Microcalorimeter design for fast-neutron spectroscopy

We are developing microcalorimeters for fast-neutron spectroscopy. The goal is to develop a detector with an energy resolution of 0.1% for 1–20 MeV neutrons with an efficiency of 1%. We discuss the design of such a detector and present the first results of a transition edge sensor based microcalorimeter with a small TiB₂ absorber. The best energy resolution obtained was 5.5 keV FWHM for a total energy deposition of 2.792 MeV by thermal neutrons.     

Application of CLTD’s for High Resolution Mass Identification and for Stopping Power Measurements of Heavy Ions

An array of calorimetric low temperature detectors (CLTD’s) for energy sensitive detection of heavy ions was combined with time-of-flight (TOF) detectors to obtain a detector system for high resolution mass identification of low energy heavy ions. In addition the same setup was used to prove the ability of CLTD’s to be used in electronic stopping power measurements for heavy ions in matter. Experiments with 50?MeV ⁶³Cu and ⁶⁵Cu ions at the tandem accelerator at the MPI at Heidelberg, and with 25 to 250?MeV ²³⁸U ions at the UNILAC accelerator at GSI at Darmstadt have been performed. For ^63,65Cu at 50?MeV a mass resolution of Δm(FWHM)=0.9?amu, and for ²³⁸U in an energy range of 65 to 150?MeV a resolution of Δm(FWHM)=1.28?amu, was obtained. The results for stopping powers of ²³⁸U in carbon and gold are presented and compared with theoretical predictions and data from the literature.     

Capture-gated neutron spectrometry

The applications of a new inorganic scintillator, lithium gadolinium borate, to neutron dosimetry and spectroscopy, are described. A dosimeter using this material registers, in separate energy bins, thermal, epithermal and MeV neutrons. A spectrometer for MeV neutrons has a calculated energy resolution of 10% FWHM.     

Experimental determination of absolute efficiency and energy resolution for NaI(Tl) and germanium gamma ray detectors at energies from 2.6 to 16.1 MeV

Measurements have been made to characterize the response of NaI(Tl) and Ge(Li) gamma ray detectors to gamma rays in the energy range of 2.6 to 16.1 MeV. Both absolute efficiency and energy resolution are reported. At 16.1 MeV the absolute full energy efficiency of a 10 cm × 10 cm NaI(Tl) detector is about 2% and the energy resolution is also about 2%. For a 65 cm³ Ge(Li) detector, the full energy peak absolute efficiency at 16.1 MeV is 0.2% (the escape peak efficiencies are 5 times larger), and the fwhm energy resolution is about 0.1%.     

Performance of a scintillating glass calorimeter for electromagnetic showers

A scintillating glass electromagnetic calorimeter consisting of 3 × 3 moduls of 8 × 8 × 66 cm³ each has been studied with electrons in the energy interval 14.7 MeV < E < 6000 MeV. An energy resolution of σ_E/E[%] = √1.6²/E[GeV] + 1.0² was achie spatial resolution turns out to be of the order σ = 4 to 8 m depending on the impact point and the angle of incidence; it improves with increasing energy. The observations are in excellent agreement with the result of an EGS Monte Carlo simulation of the detector including optical effects and photoelectron statistics.     

Ultra-high Resolution Alpha Particle Spectrometry with Transition-Edge Sensor Microcalorimeters

Alpha particle spectrometry is a powerful analytical tool for nuclear forensics and environmental monitoring. Microcalorimeter detectors have been shown to yield nearly an order of magnitude better energy resolution (1.06?keV FWHM at 5.3?MeV) than current state-of-the-art silicon detectors (8–10?keV FWHM at 5.3?MeV). This superior resolution allows isotopic analysis with a single non-consumptive measurement of samples that contain multiple radioisotopes with overlapping alpha energies. Measurement of such a sample with a silicon detector would require expensive and time-consuming radiochemical separations. We are developing two alpha spectrometer systems with superconducting transition-edge sensor microcalorimeters. The first system has eight independent detector channels that measure eight different alpha sources, and is optimized for detector development experiments. The second system incorporates a prototype cryogenic load lock that allows for rapid exchange of alpha samples. This paper will present results from these two systems.     

H+ and He+ spectroscopy using silicon pin photodiodes

Silicon PIN photodiodes have been used in detecting H⁺ and He⁺ ions from a 1 MeV accelerator. Energy resolutions (FWHM) from 2.0 keV (at 16 keV) to 4.7 keV (at 1 MeV) for H⁺ and from 3.4 keV (at 22 keV) to 9.8 keV (at 700 keV) for He⁺ have been measured at room temperature. Resolution measurements over this energy range using a premium PIPS detector have also been performed. A comparison between the two detectors shows that the photodiodes exhibit better energy resolution over the whole energy range for H⁺, and comparable resolution for He⁺. It is argued that the resolution of the photodiode can be further improved by manufacturing a device with thinner entrance window.     

Development of cryogenic alpha spectrometers using metallic magnetic calorimeters

Cryogenic particle detectors have recently been adopted in radiation detection and measurement because of their high energy resolution. Many of these detectors have demonstrated energy resolutions better than the theoretical limit of semiconductor detectors. We report the development of a micro-fabricated magnetic calorimeter coupled to a large-area particle absorber. It is based on a planar, 1 mm² large paramagnetic temperature sensor made of sputtered Au:Er, which covers a superconducting meander-shaped pickup coil coupled to a low-noise dc-SQUID to monitor the magnetization of the sensor. A piece of gold foil of 2.5×2.5×0.07 mm³ was glued to the Au:Er film to serve as an absorber for incident alpha particles. The detector performance was investigated with an ²⁴¹Am source. The signal size comparison for alpha and gamma peaks with a large difference in energy demonstrated that the detector had good linear behavior. An energy resolution of 2.83±0.05 keV in FWHM was obtained for 5.5 MeV alpha particles.     

The High-Resolution X-Ray Microcalorimeter Spectrometer, SXS, on Astro-H

The science and an overview of the Soft X-ray Spectrometer onboard the STRO-H mission are presented. The SXS consists of X-ray focusing mirrors and a microcalorimeter array and is developed by international collaboration lead by JAXA and NASA with European participation. The detector is a 6×6 format microcalorimeter array operated at a cryogenic temperature of 50 mK and covers a 3′×3′ field of view of the X-ray telescope of 5.6 m focal length. We expect an energy resolution better than 7 eV (FWHM, requirement) with a goal of 4 eV. The effective area of the instrument will be 225 cm² at 7 keV; by a factor of about two larger than that of the X-ray microcalorimeter on board Suzaku. One of the main scientific objectives of the SXS is to investigate turbulent and/or macroscopic motions of hot gas in clusters of galaxies.     

High-resolution short range ion detectors based on 4H-SiC films

The energy resolution of SiC detectors has been studied in application to the spectrometry of α particles with 5.1–5.5 MeV energies. The Schottky barrier structure of the detector was based on a CVD-grown epitaxial n-4H-SiC film with a thickness of 26 μm and an uncompensated donor concentration of (1–2)×10¹⁵ cm^?3. An energy resolution of 0.5% achieved for the first time with SiC detectors allows fine structure of the α particle spectrum to be revealed. The average energy of the electron-hole pair formation in 4H-SiC is estimated at 7.71 eV.     

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.     

Deuterated anthracene spectrometer for 5–30 MeV neutrons

A neutron spectrometer consisting of a deuterated anthracene scintillation crystal and a pulse shape discriminator is described. Forward recoiling deuterons are selected by means of their pulse shape signatures, making use of the direction dependence of the pulse height response and scintillation decay characteristics of the crystal. The line shape of the spectrometer for monoenergetic neutrons is a single peak and the neutron energy resolution (FWHM) varies from 7% at 9 MeV to 3.5% at 22 MeV neutron energy.     

Development of a NaI(Tl) detector with superior photon energy resolution for use above 100 MeV

We have designed and tested a new high resolution NaI(Tl) total absorption scintillation counter. The detector is a cylinder composed of a 26.7 cm diameter by 55.9 cm long NaI core with a concentric 10.8 cm thick NaI annulus that is divided into quadrants. The NaI detector is surrounded by a 12.7 cm thick plastic scintillator to veto both cosmic rays and events with significant shower leakage from the NaI. High uniformity of light production and collection throughout the detector is required for superior resolution. The detector has a measured resolution of 1.3% and 1.7% FWHM for 130 MeV photons and 330 MeV electrons, respectively. Computer simulations to account for loss of resolution due to pileup and energy spread of the beam indicate that the ultimate experimental resolutions at these energies are 1.2±0.1% and 1.3±0.1%. The resolutions at these two energies are at least a factor of 2 better than that of any other total absorption scintillation counter available today. Based on shower simulations, the detector is expected to have a resolution of approximately 1.3% for collimated 130–2000 MeV photons.     

Time-of-flight neutron spectrometer for DT-plasma diagnostics

A novel technique for energy measurements of fusion neutrons from DT-plasmas has been investigated. The method is based on double interaction of neutrons in two scintillators and uses time-of-flight measurement. By using a deuterium based first detector and recording the backscattered neutrons the resolution is found to be 3.5% for 14 MeV neutrons with a flight path equal to 2 m.     

Modularized NaI(Tl) detectors in a half barrel configuration

We have constructed a modularized array of NaI(Tl) detectors in a half barrel configuration that is about 75 cm long with an inner radius of 25 cm. 96 NaI modules are surrounded by a layer of 48 modules of scintillating glass which have similar dimensions to the NaI modules. Each NaI crystal was shaped as a trapezoidal pyramid and encapsulated in a 1 mm thick aluminium container with dimensions of (43 × 94) × (110 × 94) × 377 mm³. The construction and performance are described along with the gain calibration and monitoring, the beam position sensitivity, the scattering between modules, etc. The fwhm energy resolution of a 5 × 5 array of NaI modules varied from 6.5% for incident electrons at 100 MeV to 3.6% at 1000 MeV     

Effects of proton escape on detection efficiency in thin scintillator elements and its consequences for optimization of fast-neutron imaging

Plastic scintillators are commonly used for neutron detection in the MeV energy range, based on n-p scattering and the subsequent deposition of recoil proton's kinetic energy in the detector material. This detection procedure gives a quasi-rectangular energy deposition distribution for mono-energetic neutrons, extending from zero to the neutron energy. However, if the detector sensitive element (DSE) is small, the energy deposition may be incomplete due to the recoil proton escape.In the application of neutron imaging, here exemplified by fast-neutron tomography, two conflicting requirements have been identified: (1) thin DSEs are required to obtain high spatial resolution and (2) energy discrimination may be required to reduce the influence of neutrons being scattered into the DSEs, which generally occurs at lower energies. However, at small DSE widths, the reduction of energy deposition due to recoil proton escape may cause a significant decrease in detection efficiency when energy discrimination is applied.In this work, energy deposition distributions in small-size DSEs have been simulated for Deuterium-Deuterium (DD; 2.5 MeV) and Deuterium-Tritium (DT; 14.1 MeV) fusion neutrons. The intrinsic efficiency has been analyzed as a function of energy discrimination level for various detector widths. The investigations show that proton recoil escape causes a significant drop in intrinsic detection efficiency for thin DSEs. For DT neutrons, the drop is 10% at a width of 3.2 mm and 50% at a width of 0.6 mm, assuming an energy threshold at half the incident neutron energy. The corresponding widths for a DD detector are 0.17 and 0.03 mm, respectively.Finally, implications of the proton escape effect on the design of a fast-neutron tomography device for void distribution measurements at Uppsala University are presented. It is shown that the selection of DSE width strongly affects the instrument design when optimizing for image unsharpness.     

Development of Electron Tracking Compton Camera using micro pixel gas chamber for medical imaging

We have developed the Electron Tracking Compton Camera (ETCC) with reconstructing the 3-D tracks of the scattered electron in Compton process for both sub-MeV and MeV gamma rays. By measuring both the directions and energies of not only the recoil gamma ray but also the scattered electron, the direction of the incident gamma ray is determined for each individual photon. Furthermore, a residual measured angle between the recoil electron and scattered gamma ray is quite powerful for the kinematical background rejection. For the 3-D tracking of the electrons, the Micro Time Projection Chamber (μ-TPC) was developed using a new type of the micro pattern gas detector. The ETCC consists of this μ-TPC (10×10×8 cm³) and the 6×6×13 mm³ GSO crystal pixel arrays with a flat panel photo-multiplier surrounding the μ-TPC for detecting recoil gamma rays. The ETCC provided the angular resolution of 6.6° (FWHM) at 364 keV of ¹³¹I. A mobile ETCC for medical imaging, which is fabricated in a 1 m cubic box, has been operated since October 2005. Here, we present the imaging results for the line sources and the phantom of human thyroid gland using 364 keV gamma rays of ¹³¹I.     

High Energy Resolution Cryogenic Alpha Spectrometers Using Magnetic Calorimeters

We report the recent progress on high resolution alpha spectrometers that use metallic magnetic calorimeters. The detector is composed of a meander-type magnetic calorimeter and a gold-foil absorber. The thermal connection between the magnetic sensor and the absorber consists of annealed gold wires. The signal rise time is found to be as expected, with the electronic thermal conductance of gold wires. The energy resolution of a 3.2?keV FWHM is obtained for 5.5?MeV alpha particles with possibilities for further improvements.     

Effect of neutron radiation on the photoelectric parameters of <Emphasis Type="Italic">p-n</Emphasis>-InSe structures

The effect of irradiation with fast reactor neutrons at an effective energy of 1 MeV and a fluence within Φ = 1 × 10¹⁴?5 × 10¹⁵ n/cm² on the photoelectric parameters of p-n-InSe homojunctions obtained in direct optical contact between p- and n-type semiconductors has been studied. The exposure to fast neutrons leads to an increase in the rectification coefficient and the diode ideality factor of the current-voltage characteristics with increasing neutron dose. No significant changes have been observed in the photosensitivity spectra of p-n-InSe structures irradiated to various doses, which allows these structures to be recommended for the creation of radiation-resistant photodetectors.     

A position-sensitive n-detector for neutron-fragment correlation measurements

A position-determining device has been developed for studying neutron emission in fission processes. The detector essentially consists of two photomultipliers at the ends of a cylinder of NE213 liquid scintillator (about 82 cm in length and 3 cm in diameter), yielding a position resolution of 8 cm and a time resolution of 1.2 ns for 3 MeV neutrons. The quality of the performance is illustrated by measuring the velocity and angular distributions of neutrons associated with the fission fragments from spontaneous fission of ²⁵²Cf. The experimental setup, adaptable for use with other neutron emitting fragments (e.g. heavy-ion reaction products), consisted of the position-sensitive n-detector, a thin scintillator film, and a solid-state detector.