Stopping power of 1.0–2.6 MEV protons in Mylar, Makrofol and cellulose nitrate foils

Radiation Measurements, Vol. 28. Nos 1-6. pp. 15-18, 1997

Pergamon PII: S 1350-4487(97)00029-2

© 1997 ElsevierScienceLtd Printed in GreatBritain. All rights reserved 1350-4487/97 $17.00 + 0.00

S T O P P I N G P O W E R O F 1.0-2.6 M E V P R O T O N S MAKROFOL AND CELLULOSE NITRATE

IN MYLAR, FOILS

H. A M M i , M. CHEKIRINE AND A. ADJERAD Centre de Developpement des Techniques Nucleaires, 2, Bd Frantz Fanon, B.P 1017 Alger-Gare, Algerie ABSTRACT Stopping powers of 1.0 - 2.6 MeV protons in Mylar, Makrofol and Cellulose nitrate were measured. The results have been compared with scanty experimental data in the literature and with calculated values obtained by using the TRIM 92 computer code. These values agree well with each other within uncertainties. In the case of Mylar and LR I 15, maximum deviations of 9.5% and 4.5% from the semi-emperical curves were observed. In the case of Makrofol foils, a maximum deviation of 3% was found. Considering the accuracy of theories this discrepancy is not that significant.

KEYWORDS Stopping power: protons: Makrofol KG: Mylar: Cellulose nitrate LR I 15. INTRODUCTION It is necessary to know accurately the stopping power of protons in composite materials such as Mylar, LR 115 and Makrofol. Stopping power of protons in these materials has been of considerable interest due to their wide use in various applications; e.g.. as absorbers, windows, charged particle identification and spectroscopy in nuclear physics. Many experiments have been done (Raisanen et al., 1990; Rauhala et al., 1988; Foroughi et al., 1979; Shioma et al., 1995) with proton ion beam, to measure the stopping power in Mylar. No experimental data can be found in the literature concerning the stopping power of protons in Makrofol. However, (Rauhala et al., 1992) have determined the stopping power of protons in LR 115 in the energy range 0.3 - 4.3 MeV. The objective of the present study is to provide experimental stopping power data for protons in composite materials such as Mylar (6.3 ~m), cellulose nitrate (6 pm and 12 p.m) and Makrofol type KG (10 ~m); and to compare these data with the predictions of the TRIM 92 computer code (Ziegler et al., 1992). The present experiments were performed in the energy interval of 1.0 - 2.6 MeV. EXPERIMENTAL The proton beam was generated with a 3.75 MV Van de Graaff accelerator belonging to the Center of Nuclear Techniques Development of Algiers. The experimental arrangement for the energy loss measurement is shown in Fig. 1. Collimating slits and apertures were used to limit the size and the angular divergence of the beam. Thin gold target was placed perpendicular to the beam to reduce the count rate to a reasonable level, then the reflected beam passed trough a foil of known thickness, and was analysed energetically by a surface barrier detector (50 ram2). The energy loss of proton passing through the foil was determined by observing the shift of the backscattering signal, induced by the foil. The backscanered protons were detected at a scattering angle ,9 = 130 °. The energy resolution of the detecting system was 12 keV. To extract stopping powers from the energy-loss data, the foil thicknesses were determined by weighing several foils of known area.

15

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PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE

Sc.ttert~ Chamber Detectsr

C1,C2:Collimators Proton )

II

[I

c2 ~ / ~ ~ x ~ >

/~Au 50° ~....... ]

C o n i ~ su~ Fig. 1. Experimental set-up. To extract accurate results, all parameters which affect our experiment were checked before measurements. Some of these parameters are: electronic chain associated to the detection system, vacuum in the scattering chamber, determination of foil thickness.

a) Electronics To minimise the error in signal position, a pulser was used to control the pulse height of the signal delivered by amplifier 459 from ORTEC. During all the experiments, we observed that the signal stabilised al~er 1 hour, then the pulse height became constant and no significant difference could be observed in signal position for four hours irradiation per day.

b) Vacuum Using combination of a primary and a secondary pump, the vacuum inside the scattering chamber was maintained equal to 1.33 10.3 Pa. At this presure undesirable signals could be circumvented, and only signal due to protons traversing foil were taken into account.

c) Foil thickness determination We have chosen a weighing method to determine foil thickness instead of using backscattering method, because in weighing method we can limit error in measurement to one parameter which is a value of the foil weight, but in backscattering method so many parameters must be minimised. The resulting foil thicknesses were 6.30 + 0.05 ~m for Mylar, 9.98 + 0.02 pzn for Makrofol and (6.05 + 0.06 I~zn, 12.02 + 0.06 p.m) for LR 115. For conversion to thickness in lain from unit atoms/era2, mass densities of 1.2 i, 1.48, 1.39 g/cm3 for Makrofol (Ct6HI4Os), (BAYER), cellulose nitrate (C6H9OgN2), (KODAK Pathe), mylar (CioHsO4), (CHEMPLEX industries), were assumed respectively (Rauhala et al., 1988). An accuracy of 2% is estimated for the foil thickness. The results of the energy-loss measurements for 1.0 2.6 MeV protons are given in Table 1. The experimental errors of energy loss data include the possible errors in determining the signal position and error due to energy of the beam in the backscattering experiments. Overall relative uncertainty can be estimated to be less than + 2 %.

d) Stopping power determination The stopping power at the mean ion energy E,v in the foil was obtained by dividing the energy-loss AE by the foil areal density NAX (N- atomic density, AX - foil thickness). To account for the non-linear dependence of the stopping powers on ion energy, a small correction ( Rauhala et al., 1988 ) to the mean energy Eov was applied. As a result the stopping power S=dE/dX (differential energy loss per unit path length) is taken as AE/AX at an effective ion energy Eefr.

PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE

17

Table !. Energy loss of 0.95 - 2.6 MeV proton in Mylar, LR 115 and Makrofol foils. AE in MeV E(MeV)

Mylar

E(MeV)

LR 115

E(MeV)

LR 115

E(MeV)

Makrofol

0.967

0.235

0.955

0.233 a

0.967 b

0.537

1.018

0357

1.06

0.215

1.153

0.193 a

1.060

0.482 b

1.120

0.325

1.156

0.196

1.357

0.175 a

1.156

0.431 b

1.222

0298

1.249

0.188

1.558

0.158 a

1.249

0399 b

1.323

0.275

1 447

0.184

1.752

0.149 a

1.345

0.373 b

1.427

0.260

1.543

0.175

1.946

0.126 a

1.447

0.351 b

1.529

0.241

1.640

0.172

2.154

0.123 a

1.543

0.335 b

1.631

0.230

I 737

0.163

2.355

0.113 a

1.640

0315 b

1.733

0.220

1.832

0.148

2.562

0.106 a

1.737

0.290 b

1.838

0.209

1.928

O.150

1.832

0.282 b

1.940

0.206

2.024

0.142

1.928

0.274 b

2.048

0 196

2.121

0.140

2.024

0.259 b

2.151

0.185

2.121

0.247 b

2.253

0.175

2.217

0.240 b

2.356

0.171

2.465

0.165

2.567

0.159

a ) from 6 I~m thick foil data.

b) from 12 I~m thick foil data.

R E S U L T S AND D I S C U S S I O N Proton stopping powers calculated by the TRIM 92 computer code are presented together with experimental data in Figs. 2-4. As can be seen from Fig. 2, in the case o f Makrofol, the experimental and calculated values are in good agreement, discrepancy o f 3% at maximum were observed. Against o f Makrofol and LR 115; in the case o f Mylar we observed a high deviation (10%) from the predicted values (see Fig. 3). This discrepancy is certainly due to foil inhomogeneities. Generally, in the case o f Mylar, good agreement between calculated and experimental values are observed. In the case o f cellulose nitrate, our data may be compared both with existing experimental data and with semi-empericai predictions. Slight deviation ( experimental values ~ 4% lower) at Ep ~ 1.3 MeV was observed. It is clear from Fig. 4, that no systematical differences were observed when the foil thicknesses passed from 6 gm to 12 ~un and between data point from (Rauhala et al., 1992). In conclusion, stopping powers for proton in Makrofol and LR 115 can be calculated with good accuracy by using the TRIM 92 computer code in the present energy range.

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PROCEEDINGS OF THE 18TH INTERNATIONAL CONFERENCE .Q

E

E o~ 0,10o,zs-

.÷ %

Present work

- - -

TRIM92

+ Present work - - - TRIM92 ֥-..

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i

i

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~..

0,18

0,14

?.~

I

I

O~

I,O

Proton ene rgy (Me¥)

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Proton

Fig. 2. Stopping power of proton in Makrofol.

. ÷

Mylar (6.3 ~m)

0,16

I

I

1

!,2

1,4

L6

energy

'

l

'

I

1,8

(MeV)

Fig. 3. Stopping power of proton in Mylar.

t~

E

0,35.

~

P r e s e n t w o r k (6 pro) P r e s e n t w o r k (12 ~ t m ) A R a u h a l a et al. ( 1 9 9 2) ... T R I M 9 2 +

E

'ZX

o

0,30. 0 4-,

g~ o

0,20

ffi

0,15

e~

"~. e~ @ •, . ,

O. O-F.

LR-115 .4-

0,10

i

03

1,0 Proton

1is energy

£o

£s

(MeV)

Fig. 4. Stopping power of proton in cellulose nitrate. The experimental data represented by open circle and cross were compared with calculated data from TRIM 92 computer code. Data from (Rauhala et al., 1992) are also presented for comparison.

REFERENCES Foroughi F., Vuilleumier B. and Bovet E. (1979) Stopping power and multiple scattering of Havar and Kapton for low energy protons. Nucl. Instr. and Meth. 159, 513-516. gaisanen J. and Rauhala E. (1990) Stopping powers and energy loss of Mylar, Kapton, Havar, and Nickel for Z-- 3 - 17 ions in the energy range 0.2 - 2.1 MeV/amu. Phys. Rev. B41, 3951-3958. Rauhala E. and Raisanen J. (1988) Stopping powers of 0.5 -8.3 MeV protons in Havar, Nickel, Kapton and Mylar. Nucl. Instr. andMeth. 1335, 130-134. Rauhala E., Raisanen J., Fulop Zs., Kiss A. Z. and Hunyadi 1. (1992) Slowing down of light ions in LR 115 nuclear track material. Nucl. Traek~ Radiat. Meas. 20, 611- 614. l~uhala E. and Raisanen J. (1988) Stopping powers and energy loss of 0.3-22 Mev J2C in Havar, Nickel, Kapton, and Mylar. Phys. Rev. B37, 9249- 9253. Shioma -Tsuda N., Sakamoto N. and Ogawa H. (1995) Stopping powers of Mylar for protons from 4 to 11.5 MeV. Nucl. Instr. and Meth. BI03, 255-260. Ziegler J. F. and Biersack J.P. (1992) TRIM-92 computer code (private communication).