Thin Plastic Scintillator Research Articles

Time-of-Flight Characteristics of Scintillation Counters with Fine-Mesh Photomultipliers

The characteristics of the time-of-flight system of scintillation counters with the ФЭУ-527 and R5505 fine-mesh-dynode photomultipliers for high-magnetic-field environment were measured. Scintillation counters with thin plastic scintillators 1, 3, and 5 mm thick were designed to operate in comparatively strong stray magnetic fields of up to several kilogauss. The measurements were carried out in beams of the U-10 proton synchrotron (Institute of Theoretical and Experimental Physics) with proton, π+-meson, and π–-meson momenta of 0.63, 1.03, and 1.28 GeV/c. For counters with scintillator sizes of 1 × 20 × 154 mm (BI-408) and 3 × 20 × 200 and 5 × 20 × 200 mm (Kuraray and SCSN-81), time resolutions of 45–180 ps were obtained. The time resolution of the scintillation counters, in which scintillators ∼ 20 mm thick and ФЭУ-527 photomultipliers were used, was found to be 50–80 ps.

Precise Measurement of Gamma-ray Emission Probabilities of 100Ru

To precisely determine emission probabilities of γ rays of 100Ru, β-γ coincidence measurements have been performed. A thin plastic scintillator was used to detect f rays emitted from the ground state of 100Tc produced by thermal neutron capture reaction of99 Tc, while γ rays de-exciting the excited states of 100Ru populated via the β decays were detected using a high-purity germanium detector. In the data analysis, ratios of counting rates of f rays in coincidence with one of the 100Ru γ rays to that of f-ray singles were deduced at several finite β-ray detection threshold energies. The ratios at the zero threshold energy were then deduced by extrapolating the ones at finite threshold energies to take the effect of cascading γ rays into account. From the ratios at the zero threshold energy, the emission probabilities of 539 and 591 keV γ rays of 100Ru, which are emitted following the β decay of 100Tc, were obtained to be 6.6±0.5% and 5.5±0.3%, respectively. By following the decay of the two γ rays, half-life of the 100Tc nuclide was determined to be 15.27±0.05s.

Differential dosimetry in a neutron-proton mixed field with low-pressure proportional counters.

For a mixed radiation field of neutrons and protons, radiation events were discriminated between photons, neutrons, and protons using a thin plastic scintillator. Distributions of lineal energy were measured with low-pressure proportional counters (LPPCs). To estimate the distribution of lineal energy for ICRU muscle, measurements were carried out using A-150-walled, graphite-walled, ZrO2-walled, and Zr-walled counters. Data were corrected for different atomic compositions between the A-150 plastic and ICRU muscle.

A simple method of energy calibration for thin plastic scintillator

A thin plastic scintillator is used as a trigger counter of charged particle spectrometers. Since its Compton edge is not clear, it is difficult to check up the thin plastic scintillator counters with a standard gamma-ray source. In this paper a simple method is proposed to determine the Compton edge and the energy resolution of the thin plastic scintillator by fitting the simulated spectrum to the measured. The simulated spectrum was made with a Monte Carlo program considering geometries of the plastic scintillator. This technique was examined with the plastic scintillator having thickness of 2 mm to 10 mm.

Precise Measurement of Gamma-ray Emission Probabilities of 100Ru.

To precisely determine emission probabilities of γ rays of 100Ru, β-γ coincidence measurements have been performed. A thin plastic scintillator was used to detect f rays emitted from the ground state of 100Tc produced by thermal neutron capture reaction of99 Tc, while γ rays de-exciting the excited states of 100Ru populated via the β decays were detected using a high-purity germanium detector. In the data analysis, ratios of counting rates of f rays in coincidence with one of the 100Ru γ rays to that of f-ray singles were deduced at several finite β-ray detection threshold energies. The ratios at the zero threshold energy were then deduced by extrapolating the ones at finite threshold energies to take the effect of cascading γ rays into account. From the ratios at the zero threshold energy, the emission probabilities of 539 and 591 keV γ rays of 100Ru, which are emitted following the β decay of 100Tc, were obtained to be 6.6±0.5% and 5.5±0.3%, respectively. By following the decay of the two γ rays, half-life of the 100Tc nuclide was determined to be 15.27±0.05s.

Response Function Measurements of the Self-TOF Neutron Detector for Neutrons up to 800 MeV

The Self-TOF detector has been developed for high energy neutron spectrometry behind a shield. This detector consists of a radiator, a start counter and a stop counter. The radiator is composed of 20 thin plastic-scintillation detectors and the stop counter is segmented into nine plastic-scintillation detectors. The response functions of the Self-TOF detector for high energy neutrons up to 800 MeV were measured at the HIMAC (Heavy Ion Medical Accelerator in Chiba) of the National Institute of Radiological Sciences (NIRS). The measured responses were compared with those calculated using the LCS (LAHET Code System). The LCS results considerably overestimate the measuremental results with an increase in the neutron energy. It was found that this detector can give the neutron energy spectrum by using the FERDO-U unfolding code combined with the measured response functions, and is useful for high energy neutron spectrometry because of the almost constant efficiency for neutrons above 100 MeV.

Feasibility studies of the self-TOF detector for high-energy neutron measurements in shielding experiments

The feasibility of a new type of neutron detector was studied. The detector consists of a radiator, a start counter and a stop counter. The radiator is composed of 20 thin plastic-scintillation detectors and the stop counter is segmented into nine plastic-scintillation detectors. Neutrons impinging on the radiator emit charged particles. The time of flight of protons emitted at a forward angle is measured using the start and stop counters, therefore, we call the detector the “self-TOF detector”. The proton time-of-flight spectrum is converted to the energy spectrum of neutrons using a measured response function. The basic properties of the detector, such as detection efficiency, signal-to-noise ratio, particle identification capability, and energy resolution, were studied.

The response of a NE102 scintillator to passing-through relativistic heavy ions

The response of a NE102 scintillator to He, C, Ne, Si and Ar ions has been studied at incident energies from 120 MeV up to 18 GeV when used as a transmission (Δ E) counter. The energy of the incident beam was changed by inserting an absorber of various thicknesses made of PMMA plates. The primary particles were identified and separated from projectile fragments by using the Δ E– E counter telescope method. A thin NE102 plastic scintillator and a BGO scintillator were used as a Δ E counter and a residual E counter, respectively. The energy of the primary particles was deduced by comparing the depth-dose distribution measured by an ionization chamber to those by a theoretical calculation. The light output of the NE102, d L/d x, was found to be linear to d E/d x in the low-d E/d x region, while gradually being quenched in the high-d E/d x region. This quenching was regarded as being a phenomenon independent of the particle species. The residual particle-species dependency was well indexed as a function of log ( AZ 2).

βdecayingT1/2=3.4s isomer in69Ni

A radioactive beam of ${}^{69}\mathrm{Ni}$ was produced by the fragmentation of a 70 MeV/nucleon ${}^{76}\mathrm{Ge}$ beam in a Be target. $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$-ray studies were performed using two thin plastic scintillators and two large-volume Ge detectors following implantation of the ${}^{69}\mathrm{Ni}$ nuclei into a foil of a collection wheel apparatus. A 1296-keV $\ensuremath{\gamma}$-ray transition with a half-life of 3.4(7) s was identified and has been attributed to the decay of the $\ensuremath{\nu}{p}_{1/2}^{\ensuremath{-}1}$ isomeric state in ${}^{69}\mathrm{Ni}.$ The relative population of the low-spin ${J}^{\ensuremath{\pi}}{=1/2}^{\ensuremath{-}}$ isomer to the known high-spin ${J}^{\ensuremath{\pi}}{=(17/2}^{\ensuremath{-}})$ isomer was determined to be 6:1 for the production of ${}^{69}\mathrm{Ni}$ via fragmentation of ${}^{76}\mathrm{Ge},$ based on an upper limit of 36% extracted for the ${}^{69}{\mathrm{Ni}}^{m1}$ $\ensuremath{\beta}$-decay branch to the ${3/2}^{\ensuremath{-}}$ ground state of ${}^{69}\mathrm{Cu}.$ The half-life and branching of the ${}^{69}{\mathrm{Ni}}^{m1}$ $\ensuremath{\beta}$ decay is discussed in light of possible two particle--two hole excitations in the low-energy structure of ${}^{69}\mathrm{Cu}.$

Single ion hitting to living samples

Single ion hit system for living biological samples has been designed. An external scanning microbeam system with about 1 μm spatial resolution, a fast beam chopping system with less than 5 ns and a thin plastic scintillator based transmission-type detection system are combined together at the JAERI light ion microbeam system. The first step to develop a single ion facility was completed in this work. The next steps to verify the reliability of the total system have been started.

A neutron detector for (p,np) coincidence studies

A neutron detector with moderate energy resolution (∼3 MeV) has been built for neutrons in the energy range 75–175 MeV. The detector was designed for coincidence scattering experiments. The design eliminates the need for long neutron flight paths necessary for comparable energy resolution time-of-flight measurements with a comparable efficiency-solid angle product (0.02 msr). The detector consists of thin plastic scintillators in which the neutron undergoes n–p elastic scattering. The second-scattered protons are tracked by drift chambers and detected in a sodium iodide array. The design motivations and features are presented along with results from detailed in-beam experimental tests.

The response of a BGO scintillator to relativistic heavy ions

The response of a BGO scintillator to He, C, Ne, Si and Ar ions has been studied at incident energies from 120 MeV up to 18 GeV for the first time. The energy of incident beam was changed by inserting an absorber of various thicknesses made of PMMA plates. The primary particles were identified and separated from projectile fragments by using the ΔE−E counter telescope method. A thin NE102A plastic scintillator and a BGO scintillator were used as a ΔE counter and a residual E detector, respectively. The energy of the primary particles was deduced by comparing the depth-dose distribution measured by an ionization chamber to those by a theoretical calculation. The light output of the BGO scintillator was found to be linear in this energy region. The dependency of the light output on the particle species was well indexed as a function of log (AZ2).

A position-sensitive alpha detector using a thin plastic scintillator combined with a position-sensitive photomultiplier tube

A position-sensitive alpha detector was developed and tested. The alpha detector consists of a thin plastic scintillator, a position-sensitive photomultiplier tube, a position calculation circuit and a personal computer based data acquisition system. Because the thin plastic scintillator has high-detection efficiency for alpha particles while it has low-sensitivity for beta particles or gamma ray, the detector can selectively detect alpha particles with low background counts. The spatial resolution of the detector was approximately 3 mm FWHM. An autoradiographic images of plutonium distribution in the lung of an animal as well as an image of an uranium particle were successively obtained. Spatial and energy distribution of radon daughters could also be measured. We conclude that the developed position-sensitive alpha detector is useful for some applications such as plutonium detection or alpha autoradiography as well as distribution analysis of radon daughters.

Thin Beta-ray Detectors using Plastic Scintillator Combined with Wavelength-shifting Fibers for Surface Contamination Monitoring

A thin β-ray detector for surface contamination monitoring has been newly developed. This detector, which we call a “wavelength-shifting” β-ray detector, consists of a thin square plastic scintillator plus wavelength-shifting fibers (WLSFs) to collect scintillation photons. The WLSFs are attached to opposite edges of the scintillator, where they convert highly concentrated scintillation photons into fluorescence. The fluorescent photons can either be detected directly at the ends of the WLSFs or through transparent optical fibers by small photo-multiplier tubes (PMTs). This design provides a thin detector profile while offering good β-ray detection performance.We first carry out a theoretical evaluation of the light output of this design. Then we describe verification tests aimed at device evaluation, including some performance tests using trial-manufactured detectors. The results demonstrate that the new design offers good sensitivity and uniformity, and that the required detection limit for surface contamination monitoring is achieved. Finally, we confirm that the newly developed detectors are suitable for practical application.

Thin Beta-ray Detectors using Plastic Scintillator Combined with Wavelength-shifting Fibers for Surface Contamination Monitoring.

A thin β-ray detector for surface contamination monitoring has been newly developed. This detector, which we call a “wavelength-shifting” β-ray detector, consists of a thin square plastic scintillator plus wavelength-shifting fibers (WLSFs) to collect scintillation photons. The WLSFs are attached to opposite edges of the scintillator, where they convert highly concentrated scintillation photons into fluorescence. The fluorescent photons can either be detected directly at the ends of the WLSFs or through transparent optical fibers by small photo-multiplier tubes (PMTs). This design provides a thin detector profile while offering good β-ray detection performance. We first carry out a theoretical evaluation of the light output of this design. Then we describe verification tests aimed at device evaluation, including some performance tests using trial-manufactured detectors. The results demonstrate that the new design offers good sensitivity and uniformity, and that the required detection limit for surface con...

Reduction of γ-ray background in the use of 32 keV X-rays from 137Cs sources by a gating method with a thin plastic scintillation detector

In the use of 32 keV K X-rays from 137Cs sources for the calibration of low energy photon spectrometers, a new method was developed to reduce remarkably the background continuum due to 662 keV γ-rays. This method is based upon a gating technique by the use of a 4π detector composed of thin plastic scintillator sheets which sandwich the 137Cs source. Since all X-rays from the 137Cs source are coincident with monoenergetic internal conversion electrons, the X-ray response of the photon spectrometer remains unchanged, whereas γ-ray signals are rejected by gating. This method was tested successfully for three different photon spectrometers.

Characterization of fluor concentration and geometry in organic scintillators for in situ beta imaging

Development of a small area (1-2 cm/sup 2/) in situ beta imaging device includes optimization of the front end scintillation detector, which is fiber optically coupled to a remote photon detector. Thin plastic scintillation detectors, which are sensitive to charged particles, are the ideal detectors due to the low sensitivity to ambient gamma backgrounds. The light output of a new binary plastic scintillator was investigated with respect to increasing concentrations of the fluor (0.5-2.0% by weight) and varying thickness cylindrical configurations of the intended imaging detector. The fluor had an emission maximum increasing from 431 to 436 nm with increasing fluor concentration. The decay time(s) had two components (0.38 and 1.74 ns). There was an /spl sim/20% increase in light output with increasing fluor concentration, measured with both /sup 204/Tl betas and conversion electrons from /sup 207/Bi. The highest light output of this new scintillator was measured to be /spl sim/30% lower than BC404. Simulations predicted the 1.5 mm scintillator thickness at which light output and energy absorption for /spl sim/700 keV electrons (e.g., from /sup 204/Tl, /sup 18/F) were maximized, which corresponded with measurements. As beta continua are relatively featureless, energy calibration for the thin scintillators was investigated using Landau distributions, which appear as distinct peaks in the spectra. As the scintillators were made thinner, gamma backgrounds were shown to linearly decrease.

Level lifetimes in neutron-rich Ru isotopes

The neutron-rich Ru isotopes are situated between the strongly deformed Sr-Zr region with axial deformation of f l _ 0.40 [1] and the spherical Cd-Sn region. Evidence for triaxiality of even-even Ru isotopes has been presented in [2-5], and lifetimes of some of their 2 + states have been measured in fission studies [6-9]. It seems, however, that in these experiments the nearly identical energies of the 2 + ---* 0 + transitions in l~ and 11~ could not be separated. Therefore, high-resolution measurements are required in order to perceive the evolution of deformation with increasing neutron number. So far only few measurements by the delayed-coincidence method [10] have been performed on chemically or massseparated isotopes. Therefore, a systematic study of level lifetimes in neutron-rich Ru nuclei has been undertaken at the Mainz TRIGA reactor. Fission products were obtained from thermal-neutron induced fission of 249Cf. Technetium isotopes were chemically separated within 2 s by the on-line SISAK method [11], allowing the study of levels and lifetimes of their/3decay daughters. Primarily, the short-lived activities of 1~ to 111Tc were measured, whereas long-lived decay products were kept at a low level due to the continuous flow of the liquid phase (containing the technetium activity) passing the detectors. Apart from Tc, also small contaminations of short-lived Ag isotopes were observed in the 7-spectra. The detector setup consisted of a thin plastic scintillator for fi-particles and two Ge-detectors for 7-rays, one being a planar diode with good energy resolution and timing properties (7 ns at 100 keV) and the other a medium-size coaxial detector. Coincidence events from all detector pairs were recorded with the GOOSY mult iparameter system. The delayed coincidences between the fl-scintillator and the planar 7-detector were used for the measurement of the shortest lifetimes. With this setup, a systematical accuracy of the order of 0.05ns could be obtained for the strongest "/-peaks. The 7-7 coincidences were used to check for contaminations in the 7-gates from the planar detector applied for the fl-

Measurement of Fragment Mass Dependent Kinetic Energy and Neutron Multiplicity for Thermal Neutron Induced Fission of Plutonium-239

Kinetic energy and neutron multiplicity as a function of fragment mass were measured for the thermal neutron induced fission of 239Pu. By measuring the velocities and energies of two fission fragments simultaneously, both of the pre-neutron emission fragment mass m* and the post-neutron mass m were obtained. The fragment mass dependent neutron multiplicity ν(m*) was deduced by subtracting m from m*. The fragment mass dependent total kinetic energy TKE(m*) was also obtained from this data. The fragment velocity was measured by time-of-flight (TOF) method, for which the start signal was triggered by a very thin plastic scintillation film detector (TFD) and the stop signal was obtained by a silicon surface barrier detector (SSBD) which was also used for the measurement of [he fragment kinetic energy. The present result of ν(m*) is in good agreement with that of Apalin et al. and that in the light fragment region of Fraser et al. The obtained TKE(m*) agrees well with the data of Wagemans et al. A calculation was carried out with the model proposed by Brosa et al. who assumed multichannel fission paths and a random neck rupture. It is seen that the calculated results of both fragment mass dependent kinetic energy and neutron multiplicity represent experimental data well.

Production and thickness determination of thin plastic scintillator foils

A method of making large thin plastic scintillator foils with good uniformity is presented. The use of Fourier Transform Infrared Spectroscopy (FTIR) to test the foil uniformity and to establish an empirical thickness calibration curve is described.