U. Holm

Radiation stability of plastic scintillators and wave-length shifters

The radiation stability of plastic scintillators and wave-length shifters for the calorimeter of the ZEUS detector at HERA has been investigated by irradiating them with low energy protons and a Co gamma -source. Changes in light yield and absorption length have been measured with a xenon flash lamp. Absorbed total doses were 0.1-25 kGy for dose rates of 0.03 up to 10 kGy/h. Different surrounding atmospheres have been applied. The scintillator SCSN-38 shows a strong decrease of the absorption length with a fast recovery in air to a low permanent damage. The permanent loss in light yield is 4% for a dose of 10 kGy. The WLS Y-7 and K-27 dissolved in PMMA have small permanent damages in air and strong ones in nitrogen where no recovery takes place. Dose rate effects have not been seen either for the SCI or for the WLS. >

Neutron-irradiated plastic scintillators

The polystyrene (PS)-based scintillator SCSN38, pure PS and pure polymethylmethacrylate (PMMA) have been irradiated with a beam of fast neutrons and with reactor neutrons. The radiation-induced permanent optical absorption coefficients after total annealing in air are compared with data for γ irradiations. The strong differences might be due to the high linear energy transfer (LET) of the recoil protons elastically scattered by the neutrons.

Recovery and permanent radiation damage of plastic scintillators at different dose rates

The radiation stability of plastic scintillators and wavelength shifters for the calorimeter of the ZEUS detector has been investigated by irradiating them with protons, a /sup 60/Co source, and depleted uranium. Changes in light yield, absorption length, and absorption coefficient have been measured for storage in inert and oxygen atmospheres during and after irradiation. Radiation doses of up to 40 kGy with dose rates of 30 to 2000 Gy/h have been applied. The polystyrene-based scintillator SCSN-38 and the wavelength shifters Y-7 and K-27 in PMMA (polymethyl methacrylate) initially show a strong additional absorption but then recover in air to a low permanent damage (at 10 kGy) which is proportional to the applied dose. Series investigations on samples of all production cycles of the ZEUS scintillators at high dose rates show only minor differences in radiation hardness. >

Response of plastic scintillators in magnetic fields

The dependence of the light yield on magnetic field has been measured up to 0.45 T for the plastic scintillators NE-102A, SCSN-38, and Polivar. The scintillators were excited by 25-MeV protons, 5.9-keV X-rays, and UV light. When excited with ionizing radiation an increase of light yield is observed. For SCSN-38 of 2.7-mm thickness it amounts to 0.3%, 0.9%, 1.1%, and 3.3% at 1, 10, 100 and 450 mT, respectively. Ne-102A behaves similarly whereas a polymethyl methacrylate (PMMA)-based scintillator shows a stronger field dependence. >

On the formation of shortlived absorption centers during irradiation of plastic scintillators

There is strong evidence that shortlived absorption centers are produced during the irradiation of plastic scintillators. A broad absorption band ranging from 450–750 nm with a peak at a wavelength of 575 nm has been observed during the irradiation of the scintillating fiber BCF-12 with γ rays. Considerable absorption was detected at extremely low doses (D ≈ 10 – 20 Gy). The transmission was measured during and after irradiation as a function of wavelength and time. The time dependence can be described quantitatively by a simple kinetic model.

Let effects of neutron irradiated plastic scintillators

Abstract The induced optical absorptions of polymers polystyrene (PS), polymethylmethacrylate (PMMA) and polyvinyltoluene (PVT), irradiated by neutrons and in γ fields, were measured for equal doses. The polymers are the most important bases for the use as plastic scintillators. The permanent damage in PS and PVT after recovery in air is larger for neutron than for γ irradiation. Electron spin resonance measurements (PS, PMMA) of involved radicals gave insight into radical kinetics during the recovery process. Correlations between radicals and optical absorption bands were found.

Influence of temperature treatment on radiation stability of plastic scintillator and wave-length shifter

The influence of temperature treatment before or after irradiation on the radiation damage of plastic scintillators and wavelength shifters has been measured. The PMMA (polymethyl methacrylate)-based wavelength shifters show strong recovery for heating in argon after irradiation, whereas the polystyrene-based scintillator SCSN-38 in air suffers from heating not only before but also after irradiation. UV absorbants added to wavelength shifter material Y-7 in PMMA are responsible for additional radiation damage in the scintillator/wavelength shifter system SCSN-38/Y-7 if their cutoff wavelengths are higher than 360 nm.<<ETX>>

Evidence for the creation of short-lived absorption centers in irradiated scintillators

Abstract Strong evidence has been observed for the formation of short-lived absorption centers during irradiation of the scintillating fiber BCF-12. The fiber has been exposed to γ-rays from a 137 Cs source. In addition to earlier investigations which started after the end of the irradiation the damaging process was now studied also during irradiation. The measured behaviour during and after irradiation is described quantitatively by a simple theoretical model.

Radiation damage by neutrons to plastic scintillators

Polystyrene based scintillator SCSN38, wavelength shifter Y7 with polymethylmethacrylate matrix and pure PMMA light guide GS218 have been irradiated in the mixed field of a pool reactor. About 74% of the released dose was caused by the /spl gamma/ field, 26% by fast neutrons (SCSN38). The total dose ranged from 1.7 to 91 kGy. The measurements were made using alanine dosimeters. Transmission and fluorescence of the samples has been measured before and several times after irradiation, The results show no differences to former irradiations in pure /spl gamma/ fields.<<ETX>>

A Fast Cyclotron Beam Emittance Measuring Device

A fast emittance and beam profile measuring device for charged particle beams of energies up to about 30 MeV protons is described. It makes use of digitally driven compact beam deflection magnets which deliver sufficiently deflecting triangular wave fields up to frequencies of 1 kHz. Two-dimensional emittances or beam profiles can be produced with 16 frames per second on an oscilloscope. Alternatively, the data can be transferred to a PDP-11 computer with 0.3 frames per second.