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detectors [2013/10/17 10:51]
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detectors [2013/10/17 11:07]
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| Some experiments are particularly sensitive to the incoming positions and angles of the nuclei impinging on the target. Two tracking parallel plate avalanche counters (PPAC) are installed in the [[Stations#Intermediate Plane|intermediate plane station]] of the [[Introduction#Analysis Line|analysis line]]. The position and angles measured with both PPACs are transformed into the corresponding coordinates in front of the target, using the transfer matrix of the second half of the analysis line. The analysis line [[Magnets#Spectrograph Dipole|dipole magnets]] downstream of the intermediate image plane filter the particles produced in the tracking detectors, which would otherwise contaminate the data.\\ | Some experiments are particularly sensitive to the incoming positions and angles of the nuclei impinging on the target. Two tracking parallel plate avalanche counters (PPAC) are installed in the [[Stations#Intermediate Plane|intermediate plane station]] of the [[Introduction#Analysis Line|analysis line]]. The position and angles measured with both PPACs are transformed into the corresponding coordinates in front of the target, using the transfer matrix of the second half of the analysis line. The analysis line [[Magnets#Spectrograph Dipole|dipole magnets]] downstream of the intermediate image plane filter the particles produced in the tracking detectors, which would otherwise contaminate the data.\\ |
| Each PPAC has an active area of 10 cm x 10 cm and is filled with isobutane at a typical __pressure of 5 torr__. The detector consists of a cathode foil with a series of aluminum strips oriented in the non-dispersive direction, followed by an anode plate and a second cathode foil with the strips oriented in the dispersive direction (see [[Fig xxx]]). A total of 128 pads are connected to the strips of each cathode foil. The x and y positions are determined from the charge distribution on the pads. The position calibration was done using the pad pitch of 1.27 mm.\\ | Each PPAC has an active area of 10 cm x 10 cm and is filled with isobutane at a typical __pressure of 5 torr__. The detector consists of a cathode foil with a series of aluminum strips oriented in the non-dispersive direction, followed by an anode plate and a second cathode foil with the strips oriented in the dispersive direction (see [[Fig xxx]]). A total of 128 pads are connected to the strips of each cathode foil. The x and y positions are determined from the charge distribution on the pads. The position calibration was done using the pad pitch of 1.27 mm.\\ |
| The particles transmitted through the PPAC ionize the gas, producing electrons and positive ions. The drift of electrons towards the central anode plane induces an image charge on the aluminum strips. The signal generated on a given pad is sent to a preamplifier, and processed by a switch capacitor array (SCA), which acts as an analogic memory. Since the signals of this detector are generated before a valid trigger occurs, they need to be temporarily recorded until the trigger is received. The SCA samples the signals from the detector with a period of 200 ns and saves the data on a continuous mode, generating an analogic buffer. When a valid trigger is received, the sampling stops and the SCA pointer moves back in the buffer by a number of samplings pre-defined according to the time passed between the tracking signal and the valid trigger. In this way, the valid trigger is correlated with the tracking signal corresponding to the same event. The reading algorithm is lead by the FPGA chips of a XLM72 VME module. The PPACs can work at maximum rates in the range from | The particles transmitted through the PPAC ionize the gas, producing electrons and positive ions. The drift of electrons towards the central anode plane induces an image charge on the aluminum strips. The signal generated on a given pad is sent to a preamplifier, and processed by a switch capacitor array (SCA), which acts as an analogic memory. Since the signals of this detector are generated before a valid trigger occurs, they need to be temporarily recorded until the trigger is received. The SCA samples the signals from the detector with a period of 200 ns and saves the data on a continuous mode, generating an analogic buffer. When a valid trigger is received, the sampling stops and the SCA pointer moves back in the buffer by a number of samplings pre-defined according to the time passed between the tracking signal and the valid trigger. In this way, the valid trigger is correlated with the tracking signal corresponding to the same event. The reading algorithm is lead by the FPGA chips of a [[http://wwwp.cord.edu/dept/physics/mona/manuals/XLM72UM.pdf|XLM72]] VME module. The PPACs can work at maximum rates in the range from |
| 1 x 10<sup>5</sup> to 1 x 10<sup>6</sup> particles per second. The efficiency is significantly reduced for light nuclei (typically below Z=10). | 1 x 10<sup>5</sup> to 1 x 10<sup>6</sup> particles per second. The efficiency is significantly reduced for light nuclei (typically below Z=10). |
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| ===== Ionization Chamber ===== | ===== Ionization Chamber ===== |
| An ionization chamber downstream of both [[Detectors#Cathode Readout Drift Chambers (CRDC)|CRDCs]] is used to identify the Z number of the transmitted nuclei from their energy loss. The detector has an active volume of __xxx cm x xxx cm x xxx cm__ and is filled with P10 gas (90% argon, 10% methane) at a typical pressure of 300 torr, although this value can be increased up to 600 torr for light nuclei. A technical layout of the detector is shown in [[Fig. xxx]]. The detector consists of 16 stacked-parallel plate ion chambers with narrow anode-cathode gaps, placed along the detector’s central axis. The plates are constructed from 70 mg/cm<sup>2</sup> polypropylene with 0.05 µm of aluminum evaporated on each side. The entrance and exit windows of the chamber are made of 14 mg/cm<sup>2</sup> Mylar with an overlay of Kevlar filaments and epoxy.\\ | An ionization chamber downstream of both [[Detectors#Cathode Readout Drift Chambers (CRDC)|CRDCs]] is used to identify the Z number of the transmitted nuclei from their energy loss. The detector has an active volume of __xxx cm x xxx cm x xxx cm__ and is filled with P10 gas (90% argon, 10% methane) at a typical pressure of 300 torr, although this value can be increased up to 600 torr for light nuclei. A technical layout of the detector is shown in [[Fig. xxx]]. The detector consists of 16 stacked-parallel plate ion chambers with narrow anode-cathode gaps, placed along the detector’s central axis. The plates are constructed from 70 mg/cm<sup>2</sup> polypropylene with 0.05 µm of aluminum evaporated on each side. The entrance and exit windows of the chamber are made of 14 mg/cm<sup>2</sup> Mylar with an overlay of Kevlar filaments and epoxy.\\ |
| The principle of operation of the ionization chamber is illustrated in [[Fig. xxx]]. The electrons and positive ions liberated by the ionization of the gas along the particle trajectory drift towards the closest anode-cathode pair. The drifting electrons and ions absorb the energy stored in the detector capacity and produce a voltage change of the anodes across the resistor. The main advantages of the anode-cathode configuration is that the electrons and ions are collected on a very short distance (about 1.5 cm), thus reducing pile-up and position dependence of the signals. Moreover, dividing the detector into 16 sections reduces the detector capacitance and consequently its noise. The operating voltage depends on the charge of the measured nuclei (e.g. __xxx for xxx and xxx for xxx__). Each anode is attached to a small preamplifier inside the ion chamber. This significantly reduces the electronic noise, although it involves the venting of the whole chamber whenever a malfunctioning preamplifier needs to be replaced. The electronic signals from the preamplifier are sent into a 16-channel | The principle of operation of the ionization chamber is illustrated in [[Fig. xxx]]. The electrons and positive ions liberated by the ionization of the gas along the particle trajectory drift towards the closest anode-cathode pair. The drifting electrons and ions absorb the energy stored in the detector capacity and produce a voltage change of the anodes across the resistor. The main advantages of the anode-cathode configuration is that the electrons and ions are collected on a very short distance (about 1.5 cm), thus reducing pile-up and position dependence of the signals. Moreover, dividing the detector into 16 sections reduces the detector capacitance and consequently its noise. The operating voltage depends on the charge of the measured nuclei (e.g. __xxx for xxx and xxx for xxx__). Each anode is attached to a small preamplifier inside the ion chamber. This significantly reduces the electronic noise, although it involves the venting of the whole chamber whenever a malfunctioning preamplifier needs to be replaced. The electronic signals from the preamplifier are sent into a [[https://groups.nscl.msu.edu/nscl_library/manuals/caen/MOD.N568B.pdf|CAEN N568B]] 16-channel shaper/amplifier with remotely adjustable gains. The output signals feed a [[https://groups.nscl.msu.edu/nscl_library/manuals/phillips/7164H.pdf|Phillips 7164H]] ADC.\\ |
| [[https://groups.nscl.msu.edu/nscl_library/manuals/caen/MOD.N568B.pdf|CAEN N568B shaper/amplifier]] with remotely adjustable gains. The output signals feed a [[https://groups.nscl.msu.edu/nscl_library/manuals/phillips/7164H.pdf|Phillips 7164H ADC]].\\ | The energy-loss resolution of the ionization chamber can be significantly improved after correcting the position and momentum dependences. Elements up to Z=50 can be separated. |
| The energy-loss resolution of the ionization chamber can be significantly improved, after correcting the position and momentum dependences. Elements up to Z=50 can be separated. | |
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| ===== Hodoscope ===== | ===== Hodoscope ===== |
| A Cs(Na) hodoscope detector located downstream of the E1 scintillator is used to measure the total kinetic energy of implanted nuclei, allowing the identification of different charge states. An additional use recently tested is the measurement of isomer -rays emitted from implanted nuclei. | A Cs(Na) hodoscope detector located downstream of the [[Detectors#Plastic scintillators|E1 scintillator]] is used to measure the total kinetic energy of implanted nuclei, allowing the identification of different charge states. An additional use recently tested is the measurement of isomer gamma-rays emitted from implanted nuclei.\\ |
| The hodoscope is composed 32 sodium-doped cession iodide, CsI(Na), scintillating 5.1 cm-thick crystals manufactured by ScintiTech. Each crystal is 5.1 cm-thick, has an active area of 7.6 cm × 7.6 cm, and is attached to a photomultiplier (Hamamatsu R1307). The photo-cathodes are made of a bi-alkali material with a transmission peak at 420 nm. The 32 crystals are arranged in eight rows of 4 crystals each so as to cover approximately the same solid angle than the CRDCs. The frontal and lateral sides of each crystal are covered with two 150-um thick layers of a white Teflon reflective material, to provide light shielding between the crystals. The photocathodes are connected to a CAEN N568B shaping amplifier, followed by an Phillips 7164H 12-bit ADC. The signals from the crystals are gain-matched to a middle position in the ADC spectra by varying the biases of each photocathode. | The hodoscope is composed 32 sodium-doped cession iodide CsI(Na) scintillating crystals manufactured by [[http://www.scintitech.com/|ScintiTech]]. Each crystal is 5.1 cm-thick, has an active area of 7.6 cm x 7.6 cm, and is attached to a photomultiplier ([[https://www.hamamatsu.com/jp/en/R1307.html|Hamamatsu R1307]]). The photo-cathodes are made of a bi-alkali material with a transmission peak at 420 nm. The 32 crystals are arranged in eight rows of 4 crystals each so as to cover approximately the same solid angle than the CRDCs. The frontal and lateral sides of each crystal are covered with two 150-µm thick layers of a white Teflon reflective material to provide light shielding between the crystals. The photocathodes are connected to a [[https://groups.nscl.msu.edu/nscl_library/manuals/caen/MOD.N568B.pdf|CAEN N568B]] 16-channel shaper/amplifier, followed by a [[https://groups.nscl.msu.edu/nscl_library/manuals/phillips/7164H.pdf|Phillips 7164H]] 12-bit ADC. The signals from the crystals are gain-matched to a middle position in the ADC spectra by varying the biases of each photocathode. |
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