P. Sousa

Optimization of electric field distribution by free carrier injection in silicon detectors operated at low temperatures

We present a study of the modeling of the electric field distribution, which is controlled by injection and trapping of nonequilibrium carriers, in Si detectors irradiated by high neutron fluences. An analytical calculation of the electric field distribution in detectors irradiated by neutrons up to fluences of 1 /spl middot/ 10/sup 14/ to 5 /spl middot/ 10/sup 15/ cm/sup -2/ shows the possibility of reducing the full depletion voltage at low temperatures via hole injection. For this calculation, we use the detector operating parameters and equivalent neutron fluences expected for Large Hadron Collider experiments. The results of the calculation are in good qualitative agreement with published experimental data, lending strong support for the model and for an earlier proposal of electric field manipulation by free carrier injection.

Gamma spectroscopy and optoelectronic imaging with hybrid photon detector

Abstract Hybrid Photon Detectors (HPD) detect light via photocathodes and accelerate the emitted photoelectrons by an electric field towards silicon PIN-anodes, where they are absorbed and generate electronic signals. We have developed two specific types of HPDs: (1) Hybrid photomultiplier tubes for photon counting and gamma spectroscopy; (2) Imaging silicon pixel array tubes for optoelectronic cameras. This paper will illustrate the main achievements, which we obtained in the last years, and will describe and discuss our present main RD 29.40; 29.30; 87.59

Estimation of the collective dose in the Portuguese population due to medical procedures in 2010

In a wide range of medical fields, technological advancements have led to an increase in the average collective dose in national populations worldwide. Periodic estimations of the average collective population dose due to medical exposure is, therefore of utmost importance, and is now mandatory in countries within the European Union (article 12 of EURATOM directive 97/43). Presented in this work is a report on the estimation of the collective dose in the Portuguese population due to nuclear medicine diagnostic procedures and the Top 20 diagnostic radiology examinations, which represent the 20 exams that contribute the most to the total collective dose in diagnostic radiology and interventional procedures in Europe. This work involved the collaboration of a multidisciplinary taskforce comprising representatives of all major Portuguese stakeholders (universities, research institutions, public and private healthcare providers, administrative services of the National Healthcare System, scientific and professional associations and private service providers). This allowed us to gather a comprehensive amount of data necessary for a robust estimation of the collective effective dose to the Portuguese population. The methodology used for data collection and dose estimation was based on European Commission recommendations, as this work was performed in the framework of the European wide Dose Datamed II project. This is the first study estimating the collective dose for the population in Portugal, considering such a wide national coverage and range of procedures and consisting of important baseline reference data. The taskforce intends to continue developing periodic collective dose estimations in the future. The estimated annual average effective dose for the Portuguese population was of 0.080±0.017 mSv caput(-1) for nuclear medicine exams and of 0.96±0.68 mSv caput(-1) for the Top 20 diagnostic radiology exams.

A new ultra radiation hard cryogenic silicon tracker for heavy ion beams

AbstractWe have designed and built a new hodoscope for heavy ion beams consisting of two tracking stations equippedwith silicon microstrip detectors operated at 130K. Preliminary results from tests performed in the high intensityCERN-SPSPbionbeamshowthatwewereabletodetectandidentifyeachincomingionuptoabeamintensityofB10 7 ions/s.Thebeamprofilecouldbemonitoredon-linewith50mmresolution.Thedetectorperformedsatisfactoryevenafteradoseof90740Grad.r 2002ElsevierScienceB.V.Allrightsreserved. PACS:07.77. n;85.30.ZKeywords:Cryogenicsilicondetectors;Heavyions 1. IntroductionIn the framework of the CERN NA60 [1] andRD39Collaborations [2], we have developed anew cryogenic beam hodoscope, hereafter namedBeamscope, based on silicon microstrip detectorsoperated at 130K. This detector represents thefirst application in a high energy physics experi-mentofthecryogenicsilicontechnology,triggeredbythediscoveryofthe‘‘Lazaruseffect’’[3]in1998anddevelopedbyRD39.Operationofsiliconatcryogenictemperaturesisanattractivetechnologyindeedforapplicationinharsh environments. It has been shown [4,5] thatheavily irradiated silicon detectors operatedaround 130K have charge collection efficiency

Silicon detectors irradiated ''in situ'' at cryogenic temperatures

Though several studies have proved the radiation tolerance of silicon detectors at cryogenic temperatures, following room temperature irradiation, no previous investigation has studied the behaviour of detectors irradiated ‘‘in situ’’ at low temperatures. In this work, effects of irradiation of 450 GeV protons at 83 K will be presented, showing that after a dose of 1.2 � 10 15 pc m � 2 a charge collection efficiency (CCE) of 55% is reached at 200 V before the annealing. The same results were found at the end of the irradiation, after the sample has spent more then one year at room temperature. This shows that the CCE recovery by low temperature operation is not affected by the temperature of irradiation and by the reverse annealing. r 2002 Elsevier Science B.V. All rights reserved.

A new technique for the investigation of deep levels on irradiated silicon based on the Lazarus effect

A new technique for the investigation of deep levels on irradiated silicon by measuring the charge collection efficiency (CCE) of samples from 220 K down to 90 K is presented here. The temperature and time dependencies of the CCE have been measured with unprecedented precision and resolution for standard and oxygenated silicon diodes, and the data obtained have been analyzed in the framework of the Lazarus effect and polarization models, extracting information about the radiation-induced deep levels in the materials. Results are presented and discussed in terms of these models and what can be inferred from them when applied to experimental data.

Cryogenic technology for tracking detectors

A low-mass cryogenic cooling technique for silicon sensor modules has been developed in the framework of the RD39 Collaboration at CERN. A prototype low-mass beam tracker cryostat has been designed, constructed and tested for applications in fixed target experiments. We shall report here briefly the main features and results of the system.

Radiation hard position-sensitive cryogenic silicon detectors: the Lazarus effect

The discovery of the so-called Lazarus e!ect, namely the recovery of the charge collection e

Study of scattered radiation during fluoroscopy in hip surgery

ciency (CCE) of irradiated silicon detectors by means of cryogenic cooling has entailed an increasing interest in the behavior of silicon detectors at cryogenic temperatures. We have measured the CCE of a silicon p}i}n diode detector previously irradiated with an equivalent #uence of 1]1015 n/cm2 neutrons of 1 MeV energy. The charge collection e

Scatter fraction with simulations

ciency has been measured at 77 K, showing that the low-temperature operation considerably decreases the bias current. This is also the case when forward voltage bias is applied, which then becomes a suitable option. In this condition, the sample shows a charge collection e