Hodoscope performance for the cosmic ray set-up of the MDT-BIS chamber Beatrice

Transcription

1 ATLAS Internal Note 7 December 2002 Hodoscope performance for the cosmic ray set-up of the MDT-BIS chamber Beatrice R.M. Avramidou 1, M. Dris 1, E.N. Gazis 1, O. Kortner 2, S. Palestini 3 1 NTU, Athens, Greece 2 MPI, Munich, Germany 3 CERN, Geneva, Switzerland ABSTRACT A hodoscope consisting of a set of scintillation counters has been instrumented for triggering on cosmic rays used for the study of the performance of the ATLAS MDT-BIS chamber Beatrice at the X5/GIF (Gamma Irradiation Facility) at CERN. In this note the set-up is described and results from calculations and measurements for the hodoscope performance are provided. 1

2 1. Introduction The operation of the ATLAS muon detectors, under the conditions of the Large Hadron Collider (LHC), which has been designed for a high luminosity of cm -2 s -1 and beam crossings for every 25 ns, will be characterized by large sustained hit rates reaching 100 Hz/cm 2 [1] in the forward regions of the muon spectrometer. In their majority these hits result from secondary reactions of low energy neutrons emerging from the calorimeter and the beam line shielding, which produce photons. Taking into account a safety factor 5 the maximum count rate at which the chambers have to be tested is 500 Hz/cm 2. In the particular case of the MDT-BIS Beatrice, which has a tube diameter of 3 cm and a length of 170 cm the expected rate per tube is 255 khz. The Gamma Irradiation Facility (GIF) [2],[3] at CERN is a test area where muon detectors are exposed to a high energy muon beam in the presence of an adjustable high background flux of photons with the aim of simulation of the operating environment at the LHC. A system of remotely controlled lead filters is used to vary the rate within a range of four orders of magnitude for the chamber performance study as a function of the rate. Outside the beam running period measurements are taken using cosmic ray muons under the photon background. For this purpose a system of scintillation counters has been used in order to provide the trigger for cosmic rays and the coordinates of each incident muon. In this note the set-up and the performance of this hodoscope will be presented. More precisely, the test set-up and the operation principle are described, Monte Carlo simulations and some theoretical calculations are given, and the hodoscope performance is presented. Results from measurements during the hodoscope operation at the GIF are also shown. 2. Purpose and Description of the Hodoscope The hodoscope is a system of scintillators for the muon cosmic ray trigger used for the study of the performance of the ATLAS MDT-BIS chamber Beatrice at the X5/GIF. The hodoscope provides the transverse and longitudinal coordinates of the incident muon for the pattern recognition, the track reconstruction, and the correction for the signal propagation along the wire and also the correction for the time of flight. The hodoscope consists of two planes each one of which has two layers of overlapped plastic scintillators, as it is shown in figure 1. The scintillation counters have a length of 1.15 m, width of 0.19 m and height of 0.02 m, while their overlapping area is ~ m 2. The two planes are in a distance of 4 m at the final set-up at the X5/GIF area, while at the initial test set-up this distance was 0.82 m (figure 2). Each scintillator is connected to a light guide and a photomultiplier. From each photomultiplier both an analog and a digital signal outputs are provided. The analog signal is 2

3 fed through an internal preamplifier to an internal constant fraction discriminator 1 [4]. The digital signal (at the output of the discriminator) is preferred from point of view of the external system simplification and the smaller sensitivity to signal amplitude, distortion, and noise during its transmission through long cables. The analog signal can be used for test and debugging purposes, but also in case of internal electronic problems or possible set-up modifications. Figure 1: System for the cosmic ray trigger. It consists of two planes of plastic scintillation counters. Figure 2: Initial set-up of the hodoscope system for test and debugging purposes. 3. Hodoscope system operation principle The logic diagram of the hodoscope system [5] is shown in the following figure (figure 3). The digital signal from each photomultiplier, in groups of six scintillators-photomultipliers, comes in a NIM in-nim out unit, where it is split in two branches. The first branch for the coordinate determination ends in the stop input of a TDC unit [6] after the appropriate timing delay. The second branch is driven in the input of a Logic FAN in - FAN out unit [7], which operates under the OR logic. In the case that there is a signal coming from at least one of the six scintillators of each layer the FAN in - FAN out unit output goes in a meantimer unit [8]. 1 The constant fraction triggering technique is the most efficient method because the digital signal is generated at a constant fraction of the peak height to produce an essentially walk-free timing signal. So the taken signal is independent of the initial pulse height and the best timing resolution can be achieved. 3

4 Figure 3: Logic diagram of the hodoscope system. Each meantimer unit accepts the signals from the two layers of the overlapped scintillators at its inputs. At its output it provides a pulse of duration equal to the total overlap time of the two input signals and in a time distance from the first pulse equal to the half of their time difference plus the unit delay. So by the use of the meantimer, the resulting signal corresponds to a track in the middle of the scintillation counters. Its operation principle is similar to the one of the coincidence unit with the advantage that it provides additional timing information. This happens because the provided signal is time related to the first pulse and the time difference of the two incoming pulses, whereas in the case of the coincidence unit the resulting pulse is related only to the second pulse. The meantimer time resolution is 1 ns. The meantimer output terminates via a discriminator unit [9] in a coincidence unit [10] and after this in a delay unit (for reduction of the start-stop window so that the noise to be decreased) and finally in a FAN in - FAN out unit, which provides the start to the TDC unit. The time resolution of the TDC is 50 ps in the scale of 100 ns. The FAN in - FAN out unit provides also an input to a feedback circuit with a flip-flop, which gives an inhibit pulse when it receives a trigger and prevents accepting other triggers (coincidence veto). This happens up to the moment at which the personal computer which controls the system stores the data and sends a flopping pulse, so that new data to be received. The hodoscope system, as it has been already mentioned, provides the trigger signal for the muon measurements and also the transverse and longitudinal coordinate of the muon track. The transverse coordinate is provided by the pair of scintillators in each plane, which 4

5 gave the signal and which overlap by the half of their width. In this way the accuracy at the determination of the transverse coordinate is (9.5±0.5) cm and the standard deviation equals to ( 10 / 12 ± 0.5 / ± 0. 1 ) cm [11]. The longitudinal coordination comes out from the knowledge of the point along the scintillator, where the muon interacted and is taken from the time measured by the TDC according to the following calculations. If we suppose that the muon traverses the plane of the overlapping scintillators and interacts at a distance x from the one scintillator s edge and at a distance l-x from the other s edge along their length the TDC time measurements will be correspondingly t t x = t + + (1) c 1 0 delay t trigger l - x = (2) c 2 t delay t trigger where t0: the absolute time that the muon traversed the scintillators, x: distance between the interaction point and the edge of the scintillator, l: the length of the scintillator, c = ceff /n: propagation velocity in the scintillator and n=1.5 the plastic scintillator refraction index, delay: delays caused in the photomultiplier, the internal electronics, the cables and the unit delays, ttrigger: the trigger signal time (TDC start). Subtracting the equations (1) and (2) we take t 1 t 2 2x l = c, (3) so the longitudinal coordinate is given by the following expression while adding them we take l + (t t 2 )c x =, (4) 2 1 l t 1 + t 2 = 2t delay 2t trigger (5) c from which the t 0 value can be calculated. 5

6 4. Cosmic ray muons The muon chambers are usually tested for their performance with cosmic rays, over their whole area at low rate and at test beams at high rates but over a small area (typically cm 2 ). Most of the cosmic ray muons are produced high in the atmosphere (typically 15 km) by the decay of charged mesons and they reach the ground with a mean energy of approximately 4 GeV [12]. Their energy and angular distribution reflect a convolution of production spectrum, energy loss in the atmosphere, and decay. The integral intensity of vertical muons above 1 GeV/c at sea level is approximately 70 m -2 s -1 sr -1, which can be written in the form I 1 cm -2 min -1 for horizontal detectors. The overall angular distribution of muons at the ground is proportional to cos 2 θ, which is characteristic of muons with energy ~3 GeV. Some typical sea-level values for cosmic muon flux [13] are the following: Flux per unit solid angle per unit horizontal area about vertical direction I υ =80 m -2 s -1 sr -1 and total flux crossing unit horizontal area from above J 1 =130 m -2 s -1. So I j( θ = 0 φ ) (θ = zenith angle, φ = azimuthal angle) (6) υ, and where J 1 = j( θ, φ ) cosθ dω, (7) θ π / 2 j = 80 cos 2 θ (m -2 s -1 sr -1 ) (8) and d Ω = sinθ dθ dφ (9) Substituting equation (8) into (7) we obtain 3 J 1 = 80 cos θ dω (10) θ π / 2 Taking into account that the hodoscope consists of two planes of 6 scintillators each, with dimensions ~1.05 m (overlapping length) and 0.19 m (width) at a distance of ~4 m the expected cosmic muon rate is calculated as follows: A = j(cos θ i Ωi k (cos k = 1 i= 1 k= 1 i= 1 3 ) A = j θ i Ω i ) k R = J, (11) where, A is the area of each scintillator (1.05 m 0.19 m = 0.20 m 2 ), i refers to the lower layer and k to the upper one, 4 4 cosθ i = = (12) r 2 i 4 + x 2 i 6

7 A 0.20 and Ω i = 2 = 2 (13) r r i i where xi is the distance from center to center of the scintillators (figure 4). Figure 4: Hodoscope system. Substituting the appropriate values in expression (11), it comes out that R=6.9 Hz. In the case that the distance between the layers is 0.82 m the cosmic muon rate is R=108 Hz. Their difference has its origin in the different acceptance of incident muon track angles. The measured rate is expected to be slightly lower due to inefficiencies of the system. These inefficiencies are caused by the small gaps between the scintillators, which are of the order of a few mm (3-5 mm). 5. Measurements and results For the hodoscope performance various extensive studies have taken place. The results of the most significant of them are provided. As a first step the TDC units have been calibrated in order to determine the conversion function (t = a channels + b) of TDC channels to time (ns). For this purpose a pulse generator was used, the signal of which was divided in two parts. The first comes in the TDC start and the other after a known delay (measured with an oscilloscope) comes in the TDC stop. This procedure is repeated in regular time intervals for the control of the result stability. The following measurements were taken with the test set-up of figure 2, where the scintillators planes distance is 0.8 m. 7

8 In order to simulate the final set-up, where the distance between the planes of the scintillators is 4 m one of the discriminators is connected with the coincidence unit input via a 16 ns cable and the other discriminator via a 2 ns cable, which results in a time difference of 14 ns. This number equals approximately the time of flight of muons for the distance of ~4 m. In this way it is possible to define, which scintillator plane gives second the signal at the coincidence unit and, consequently, which plane gives the trigger signal and the start at the TDC unit. Both possibilities have been tested for this initial test set-up. This choice of the origin of the trigger signal has an influence to the TDC spectra, as it is obvious in the following observations. In figure 5 typical TDC spectra are shown, which come out from two different scintillators, which belong to the two different planes. All the scintillators have similar spectra except the last ones (close to the system edges), which are overlapped by half of their width and they appear to have fewer events (figures 6-7). Figure 5: Typical time spectra from two scintillators. The scintillator number 25 belongs to the upper plane, while the scintillator number 9 belongs to the lower one. The trigger signal comes from the upper plane. Figure 6: Hit distribution in the upper hodoscope (Monte Carlo simulation) [14]. Figure 7: Hit distribution in the lower hodoscope (Monte Carlo simulation) [14]. 8

9 Their width provides the time needed for a photon to traverse the scintillator length. This width is larger for the scintillator number 9 that belongs to the lower plane compared to the scintillator number 25, which belongs to the upper one. The explanation is the following. The trigger signal comes from the upper plane 2, so in the width of the lower plane scintillator there is also the contribution of the variation of the muon time of flight between the two planes which ranges from 2.7 ns (shortest distance) to 4.4 ns (largest distance) and is connected to this particular geometry. For this reason for this particular set-up and for the most of the measurements the trigger signal comes from the lower plane, in order that the time of flight to be included at the TDC start measurement. At the final set-up, the muon time of flight time has a smaller variation from 13.7 ns to 14.1 ns due to different acceptance in track angles 32. In this case the trigger signal comes from the lower plane, which is much closer to the chamber and the corrections needed for the time of flight are smaller. Another effect provoked from the choice of the plane, which provides the trigger signal, is the existence of a time correlation between two overlapping scintillators. Plotting the time t 1 (equation 1) as a function of the time t 2 (equation 2) for two overlapping scintillators a linear relation is expected, as these times are correlated each to the other. In figure 8 the time correlation of two pairs of overlapping scintillators, which belong to different planes, is shown. Figure 8: Time correlation of two pairs of overlapped scintillators. The pair (a) belongs to the upper plane, whereas the pair 3-6 (b) is just below at the lower plane. The trigger signal comes from the upper plane. The correlation is observed (figure 8a) only for the upper plane, which gives the trigger signal, while at the lower plane the measurements appear to be uncorrelated. The explanation 2 Since the upper counter is part of the trigger some uncertainties in the timing measurement are canceled in the difference triggerdifference. 3 The maximum angle of the accepted muon tracks between the extreme points of the hodoscope is 15, as to the vertical direction, in the case that the distance of the scintillator planes is 4.10 m and 52 when this distance is 0.82 m. 9

10 follows. The TDC start signal is provided from the second pulse, in this case from the upper plane and it is independent from the time that the first pulse arrives (figure 9). Consequently the times measured by the TDC (start-stop) for this plane are linearly correlated one to the other. The TDC times measured for the other plane appear to be uncorrelated due to the variation of the muon time flight between the two planes (figure 10). Modifying the existing set-up and using a different trigger signal for each plane separately, this effect disappears and the TDC measured times are correlated for all the pairs of scintillators, independently from the plane where they belong. The dispersion around the correlation line is due to the scintillator multiple hits. Taking into account only four hits (one per plane) these points are not present. Figure 9: The TDC start signal comes out from the second pulse, independently of the moment that the first one arrives. Figure 10: The muon time of flight between the two planes ranges from 2.7 ns to 4.4 ns. Studying more deeply the times measured by the TDC units, useful information and conclusions are obtained. The time differences of the overlapping scintillators are distributions centered at zero and independent of the start time as this is effaced. The deviation from zero corresponds to the correction, which has to be added (offset) and it is due to the scintillators, their electronics, and different cable delays. The distribution width is an indication, the double of the time that is needed for a photon to traverse the scintillator length (9±1 ns). The sums are narrow distributions for the plane, which provides the trigger signal and wider for the other one for the reason, that has already been explained. In figure 11 the time differences for each pair of the overlapping scintillators are shown. The event number increases from the sides to the middle, where this number remains constant. This fact is expected due to the angular distribution of muons at the ground. The effect of muon impinging angles is shown in figure 12. The differences of the photon time of flight for the pair of the scintillators 13 and 16 (upper plane) are presented in case that the muon interacts with the scintillators of the lower plane, which are at a distance cm compared to this pair. It is obvious that the probability is higher for small impinging angles and becomes smaller with the increase of the distances and consequently of the corresponding angles. This is expected, as the overall angular distribution of muons at the ground is proportional to the quantity cos 2 θ (figure 13) [12]. The second of the double line 10

11 indicates the same calculations for the pair of the scintillators 1 and 2, which is just below the pair 13 and 16. In the same plot it is obvious that the time needed for the photon propagation along the scintillator is (9±1) ns. Longitudinal coordinate=f(transverse coordinate of scintillators) t t 1 2 Figure 11: Time differences for all the pairs of the overlapping scintillators of the lower plane. t t 1 2 Figure 12: The differences of the photon time of flight for the pair of the scintillators 13 and 16 (upper plane), in case that the muon interacts with the scintillators of the lower plane, which are at a distance cm compared to this pair. The light propagation speed in a plastic scintillator is c =c/n=c/1.5=20 cm/ns. So the expected total time of flight is 5.2 ns. Due to the multiple reflections of light in the plastic scintillator caused by its defects and the discriminator effects 41 this time was proven to be larger, of the order of (9±1) ns and the propagation speed (11.5±1.3) cm/ns. 4 This type of discriminator, in order to be functional, needs a significant amount of photons for which the contribution of the direct photon is not enough, but also the reflected ones are needed. 11

12 Figure 13: Distribution of the muon impinging angles (Monte Carlo Simulation) [14]. In order to study the system timing resolution a small scintillator with dimensions of cm 3, has been used and it was put on the scintillator number 2. The small scintillator, which is connected with a discriminator and the appropriate delay cables, provides the trigger signal at the coincidence of the three scintillators, the small one and the pair 1,2. The resolution, which comes out (figure 14) is the combination of the two scintillators (small and scintillation number 2), but the contribution of the small one is very low due to its dimensions. The total system resolution is estimated to be ns and the spatial resolution is 20 cm 5. In figure 14 the two small peaks on the right side of the time spectrum, which count approximately 15 events (~1% of the total number of events), are probably due to accidental hits. In order to verify this observation, a series of measurements have been performed for the determination of the accidental hits. This procedure was based on the idea of delaying one of the two planes, so as the second one to be outside the coincidence time window, which means to be completely off the coincidence curve [4]. The various results proved that the accidental coincidences were less than 1% of the real ones. 5 This resolution is adequate for our purposes. The resolution needed for the chamber is 80 / 8 30 µm. The tube radius is 15 mm and the total drift time is ~700 ns, so the drift velocity is ~20 µm/ns. In order to reach the resolution of 30 µm, a timing resolution of 1.5 ns is required, which for the given propagation speed in the scintillator corresponds to a spatial resolution. 12

13 Figure 14: System resolution of the small and large scintillators. 6. Hodoscope measurements at the X5/GIF area The area X5/GIF (Gamma Irradiation Facility) is the test region where the MDT-BIS chamber Beatrice was exposed to cosmic rays in the presence of an adjustable high background flux of photons (figure 15), simulating the background of the Large Hadron Collider environment. The radioactive source is 137 Cs with a half-life of 30 years and radioactivity 740 GBq (5/3/1997), which emits 662 kev photons (figure 16). The photon emission rate control is achieved by the use of lead filters, which can vary the rate within a range of four orders of magnitude providing 17 possible attenuation factors (1, 2, 5, 10, 20, 40, 50, 100, 200, 250, 500, 1000, 2000, 2500, 4000, 5000, 10000). 13

14 Figure 15: Layout of the X5/GIF area. Figure 16: Decay diagram for the radioactive source 137 Cs. The MDT-BIS chamber Beatrice was placed in this region (figure 17) for the study of its performance with cosmic muons, under the photon background, and also for ageing studies. The MDT-BIS chamber consists of two multilayers composed of four layers each. Each layer consists of thirty cylindrical aluminum drift tubes 1.7 m long (including the endplugs) with a diameter of 0.3 m. The multilayers are separated by seven 6 mm thick aluminum strips. The chamber has an inclination of ~45 in order to accept both the cosmic ray muons and the source photons. The chamber ( m 2 ) is almost entirely covered by the hodoscope (~ m 2 ), whose planes are put in a distance of ~4 m each from other and in a transverse position according to the chamber. This position is chosen because it provides the coordinate for the correction of the signal propagation along the wire with higher accuracy. The space between the planes is such that the upper plane to be out of the gamma source range and to accept only the scattered photons. It is shielded from the scattered photons, which have a wide distribution in angle and energy, by a lead layer of 1 cm width and by an additional piece of lead of 2 cm, which covers the ¾ of the scintillators overlap area. The lower plane lies in the irradiation cone and is exposed to both direct and scattered photons. It is covered by lead bricks of 5 cm thickness (appendix 1) [5]. At this area measurements were taken on the hodoscope rate using different filters that correspond to different source attenuation factors (figure 18). In the first plot the hodoscope rate after the coincidence is shown, while in second and third plots the rates for the upper and lower plane are shown. In the first plot also the theoretical calculation of accidentals is shown Accidentals = σ R t R b, where R t is the rate of the upper plane, R b [4] is the rate of the lower plane and σ is the system resolution, which is equal to the sum of the discriminator pulse duration of each plane, during which the trigger coincidence is possible to happen. 14

15 Figure 17: Hodoscope and chamber set-up at the X5/GIF area. Studying the previous figure several observations come out. The coincidence rate up to the use of filter 5 is approximately the one expected from the calculations (paragraph 4). There is a small difference of Hz (5%), which is caused by the existence of the small gaps in the system along the scintillator touching surfaces. For filters 1,2 and 5 there is a significant contribution from the accidental coincidences, which increases the rate. Having a look at the coincidence rates of the independent hodoscope planes (bottom and top multilayer), there is an obvious difference between their rates. The explanation is that the bottom plane is exposed to both direct and scattered photon radiation, while the upper one only to the scattered one. The exact ratio of the direct and indirect radiation depends on the distance from the source, the absorption filter, and the exact geometry of the system. The direct radiation predominates in distances close to the source, whereas the indirect radiation increases closer to the walls. Calculating the ratio of the rate of the bottom plane versus the rate of the top one, which is equal to the ratio of the total versus the indirect radiation, it is obvious that the ratio 15

16 decreases with the filter absorption coefficient increment. This means that the scattered photon radiation increases with the use of thicker lead filters, which is expectable. Accidentals Planes s Coincidence Source attenuation factors Figure 18: Hodoscope rate measurements at the X5/GIF area. The indirect radiation also depends on the full geometry of the system, the source, filters, floor and walls, and surrounding material. The bottom hodoscope plane is shielded by 5 cm thick lead bricks on its upper surface, but it is not shielded at its lower surface, which means that it accepts an amount of scattered photons from the floor. The top plane is shielded 16

17 at its lower surface by lead sheets of 1-3 cm thickness, which is quite sufficient for soft scattered photons emerging from the floor and the walls. Its upper surface is not shielded, as the area in not covered (building roof many meters high). 6. Conclusions The hodoscope for MDT-BIS chamber Beatrice muon cosmic ray measurements is designed to provide the trigger and the incident muon coordinates for the pattern recognition and the appropriate timing corrections. The total system resolution is estimated to be 1,5-2 ns and the spatial resolution is 20 cm. The measured cosmic muon rate is the expected, according to the calculations. A small difference of the order of 5% is due to the inefficiency of the system. With the gamma radioactive source on, the coincidence rate is still the calculated one up to the use of the absorption filter 5. For filters 1,2 and 5 there is a significant contribution from the accidental coincidences. The coincidence rates of the independent hodoscope planes are different due to the fact that the bottom plane is exposed to both direct and scattered photon radiation, while the upper one only to the scattered photons. Acknowledgements We would like to thank A. Kojine, V. Goriatchev for providing the counters and helping in the first commissioning of the hodoscope, E. Christidi and S. Zimmermann for their contribution on the hodoscope set-up and D. Fassouliotis for his modifications on the set-up. Special thanks to T. Alexopoulos and Y. Tsipolitis for their helpful discussions and to G. Stavropoulos for his help and his marvelous ideas. We have also to thank cordially Prof. D. Schaile and Prof. A. Staude for their financial support and MPI people for their hospitality during the work on the Monte Carlo simulation project. We are also very grateful to J. Berbiers for his endless time of discussions and his technical assistance in providing things and repairing problematic components and to W. Andreazza for his technical support. 17

18 Appendix 1 The attenuation of a photon beam through matter is exponential with respect to the thickness and it is provided by the following equation I µ ρ x = I 0 e, (A.1) where I is the intensity after a distance x in the material, I 0 is the incident beam intensity, µ is the attenuation coefficient, which is characteristic of the absorbing material and is directly related to the total interaction cross section, and ρ is the density of the material [5]. For the shielding of the lower hodoscope plane, which is exposed to 662 kev photons, lead bricks of 5 cm width have been used, that provide a shielding protection, as is seen in the following calculations. Taking into account that the lead density is ρ Pb =11.35 g/cm 3 and the attenuation coefficient in lead for the energy of ~662 kev is µ=0.11 cm 2 /gr [15], the photon flux is calculated as a function of the depth in the lead absorber for different source absorption filters (Figure A.1). The incident flux for direct radiation (E γ =662 kev), which corresponds to the photon flux at 300 cm distance from the source, along the axis of the irradiation field varies from I 0 = cm -2 s -1 for attenuation factor 1 (no filters) up to I 0 = cm -2 s -1 for attenuation factor 100 [2]. The figure A.2 shows the photon flux I 0 /I as a function of the lead width. Figure A.1: Photon flux as a function of lead width for different attenuation filters. Figure A.2: Photon flux I 0 /I as a function of the lead width. 18

19 References [1] ATLAS, Muon Spectrometer, Technical Design Report, CERN/LHCC/97-22, ATLAS TDR 10, 31 May [2] A facility for the test of large area muon chambers at high rates, S. Agosteo et al, CERN- EP , CERN-SL EA, Geneva, CERN, 16 Feb 2000, Nucl. Instrum. Methods Phys. Res., A: 452 (2000) no.1-2, pp [3] [4] Techniques for Nuclear and Particle Physics Experiments, W. Leo, Springer-Verlag, [5] Testing of MDT chambers for ATLAS in X5/GIF area at CERN, E. Christidi, Diploma Thesis, CERN, December [6] Le Croy 2228A, CAMAC TDC, Manual. [7] Le Croy Model 429A, NIM Logic FAN in-fan out, Manual. [8] Le Croy 62432NS, NIM Octal Meantimer, Manual. [9] Le Croy Model 623, NIM Octal Discriminator, Manual. [10] Le Croy Model 465, NIM Triple 4-Fold Coincidence Unit, Manual. [11] Statistics, R. Barlow, Ed. J. Wiley, August [12] The European Physical Journal C, Review of particles Physics, Springer, Volume 3, Number 1-4, [13] Particle Physics Booklet, Particle Data Group, Springer, July [14] MTGEANT-4, The Munich test-stand simulation programme, Manual for version 1.0, O. Kortner, September [15] Tables of X-ray mass attenuation coefficients and mass energy-absorption coefficients 1 kev to 20 MeV for elements Z=1 to 92 and 48 additional substances of dosimetric interest, J. H. Hubbell, S. Mseltzer, NISTIR-5632, May 1995, ( 19