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Energy-loss measurement of 132Xe in lead by a nuclear track technique
Nuclear Instruments and Methods in physics Research B36 (1989) 276-281 North-Holland, Amsterdam
276
ENERGY-LOSS
MEASUREMENT
Atul SAXENA
and K.K. DWIVEDI
OF 132Xe IN LEAD BY A NUCLEAR
TRACK ~C~IQUE
*
Deparfment of Chemisfv, _Vorth-Eastern Hill University, Shiliosg 793 003, India
E. REICHWEIN
and G. FIEDLER
II. Physikalisches Insfitut, Justus-Liebig Uniuersitiit,D-6300 Giessen, FRG Received 1 July 1987 and in revised from 2 November 1988
A simple nuclear track technique has been described to measure energy-loss rate of any heavy ion in any medium. Here we present the results obtained from our measurements of energy-loss rate of 17.0 hileV/u r3’Xe ions in lead using special zinc phosphate (ZnP) glass detector. The errors in measurement range from 5-10%. Experimental energy-loss data has been compared with calculated values. The significance of the results and scope of the track technique is discussed.
1. Introduction Solid state nuclear track detectors offer several applications not only in the field of nuclear physics but also in many diverse fields of study [1,2]. During the last couple of years some new detectors such as CR-39 and ZnP-glass were identified and developed 13-5) with enhanced sensitivity and resolution. The shape and size of heavy ion tracks in such detectors are dependent on the mass, charge and energy of the track forming ions as well as on the stopping-power of the media. Thus after appropriate calibration, it is possible to use these track detectors for measuring energy-loss rate of any heavy ion in any medium. Recently, track technique has been employed to measure ranges and energy-loss of heavy ions in certain track forming solids [6,7]. Saxena et al. [6] have measured ranges and energy-loss of 16.34 MeV/u =‘U in Makrofol-N on the other hand Swarnali Ghosh et al. [7] have presented data for 18.56 MeV/u 4oAr in Lexan poiycarbonate. In this paper we describe a simple method for measuring energy-loss rate of 17.0 MeV/u t3’ Xe in metallic lead using ZnP-glass track detector. Our experimental results are compared with the theoretical values obtained from computer code DEDXT [S] based on stopping-power equations of Mukhetji and coworkers [9-111.
calibrated for a desired heavy ion in terms of maximum etchable track length as a function of ion energy. Then several targets of any material with precisely known thickness are placed before the detectors and exposed to a collimated beam of the same heavy ions. The energyloss of the transmitted ions may be directly obtained from the values of the measured maximum etchable track lengths and the calibration curve. The basic principle of the track technique is illustrated in a schematic diagram (fig. 1). It represents the depth of penetration of ‘32Xe (17.0 MeV/u) ions in a few ZnP-glass detectors after passing through lead targets. From these penetration depths (track lengths, L,), the transmitted energy (E,) of the ion is determined and an energy-loss curve is obtained by plotting E, as a function of target thickness. For a given target thickness X, the energy-loss may be obtained by the relation AE=(E;-E;‘),
(1)
where Ei and EC are energies of the ion before and after its passage through an effective target thickness AX respectively. The value of AX is equal to the thickness difference of any two nearby targets X, and X, and is given by AX=
(Xz - Xi).
(2)
2. The track technique
Hence, the energy-loss rate (ELR) from the following equation.
The basic principle involved in this track technique is very simple. First of all a sensitive track detector is
(ELR) E,,X, = E,
* To whom all correspondence should be addressed.
where E,
0168-583X/89/$03.50
(North-Holland
Q Elsevier
Science
Publishers
Physics Publishing Division)
B.V.
2
and X,
can be determined
1
are the mean energy of the ion and
A. Saxenn
160 ,
2LO L,
, 80, , 7 7
Collipated
ions
Ei = 17.0 MVIU
,“,O
,16,0
et al. /
Energy loss of ““Xe
211
the vacuum chamber at a height of nearly 15 cm above the boat containing lead metal. After deposition, all the target-detector plates were weighed again. It was found that fairly uniform (within 3%) targets of Pb were deposited irrespective of their positions. For the present experiment, targets of varied thickness (1.6-124.8 mg/cm2) were prepared by successive evaporations and their thickness were determined by weighing technique. In order to protect these targets from air and moisture, which attack the metal and form thin surface layer of oxycarbonate, vacuum desiccators were used to preserve the targets. This has prevented oxidation and thereby mirror like surface lusture of the targets was retained.
,2rjOp
-----_
I
in lead
/---__
3.2. Irradiations
P b-targets
ZnP-glass
detectors
Fig. 1. A schematic diagram showing the basic principle of the measurement of energy-loss of 17.0 MeV/u i3’Xe ions in lead using ZnP-glass detector.
the mean spond to
target
thickness
respectively.
These
corre-
3.3. Chemical etching
E,=(E;+Er)/2
and X,=(X,+X,)/2.
(5)
In the present work, the energy-loss rate of 132Xe in lead is determined from the experimental energy-loss curve.
3. Experimental 3. I. Preparation
All irradiations were done at X0 channel of UNILAC, GSI Darmstadt. Samples were fitted in special holders and arranged in sample magazines. An automatic sample carrier-cum-changer was used to align samples in any desired orientation with respect to ion beam. A well collimated beam of 132Xe ions with an initial energy of 17.0 MeV/u was used to expose targets and detectors at incident angle of 45O with respect to the surface. An optimum ion dose of 2 X lo4 crnm2 has been used. Several ZnP-glass detectors without any target material were also exposed to 13’Xe ions of varied energies (1.4-17.0 MeV/u) in order to obtain a calibration curve between 132Xe ion energies and maximum etchable track lengths in ZnP-glass detector.
After irradiation, layers of Pb targets were removed by dissolving in aqua regia at room temperature. ZnPglass detectors were then thoroughly washed in distilled water and dried in air. All the glass detectors were then etched in 6N NaOH at 55 o C. The etching process was carried out in steps and terminated when rounded track-tips were observed. The etching time ranges between 40-100 min. After appropriate etching and washing the detectors were dried under vacuum.
of detectors and targets 3.4. Meusurement of truck length
Thin plates of ZnP-glass detectors were obtained from bulk material (chemical composition: B,.,,O,,.,,and specific gravity 2.686 g/ml) *I,.,Si,,,,P,,.,,Zn,., by cutting in the size of (25 X 15 X 1.5) mm. These detector plates were polished in order to produce background free and optically plain surfaces. Each detector plate was examined under microscope for surface smoothness and then weighed over semi-microbalance. High purity (4nines) lead was used to prepare targets by vacuum evaporation-deposition technique. Fifteen detector plates were fixed in a mount and placed inside
Well defined, narrow conical tracks of ‘32Xe ions in ZnP-glass were observed at ordinary magnifications. Lengths of the etched tracks have been measured at random all over the detector surface in order to minimize the effect due to variation in target thickness. Track diameters and projected track lengths were measured with the help of an optical microscope at a magnification of 1000 X . A measuring accuracy of + 0.5 pm has been achieved at this magnification. From measured data, the maximum etchable true track lengths
278
A. Saxena et al. / Energy loss of ‘32Xe in lead
were obtained from the equation given by Dwivedi and Mukheji [12]. It is well known [13] that chemical etching reveals only that portion of tracks for which energy-deposition rate is above a critical value (dE/dX),. This critical energy-deposition rate is also called track registration threshold and the sensitivity of SSNTD is characterized by this parameter. If the total length of damaged trail (range) is R and the maximum etchable track length is L, then the portion of range remaining unetched or the range deficit (AR) is obtained by AR=(R-L).
(6)
For ZnP-glass detector the track registration threshold (dE/dX). was found to be 13.0 MeV mgg’ cm2 [14]. This corresponds to a range deficit of less than 2 pm and to a lower energy cut-off value of about 7 MeV for ‘32Xe ions. Since the detector calibration is done in terms of maximum etchable track lengths, therefore, the value of lower energy cut-off has no influence on the experimental results.
n=3 GG,
Maximum etchable track length (pm)
1.40 4.70 7.35 7.50 8.38 8.82 9.83 10.87 12.00 13.18 14.13 15.05 15.60 16.08 16.54 17.00
16.2kO.5 =) 42.4 + 0.6 =) 60.3 f 0.6 62.0 i 1.1 b, 69.0 f 1.2 b, 71.0*1.4 s2.2*1.3 87.0 * 1.3 93.4+ 1.1 104.5 * 1.1 112.0 * 1.2 122.3 + 0.8 127.8 + 0.6 133.0i0.6 137.1* 0.9 145.4i 0.6
b, Data from ref. [16].
ZnP-glass detectors were calibrated for energy measurements of ‘32Xe in terms of maximum etchable track lengths. Several ZnP-glass detectors were exposed to ‘32Xe ions of varied energies (1.4-17.0 MeV/u) at 30 o and 45O with respect to detector surface. Ion energies were precisely measured with the help of a TOF system at UNILAC. Nuclear tracks were fully developed by chemical etching in 6N NaOH at 55 o C for a period of 40-100 min. Maximum etchable true track lengths were measured as mentioned in the previous section. Measured track lengths and energies of ‘32Xe ions are listed in table 1. A few low energy data are taken from other references [15,16]. Fig. 2 shows a calibration curve for i3* Xe ions in ZnP-glass detector. It is drawn by fitting a one dimensional third order polynomial of the type c
Energy (MeV/u)
a) Data from ref. [15].
3.5. Detector calibration
E,=
Table 1 Maximum etchable track lengths of 13’Xe ions in ZnP-glass at different energies. Tracks are etched in 6N NaOH at 55OC. Only statistical uncertainties are shown here.
(7)
n=O
where E, is the transmitted energy (in MeV) of the ion after traversing through a target of thickness X. Lx (in pm) is the track length of the ion of energy E, in the track detector and (Y, is the best set of coefficients of one dimensional polynomial fit. As obtained in the present experiment, the values of coefficients (LY,) are listed in table 2. Using these coefficients and the measured track length in ZnP-glass detector, the transmitted energies of 13’Xe have been obtained with fair accuracy. 3.6. Energy-loss measurement An energy-loss curve may be constructed by plotting energy of the transmitted ions as a function of target
-
132
zoo-
E
Xe in ZnP Glass
Experimental
t
160-
. Present
S
IZO-
.
data from work
o Cmmbach Routenberg
G 80:: 2
co-
o 0
,,,,,,,,,,,,,I 2
III, 4
6
8
10
12
14
I 16
18
ION ENERGY (MeVlu)
Fig. 2. A calibration curve obtained by a one dimensional third order polynomial fit to the measured track length-energy data of 13*Xe ion in ZnP-glass detector.
Table 2 Values of best set of coefficients of one dimensional third order polynomial fit (a) (Y,: for calibration curve between energy and track length and (b) &: energy-loss curve between energy and target thickness. ”
Coefficients
Pm
%I
0 1
2 3
0.1699 0.1025 0.1236 -0.6110
E+02 E+ 02 E+ 00 E-03
0.2254 -0.1417 -0.4414 0.3613
E+04 E+02 E+OO E-02
A. Saxena
ION
0 g-
2L 1 132
ENERGY
6 II!III
8
Xe in ZnP
10
(MeVlu 12
Glass
TRACK
LENGTH
11
3.7 Experimental
1 16 1
I21
18 1
20
(11
(pm1
Fig. 3. Typical energy and track length spectra are shown for r3*Xe ions in ZnP-glass detector after passing through Pbtargets of varied thickness. The initial beam energy was 17.0 MeV/u.
thickness. For ‘32Xe ions in lead, the experimental data are fitted by a one dimensional third order polynomial which is represented as n=3 Ex=
c
,4,X”,
279
et al. / Energy loss of ‘32Xein lead
(8)
II=0
where E, is the transmitted energy (in MeV) of the ion after penetrating through a target thickness X (in mg/cm2) and p, is the best set of coefficients of the polynomial fit. These coefficients are also given in table 2. Using eq. (S), the energies Ei and EC may be obtained for any two target thickness Xi and X, respectively. From these the energy-losses (AE) are determined for any corresponding target thickness (AX).
errors
The energy of heavy ions impinged on the targets is measured accurately (within 0.1%) with the help of a TOF system at UNILAC, Darmstadt. It was found that Pb-targets were uniform within 3% except the thinnest one for which it was nearly 7%. Track lengths are measured within an accuracy of +0.5 ym. The broadening of energy distribution of the degraded ions is clearly reflected in track length distribution curves. Fig. 3 shows such distributions for initial energy and 5 degraded energies of ‘32Xe in lead targets. Nearly 200-300 tracks were measured for each distribution. It has been observed that full-width at half maximum (FWHM) gradually increases with target thickness. Table 3 contains several parameters such as energy-loss and track length distribution of 132Xe ions along with target thickness and standard deviations. The experimental errors in the energy-loss measurements have been estimated to be about 5-10%.
4. Results and discussion In table 4 we present our experimental results obtained for energy lost by 132Xe ions in passing through lead targets of varied thickness. The energy (E,) of the transmitted ion is derived from the calibration curve or from eq. (7) for a measured track length (L,). An energy-loss curve is generated by plotting E, against target thickness (X) and is shown in fig. 4. From this curve, the values of energy-loss rate of 132Xe in lead as a function of mean target thickness (X,) and mean ion energy (Em) have been obtained using the method described in section 3.6. Table 5 lists the values of experimental energy-loss rate (ELR) for every 5 mg/cm2
Table 3 Energy-loss and track length distribution of 13*Xe ions in a few lead targets of varied thickness Parameters a)
Xi
@g/cm* )
AE (MeV/u) -% (MeV/u) Lx (pm) eE (MeV/u) eL (pm) N
Reference number of the peak in fig. 3
(1)
(2)
(3)
(4)
(5)
(6)
0.0 0.0 17.0 144.0 0.1 1.2 305
8.51 1.0 15.9 132.1 0.1 1.5 240
19.5 3.0 13.9 111.8 0.15 1.8 225
34.2 6.1 10.6 86.6 0.2 2.0 215
53.0 11.1 5.9 51.0 0.3 3.0 260
72.2 14.8 2.2 21.2 0.5 5.5 220
‘) Xi = Pb-target thickness in mg/cm*. A E = energy lost by ‘32Xe ion of 17.0 MeV/u. E, = energy of the ion as obtained from the calibration curve. L, = length of the maximum etchable tracks for ion energy E,. oE = FWHM with respect to ion energy distribution. oL = FWHM with respect to track length distribution. N = number of tracks measured.
280
A. Saxena et al. / Energy loss of ‘32Xe in lead
Table 4 Values of maximum etchable track length (L,) lead targets of thickness (X).
and corresponding transmitted energy (E,)
Maximum etchable track length L,
Target thickness X (pm)
(mg/cm’
No target 1.4kO.l 4.2+0.1 7.5 + 0.2 12.0 + 0.3 17.2 + 0.4 22.2 * 0.5 24.5 + 0.6 30.1+ 0.8 38.2 & 0.8 46.7 + 0.9 60.0+1.1 63.6rt1.4 97.0 + 1.6 110.0 + 2.0
No target 1.6 +O.l 4.8 + 0.1 8.5 f 0.2 13.6+0.3 19.5 +0.4 25.2*0.6 27.8 + 0.7 34.2 + 0.9 43.4 + 0.9 53.0+1.0 68.1+ 1.2 72.2 + 1.4 110.1 f 1.7 124.8 + 2.2
144.0 + 1.2 141.6 + 1.3 138.8 + 1.6 132.1+ 1.0 119.6kl.l 111.8+1.5 101.1* 1.0 96.6 + 1 .O 86.6 + 1.5 65.4kl.S 51.0 f 2.2 28.5 k 3.5 21.2k5.7 no tracks no tracks
of target thickness, the corresponding mean ion energy and the calculated energy-loss rate of 13’Xe in lead using computer code DEDXT [8] based on stoppingpower equations of Mukherji and coworkers [9-111. Plots of (ELR) versus Em and X, are shown in fig. S(a) and fig. 5(b), respectively. Discrepancies between experimental and calculated energy-loss rate range from 2 to 15%. From this comparison we cannot make any meaningful assessment about the validity of the stopping-power equation of Mukherji and coworkers [9-111 unless the measurements are done for several other ions in different elements and complex media.
5. Conclusions Energy measurement of heavy ions require highly sophisticated instruments such as recoil proton spec-
-
201
I
13’Xe in Lead (Initialenergy
01 0
,
,
,
,
,
,
IO
20
30
40
50
60
TARGET
Energy of the transmitted ion E,
(pm)
)
THICKNESS
17.0 MeVlu)
70
60
90
100
(urn)
Fig. 4. A plot showing energy-loss data for 13’Xe in Pb. Experimental data points are fitted with a one dimensional polynomial of third order.
of 13’Xe ions after traversing through
(MeV)
(MeV/u)
2244.0 2229.5 2178.0 2104.1 1987.9 1836.1 1675.1 1597.2 1399.2 1104.8 801.2 386.7 293.0 -
17.0 16.89 16.50 15.94 15.06 13.91 12.69 12.10 10.60 8.37 6.07 2.93 2.22
trometer [17-191, magnetic spectrometer [20], Time-offlight (TOF) [21,22] and double time of flight (DTOF) [23] systems. Although these systems are capable of more precise measurements as compared to the proposed nuclear track technique, but due to its simplicity and low cost the track techniques may be considered as
Table 5 Values of experimental and theoretical energy-loss rate of ‘32Xe in lead at various mean target thickness and ion energies Mean target thickness X,
Energy-loss rate (ELR) (MeV mg-’ cm’)
Mean ion energy E,
(w/cm*
Exp. ‘)
Theoret. b,
(MeV)
20.2 22.5 24.9 27.2 28.4 29.6 30.8 32.0 32.0 32.0 30.8 28.4 26.0 21.3 17.8 14.2 9.5 7.2
23.6 24.0 24.5 25.1 25.7 26.4 27.1 27.7 28.1 28.5 28.4 27.9 26.7 24.3 19.7 15.1 11.2 8.7
2172.5 2071.8 1954.3 1822.9 1680.3 1531.2 1372.2 1212.2 1051.8 893.6 740.5 595.2 460.3 338.5 232.6 145.3 79.3 37.2
5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.0 75.0 80.0 85.0 90.0
)
a> Experimental - present work. b, Theoretical - refs. [S-11].
A. Saxena
et al. / Energy loss of '32Xein lead
::r-.-_!i 100
800
1200 E, IMeV
0
20
60
LO x,
1600
2000
1
80
100
tmglcm2)
Fig. 5. Plots of experimental energy-loss rate of i3*Xe in lead along with theoretical values [S-11] as a function of (a) mean target thickness E, and (b) mean ion energy X,,,
handy and useful. Though in this technique, the track detector needs to be calibrated for each ion, but once it is done, the detector can be used to measure energy-loss of any ion in any material. Present investigation provides a simple experimental technique for measuring energy-loss rate of any heavy ion in any media using a sensitive solid state nuclear track detector. quite
We wish to thank Dr. R. Spohr, Dr. J. Vetter and other staff at UNILAC, GSI, Darmstadt for providing irradiation facilities. One of us (K.K.D.) thanks DAAD (Bonn, West Germany) and UGC (New Delhi, India) for the award of academic exchange fellowship. We also thank the German Agency for Technical Cooperation (DGTZ) FRG for an equipment grant.
References [l] R.L. Fleischer, P.B. Price and R.M. WaIker, Nuclear Tracks in Solids: Principles and Applications (University of California Press, Berkeley, 1975) Chapter 10, p. 562. [2] B.E. Fischer and R. Spohr, Rev. Mod. Phys. 55 (1983) 907.
281
[3] B.G. Cartwright, E.K. Shirk and P.B. Price, Nucl. Instr. and Meth. 153 (1978) 457. [4] J. Aschenbach, G. Fiedler, H. S&reck-Kiillner and G. Siegert, Nucl. Instr. and Meth. 116 (1974) 389. [5] G. Fiedler, J. Aschenbach, W. Otto, T. Rautenberg, U. Steinhauser and G. Siegert, Nucl. Instr. and Meth. 147 (1977) 35. [6] A. Saxena, K.K. Dwivedi. R.K. Poddar and G. Fiedler, Pramana-J. Phys. 29 (1987) 485. [7] S. Ghosh, A. Saxena and K.K. Dwivedi, Pramana-J. Phys. 31 (1988) 197. [8] K.K. Dwivedi, A Program for Computation of Heavy Ion Ranges, Track Lengths and Energy-Loss Rate in Elemental and Complex Media, presented at 14th Inf. Conf. on SSNTD, Lahore (1988) Nucl. Tracks. and Radiat. Mass. (1988) in press. [9] S. Mukherji and B.K. Srivastava, Phys. Rev. B9 (1974) 3708. [lo] B.K. Srivastava and S. Mukherji, Phys. Rev. Al4 (1976) 718. [ll] S. Mukherji and A.K. Nayak, Nucl. Instr. and Meth. 159 (1979) 421. [12] K.K. Dwivedi and S. Mukherji, Nucl. Instr. and Meth. 161 (1979) 317. [13] R.L. FIeischer, P.B. Price and R.M. Walker, Ann. Rev. Nucl. Sci. 15 (1965) 1. [14] J. Raju, Nuclear Tracks of 350 MeV 90Zr Ion in Solid Dielectrics, M.Sc. Dissertation (unpublished), North-Eastern Hill University, Shillong (1988) p. 23. [15] P. Crombach, Diploma Thesis (unpublished), Justus-Liebig Universitat, Giessen (1983) p. 44. [16] T. Rautenberg, Diploma Thesis (unpublished), JustusLiebig Universitat, Giessen (1980) p. 19. [17] R. Bimbot, S. Della Negra, D. Gardes, H. Gamin, A. Fleury and F. Hubert, Nucl. Instr. and Meth. 153 (1978) 161. [18] R. Bimbot, D. Gardes, H. Gauvin, A. Fleury and F. Hubert, Nucl. Instr. and Meth. 174 (1980) 231. [19] R. Bimbot, S. Della Negra, D. Gardb, H. Gamin and B. Tamain, Rev. Phys. Appl 13 (1978) 393. [20] R. Bimbot, H. Gauvin, I. OrIionge, R. Anne, G. Bastin and F. Hubert, Nucl. Instr. and Meth. B17 (1986) 1. [21] R.L. Hahn, KS. Toth, R.L. Ferguson and F. Plasil, Nucl. Instr. and Meth. 180 (1981) 581. [22] H. Geissel, Y. Laichter, T. Kitahara, J. KIabunde, P. StrehI and P. Armbruster, Nucl. Instr. and Meth. 206 (1983) 609. [23] H. Geissel, Y. Laichter, W.F.W. Schneider and P. Armbruster, Nucl. Instr. and Meth. 194 (1982) 21.
276
ENERGY-LOSS
MEASUREMENT
Atul SAXENA
and K.K. DWIVEDI
OF 132Xe IN LEAD BY A NUCLEAR
TRACK ~C~IQUE
*
Deparfment of Chemisfv, _Vorth-Eastern Hill University, Shiliosg 793 003, India
E. REICHWEIN
and G. FIEDLER
II. Physikalisches Insfitut, Justus-Liebig Uniuersitiit,D-6300 Giessen, FRG Received 1 July 1987 and in revised from 2 November 1988
A simple nuclear track technique has been described to measure energy-loss rate of any heavy ion in any medium. Here we present the results obtained from our measurements of energy-loss rate of 17.0 hileV/u r3’Xe ions in lead using special zinc phosphate (ZnP) glass detector. The errors in measurement range from 5-10%. Experimental energy-loss data has been compared with calculated values. The significance of the results and scope of the track technique is discussed.
1. Introduction Solid state nuclear track detectors offer several applications not only in the field of nuclear physics but also in many diverse fields of study [1,2]. During the last couple of years some new detectors such as CR-39 and ZnP-glass were identified and developed 13-5) with enhanced sensitivity and resolution. The shape and size of heavy ion tracks in such detectors are dependent on the mass, charge and energy of the track forming ions as well as on the stopping-power of the media. Thus after appropriate calibration, it is possible to use these track detectors for measuring energy-loss rate of any heavy ion in any medium. Recently, track technique has been employed to measure ranges and energy-loss of heavy ions in certain track forming solids [6,7]. Saxena et al. [6] have measured ranges and energy-loss of 16.34 MeV/u =‘U in Makrofol-N on the other hand Swarnali Ghosh et al. [7] have presented data for 18.56 MeV/u 4oAr in Lexan poiycarbonate. In this paper we describe a simple method for measuring energy-loss rate of 17.0 MeV/u t3’ Xe in metallic lead using ZnP-glass track detector. Our experimental results are compared with the theoretical values obtained from computer code DEDXT [S] based on stopping-power equations of Mukhetji and coworkers [9-111.
calibrated for a desired heavy ion in terms of maximum etchable track length as a function of ion energy. Then several targets of any material with precisely known thickness are placed before the detectors and exposed to a collimated beam of the same heavy ions. The energyloss of the transmitted ions may be directly obtained from the values of the measured maximum etchable track lengths and the calibration curve. The basic principle of the track technique is illustrated in a schematic diagram (fig. 1). It represents the depth of penetration of ‘32Xe (17.0 MeV/u) ions in a few ZnP-glass detectors after passing through lead targets. From these penetration depths (track lengths, L,), the transmitted energy (E,) of the ion is determined and an energy-loss curve is obtained by plotting E, as a function of target thickness. For a given target thickness X, the energy-loss may be obtained by the relation AE=(E;-E;‘),
(1)
where Ei and EC are energies of the ion before and after its passage through an effective target thickness AX respectively. The value of AX is equal to the thickness difference of any two nearby targets X, and X, and is given by AX=
(Xz - Xi).
(2)
2. The track technique
Hence, the energy-loss rate (ELR) from the following equation.
The basic principle involved in this track technique is very simple. First of all a sensitive track detector is
(ELR) E,,X, = E,
* To whom all correspondence should be addressed.
where E,
0168-583X/89/$03.50
(North-Holland
Q Elsevier
Science
Publishers
Physics Publishing Division)
B.V.
2
and X,
can be determined
1
are the mean energy of the ion and
A. Saxenn
160 ,
2LO L,
, 80, , 7 7
Collipated
ions
Ei = 17.0 MVIU
,“,O
,16,0
et al. /
Energy loss of ““Xe
211
the vacuum chamber at a height of nearly 15 cm above the boat containing lead metal. After deposition, all the target-detector plates were weighed again. It was found that fairly uniform (within 3%) targets of Pb were deposited irrespective of their positions. For the present experiment, targets of varied thickness (1.6-124.8 mg/cm2) were prepared by successive evaporations and their thickness were determined by weighing technique. In order to protect these targets from air and moisture, which attack the metal and form thin surface layer of oxycarbonate, vacuum desiccators were used to preserve the targets. This has prevented oxidation and thereby mirror like surface lusture of the targets was retained.
,2rjOp
-----_
I
in lead
/---__
3.2. Irradiations
P b-targets
ZnP-glass
detectors
Fig. 1. A schematic diagram showing the basic principle of the measurement of energy-loss of 17.0 MeV/u i3’Xe ions in lead using ZnP-glass detector.
the mean spond to
target
thickness
respectively.
These
corre-
3.3. Chemical etching
E,=(E;+Er)/2
and X,=(X,+X,)/2.
(5)
In the present work, the energy-loss rate of 132Xe in lead is determined from the experimental energy-loss curve.
3. Experimental 3. I. Preparation
All irradiations were done at X0 channel of UNILAC, GSI Darmstadt. Samples were fitted in special holders and arranged in sample magazines. An automatic sample carrier-cum-changer was used to align samples in any desired orientation with respect to ion beam. A well collimated beam of 132Xe ions with an initial energy of 17.0 MeV/u was used to expose targets and detectors at incident angle of 45O with respect to the surface. An optimum ion dose of 2 X lo4 crnm2 has been used. Several ZnP-glass detectors without any target material were also exposed to 13’Xe ions of varied energies (1.4-17.0 MeV/u) in order to obtain a calibration curve between 132Xe ion energies and maximum etchable track lengths in ZnP-glass detector.
After irradiation, layers of Pb targets were removed by dissolving in aqua regia at room temperature. ZnPglass detectors were then thoroughly washed in distilled water and dried in air. All the glass detectors were then etched in 6N NaOH at 55 o C. The etching process was carried out in steps and terminated when rounded track-tips were observed. The etching time ranges between 40-100 min. After appropriate etching and washing the detectors were dried under vacuum.
of detectors and targets 3.4. Meusurement of truck length
Thin plates of ZnP-glass detectors were obtained from bulk material (chemical composition: B,.,,O,,.,,and specific gravity 2.686 g/ml) *I,.,Si,,,,P,,.,,Zn,., by cutting in the size of (25 X 15 X 1.5) mm. These detector plates were polished in order to produce background free and optically plain surfaces. Each detector plate was examined under microscope for surface smoothness and then weighed over semi-microbalance. High purity (4nines) lead was used to prepare targets by vacuum evaporation-deposition technique. Fifteen detector plates were fixed in a mount and placed inside
Well defined, narrow conical tracks of ‘32Xe ions in ZnP-glass were observed at ordinary magnifications. Lengths of the etched tracks have been measured at random all over the detector surface in order to minimize the effect due to variation in target thickness. Track diameters and projected track lengths were measured with the help of an optical microscope at a magnification of 1000 X . A measuring accuracy of + 0.5 pm has been achieved at this magnification. From measured data, the maximum etchable true track lengths
278
A. Saxena et al. / Energy loss of ‘32Xe in lead
were obtained from the equation given by Dwivedi and Mukheji [12]. It is well known [13] that chemical etching reveals only that portion of tracks for which energy-deposition rate is above a critical value (dE/dX),. This critical energy-deposition rate is also called track registration threshold and the sensitivity of SSNTD is characterized by this parameter. If the total length of damaged trail (range) is R and the maximum etchable track length is L, then the portion of range remaining unetched or the range deficit (AR) is obtained by AR=(R-L).
(6)
For ZnP-glass detector the track registration threshold (dE/dX). was found to be 13.0 MeV mgg’ cm2 [14]. This corresponds to a range deficit of less than 2 pm and to a lower energy cut-off value of about 7 MeV for ‘32Xe ions. Since the detector calibration is done in terms of maximum etchable track lengths, therefore, the value of lower energy cut-off has no influence on the experimental results.
n=3 GG,
Maximum etchable track length (pm)
1.40 4.70 7.35 7.50 8.38 8.82 9.83 10.87 12.00 13.18 14.13 15.05 15.60 16.08 16.54 17.00
16.2kO.5 =) 42.4 + 0.6 =) 60.3 f 0.6 62.0 i 1.1 b, 69.0 f 1.2 b, 71.0*1.4 s2.2*1.3 87.0 * 1.3 93.4+ 1.1 104.5 * 1.1 112.0 * 1.2 122.3 + 0.8 127.8 + 0.6 133.0i0.6 137.1* 0.9 145.4i 0.6
b, Data from ref. [16].
ZnP-glass detectors were calibrated for energy measurements of ‘32Xe in terms of maximum etchable track lengths. Several ZnP-glass detectors were exposed to ‘32Xe ions of varied energies (1.4-17.0 MeV/u) at 30 o and 45O with respect to detector surface. Ion energies were precisely measured with the help of a TOF system at UNILAC. Nuclear tracks were fully developed by chemical etching in 6N NaOH at 55 o C for a period of 40-100 min. Maximum etchable true track lengths were measured as mentioned in the previous section. Measured track lengths and energies of ‘32Xe ions are listed in table 1. A few low energy data are taken from other references [15,16]. Fig. 2 shows a calibration curve for i3* Xe ions in ZnP-glass detector. It is drawn by fitting a one dimensional third order polynomial of the type c
Energy (MeV/u)
a) Data from ref. [15].
3.5. Detector calibration
E,=
Table 1 Maximum etchable track lengths of 13’Xe ions in ZnP-glass at different energies. Tracks are etched in 6N NaOH at 55OC. Only statistical uncertainties are shown here.
(7)
n=O
where E, is the transmitted energy (in MeV) of the ion after traversing through a target of thickness X. Lx (in pm) is the track length of the ion of energy E, in the track detector and (Y, is the best set of coefficients of one dimensional polynomial fit. As obtained in the present experiment, the values of coefficients (LY,) are listed in table 2. Using these coefficients and the measured track length in ZnP-glass detector, the transmitted energies of 13’Xe have been obtained with fair accuracy. 3.6. Energy-loss measurement An energy-loss curve may be constructed by plotting energy of the transmitted ions as a function of target
-
132
zoo-
E
Xe in ZnP Glass
Experimental
t
160-
. Present
S
IZO-
.
data from work
o Cmmbach Routenberg
G 80:: 2
co-
o 0
,,,,,,,,,,,,,I 2
III, 4
6
8
10
12
14
I 16
18
ION ENERGY (MeVlu)
Fig. 2. A calibration curve obtained by a one dimensional third order polynomial fit to the measured track length-energy data of 13*Xe ion in ZnP-glass detector.
Table 2 Values of best set of coefficients of one dimensional third order polynomial fit (a) (Y,: for calibration curve between energy and track length and (b) &: energy-loss curve between energy and target thickness. ”
Coefficients
Pm
%I
0 1
2 3
0.1699 0.1025 0.1236 -0.6110
E+02 E+ 02 E+ 00 E-03
0.2254 -0.1417 -0.4414 0.3613
E+04 E+02 E+OO E-02
A. Saxena
ION
0 g-
2L 1 132
ENERGY
6 II!III
8
Xe in ZnP
10
(MeVlu 12
Glass
TRACK
LENGTH
11
3.7 Experimental
1 16 1
I21
18 1
20
(11
(pm1
Fig. 3. Typical energy and track length spectra are shown for r3*Xe ions in ZnP-glass detector after passing through Pbtargets of varied thickness. The initial beam energy was 17.0 MeV/u.
thickness. For ‘32Xe ions in lead, the experimental data are fitted by a one dimensional third order polynomial which is represented as n=3 Ex=
c
,4,X”,
279
et al. / Energy loss of ‘32Xein lead
(8)
II=0
where E, is the transmitted energy (in MeV) of the ion after penetrating through a target thickness X (in mg/cm2) and p, is the best set of coefficients of the polynomial fit. These coefficients are also given in table 2. Using eq. (S), the energies Ei and EC may be obtained for any two target thickness Xi and X, respectively. From these the energy-losses (AE) are determined for any corresponding target thickness (AX).
errors
The energy of heavy ions impinged on the targets is measured accurately (within 0.1%) with the help of a TOF system at UNILAC, Darmstadt. It was found that Pb-targets were uniform within 3% except the thinnest one for which it was nearly 7%. Track lengths are measured within an accuracy of +0.5 ym. The broadening of energy distribution of the degraded ions is clearly reflected in track length distribution curves. Fig. 3 shows such distributions for initial energy and 5 degraded energies of ‘32Xe in lead targets. Nearly 200-300 tracks were measured for each distribution. It has been observed that full-width at half maximum (FWHM) gradually increases with target thickness. Table 3 contains several parameters such as energy-loss and track length distribution of 132Xe ions along with target thickness and standard deviations. The experimental errors in the energy-loss measurements have been estimated to be about 5-10%.
4. Results and discussion In table 4 we present our experimental results obtained for energy lost by 132Xe ions in passing through lead targets of varied thickness. The energy (E,) of the transmitted ion is derived from the calibration curve or from eq. (7) for a measured track length (L,). An energy-loss curve is generated by plotting E, against target thickness (X) and is shown in fig. 4. From this curve, the values of energy-loss rate of 132Xe in lead as a function of mean target thickness (X,) and mean ion energy (Em) have been obtained using the method described in section 3.6. Table 5 lists the values of experimental energy-loss rate (ELR) for every 5 mg/cm2
Table 3 Energy-loss and track length distribution of 13*Xe ions in a few lead targets of varied thickness Parameters a)
Xi
@g/cm* )
AE (MeV/u) -% (MeV/u) Lx (pm) eE (MeV/u) eL (pm) N
Reference number of the peak in fig. 3
(1)
(2)
(3)
(4)
(5)
(6)
0.0 0.0 17.0 144.0 0.1 1.2 305
8.51 1.0 15.9 132.1 0.1 1.5 240
19.5 3.0 13.9 111.8 0.15 1.8 225
34.2 6.1 10.6 86.6 0.2 2.0 215
53.0 11.1 5.9 51.0 0.3 3.0 260
72.2 14.8 2.2 21.2 0.5 5.5 220
‘) Xi = Pb-target thickness in mg/cm*. A E = energy lost by ‘32Xe ion of 17.0 MeV/u. E, = energy of the ion as obtained from the calibration curve. L, = length of the maximum etchable tracks for ion energy E,. oE = FWHM with respect to ion energy distribution. oL = FWHM with respect to track length distribution. N = number of tracks measured.
280
A. Saxena et al. / Energy loss of ‘32Xe in lead
Table 4 Values of maximum etchable track length (L,) lead targets of thickness (X).
and corresponding transmitted energy (E,)
Maximum etchable track length L,
Target thickness X (pm)
(mg/cm’
No target 1.4kO.l 4.2+0.1 7.5 + 0.2 12.0 + 0.3 17.2 + 0.4 22.2 * 0.5 24.5 + 0.6 30.1+ 0.8 38.2 & 0.8 46.7 + 0.9 60.0+1.1 63.6rt1.4 97.0 + 1.6 110.0 + 2.0
No target 1.6 +O.l 4.8 + 0.1 8.5 f 0.2 13.6+0.3 19.5 +0.4 25.2*0.6 27.8 + 0.7 34.2 + 0.9 43.4 + 0.9 53.0+1.0 68.1+ 1.2 72.2 + 1.4 110.1 f 1.7 124.8 + 2.2
144.0 + 1.2 141.6 + 1.3 138.8 + 1.6 132.1+ 1.0 119.6kl.l 111.8+1.5 101.1* 1.0 96.6 + 1 .O 86.6 + 1.5 65.4kl.S 51.0 f 2.2 28.5 k 3.5 21.2k5.7 no tracks no tracks
of target thickness, the corresponding mean ion energy and the calculated energy-loss rate of 13’Xe in lead using computer code DEDXT [8] based on stoppingpower equations of Mukherji and coworkers [9-111. Plots of (ELR) versus Em and X, are shown in fig. S(a) and fig. 5(b), respectively. Discrepancies between experimental and calculated energy-loss rate range from 2 to 15%. From this comparison we cannot make any meaningful assessment about the validity of the stopping-power equation of Mukherji and coworkers [9-111 unless the measurements are done for several other ions in different elements and complex media.
5. Conclusions Energy measurement of heavy ions require highly sophisticated instruments such as recoil proton spec-
-
201
I
13’Xe in Lead (Initialenergy
01 0
,
,
,
,
,
,
IO
20
30
40
50
60
TARGET
Energy of the transmitted ion E,
(pm)
)
THICKNESS
17.0 MeVlu)
70
60
90
100
(urn)
Fig. 4. A plot showing energy-loss data for 13’Xe in Pb. Experimental data points are fitted with a one dimensional polynomial of third order.
of 13’Xe ions after traversing through
(MeV)
(MeV/u)
2244.0 2229.5 2178.0 2104.1 1987.9 1836.1 1675.1 1597.2 1399.2 1104.8 801.2 386.7 293.0 -
17.0 16.89 16.50 15.94 15.06 13.91 12.69 12.10 10.60 8.37 6.07 2.93 2.22
trometer [17-191, magnetic spectrometer [20], Time-offlight (TOF) [21,22] and double time of flight (DTOF) [23] systems. Although these systems are capable of more precise measurements as compared to the proposed nuclear track technique, but due to its simplicity and low cost the track techniques may be considered as
Table 5 Values of experimental and theoretical energy-loss rate of ‘32Xe in lead at various mean target thickness and ion energies Mean target thickness X,
Energy-loss rate (ELR) (MeV mg-’ cm’)
Mean ion energy E,
(w/cm*
Exp. ‘)
Theoret. b,
(MeV)
20.2 22.5 24.9 27.2 28.4 29.6 30.8 32.0 32.0 32.0 30.8 28.4 26.0 21.3 17.8 14.2 9.5 7.2
23.6 24.0 24.5 25.1 25.7 26.4 27.1 27.7 28.1 28.5 28.4 27.9 26.7 24.3 19.7 15.1 11.2 8.7
2172.5 2071.8 1954.3 1822.9 1680.3 1531.2 1372.2 1212.2 1051.8 893.6 740.5 595.2 460.3 338.5 232.6 145.3 79.3 37.2
5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.0 75.0 80.0 85.0 90.0
)
a> Experimental - present work. b, Theoretical - refs. [S-11].
A. Saxena
et al. / Energy loss of '32Xein lead
::r-.-_!i 100
800
1200 E, IMeV
0
20
60
LO x,
1600
2000
1
80
100
tmglcm2)
Fig. 5. Plots of experimental energy-loss rate of i3*Xe in lead along with theoretical values [S-11] as a function of (a) mean target thickness E, and (b) mean ion energy X,,,
handy and useful. Though in this technique, the track detector needs to be calibrated for each ion, but once it is done, the detector can be used to measure energy-loss of any ion in any material. Present investigation provides a simple experimental technique for measuring energy-loss rate of any heavy ion in any media using a sensitive solid state nuclear track detector. quite
We wish to thank Dr. R. Spohr, Dr. J. Vetter and other staff at UNILAC, GSI, Darmstadt for providing irradiation facilities. One of us (K.K.D.) thanks DAAD (Bonn, West Germany) and UGC (New Delhi, India) for the award of academic exchange fellowship. We also thank the German Agency for Technical Cooperation (DGTZ) FRG for an equipment grant.
References [l] R.L. Fleischer, P.B. Price and R.M. WaIker, Nuclear Tracks in Solids: Principles and Applications (University of California Press, Berkeley, 1975) Chapter 10, p. 562. [2] B.E. Fischer and R. Spohr, Rev. Mod. Phys. 55 (1983) 907.
281
[3] B.G. Cartwright, E.K. Shirk and P.B. Price, Nucl. Instr. and Meth. 153 (1978) 457. [4] J. Aschenbach, G. Fiedler, H. S&reck-Kiillner and G. Siegert, Nucl. Instr. and Meth. 116 (1974) 389. [5] G. Fiedler, J. Aschenbach, W. Otto, T. Rautenberg, U. Steinhauser and G. Siegert, Nucl. Instr. and Meth. 147 (1977) 35. [6] A. Saxena, K.K. Dwivedi. R.K. Poddar and G. Fiedler, Pramana-J. Phys. 29 (1987) 485. [7] S. Ghosh, A. Saxena and K.K. Dwivedi, Pramana-J. Phys. 31 (1988) 197. [8] K.K. Dwivedi, A Program for Computation of Heavy Ion Ranges, Track Lengths and Energy-Loss Rate in Elemental and Complex Media, presented at 14th Inf. Conf. on SSNTD, Lahore (1988) Nucl. Tracks. and Radiat. Mass. (1988) in press. [9] S. Mukherji and B.K. Srivastava, Phys. Rev. B9 (1974) 3708. [lo] B.K. Srivastava and S. Mukherji, Phys. Rev. Al4 (1976) 718. [ll] S. Mukherji and A.K. Nayak, Nucl. Instr. and Meth. 159 (1979) 421. [12] K.K. Dwivedi and S. Mukherji, Nucl. Instr. and Meth. 161 (1979) 317. [13] R.L. FIeischer, P.B. Price and R.M. Walker, Ann. Rev. Nucl. Sci. 15 (1965) 1. [14] J. Raju, Nuclear Tracks of 350 MeV 90Zr Ion in Solid Dielectrics, M.Sc. Dissertation (unpublished), North-Eastern Hill University, Shillong (1988) p. 23. [15] P. Crombach, Diploma Thesis (unpublished), Justus-Liebig Universitat, Giessen (1983) p. 44. [16] T. Rautenberg, Diploma Thesis (unpublished), JustusLiebig Universitat, Giessen (1980) p. 19. [17] R. Bimbot, S. Della Negra, D. Gardes, H. Gamin, A. Fleury and F. Hubert, Nucl. Instr. and Meth. 153 (1978) 161. [18] R. Bimbot, D. Gardes, H. Gauvin, A. Fleury and F. Hubert, Nucl. Instr. and Meth. 174 (1980) 231. [19] R. Bimbot, S. Della Negra, D. Gardb, H. Gamin and B. Tamain, Rev. Phys. Appl 13 (1978) 393. [20] R. Bimbot, H. Gauvin, I. OrIionge, R. Anne, G. Bastin and F. Hubert, Nucl. Instr. and Meth. B17 (1986) 1. [21] R.L. Hahn, KS. Toth, R.L. Ferguson and F. Plasil, Nucl. Instr. and Meth. 180 (1981) 581. [22] H. Geissel, Y. Laichter, T. Kitahara, J. KIabunde, P. StrehI and P. Armbruster, Nucl. Instr. and Meth. 206 (1983) 609. [23] H. Geissel, Y. Laichter, W.F.W. Schneider and P. Armbruster, Nucl. Instr. and Meth. 194 (1982) 21.