Characterization of liquid scintillation detectors

Five scintillation detectors of different scintillator size and type were characterized. The pulse height scale was calibrated in terms of electron light output units using photon sources. The response functions for time-of-flight (TOF)-selected monoenergetic neutrons were experimentally determined and also simulated with the NRESP code over a wide energy range. A comparison of the measured and calculated response functions allows individual characteristics of the detectors to be determined and the response matrix to be reliably derived. Various applications are discussed.     

Metrological support of fast wide-range scintillation detectors

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 51–52, June, 1992.     

Efficiency calibration of large volume liquid scintillation detectors

An array of seven large (10 cm thick by 20 cm diameter) NE213 scintillation detectors for use in neutron time-of-flight experiments has been calibrated to determine a matrix of relative detection efficiency as a function of incident neutron energy and detector bias. This matrix is then used to determine the relative efficiency for neutron groups in time-of-flight spectra to which an efficiency-optimizing dynamic bias has been applied.     

A study of light collection efficiency in scintillation detectors

A group of computer programs was set up to study the light of collection efficiency in scintillation detectors with rectangular cross sections. The input conditions can be chosen arbitrarily, including: the size, light attenuation length and refraction index of the scintillator and light guide, the refraction index of the coupling medium, the reflection characteristics of the walls, and the position of light sources. A few examples are discussed in this article.     

Kinetics of excitation in TL and OSL detectors

Kinetic equations for the semi-localized transitions (SLT) model are presented describing charge carrier’s kinetics for the excitation and fast relaxation stages. The formulation allows for dose dependence studies of thermoluminescence (TL) and optically stimulated luminescence (OSL) detectors based on the SLT model. The sets of equations were solved numerically demonstrating temporal evolution of all variables of the SLT model during excitation and fast relaxation. The influence of the dose rate on excitation kinetics is shown.     

Instrumentation for multistep excitation of lithium atoms to Rydberg states

We have developed a diode laser apparatus to excite Li from its ground 2S state, through 2P and 3S, to its Rydberg states with three cw diode lasers operating at λ = 671 nm, 813 nm, and 630-635 nm. A He-Ne laser at λ = 633 is sometimes used in place of the 635-nm diode laser for the last step. The output power of each of these lasers was ~1 mW. We describe our technique of locking the first two lasers on Li resonance lines by obtaining a fluorescent signal from the second decay (3S ? 2P) that is normally overpowered by a strong background of fluorescent light from the first decay (2P ? 2S). We used two balanced photodiodes to reject the strong fluorescent light without loss of collection efficiency. A rejection ratio as high as 100 has been obtained.     

An empirical formula for the impact excitation coefficient of xenon-filled scintillation counters

The dependence of the light output of a xenon-filled proportional scintillation counter on the electric field intensity and on the pressure of xenon has been investigated. An empirical formula for the impact excitation coefficient has been suggested.     

Performance of a neutron multiplicity filter composed of six liquid scintillation detectors

A neutron multiplicity filter was constructed to investigate the excited states in neutron-deficient nuclei produced via heavy-ion reactions. The arrangement and the performance of the system are discussed and the usefulness of the system is demonstrated.     

On improving the track development properties of soda glass detectors

A detailed study of track development properties of soda glass detectors is carried out by varying the etching parameters, i.e. etching time, etchant temperature and the composition of the etching solution. The etch product layer (EPL) which mainly limits the sensitivity of these detectors is dissolved chemically as soon as it is formed. The largest observable etch pit diameter by the use of this method is almost double the one obtained using HF. Room temperature (39 ± 1)°C appears to be the optimum temperature for etching of soda glasses in this solution. The spectrometric response of soda glasses to fission fragments of ²⁵²Cf has also been studied, using this solution. The energy resolution of soda glass detectors is seen to improve and become comparable with the energy resolution of phosphate glass detectors.     

Doping of glass with lithium ion

Doping of glass with lithium ion can be accomplished by exposing the glass to a solution of organic solvent containing a soluble lithium ion salt, such as LiBr and a small amount of water. Under such conditions, the activity of solvated Li+ is very high causing it to partition into the hydrated glass surface. Laser-induced breakdown spectroscopy and atomic absorption spectroscopy have been used to monitor the partitioning between glass and organic phase, respectively.     

Use of ferroelectric-crystal detectors for electron dosimetry

A ferroelectric detector system was designed for measurement of dose rate in high-energy electron beams. It was found that a simple lead zirconate-titanate ceramic responds reproducibly to a chopped electron beam by ferroelectric conversion of the resulting pulsed temperature rise to a proportional output voltage. Response as a function of dose rate is linear, the rate of response being a function of incident energy. As a calorimetric dose-rate meter the detector is responsive with response improving as energy is reduced. The detector can be used over a broad range of energies not usually accessible with a single detector.     

Characteristics of the ATLAS and CMS detectors

The goal for the detection of new physics processes in particle collisions at Large Hadron Collider energies, combined with the broad spectrum of possibilities for how the physics might be manifest, leads to detectors of unprecedented scope and size for particle physics experiments at colliders. The resulting two detectors, ATLAS (A Toroidal LHC ApparatuS) and CMS (compact muon spectrometer), must search for the new physics processes within very complex events arising from the very high-energy collisions. The two experiments share many basic design features-in particular, the need for very selective triggering to weed out the bulk of the uninteresting events; the order in which detector types are arrayed in order to provide maximum information about each event; and the very large angular coverage required to constrain the energy carried by any non-interacting particles. However, within these basic constraints, the detectors are quite different given the different emphases placed on issues such as resolution and background rejection. Both common features and the distinct differences will be presented.     

Improved response function calculations for scintillation detectors using an extended version of the MCNP code

The analysis of (e,e′n) experiments at the Darmstadt superconducting electron linear accelerator S-DALINAC required the calculation of neutron response functions for the NE213 liquid scintillation detectors used. In an open geometry, these response functions can be obtained using the Monte Carlo codes NRESP7 and NEFF7. However, for more complex geometries, an extended version of the Monte Carlo code MCNP exists. This extended version of the MCNP code was improved upon by adding individual light-output functions for charged particles. In addition, more than one volume can be defined as a scintillator, thus allowing the simultaneous calculation of the response for multiple detector setups. With the implementation of ¹²C(n,n′3α) reactions, all relevant reactions for neutron energies E_n<20 MeV are now taken into consideration. The results of these calculations were compared to experimental data using monoenergetic neutrons in an open geometry and a ²⁵²Cf neutron source in the complex Darmstadt setup, where in both cases excellent agreement was found.     

Containerless processing of a lithium disilicate glass

Glasses of Li₂O · 2SiO₂ (LS₂), and LS₂ doped with 0.001 wt% platinum (LS₂ + 0.001 wt% Pt) compositions were melted, cooled and reheated at controlled rates while levitated (containerless) inside an electrostatic levitator (ESL) furnace at the NASA Marshall Space Flight Center. The experiments were conducted in vacuum using spherical, 2.5–3 mm diameter, glass samples. The measured critical cooling rate for glass formation, R _c, for the LS₂ and LS₂ + 0.001 wt% Pt glasses processed at ESL were 14 ± 2 °C/min and 130 ± 5 °C/min, respectively. The values of R _c for the same LS₂ and LS₂ + 0.001 wt% Pt glasses processed in a container were 62 ± 3 °C/min and 162 ± 5 °C/min, respectively. The effective activation energy for crystallization, E, for this LS₂ glass processed without a container at ESL, was higher than that for an identical glass processed in a container. These results suggest that the glass formation tendency for a containerless LS₂ melt is significantly increased compared to an identical melt in contact with a container. The absence of heterogeneous nucleation sites that are inherently present in all melts held in containers is believed to be the reason for the increased glass forming tendency of this containerless melt.     

Study of lithium behaviour in Si(Li) detectors

In this paper we describe the fabrication of a conventional lithium compensated silicon detector (Si(Li)) realized on Topsil silicon with bulk resistivity 0.9 to , using the process of ion drift introduced by Pell. Preliminary results of electrical and nuclear characterization are shown. A leakage current value of 4 pA is obtained under reverse bias voltage of , at pressure of and 113 K. An alpha test using triple source ²⁴¹Am, ²³⁹Pu, ²³³U was carried and a resolution on ²⁴¹Am peak around 42 keV was obtained with this type of detector. The fabricated detector present a good electrical and nuclear characteristics that can be used in X-ray spectrometry and widespread applications in research science, environment monitoring and natural radioactivity. The main contribution of this work is the demonstration of an easy-to-implement, low cost detector set that can be achieved with an inexpensive n⁺p diode.