Performance of a BGO calorimeter with photodiode readout and with photomultiplier readout at energies up to 10 GeV

Bismuth germanate (BGO) calorimeter arrays, consisting of up to 12 elements of 30 × 30 × 200 mm³ have been tested at the CERN PS with pions and electrons of up to 10 GeV/c momentum, and at SIN with pions, electrons and protons up to 450 MeV/c. Both photomultiplier (PM) and photodiode (PD) readouts were used. Accurate calibration in the 100 MeV energy range was achieved with stopping protons, stopping pions and minimum ionizing pions. With 212 MeV electrons and PM readout, a time resolution of the BGO signal of 640 ps fwhm has been measured. The energy resolution for electrons above 1 GeV (PD readout) was found to be roughly constant at σ/E ～ 1%. This is consistent with a negligible intrinsic resolution for BGO at these energies, after taking into account shower leakage and PD noise. For electrons of 92 and 200 MeV, we obtained (PM readout) energy resolutions close to the theoretical limit given by photon statistics and shower leakage. The electron/hadron separation was better than 1:500 over the energy range of 0.5 to 10 GeV, and improved to better than 1:1000 after a simple pattern cut. The energy deposition of the e.m. showers, both laterally and longitudinally (rear leakage), was found to be in agreement at the 0.1% level with Monte Carlo calculations using the SLAC-EGS program.     

Characteristics of a mini Drift chamber

The characteristics of a drift chamber with 3 mm drift gap were investigated at a particle beam momentum of 10 GeV/c. The chamber has good linearity of the drift characteristics. It was tested and could reliably work in a particle flux of ∼ 3 × 10⁵ s⁻¹ cm⁻². A spatial resolution of ∼ 45 μm in the centre of the drift gap has been achieved.     

Development of a Position Sensitive Neutron Detector with High Efficiency and Energy Resolution for Use at High-Flux Beam Sources

We are developing a high-efficiency neutron detector with 1 cm position resolution and coarse energy resolution for use at high-flux neutron source facilities currently proposed or under construction. The detector concept integrates a segmented ³He ionization chamber with the position sensitive, charged particle collection methods of a MicroMegas detector. Neutron absorption on the helium produces protons and tritons that ionize the fill gas. The charge is amplified in the field region around a wire mesh and subsequently detected in current mode by wire strips mounted on a substrate. One module consisting of a high-voltage plate, a field-shaping high-voltage plate, a grid and wire strips defines a detection region. For 100 % efficiency, detector modules are consecutively placed along the beam axis. Analysis over several regions with alternating wire strip orientation provides a two-dimensional beam profile. By using ³He, a 1/v absorption gas, each axial region captures neutrons of a different energy range, providing an energy-sensitive detection scheme especially useful at continuous beam sources.     

A detection system using drift chambers for the SPES4 spectrometer at Laboratoire National Saturne

We describe the “drift chamber” detection setup of SPES4, the 4 GeV/c spectrometer at Laboratoire National Saturne. The particle identification is performed by combining magnetic rigidity selection with energy loss and time of flight measurements. This allows to separate analysed isotopes from Z = 1 to at least Z = 10 up to a rigidity of 4 GeV/c. A charge resolution of ΔZ_rms = 0.1 and a time resolution of Δt_rms = 120 ps for ¹⁸Ne at about 3 GeV/c per Z are easily obtained. Two sets of multiwire drift chambers are used to measure and reconstruct the particle trajectories at the output of the system. A position resolution better than Δx_rms = 160 μm can be achieved in the focal plane. This corresponds to a momentum resolution of Δδ_rms = 0.22 × 10⁻⁴. The performances of SPES4 (Δδ_rms = 2.2 × 10⁻⁴) can then be wholly exploited.     

The argus time-of-flight system

The time-of-flight system of the ARGUS detector at the DORIS e⁺e^? storage ring consists of 64 barrel scintillation counters covering 75% of 4π, and 2 × 48 end cap counters, covering 17% of 4π. The barrel counters are viewed by two phototubes each, while the end cap counters have one tube only. The time-of-flight system serves as a part of the fast trigger and identifies charged particles. The time resolution achieved during the first year of ARGUS operation is 210 ps for Bhabhas (which are used for the off-line monitoring of the system), and 220 ps for hadrons, both in barrel and end cap counters. This converts into a three standard deviation mass separation up to 700 MeV/c between pions and kaons and 1200 MeV/c between kaons and protons. Electrons can be separated from heavier particles up to 230 MeV/c.     

Production of muons for fusion catalysis using a migma configuration

Muon-catalyzed fusion requires a very efficient means of producing muons. We describe a muon-producing magnetic-mirror scheme with triton migma that may be more energy efficient than any heretofore proposed. If one could catalyze 200 fusions per muon and employ a uranium blanket that would multiply the neutron energy by a factor of 10, one might produce electricity with an overall plant efficiency (ratio of electric energy produced to nuclear energy released) approaching 30%.The self-colliding arrangement of triton orbits will result in many π⁻'s being produced near the axis of the magnetic mirror. The pions quickly decay into muons, which are transported into a small (few cm diameter) reactor chamber producing approximately 1 MW/m² neutron flux on the chamber walls.     

How to use electrodeless drift chambers in experiments at accelerators

Several types of wide-gap electrodeless drift chambers, including those with dimensions 1×1 m², have been tested at accelerator beams. The chambers work with high efficiency (>99%), good spatial resolution (σ = 0.2−0.4 mm) and good linearity at flux rates up to 2×10⁵ particles⁻¹ per wire in spill, which corresponds to 3×10⁶ particles/s m² on colliders.It is shown that at the proper mode of operation beam intensity oscillations within the range of up to 4×10⁵ particles/spill per wire do not affect the chamber efficiency.     

On the possibility of increasing the efficiency of pion therapy for cancer

It is suggested that cancer cells be killed by combining the bombardment of a tumor with pions and the introduction of uranium in the tumor. A minimum concentration of U²³⁸ in the tumor that is necessary for significantly increasing the therapeutic effect of pion bombardment is estimated to be within 3.4 × 10^?2 ? 1.1 × 10^?1 g/cm³.     

The possibility of using antiproton annihilation on uranium and thorium nuclei for killing cancer cells

It is proposed to kill cancer cells by a combined treatment involving the bombardment of a tumor with antiprotons and the introduction of U²³⁸ or Th²³² isotopes into the tumor. A minimum density of fissile elements in the tumor that is necessary for significant improvement of the action of antiproton bombardment is estimated approximately as (1.7–3.4) × 10^?2 g/cm³ for U²³⁸ and (1.7–3.3) × 10^?2 g/cm³ for Th²³².     

Irradiation effects on AlGaN HFET devices and GaN layers

AlGaN/GaN heterostructure field effect transistors (HFETs) were irradiated with protons as well as carbon, oxygen, iron and krypton ions of high (68 and 120 MeV) and low (2 MeV) energy with fluences in the range from 1 × 10⁷ to 1 × 10¹³ cm^?2. High energy irradiation with protons, carbon and oxygen produced no degradation in devices while krypton irradiation at the fluence of 1 × 10¹⁰ cm^?2 resulted in a small reduction of 2% in the transconductance. Similarly, for GaN samples irradiated with protons, carbon and oxygen at high energy no changes were seen by XRD, PL and Hall effect, while changes in lattice constant and a reduction in PL intensity were observed after irradiation with high energy krypton. Low energy irradiation with carbon and oxygen at a fluence of 5 × 10¹⁰ cm^?2 results in small change in the device performance while remarkable changes in device characteristics are seen at a fluence of 1 × 10¹² cm^?2 for carbon, oxygen, iron and krypton irradiation. Similarly changes are also observed by XRD, PL and Hall effect for the thick GaN layer irradiated at the fluence of 1 × 10¹² cm^?2. The device results and GaN layer properties are strongly correlated.     

Studies of photon induced desorption of surface gas within an aluminium vacuum chamber using an X-ray source

The role of photon induced desorption of gases arising from hard X-rays has been investigated within a vacuum chamber of aluminium alloy (Extrudal) as proposed for the new European LEP accelerator. The radiation was derived from a commercial 100 kV X-ray unit, and was introduced into the test chamber of length around 1 m by means of an end window formed of aluminium foil 25 ωm thick. In this manner a photon flux density of up to some 10⁹ photons cm² s^?1 irradiated a total surface area of around 4 × 10³ cm². The mean energy of the radiation was continuously variable in the range 9–30 keV. Measurements of desorption efficiency appropriate to each species of desorbed gas have been carried out with chamber pressures at around 1.5 × 10^?8 and 5 × 10^?11 torr attained, respectively, with evacuation at room temperature and following bakeout at 150°C. Studies have further been extended to assess the contribution of the pretreatment of the chamber by glow discharge cleaning in argon gas. In all cases the desorbed gas species under irradiation are predominantly H₂ and CO₂ which contribute in excess of 80% of the total desorption. The relative preponderance of these species is influenced by the treatments of bakeout and glow discharge cleaning, although the total desorption efficiency at around 10^?1 mol photon^?1 is not strongly affected by these actions. The desorption efficiencies of all species and at all stages of preparation of the chamber are found to decrease with increasing mean energy of the radiation, a factor of reduction of one third being observed over the range of energies available in the test.     

Evaluation of the pull-out test to determine strength of in-situ concrete

A degree of correlation exists between compressive strength of 6×12-in (15×30-cm) concrete cylinders cured under standard conditions and pull-out strength of concrete cured under field conditions. The ratio pull-out strength: compressive strength varies directly with the compressive strength of concrete. At 3 days, this ratio varies from 18% for 4 795 (32.9 MN/m²) concrete to 46% for 1 145 psi (7.9 MN/m²). However, for any strength level the ratio does not change significantly with age. For the same concrete mix, the pull-out strength increased with increasing age, indicating the possible usefulness of these tests for comparative studies. The 28-day standard deviation and coefficient of variation of strength from pull-out test results varied from 15 to 45 psi (0.10 to 0.31 MN/m²) and from 2.3 to 5.0% respectively. The corresponding values from compressive strength test results were 4 to 120 psi (0.03 to 0.82 MN/m²) and 0.2 to 3.0% respectively, except for one mix for which the above values were 680 psi (4.7 MN/m²) and 11.4%.     

Studies of photon induced gas desorption using synchrotron radiation

In view of finalizing the design of the vacuum system of the Large Electron and Positron Storage Ring (LEP) we have studied synchrotron radiation induced neutral gas desorption. A 3 m section of an aluminum vacuum chamber has been exposed to the photon beam emerging from the electron storage ring DCI in Orsay, under conditions closely simulating the environment in a particle acceletor. In order of importance the gases desorbed were H₂, CO₂, CO and CH₄ with H₂O practically absent. Under the experimental conditions of an unbaked chamber and 11 mrad glancing incidence of the photons, the initial molecular desorption yields for these gases were typically 0.5, 8 × 10^?2, 2 × 10^?2 and 8 × 10^?3 molecules per photon respectively. These values could be reduced by about 1 to 2 orders of magnitude during continued photon exposure and most cases without evidence that this ‘beam cleaning action’ would be limited. After exposure to air and pumpdown of the previously cleaned chamber, we observe a significant memory effect. The dependence of the photon desorption on the angle of incidence has been studied down to a glancing angle of 11 mrad showing a definite deviation from the previously assumed 1/sin ø scaling. The implications of the results in terms of the expected beam-gas lifetime in LEP are discussed.     

A large aperture spectrometer at Fermilab to study high mass dimuons

A large acceptance forward spectrometer located in a unique antiproton enriched beam has been used at Fermi National Accelerator Laboratory by Experiment 537 to study the production of high mass muon pairs. When the beam was operated at a momentum of 125 GeV/c, it had a flux of 1.5 × 10⁷ particles per second of which 18% were antiprotons. The spectrometer was of closed geometry design and used drift chambers as the tracking elements. Operating over a relatively short period, the experiment accumulated the largest sample of antiproton-induced high mass dimuons of any experiment to date. The contamination of this data by pion-induced dimuons was less than 0.5%.     

A mercury jet as gas target window for high current beams

A mercury vapour jet is used to seal a 1 cm² aperture between a gas volume (“target chamber”) and the beam-line system. The possible pressure differences and the leakage related to the different target gas pressures have been investigated. Pressure gradients from 10¹ to 10⁻³ mbar and leakages of less than 3×10⁻³ mbar 1/s have been observed. The maximum target pressure was p_T=36 mbar.     

Potential sputtering of hydrogen atoms on various surfaces with slow highly-charged ions

Several recent findings on a new sputtering mechanism of hydrogen with slow highly-charged ions are discussed. The sputtering yields of protons were proportional to q^∼5 for q≲10 independent of the surface condition for both untreated and well-defined surfaces, where q is the charge state of the ion. This q^∼5 dependence started to level off for q≲10. The yield for the Si(100)1×1–H surface was ten times larger than that for the Si(100)2×1–H surface although the stoichiometric hydrogen abundance of the former is only twice that of the latter. The key quantity to govern the yield is proposed to be surface roughness, which also influences the energy distribution of sputtered protons. These findings were consistently explained with a pair-wise potential sputtering model involving two successive electron transfers which follow the classical over barrier mechanism.     

In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

Development of an inconel self powered neutron detector for in-core reactor monitoring

The paper describes the development and testing of an Inconel600 (2 mm diameter×21 cm long) self-powered neutron detector for in-core neutron monitoring. The detector has 3.5 mm overall diameter and 22 cm length and is integrally coupled to a 12 m long mineral insulated cable. The performance of the detector was compared with cobalt and platinum detectors of similar dimensions. Gamma sensitivity measurements performed at the ⁶⁰Co irradiation facility in 14 MR/h gamma field showed values of −4.4×10⁻¹⁸ A/R/h/cm (−9.3×10⁻²⁴ A/γ/cm²-s/cm), −5.2×10⁻¹⁸ A/R/h/cm (−1.133×10⁻²³ A/γ/cm²-s/cm) and 34×10⁻¹⁸ A/R/h/cm (7.14×10⁻²³ A/γ/cm²-s/cm) for the Inconel, Co and Pt detectors, respectively. The detectors together with a miniature gamma ion chamber and fission chamber were tested in the in-core Apsara Swimming Pool type reactor. The ion chambers were used to estimate the neutron and gamma fields. With an effective neutron cross-section of 4b, the Inconel detector has a total sensitivity of 6×10⁻²³ A/nv/cm while the corresponding sensitivities for the platinum and cobalt detectors were 1.69×10⁻²² and 2.64×10⁻²² A/nv/cm. The linearity of the detector responses at power levels ranging from 100 to 200 kW was within ±5%. The response of the detectors to reactor scram showed that the prompt response of the Inconel detector was 0.95 while it was 0.7 and 0.95 for the platinum and cobalt self-powered detectors, respectively. The detector was also installed in the horizontal flux unit of 540 MW Pressurised Heavy Water Reactor (PHWR). The neutron flux at the detector location was calculated by Triveni code. The detector response was measured from 0.02% to 0.07% of full power and showed good correlation between power level and detector signals. Long-term tests and the dynamic response of the detector to shut down in PHWR are in progress.