightly smaller uncertainties than the ‘‘standard method’’ (change in thickness) This comes from the use at the same time of both cone heights and base diameter measurements of tracks. The values obtained by the two methods are in reasonable agreement

(a) (b) (c) Place the samples in the same positions in the rack if etching performed in more steps

(a) (b) CR39 sheets after target CR39 sheets before target Survived beam Fragments Target Incident beam Exposure geometry for the relativistic heavy ions for calibration of both CR39 and Makrofol NTDs. (a) tracks of beam ions before the target and (b) beam tracks and a fragment track after the target from the 0.41 A GeV Fe26+ exposure, see the tracks marked with a red circle.

TRACK SHAPE PARAMETERS Track diameter: D = 2v B t[(v T -v B )/(v T +v B )] 1/2 Track length: L e = (v T -v B ).t Reduced etch rate: p = v T /v B G = 6.3x 158 AGeV Pb 82+ G = 6.3x AGeV Fe 26+ VBtVBt LVTtVTt D

IMPROVEMENTS ON CHEMICAL PROCESSING Tracks of 158 A GeV Pb ions in CR39 IMPROVEMENTS ON CHEMICAL PROCESSING Tracks of 158 A GeV Pb ions in CR39 6N NaOH, 70 0 C, 30 hr 6N NaOH, 70 0 C, 30 hr Z/  (min.) ~ 5 Z/  (min.) ~ 5 20 X 6N NaOH + 1% alcohol 70 0 C, 40 hr 6N NaOH + 1% alcohol 70 0 C, 40 hr Z/  (min.) ~ 7 Z/  (min.) ~ 7

TRACKS OF 158 A GEV Pb 82+ IONS + FRAGMENTS IN MAKROFOL 6N KOH + 30% ethyl alcohol, 10 h, 45 0 C 50 X 6N NaOH, 95 h, 50 0 C 20 X Makrofol, 50 o C, 6N KOH + 20% ethyl alcohol 8 h (a) normal incidence and (b) for 45 incidence, 20 X 50 X Z/  (min.) ~ 50 OLDOLD NEWNEW

CALIBRATION GRAPH FOR CR39 By thickness Method For each detected charge  Restricted Energy Loss (REL)

REL (MeV cm 2 g -1 ) By D-L e Method 6N NaOH 70 o C, 30h 1.11 ± 0.07  m/h CALIBRATION GRAPH FOR CR39

Comparison for CR39 NTDs exposed to 158 A GeV In 49+ and Pb 82+ heavy ions and etched under different “soft” condition. Notice the p values at Z = 40 and 49 for two etching conditions for CR39. A sharp rise in sensitivity is evident for etching with small fraction of alcohol after Z/   20. Z = By D-L e Method CALIBRATION COMPARISON FOR CR39

RESPONSE CURVES FOR CR39 AND MAKROFOL Comparison for CR39 NTDs exposed to 158 A GeV In 49+ and Pb 82+ heavy ions and etched under different “soft” condition. Notice the p values at Z = 40 and 49 for two etching conditions for CR39. A sharp rise in sensitivity is evident for etching with small fraction of alcohol after Z/   20. By D-L e Method

LENGTH AND BASE AREA OF TRACKS IN CR39 EXPOSED TO Pb 82+ IONS (158 A GEV) LENGTH AND BASE AREA OF TRACKS IN CR39 EXPOSED TO Pb 82+ IONS (158 A GEV) Z = 82e D = 75  m L = 650  m Z = 65e D = 69  m L = 169  m Z = 76e D = 74  m L = 425  m Z = 20e D = 40  m L = 23  m Z = 45e D = 59  m L =77  m