Effects of irradiation of energetic heavy ions on digital pulse shape analysis with silicon detectors

The next generation of 4π detector arrays for heavy ion studies will largely use Pulse Shape Analysis to push the performance of silicon detectors with respect to ion identification. Energy resolution and pulse shape identification capabilities of silicon detectors under prolonged irradiation by energetic heavy ions have thus become a major issue. In this framework, we have studied the effects of irradiation by energetic heavy ions on the response of neutron transmutation doped (nTD) silicon detectors. Sizeable effects on the amplitude and the risetime of the charge signal have been found for detectors irradiated with large fluences of stopped heavy ions, while much weaker effects were observed by punching-through ions. The robustness of ion identification based on digital pulse shape techniques has been evaluated

A single-chip telescope for heavy-ion identification

A ΔE-E telescope exploiting a single silicon chip for both ΔE measurement and scintillation light collection has been tested. It is a Si-CsI(Tl) telescope tailored for mass identification of light charged particles and intermediate mass fragments. A procedure based on two different shaping filters allows for extraction of the ΔE-E information from the single silicon signal. The quality of the obtained fragment identification is expressed in terms of a figure of merit and compared to that of a standard ΔE-E telescope. The presented configuration could be a good candidate for the basic cell of a large solid angle array of ΔE-E telescopes, given the reduction in complexity and cost of the front-end electronics

Particle identification using the (DELTA)E-E technique and pulse shape discrimination with the silicon detectors of the FAZIA project

The response of silicon-silicon-CsI(Tl) and silicon-CsI(Tl) telescopes to fragments produced in nuclear interactions has been studied. The telescopes were developed within the FAZIA collaboration. The capabilities of two methods are compared: (a) the standard ΔE-E technique and (b) the digital Pulse Shape Analysis technique (for identification of nuclear fragments stopped in a single Si-layer). In a test setup, nuclear fragments covering a large range in nuclear charge, mass and energy were detected. They were produced in nuclear reactions induced by a 35A MeV beam of 129Xe impinging on various targets. It was found that the ΔE-E correlations allow the identification of all isotopes up to Z∼25. With the digital Pulse Shape Analysis it is possible to fully distinguish the charge of stopped nuclei up to the maximum available Z (slightly over that of the beam, Z=54)

Test of FAZIA prototypes at LNS.

The response of a few silicon-silicon-CsI(Tl) and silicon-silicon telescopes with high quality detectors developed within the FAZIA collaboration [1] is tested in this work. The silicon detectors were manufactured from “random cut” wafers to avoid channeling effects and are characterized by a high dopant homogeneity. One siliconsilicon telescope was mounted on a rotating platform to compare its response in case of front and rear injection. Another silicon detector was mounted on a motorized support, sliding to angles very close to the beam (~0.5°), in order to measure the effects of radiation damage on energy resolution and PSA. Beams of 84Kr and 129Xe at 35A MeV, impinging on targets of natNi, 93Nb, 120Sn and Au, produced fragments over a large range of charge, mass and energy. The aim was to explore the capabilities of various solutions exploiting the digital techniques of Pulse Shape Analisys (PSA) for the Z and A identification of stopped ions. It has been found that PSA is able to fully discriminate the charge of stopped ions up to the maximum available Z (that of the beam, Z=54). The ΔE-E correlations of the first two silicon detectors can separate all the nuclides up to Z~25 and no difference in resolution between front and rear injection is observed. The experimental data also provide some preliminary information about the effects of radiation damage on energy resolution and PSA for high fluences of heavy ions

The FAZIA project in Europe: R&D phase

The goal of the FAZIA Collaboration is the design of a new-generation 4 detector array for heavy-ion collisions with radioactive beams. This article summarizes the main results of the R&D phase, devoted to the search for significant improvements of the techniques for charge and mass identification of reaction products. This was obtained by means of a systematic study of the basic detection module, consisting of two transmission-mounted silicon detectors followed by a CsI(Tl) scintillator. Significant improvements in E-E and pulse-shape techniques were obtained by controlling the doping homogeneity and the cutting angles of silicon and by putting severe constraints on thickness uniformity. Purposely designed digital electronics contributed to identification quality. The issue of possible degradation related to radiation damage of silicon was also addressed. The experimental activity was accompanied by studies on the physics governing signal evolution in silicon. The good identification quality obtained with the prototypes during the R&D phase, allowed us to investigate also some aspects of isospin physics, namely isospin transport and odd-even staggering. Now, after the conclusion of the R&D period, the FAZIA Collaboration has entered the demonstrator phase, with the aim of verifying the applicability of the devised solutions for the realization of a larger-scale experimental set-up