Transcript Slide 1

Bulk etch rate measurements
and calibrations
of plastic nuclear track detectors
V. TOGO
INFN - BOLOGNA
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
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.) (C12H18O7; 1.32 g/cm3)
Standard INTERCAST CR39: mainly used for sun glasses
Improved in order to achieve:
• low detection threshold; (Z/b ~ 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) (C16H14O3 ; 1.29 g/cm3)
Polycarbonate films
•
high quality transmission,
•
excellent surface uniformity
•
high detection threshold; (Z/b ~ 50)
EXPOSURE SET UP
Fragments
Incident beam
Survived beam
Target
50 cm
Target
CR39
Air gap
Beams:
► SPS@ CERN (Geneva) 158 A GeV Pb82+ & In49+
ETCHING CONDITIONS
CR39
in 6 N NaOH + 1% ethyl alcohol at 70°C for 40 h
MAKROFOL
in 6 N KOH + 20% ethyl alcohol at 50°C for 8 h
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 (VB) MEASUREMENTS
By Thickness method
Original Surface
vBt
Etched Surface
vB = 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 (VB) MEASUREMENTS
By D-Le method
D
Le
Normally incident particle
The bulk etch rate from the
cone height and base diameter
measurements
D and Le measured with a Leica
optical microscope coupled to a
CCD camera and a video monitor
Le obtained by multiplying
the measured cone height by the
refractive index n of the etched
detector material
BULK ETCH RATE (VB) MEASUREMENTS
By D-Le method
D
Le  (vT  v B )t
Le

D2
v B  
4tLe

D  2v B t


1


(vT  v B )
(vT  v B )
 4L 2 
e

1
2 
D 


CALIBRATION OF CR39
(a)
(b)
Z/b = 49
Z/b = 10
Z/b = 46
20
30
40
Area distribution (measurement on two faces) of 158 A GeV 49In
ions and their fragments in CR39 after 40 h etching in 6N
NaOH+1 % Ethyl Alcohol (by volume) at 70 oC
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/b = 40, 45, 49; for Z/ b ≤ 37 the errors are
inside the black points.
CALIBRATION OF MAKROFOL
(a)
(b)
Z/b = 82
Z/b = 78
83
78
70
60
Z/b = 51
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 oC.
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/b = 70, 75, 77; for Z/b ≤ 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
Fragments
Incident beam
Survived beam
Target
CR39 sheets before target
CR39 sheets after target
Exposure geometry for the relativistic heavy ions for calibration of
both CR39 and Makrofol NTDs.
(a)
(b)
(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
VB
t
VT
t
L
D
0.414 AGeV Fe26+
158 AGeV Pb82+
Track diameter:
D = 2vBt[(vT-vB)/(vT+vB)]
1/2
Track length:
Le = (vT-vB).t
Reduced etch rate:
G = 6.3x
p = vT/vB
G = 6.3x
IMPROVEMENTS ON CHEMICAL PROCESSING
Tracks of 158 A GeV Pb ions in CR39
20 X
6N NaOH, 70 0C, 30 hr
Z/b(min.) ~ 5
20 X
6N NaOH + 1% alcohol 70 0C, 40 hr
Z/b(min.) ~ 7
TRACKS OF 158 A GEV Pb82+ IONS + FRAGMENTS
IN MAKROFOL
O
L
D
20 X
6N NaOH, 95 h, 50 0C
50 X
6N KOH + 30% ethyl alcohol, 10 h, 45 0C
N
E
W
20 X
50 X
Makrofol, 50 oC, 6N KOH + 20% ethyl alcohol 8 h (a) normal
incidence and (b) for 45 incidence,
CALIBRATION GRAPH FOR CR39
For each detected charge  Restricted Energy Loss (REL)
z 2 Z  1 2me c 2b 2  2 Tmax

 dE 
2
REL   
 K 2  ln

b


b A 2
I2
2 
 dx  E Tmax
By thickness Method
CALIBRATION GRAPH FOR CR39
6N NaOH 70 oC, 30h
1.11 ± 0.07 mm/h
By D-Le Method
REL (MeV cm2 g-1)
CALIBRATION COMPARISON FOR CR39
67
49
By D-Le Method
40
60
20
49
Z = 10
40
10
20
Comparison for CR39 NTDs exposed to 158 A GeV In49+ and Pb82+ 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/b  20.
RESPONSE CURVES FOR CR39 AND MAKROFOL
By D-Le Method
Comparison for CR39 NTDs exposed to 158 A GeV In49+ and Pb82+ 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/b  20.
LENGTH AND BASE AREA OF TRACKS IN
CR39 EXPOSED TO Pb82+ IONS (158 A GEV)
Z = 20e
D = 40 mm
L = 23 mm
Z = 45e
D = 59 mm
L =77 mm
Z = 65e
D = 69 mm
L = 169 mm
Z = 76e
D = 74 mm
L = 425 mm
Z = 82e
D = 75 mm
L = 650 mm