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In a calorimeter with silicon readout, the use of a combination of low- Z (Fe) and high- Z (Pb) materials as absorbers allows the transformation of the electron energy distribution of the incident showers in two media with different critical energies via the filtering effect. As a result, the visible electromagnetic energy and consequently the value of the e/mip ratio can be substantially reduced as a function of the thickness of the high- Z (Pb) material present in the absorber. Measurements of this effect for a set of Si/Fe+Pb calorimeter configurations are presented and discussed. The filtering effect makes possible the achievement of the compensation condition.

In a calorimeter with silicon readout, operated at the CERN-Proton Synchrotron, the use of a combination of low-Z (Fe) and high-Z (Pb) materials as absorbers allows the transformation of the electron energy distribution of the incident showers in two media with different critical energies via the filtering effect. As a result, a ratio varying from e/π>1 to e/π

In silicon sampling calorimeters, a local hardening effect occurs when inserting a small thickness of low-Z material next to the thin active layer. This effects, which modifies appreciably the electromagnetic response, allows the control of the relative responses to hadronic and electromagnetic showers. A thorough study of lateral shower profiles has been undertaken to improve the precision of the measurement of the absolute electromagnetic response. The main features of the local hardening effect as a function of the thickness of low-Z material are explained by a 1/E distribution of ionizing particles inside the shower, while those of the lateral profile are explained by an exponential radial distribution.

In an Si/U hadron calorimeter, using a combination of low-Z and high-Z materials for the absorber allows the reduction of the calorimeter response to the electromagnetic component of the incoming hadronic showers (the local hardening effect). As a result, a ratio varying from e/ pi >1 to e/ pi >

A detailed study of neutron irradiated n-type silicon detectors was carried out including leakage current measurements after first and second irradiation, annealing procedures optimization, deep level transient spectroscopy (DLTS), and thermally stimulated currents (TSC) analyses of the produced defects in the bulk of the detectors.

Experimental evidence has been found for a filtering effect on the soft electron component in electromagnetic showers when combinations of low-Z and high-Z materials are used as absorbers. The filtering effect can be fully exploited to reduce the electromagnetic calorimeter response, making it possible to achieve the compensation condition in a Si/Fe+Pb calorimeter with an effective interaction length almost equal to that of Fe. The action of Fe on Pb, by modifying the critical energy during the electromagnetic shower development, leads to a yield of soft electrons (and very few photons) that are stopped in subsequent absorber layers and/or absorbed by the G10 plates. Recent measurements performed with an enlarged Si/Fe+Pb calorimeter support the idea; the authors have shown that an electromagnetic energy smaller than the hadronic energy is possible once particular FePb configurations are used. >

The condition for obtaining a calorimetric response linear with energy for hadronic showers and an energy resolution that improves as the incident energy increases is the equalization of the electromagnetic (e) and the hadronic (pi) signal responses. This equalization is obtained by exploiting a local hardening effect realized through the insertion of low-Z thin plates between the high-Z absorbers and the active material in a hadronic calorimeter with silicon readout. This effect, which allows the reduction of the calorimeter response to the electromagnetic component of the incoming hadronic showers, has been investigated for different low-Z materials. The relevance of some aspects of this study to the radiation hardness of the calorimeters is also addressed.

The compensation condition (e/ π = 1) is discussed. It mainly determines the performances of the silicon calorimeters to be used at the next generation of hadronic colliders (LHC, UNK, SSC).

In a hadronic calorimeter with silicon readout, a combination of thin plates oflow- Z andhigh- Z materials used as absorbers enables the reduction of the calorimeter response to the electromagnetic component of the incoming hadronic showers (the “local hardening effect”). As a result, a ratio varying from e/π> 1 toe/π>is obtained as a function of thelow- Z material thickness, demonstrating the possibility of achieving the compensation condition(e/π= 1)by exploiting the local hardening effect.

Equalization between the electromagnetic and the hadronic signals is the condition for obtaining the linear response of a calorimeter to hadronic showers and an energy resolution that improves as the incident energy increases. In a calorimeter with silicon readout, the use of a combination of low- Z and high- Z materials as absorbers allows the transformation of the electron energy distribution of the incident showers in two media with different critical energies. As a result, the response of the calorimeter to incoming showers is modified to achieve the compensation condition ( e π =1) .

The SICAPO Collaboration project to build a perfectly compensating hadron calorimeter using silicon as the active medium, is described. The insertion of low-Z material (G10 plates) in front or at the rear of the silicon detectors allows fine tuning of the calorimeter response to electromagnetic showers. This is a new approach to obtaining compensation. The tuning can be exploited to obtain e/π = 1 (compensation condition). The expected performance ranks this calorimeter among the best candidates to face the severe constraints requested by the next generation of colliders.

The condition for obtaining the linear response of a calorimeter to hadronic showers and an energy resolution improving as the incident energy increases is the equalization between the electromagnetic and the hadronic signals. This equalization is obtained within a new approach exploiting a local hardening effect that is realized by inserting low-Z absorbers next to the silicon readout detectors. In this way, the calorimeter response to the electromagnetic component of the hadronic shower is reduced. A systematic investigation of the visible energy response for electromagnetic showers in Si/U and Si/W calorimeters has been carried out for incoming electron energies of 2, 4, and 6 GeV. The insertion of low-Z material (G10 plates) in front or at the rear of the silicon detectors allows a fine tuning of the calorimeter response.

The effect of damage produced in silicon detectors by neutron irradiation at room temperature is examined by using the experimental technique of deep-level transient spectroscopy. The production of three defects, the A centre, the E centre, and the divacancy, is reported. The divacancy is especially important in neutron damage in silicon. There is evidence of some defects generated during annealing. It has been found that the properties of the point defects outside the clusters are the main results obtained with DLTS methods.

In a calorimeter with silicon readout, the use of a combination of low-Z (Fe) and high-Z (Pb) materials as absorbers enables the transformation of the electron energy distribution of the incident showers in two media with different critical energies via the filtering effect. As a result, the electromagnetic energy value can be substantially reduced as a function of the thickness of high-Z (Pb) material present in the absorber. Measurements of this effect for a set of Si/{Fe + Pb} calorimeter configurations are presented and discussed. A direct consequence of the filtering effect is to enable the achievement of the compensation condition.