Plastic Scintillator Anticoincidence Shield Research Articles

A second level trigger for the PAMELA satellite experiment

The PAMELA space experiment will be launched on-board of a Russian Resurs DK1 satellite towards the end of 2005. The main scientific goal is the study of the antimatter component of the cosmic radiation. Three years of data taking will provide unprecedented statistics for antiprotons (80 MeV–190 GeV) and positrons (50 MeV–270 GeV) and will set the upper limit for the ratio He ¯ / He below 10 −8. PAMELA is built around a permanent magnet silicon spectrometer, surrounded by a plastic scintillator anticoincidence shield. An electromagnetic calorimeter is used for particle identification and energy measurements. If PAMELA data exceed the storage allowance on the satellite or the daily downlink quota (20 GB), a second level trigger may be activated by uplink from ground. Information from the anticoincidence system and from the calorimeter will be included in the second level trigger condition, providing a selective reduction of data. The second level trigger condition provides a reduction of data of ∼60%, with a maximum systematic uncertainty in the proton (electron) spectra of 10% (3%). This uncertainty will be assessed during flight measuring one event every 10 without the second level trigger condition.

The anticoincidence shield of the PAMELA space experiment

The PAMELA space experiment will be launched in 2005 onboard a Russian Resurs DK1 satellite, orbiting Earth at an altitude varying between 300 and 600 km. The main scientific goal is a study of the antimatter component of the cosmic radiation. The semipolar orbit (71°) allows PAMELA to investigate a wide range of energies for antiprotons (80 MeV–190 GeV) and positrons (50 MeV–270 GeV). Three years of data taking will provide unprecedented statistics in this energy range and will set the upper limit for the ratio He ¯ / He below 10 −7. PAMELA is built around a permanent magnet silicon spectrometer, surrounded by a plastic scintillator anticoincidence shield. The anticounter scintillators are used to aid in the rejection of background from particles which do not cleanly enter the acceptance of the experiment but which are responsible for coincidental energy deposits in the trigger scintillators (‘false triggers’). Information from the anticounter system can be included as a veto in a second level trigger, to exclude the acquisition of events generated by such false triggers. The construction of the anticounter system is described, along with its functionality and performance. The read-out electronics and the LED-based monitoring system are also described. Test-beam and simulation studies of the system are reviewed.

The GLAST large area telescope instrument

The LAT instrument on the Gamma-ray Large Area Space Telescope (GLAST) project is a gamma-ray pair-conversion telescope designed to improve upon the sensitivity of the Compton Gamma-Ray Observatory EGRET instrument by at least a factor of 30. The LAT design is based upon a silicon-strip tracker/converter, a CsI calorimeter, and a plastic-scintillator anticoincidence shield. The project is approaching its critical design review and is scheduled for launch in 2006. This talk gives an overview of the LAT science objectives, the LAT design, and the status of the engineering effort and instrument production plans.

The Phobos low energy telescope charged particle experiment

The Low Energy Telescope (LET) experiment on board the Phobos 1 and 2 spacecraft measures the flux, energy spectra and elemental composition of solar energetic particles and cosmic ray nuclei from hydrogen up to iron in the energy range ≈1 to ≈75 MeV/n. The LET sensor system comprises a double d E/d X vs E solid-state detector telescope surrounded by a cylindrical plastic scintillator anticoincidence shield, and the instrument is equipped with a comprehensive particle identifier and even priority system that enables rare nuclei to be analysed in preference to the more common species. Isotope separation for light nuclei such as He is also achieved. The sensor is mounted on a rotating platform to enable coarse anisotropy measurements of low energy protons to be made.

The giant dipole resonance of mass-15 nuclei and the 12C(3He,γ0)15O and 11B(α,γ0)15N reactions

The angular distributions of the 11B(α,γ0)15N and 12C(3He, γ0)15O reactions have been measured at several energies over the giant dipole resonance (GDR) of the two residual nuclei. The 90° yield curve of the 11B(α,γ0)15N reaction has been remeasured with improved energy resolution over the energy ranges Eα = 6.89 – 8.0 and 12.8 – 15 MeV. The γ-rays were detected by a 23-cm long × 23-cm diameter NaI(Tl) crystal spectrometer enclosed in a plastic scintillator anticoincidence shield. Spins and parities of the resonances observed in the yield curves were obtained; the structure previously observed in the yield curve of the 11B(α, γ0)15N reaction between Eα = 7 and 8 MeV has been resolved into two peaks.

The 11B(d,γ0)13C reaction in the region of the giant dipole resonance

The 90° differential cross section of the 11B(d,γ0)13C reaction has been measured at deuteron energies from 1.95 to 12.0 MeV in steps varying from 100 to 200 keV. The γ-rays have been detected by a 23 cm long × 23 cm diameter NaI(Tl) crystal spectrometer enclosed in a plastic scintillator anticoincidence shield. The yield curve shows a resonant structure at the energies Eexe = 20.4 ± 0.1 and 22.0 ± 0.2 MeV.

The 11B(α,γ0)15N reaction in the giant dipole resonance region

The 90° differential cross section of the 11B(α,γ0)15N reaction has been measured at α-particle energies from 5.74 to 17.80 MeV. The γ rays have been detected by a 23 cm long × 23 cm diameter NaI(Tl) crystal spectrometer enclosed in a plastic scintillator anticoincidence shield. The yield curve shows three well separated resonances at Eexc = 16.29 ± 0.15, 18.88 ± 0.20, and 21.26 ± 0.20 MeV.

Radiative deuteron capture in 13C

The 90 differential cross section of the 13C(d, γ0)15N reaction has been measured at deuteron energies from Ed = 2.90 to 9.95 MeV in steps of 200 keV. Angular distributions have been obtained at Ed = 3.28, 3.96, 4.30, 4.76, 5.32, 5.92, 6.23, 6.63 and 7.94 MeV. The γ-rays have been detected with a 23 cm long by 23 cm diameter NaI(Tl) crystal spectrometer enclosed in a plastic scintillator anticoincidence shield. The γ-ray yield curve decreases monotonically with energy and shows a resonant behaviour at Ed = 6.65 MeV (Ex = 21.9 MeV) and a wide structure at Ed = 8.8 MeV(Ex ≈ 23.8 MeV). The angular distributions are consistent with the hypothesis that states with quantum numbers Jπ = 12+and32+ are excited in the capture process followed by emission of E1 radiation. There is also evidence of M1/E2 transitions over the whole energy region investigated.

University of Cambridge Natural Radiocarbon Measurements XIV

The dates presented in this paper comprise results of determinations made at the University Radiocarbon Dating Research Laboratory, mostly during the latter half of 1974. Radioactivity was measured with proportional counters using pure carbon dioxide at 2 atmospheres pressure as filling gas. Effects of cosmic and local environmental radiation on the counters were reduced by surrounding them completely with 1) a plastic scintillator anticoincidence shield, 7.5cm thick, viewed by 2 photomultiplier tubes operating in coincidence mode, the output pulses of which were in anticoincidence with the proportional counters signals, and 2) by a 17.5 ton lead castle.

University of Cambridge Natural Radiocarbon Measurements XIII

The dates presented here were calculated from measurements made at the University Radiocarbon Dating Research Laboratory mostly during 1973–74. The radioactivity of the samples was counted in gas proportional detectors, either silica lined (de Vrieset al, 1959) or of pure copper, filled to 2 atmospheres pressure with pure carbon dioxide. The detectors were fixed in, and completely surrounded by, a plastic scintillator anticoincidence shield mounted inside a massive lead shield to protect against environmental radiation (Switsur, Hall and West, 1970). Modern sample gas was obtained from the combustion of ad 1845 to 1855 rings of an oak tree grown near Cambridge and felled in 1950. Background samples were prepared from Welsh anthracite. The contemporary sample was frequently compared with the activity of the NBS oxalic acid international standard. Age calculations were based on the14C half-life of 5568 years and the uncertainty stated as one standard deviation calculated from the statistical analyses of sample and standards counting rates.

The reaction in the region of the giant dipole resonance

Abstract The 90° yield of the 9 Be(d , γ 0 ) 11 B reaction has been measured at deuteron energies ranging from 2.86 to 11.92 MeV in steps of 250 keV. Angular distributions have been obtained at Ed = 2.96, 6.87, 8.89 and 9.65 MeV. The γ-rays have been detected with a 23 cm × 23 cm NaI(Tl) crystal spectrometer enclosed in a plastic-scintillator anticoincidence shield. Evidence of structure has been observed in the excitation curve at Ed ≈ 3.4 and 9.65 MeV corresponding to excitation energies Eexc = 18.6 and 23.7 MeV, respectively. The angular distributions are typical of E1 transitions with a maximum at θL ≈ 90°. A calculation of the differential cross section of the inverse reaction, considered as a one-step direct process, gives results incompatible with the experiment and suggests that the 9 Be(d ,γ 0 ) 11 B reaction proceeds through excitation of the T = 1 2 component of the giant dipole resonance in 11B.

A new NaI gamma-ray spectrometer

An improved NaI gamma-ray spectrometer has been developed for the detection of 10–40 MeV gamma rays. It consists of a 25.4 cm diameter × 25.4 cm long NaI cylinder surrounded by a plastic scintillator anticoincidence shield which is 10.8 cm thick. An energy resolution of 3.2% fwhm has been achieved for 15 MeV gamma rays. It has also been observed that the uniformity of pulse-height response in large plastic scintillators with polished surfaces is far superior to that of scintillators with surfaces which are painted white.

Differential Energy Spectra of Low-Energy (<8.5 MeV per Nucleon) Heavy Cosmic Rays during Solar Quiet Times

Explorer 47 satellite observations of carbon, oxygen, and heavier nuclei differential energy spectra below 8.5 MeV/nucleon are presented for solar quiet time periods. A dE/dx vs E method for particle identification and energy determination was used. The instrumentation telescope included an isobutane proportional counter, a surface barrier Si detector, and a cylindrical plastic scintillator anticoincidence shield. The observations were performed outside the bow-shock and in the ecliptic plane. Results show an anisotropy of about 25% at 22 degrees west of the sun with a C/O ratio of 0.5 supporting a solar origin. The low energy portions of the C and O spectra have steep negative slopes, and the corresponding power law is given. Peculiarities in the O spectrum are discussed.

A Low Background Beta Counter with a Plastic Scintillator Anticoincidence Shield

The design and performance of a low background beta counter is described. The counter consists of a central gas flow proportional counter surrounded by a large plastic scintillator anticoincidence shield.