K. Wick

Construction and beam test of the ZEUS forward and rear calorimeter

Abstract The forward and rear calorimeters of the ZEUS experiment are made of 48 modules with maximum active dimensions of 4.6 m height, 0.2 m width, 7 λ depth and maximum weight of 12 t. It consists of 1 X 0 uranium plates interleaved with plastic scintillator tiles read out via wavelength shifters and photomultipliers. The mechanical construction, the achieved tolerances as well as the optical and electronics readout are described. Ten of these modules have been tested with electrons, hadrons and muons in the momentum range 15–100 GeV/ c . Results on resolution, uniformity and calibration are presented. Our main result is the achieved calibration accuracy of about 1% obtained by using the signal from the uranium radioactivity.

TEST OF THE ZEUS FORWARD CALORIMETER PROTOTYPE

Abstract Four prototype modules following the same design as the ZEUS forward calorimeter (FCAL) modules have been constructed and tested with electrons, hadrons and muons in the momentum range of 1 to 100 GeV/ c . The main topics under investigation were: calibration, uniformity of response, noise, light yield, energy resolution and the electron to hadron response (e/h ratio). The result of the measurements is presented and the expected performance of the FCAL is discussed in the light of these results.

Recovery and dose rate dependence of radiation damage in scintillators, wavelength shifters and light guides☆

Abstract The radiation damage induced by γ-rays in scintillators (mainly SCSN-38 with a polystyrene base), wavelength shifters (Y7 and K27 in PMMA) and different PMMA-base light guides and its dose rate dependence has been studied under different experimental conditions (doses D = 103−105Gy, dose rates D= (30−1000)Gy/h, gas atmospheres: Ar, N2, air). The production of new absorption centers and the deterioration of fluor molecules are the main effects caused by radiation, leading to a reduction of the primary light yield and of the attenuation length. The post-irradiation behaviour after short-term irradiations was compared with the behaviour during long-term irradiations. In the polystyrene base plastic scintillator SCSN-38 the radiation induced absorption recovers rapidly during and after irradiation, if the samples are in contact with oxygen. In different materials (light guides GS 218, GS 233, wavelength shifters Y7 and K27) with a PMMA matrix we find strong recovery in air after irradiation, but surprisingly no recovery during long-term irradiations at medium dose rates. In all investigated polymers the observed radiation damage is dose rate dependent. In addition it is shown that the PMMA-base scintillator used in the AFS calorimeter behaves completely different from all other materials studied in the present experiment.

Response of a uranium-scintillator calorimeter to electrons, pions and protons in the momentum range 0.5–10 GeV/c

Abstract We have exposed a sandwich calorimeter, consisting of 3.3 mm thick uranium pnterleaved with 2.6 mm thick scintillator tiles, to positive and negative electrons and pions and to protons in the momentum range of 0.5 to 10 GeV/c. We find that e/h is about 1 above 3 GeV/c, but decreases significantly for lower momenta. This ratio is the same for positive and negative pions and also for pions and protons of the same kinetic energy.

The ZEUS forward plug calorimeter with lead scintillator plates and WLS fiber readout

A Forward Plug Calorimeter (FPC) for the ZEUS detector at HERA has been built as a shashlik lead–scintillator calorimeter with wave length shifter fiber readout. Before installation it was tested and calibrated using the X5 test beam facility of the SPS accelerator at CERN. Electron, muon and pion beams in the momentum range of 10–100 GeV/c were used. Results of these measurements are presented as well as a calibration monitoring system based on a 60Co source.

Shortlived absorption centers in plastic scintillators and their influence on the fluorescence light yield

Abstract The process of radiation damage and its recovery were investigated during and after irradiation with X-rays. The absorption induced by X-rays in the scintillating fiber BCF-12 was measured in gas atmospheres with and without oxygen as a function of time, dose, dose rate and wavelength. The studies during irradiation showed several surprising effects: strong dose rate effects were observed. Shortlived absorption centers are formed during irradiation which decay within hours via a bimolecular reaction. The reaction constant for the decay decreases suddenly by a factor 200 in the moment when the concentration of oxygen dissolved in the fiber becomes zero. A kinetic model assuming three classes of absorption centers describes the dependence of the radiation induced absorption on dose and dose rate correctly. The influence of the shortlived absorption centers on the emitted fluorescence light yield was derived from the data as a function of dose rate.

Radiation damage of wavelength shifters and its recovery in the presence of oxygen

Abstract The radiation damage induced by γ-rays in wavelength shifters was investigated systematically at doses of 103–105 Gy. The reduction of primary light yield and transmission was measured using an UV flash lamp and a Beckman spectrometer. Strong recovery of the radiation damage was observed within one year, when the samples were stored in the presence of oxygen. It is shown that the recovery effects can be described quantitatively in the frame of a diffusion model.

Unexpected behaviour of polystyrene-based scintillating fibers during irradiation at low doses and low dose rates

Abstract The time dependence of the optical radiation damage process was studied for different fibers with polystyrene (PS) core. The fibers were irradiated with X-rays. In the present experiment the light guide BCF-98 (Bicron, clear polystyrene) was compared with the two scintillating fibers SCSF-38 and SCSF-81 (Kuraray). The light transmission through the fiber was investigated before, during and after irradiation. All investigated fibers showed unexpected effects depending on the fiber type: (1) at low doses the scintillating fibers are more sensitive to radiation than at high doses, i.e. the optical absorption rises nonlinearly with dose; (2) shortlived optical absorption centers decaying within several hours were detected in all fibers with PS core investigated up to now. Especially for SCSF-81, the annealing part is large and it totally overlaps the emission spectrum of the fiber.

Polarisation in neutron-deutron scattering at 30 MeV

Abstract The polarisation asymmetry in elastic n −d scattering has been measured at 30 MeV from 45° to 140° c.m. neutron angle with uncertainties less than 0.03.

ON THE BEHAVIOUR OF PLASTIC SCINTILLATORS DURING AN EXPERIMENT IN A HIGH DOSE RATE ENVIRONMENT

Abstract One generally assumes that the radiation damage observed in plastic scintillators which are exposed to a low dose rate radiation ( D Gy/h) in air is identical with the so-called permanent damage remaining after the end of the annealing process. This assumption is tested in the present experiment. The transmission damage was measured for two scintillating fibers (BCF-12 and SCSF81(Y7)) during and after irradiation in air. In both cases shortlived absorption centers have been observed which decay within hours. They absorb mainly light with wavelengths λ=500–700 nm. In this range of wavelengths and for the investigated doses ( D ∼ 3 kGy), the radiation induced absorption is considerably higher than the permanent damage. For radiation hardness tests of plastic scintillators especially those emitting green fluorescence light we propose to measure not only the permanent damage but also to study the behaviour during irradiation at realistic dose rates expected in future experiments.