DELPHI is a 4π detector with emphasis on particle identification, three-dimensional information, high granularity and precise vertex determination. The design criteria, the construction of the detector and the performance during the first year of operation at the large electron positron collider (LEP) at CERN are described.

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The DELPHI detector at LEP.

Purpose RBE-LET relationships for cell inactivation and hprt mutation in V79 cells have been studied with mono-energetic low-energy proton beams at the radiobiological facility of the INFN-Laboratori Nazionali di Legnaro (LNL), Padova, Italy. Materials and methods V79 cells were irradiated in mono-layer on mylar coated stainless steel petri dishes, in air. Inactivation data were obtained at 7.7, 34.6 and 37.8 keV/microm and hprt mutation was studied at 7 7 and 37.8 keV/microm. Additional data were also collected for both the end points with the proton LET already considered in our previous publications, namely 11.0, 20.0 and 30.5 keV/microm. Results A maximum in the RBE-LET relationship for cell inactivation was found at around 31 keV/microm, while the RBE for mutation induction increased continuously with LET. Conclusions The proton RBE-LET relationship for cell inactivation is shifted to lower LET values compared with that for heavier ions. For mutation induction, protons of LET equal to 7.7keV/microm gave an RBE value comparable with that obtained by helium ions of about 20 keV/microm. Mutagenicity and lethality caused by protons at low doses in the LET range 7.7-31 keV/microm were proportional, while the data at 37.8 keV/microm suggest that this may not hold at higher LET values.

RBE- LET relationships for cell inactivation and mutation induced by low energy protons in V79 cells: further results at the LNL facility

SummaryThe survival of V79 Chinese hamster cells irradiated with proton beams with energies of 0·73, 0·84, 1·16, 1·70 and 3·36 MeV, corresponding to LET values, evaluated at the cell midplane, of 34·5, 30·4, 23·9, 17·8 and 10·6 keV/μm respectively, have been studied in the dose range 0·5–6·0 Gy. As a reference, the survival curve obtained with 200 kV X-rays was used.The initial shoulder, typical of survival curves obtained with sparsely ionizing radiation, decreases as the LET increases and completely disappears at 23·9 keV/μm. This value corresponds to the maximum of the RBE, expressed as the initial slope ratio. In the energy range we have considered, the RBEs for protons are higher than those reported for other ions of comparable LET and the RBE-LET relationship results shifted to lower LET values. Our data seem to indicate that the RBE-LET curve depends on the type of radiation and this could imply that LET is not a good reference for the dose-effectiveness relationship.

RBE-LET Relationship for the Survival of V79 Cells Irradiated with Low Energy Protons

The effects of fast neutron irradiation on DNA were studied using DNA of the pBR322 plasmid (4362 base pairs), and the results compared to those obtained with 60Co gamma rays Irradiation of the plasmid DNA in solution with a neutrons beam (p34+Be) of the CERI (CNRS Orleans) cyclotron (with a flat energy spectrum from 34 MeV to low energies) results in half the yield of single-strand breaks (ssb), and 15 times higher yield of double-strand breaks (dsb) for neutrons as compared to gamma-rays Possible specificity of the neutron-induced breaks was examined: the scavenging of OH radicals by 01 mol dm-3 ethanol inhibits all neutron-induced ssb, but only 85 per cent of the dsb For gamma-irradiation, both ssb and dsb are completely inhibited in these conditions These results suggest at least three different origins for neutron-induced dsb The occurrence of around 30 per cent of dsb can be explained by a radical transfer mechanism (proposed by Siddiqi and Bothe (1987) for gamma-irradiation) Around 55 per cent of dsb may be due to the non-random distribution of radicals in high-density tracks of the secondary particles of neutrons, which results in a simultaneous attack of the two strands by OH radicals These first two processes are both OH-mediated and thus are sensitive to ethanol The direct effect of fast neutrons and their secondaries (recoil protons, alpha-particles and recoil nuclei) can account for the remaining 15 per cent of dsb, not inhibited by 01 mol dm-3 ethanol

DNA radiolysis by fast neutrons.

During the upgrading of the radiobiological facility at the Laboratori Nazionali di Legnaro (LNL) we found that uncorrected values of the proton energy were used in the past. This circumstance prompted us to perform the reevaluation of the physical parameters for all the proton beams used in our previous radiobiological investigations (Belli et al. 1987) and, subsequently, the re-evaluation of all our previous dose-response curves for inactivation and mutation induction (Belli et al. 1989, 1991). This re-evaluation leads to significant changes in the dose-response curves and in the RBE-LET relationships only at the two lowest energies (highest LET) used. These two points are not reliable for the identification of a peak in RBE-LET relationship for cell inactivation. In spite of that, the extent of the changes is not such as to modify the general conclusion previously drawn, pointing out that there is a LET range where protons are more effective than alpha-particles.

Inactivation and Mutation Induction in V79 Cells by Low Energy Protons: Re-evaluation of the Results at the LNL Facility

This paper describes the proton irradiation facility built up at the 7 MV Van de Graaff accelerator of the INFN-Laboratori Nazionali di Legnaro for radiobiological studies. The system mainly consists of two vacuum chambers, a fast tantalum shutter for intercepting the beam and a beam line containing the beam collimator arrangement and ending with a thin window for the beam extraction in air. Each chamber houses a Ta beam collimator, an Au scatterer foil for the broadening and uniformization of the proton beam over the cell samples and a solicon surface barrier detector for beam monitoring purposes. The test of the facility performance is discussed. With the double scattering system a counting rate in air as low as hundreds of protons per second and a fluence heterogeneity less than 5% within a circular field of 15 mm diameter were obtained. The first results of survival studies of Chinese hamster lung cells (V79-753B) irradiated with a 1.1 MeV proton beam are presented. For comparison, results obtained irradiating the cells with 200 kV X-rays are reported, too.

Proton irradiation facility for radiobiological studies at a 7 MV Van de Graaff accelerator

We present the performance of the DELPHI lead glass calorimeter with vacuum phototriode readout. The behaviour of the counters in magnetic fields up to 1.1 T is discussed. Experimental results, obtained with an electron beam from 7 to 50 GeV/c, on noise, linearity, energy and position resolution are presented.

Performance of the forward electromagnetic calorimeter (FEMC) for the end caps of the DELPHI detector

A prototype calorimeter of lead glass bars read by one-stage vacuum photomultipliers (triodes) has been tested at CERN with electrons in the energy range 2–30 GeV. Different glass-triode combinations have been compared. An electronic amplification noise corresponding to about 30 MeV has been obtained. The space resolution has been measured to be 4.4 mm on average.

Study of a lead glass calorimeter with vacuum phototriode read-out

We report on some images obtained with the Leak Microstructures (LM), which are elements for the detection of gas ionizing particles based on needle-point anodes. X-ray images of a mask with seven holes, 300 μm in diameter and 100 μm separated, drilled on a tantalum sheet were obtained with a very good spatial resolution. Varying the potential to the drifting electrode we put in evidence the possibility to perform a “zoom” of the image. X-ray images of a tantalum sheet of about 20×20 mm2 were obtained using a matrix of 9×9 LMs read by only 6 electronic chains (6 ADCs).

G. Galeazzi

Papers

Proton irradiation facility for radiobiological studies at a 7 MV Van de Graaff accelerator

Performance of the forward electromagnetic calorimeter (FEMC) for the end caps of the DELPHI detector

Study of a lead glass calorimeter with vacuum phototriode read-out

Imaging with the leak microstructures: preliminary results