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- This workshop was organized with the help
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- This workshop was organized with the help
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LIST of ABSTRACTS
| Scientific requirements and
prospects |
Gamma-ray Optics |
| Focal plane
instrumentation |
Ground facilities and
Flight systems |
Abrosimov Nikolai
Mosaic and gradient single crystals for gamma ray Laue lenses
One of the possible solutions on the way to gamma ray detection is a crystal diffraction lens telescope. In this case one can increase the collection area of gamma rays without to increase the detection area. There are some approaches to realize such telescope including Laue lens as diffracting unit. But the question is: what crystals could be used to build the lens?
Possible material candidates for the diffracting lens are bulk crystals of SiGe solid solutions both in form of mosaic crystals and gradient crystals. For example, two CLAIRE experiments were made using diffracting lens telescope consisted of 556 GeSi mosaic crystals (diffracting elements, 1x1 cm2) mounted in concentric rings. Recently SiGe gradient crystals were tested by R. Smither (Advanced Photon Source, Argonne National Laboratory) and the results will be presented on this conference.
This paper will describe the growth techniques used for the growth of SiGe single crystals and will give the comparison of some crystal parameters that are important for the gamma-ray lens application.Bastie Pierre
The basic principles of diffraction by crystals
Focusing of high energy X rays can be performed using crystal diffraction. However the choice of crystals is a delicate problem when a given angular resolution is required and a good efficiency is sought. In this talk, we shall give, in a qualitative way, some keys for driving the choice of the crystals.
First, the physical mechanism of the diffraction by the atoms will be recalled. Then the case of a periodic arrangment of atoms will be considered leading to the concepts of "the perfect crystal "and "the ideally imperfect crystal" allowing to define the extinction length and to introduce the two limiting cases : the dynamical and the kinematical theories for diffracted intensity calculations. In a next step, the mosaic crystal model will be presented and the old but useful notion of primary and secondary extinctions given. From these qualitative explanations, some possible ways to design efficient crystals to build an x-ray lens will be suggested though the most difficult stage will remain their elaboration.Ernst-Jan Buis
On and Off-Axis Response of Grazing Gamma-Ray Optics
If sensitive enough, future missions for nuclear astrophysics will be a great help in the understanding of supernovae explosions. In contrast to coded-mask instruments, both crystal diffraction lenses and grazing angle mirrors offer a possibility to construct a sensitive instrument to detect soft gamma-ray lines in supernovae. The most dominant gamma-ray line due to $^{56}$Ni decay in type-Ia supernovae has an energy of 158 keV. This line provides a natural objective for future missions with multilayer coated optics. An other line of interest is the positron-electron line at 511 keV, but might be out of reach for multilayers. We have studied various configurations of gamma-ray optics and determined the on and off axis response for optics in the 30-511 keV energy range. Moreover, we discuss the bandwidth of the optics. .
Courtois Pierre
Copper Mosaic Crystals for Laue Lens
A gamma Laue lens for astrophysical applications based on mosaic copper single crystals requires crystals of high quality, with a homogeneous intrinsic mosaic distribution of less than 30 seconds of arc at high diffracted energy (> 500 keV). Copper crystals being used in transmission geometry, the thickness of the crystals, which depends on the energy, needs to be optimized in order to obtain the maximum integrated intensity. The aim of this study is to show the feasibility of such a gamma Laue lens, which is a real challenge with regard to the growth and preparation of the copper crystals.
The X-ray diffraction properties of copper single crystals produced at I.L.L. were studied for x-ray energies ranging from 120 keV to 400 keV. It is shown that it is possible to grow large single crystals of copper with a uniform and very narrow intrinsic mosaic between 45 seconds and 5 minutes of arc. Several monocrystalline plates having different thickness and mosaic were then prepared from the as-grown crystals in order to measure their diffraction efficiency (peak and integrated intensity) as a function of energy. As expected, the value of the peak reflectivity (at constant x-ray energy) depends strongly on the thickness of the copper crystal and the integrated reflectivity depends strongly on the mosaic distribution. Extinction effects are also observed when measuring the width of the peak reflectivity as a function of the x-ray energy.
Some technical aspects on the preparation of copper single crystal plates are also discussed.Dante Roa
Development of a new photon diffraction imaging system for nuclear diagnostic medicine
The objective of this project is to develop and construct an innovative imaging system for nuclear medicine and molecular imaging that, by using photon diffraction, can be capable of generating 1-2 mm spatial resolution images in two or three dimensions. The proposed imaging system would be capable of detecting radiopharmaceuticals that emit 100-200 keV gamma rays which are typically used in diagnostic imaging in nuclear medicine and in molecular imaging. However, the system is expected to be optimized for the 140.6 keV gamma ray from a Tc-99m source which is frequently used in nuclear medicine. This new system will focus the incoming gamma rays in a manner analogous to a magnifying glass focusing sunlight into a small focal point on a detector's sensitive area. Focusing gamma rays through photon diffraction has already been demonstrated with the construction of a diffraction lens telescope for astrophysics and a scaled-down lens for medical imaging, both developed at Argonne National Laboratory (ANL). In addition, spatial resolutions of 3 mm have been achieved with a prototype medical lens. The proposed imaging system would be comprised of an array of photon diffraction lenses tuned to diffract a specific gamma ray energy (within 100 - 200 keV) emitted by a common source. The properties of photon diffraction make it possible to diffract only one specific gamma ray energy at a time, which significantly reduces scattering background. The system should be sufficiently sensitive to detecting small concentrations of radioactivity that can reveal potential tumor sites at their initial stages of development. Moreover, the system's sensitivity would eliminate the need for re-injecting a patient with more radiopharmaceutical if this patient underwent a prior nuclear imaging scan. Detection of a tumor site at its inception could allow for an earlier initiation of treatment which can increase the chances of patients' survival.
KEYWORDS: medical imaging, photon diffraction, radiopharmaceuticals, nuclear medicine.Frontera Filippo
HAXTEL: a Laue lens project for a deep exploration of the hard (>60 keV) X-ray sky
I will give an overview of the status of the HAXTEL project. In particular I will discuss its sceintific objectives of the project, the main features and criteria used for the Laues lenses we are developing, their development status, and the sensitivity expectations from multi-lens configurations in the 60 to 600 keV bandpass.
Halloin Hubert
Laue diffraction lenses for astrophysics : physics basis and simulations
The laws of X-ray diffraction in crystals have been written almost 100 years ago and are widely used in crystallography. Nevertheless, their application in atrophysics is much more recent, the requirements and constraints being specific to this field.
In this workshop, we will present the basics of X-ray diffraction in crystals and their application to Laue lenses in gamma-ray astrophysics. We will also underline the implications and specific constraints in gamma-rays. Finally, these theoretical predictions are compared with experimental data, through the use of Monte-Carlo simulations and the results of the CLAIRE project.Harrison Fiona
The Nuclear Spectroscopic Telescope Array (NuSTAR)
NuSTAR will be the first satellite-borne focusing telescope to image the hard X-ray (8 - 80 keV).NuSTAR's unprecedented combination of sensitivity, angular and spectral resolution allow itto carry out a number of high priority scientific investigations, including:
1) taking a census ofblack holes on all scales, achieved through deep, wide-field surveys of extragalactic fields andthe Galactic center,
2) mapping recently-synthesized material in young supernova remnants toconstrain nucleosynthesis and explosion models,
and 3) studying the spectra and time-variabilityin the most extreme AGN. In this talk I will provide an overview of the science goals, instrumentarchitecture, and results from the flight of the HEFT balloon instrument, a prototype forthe NuSTAR mission.Jensen Carsten
Small d-spacing WC/SIC multilayers for future hard x-ray telescope designs
Multilayer coatings for reflecting X-rays up to 80 keV have been studied for several years, and in May 2005 the HEFT balloon mission successfully flew 3 focusing optics using W/Si multilayers. The NASA SMEX mission NuSTAR, planned for flight in 2009, will also employ focusing mulitlayer optics of a similar design. The upper energy limit for these optics is partly constrained by how thin the bilayer thicknesses can be made without detrimental effects to the interface roughness. With new material combinations like W/SiC, WC/SiC, and Pt/SiC the interface roughness can be reduced in some cases down to 0.2 nm enabling bilayer thicknesses down to 1.0 nm to reflect effectively. The production of thinner period coatings thus enables the possibility for focusing optic designs with reasonable throughput up to several hundred keV. This will enable the investigation of the nuclear continuum and cutoff in AGN and Seyfert galaxies, as well as the Compton backscatter radiation at 170 keV emitted from accreting massive galactic objects, and the 56-Ni 158 keV line in supernova type 1a.
Koechlin Laurent
Multiwavelenght Focusing with the Sun as Gravitational Lens
We present investigations on using the space curvatures caused by the gravitational field of the sun as a means of focussing electromagnetic radiation.
The gravitation lens formed by the sun is by no means stigmatic, but it is achromatic. Its optical characteristics present a "caustic" line starting at 1200 astronomical units (UA) from the sun. A satellite or formation flying fleet moving away from the sun along or in the vicinity of this line would benefit from the microlensing effect. This would provide a powerful means of focussing radiation that cannot be focussed easily otherwise. The amplification factor could reach 10^9. The point spread function (PSF) of the sun as a lens is studied, taking into account the gravitational field deformations caused by the non symmetry of the mass distribution within and close to the sun, and by solar system bodies.
Once launched, missions of this type would be dedicated to a single field. Some possible targets are considered, such as Sagitarus A.Krizmanic John
X-ray Imaging Performance of a Phase Fresnel Lens
Diffractive/refractive optics, such as Phase Fresnel Lenses (PFL's), offer the potential to achieve exquisite imaging performance in the x-ray and gamma-ray photon regimes. In principle, the angular resolution obtained with these devices can be diffraction limited. Furthermore, improvements in signal sensitivity can be achieved as virtually the entire flux incident on a lens can be concentrated onto a small detector area. In order to experimentally verfiy the imaging performance, we have fabricated PFL's in silicon using gray-scale lithography to produce the required Fresnel profile. These devices are to be evaluated in the recently constructed 600-meter x-ray interferometry testbed at NASA/GSFC. Results on the imaging performance measurements of these silicon PFL's will be presented.
Lund Niels
Imaging with Laue lenses
Laue lenses designed to have a wide energy coverage possesses limited imaging capabilities. These can be used on-line to assure a good centering of the target object during an observation and also offers the possibility to construct spatial maps of the emission from supernova remnants.
Pareschi Giovanni (1)
Hard X-ray optics based on Bragg reflection from mosaic crystals: a review
The use of Bragg reflection optics for the hard X-ray (10 - 150 keV) astronomy is very attractive due to the wide energy band and reflection angles allowed by natural mosaic crystals. The concept already found many applications in fields different from astronomy (e.g. medical radiology and fluorescence analysis in synchrotron radiation experiments). Also the design and development of hard X-ray astronomical telescopes based on mosaic crystals was carried out by several groups, the most recent study being done at the University of Ferrara, Italy. In this paper we will review the work that has been done so far and the status of this technological approach, with a critical discussion about the design, fabrication methods, materials for the implementation of Bragg focusing systems. The perspectives of the use of Bragg telescopes in reflection configuration in future astronomical programs, and the comparison with other kinds of high energy focusing optics like multilayer coated Wolter I mirrors and Laue diffracting lens will be also be treated.
Pareschi Giovanni (2)
The SIMBOL-X hard X-ray mission
SIMBOL-X is a hard X-ray mission, operating in the 0.5 - 70 keV (extendable up to 80 keV and beyond) range, which is proposed by a consortium of European laboratories in response to the 2004 call for ideas of CNES for a scientific mission to be flown on a formation flying demonstrator. A large participation from the Italian Space Agency (ASI) is currently envisaged and under discussion. Relying on two spacecrafts in a formation flying configuration, SIMBOL-X makes uses of a 30 m focal length X-ray mirror to focus for the first time X-rays with energy above 10 keV, resulting in at least a two orders of magnitude improvement in angular resolution and sensitivity in the hard X-ray range with respect to non focusing techniques. The SIMBOL-X revolutionary instrumental capabilities will allow to elucidate outstanding questions in high energy astrophysics, related in particular to the physics of accretion onto compact objects, to the acceleration of particles to the highest energies and to resolving the sources giving rise to the Cosmic X-ray Background in the region where its spectrum peaks (30 keV). In the case, under study, that multilayer coated optics are implemented (instead of the single layer Pt mirrors of the baseline design), with the operational range extended up to 80 keV, also the investigation of 44Ti nuclear decaying lines from supernova remnant will be enabled. It must be noted that Simbol-X will also represent the necessary pathfinder experiment for other high energy missions that will make use of the formation flight architecture as e.g. XEUS and, perhaps , Constellation-X. The mission is currently in final assessment study in CNES, anda cmpetitive phase A study is expected to start, to be carried out in close collaboration with ASI, in autumn 2005, leading to a flight decision at the end of 2006. The mission science objectives, design, instrumentation (in particular for what related to the focusing optics) and status will be presented.
Pisa Alessandro
Optical properties of Laue lenses for hard X-rays (>60 keV)
We report on preliminary results obtained with a Monte Carlo (MC) code developed to study the optical properties of Laue lenses for astrophysical observations.
The MC code is written in the Python programming language and relays on open source libraries.
Among the physical quantities which can be investigated with the MC code, we paid our attention mainly to the estimation of the effective area, sensitivity, field of view (FOV) and point spread function (PSF) of the lens for observation of sources on-axis and off-axis.Ramsey Brian
Replicated Nickel Optics for the Hard-X-Ray Region
Replicated nickel optics has been used extensively in x-ray astronomy, most notable for the XMM/Newton mission. The combination of relative ease of fabrication and the inherent stability of full shell optics, make them an attractive approach for medium-resolution, high-throughput applications.
MSFC has been developing these optics for use in the hard-x-ray region. Efforts at improving the resolution of these, particularly the very-thin shells required to meet the weight budget of future missions, will be described together with the prospects for significant improvements down to the 5-arcsec level.Rando Nicola
Gamma Ray Lens - An ESA Technology Reference Study
The Science Payload and Advanced Concepts Office (SCI-A) of the ESA Science Directorate conducts a number of Technology Reference Studies (TRS) on hypothetical scientific missions that are not part of the approved Science programme. Such TRS activities allow identifying at an early stage technology development needs as well as exploring future mission scenarios.
As part of this effort, the Gamma Ray Lens (GRL) mission, a future generation gamma-ray observatory, has been the subject of a preliminary internal investigation.
The present paper provides an overview of the science goals assumed for this study, the selection of the reference mission profile, together with a preliminary description of the spacecraft design. The reference payload is also described, as well as the list of technology development activities derived from the study.Skinner Gerry
Fresnel Lenses - Why not ?
Fresnel lenses offer the possibility of concentrating the flux of X-rays or gamma-rays flux falling on a geometric area of many square metres onto a focal point which need only be a millimetre or so in diameter (and can even be very much smaller). They can do so with an efficiency that can approach 100%, and yet they are easily fabricated and have no special alignment requirements. Fresnel lenses can offer diffraction-limited angular resolution, even in a doamin where that limit corresponds to less than a micro second of arc.
Given all these attributes, it is natural to ask why Fresnel gamma ray lenses are not already being used, or at least why there is not yet any mission that plans to use the technology. Possible reasons (apart from the obvious one that nobody thought of doing so) are the narrow bandwidth of simple Fresnel lenses, their very long focal length, and the problems of target finding. It will be argued that none of these is a 'show stopper' and that this technique should be seriously considered for nuclear astrophysics.Smither Robert
High Diffraction Efficiency, Broadband, Diffraction Crystals for Use in Crystal Diffraction Lenses
One of the major goals of the MAX program is to be able to detect and measure the relative intensity of the gamma rays that are produced by the nuclear reactions that take place in a super nova explosion. The main problem in this endeavor is the very weak nature of the flux from these nuclear reactions. If the super nova were to occur in our own galaxy one could observe these gamma rays with our present satellite detectors, but this occurs only once in 100 years and therefore is not frequent enough to justify a satellite program. One must be able to detect gamma rays from super nova that occur in other galaxies. The flux from these sources is expected to be a few times 10-7 gamma rays per cm2 per sec. Thus a 100 percent efficient detector with an area of one square meter area will only detect a few gammas every 1000 sec. The expected background in this large detector will obscure the gamma ray signal. The advantage of using a crystal diffraction lens telescope is that one can separate the size of the collection area from the size of the detector. Thus one can expand the size of the lens without increasing the size of the detector. The detector can then be sized to fit the energy of the gamma ray being detected and then left unchanged as the size of the lens is increased. The crystals used to build the lens need to have both high diffraction efficiency and a relatively broad energy bandwidth and a relatively broad acceptance angle for the incident gamma rays. These last two requirements are actually the same requirement. With mosaic crystals there is a trade off between bandwidth and diffraction efficiency that limits the product of these two parameters. Thus one can have either high efficiency or large bandwidth, but not both. A recent breakthrough in our understanding of crystal diffraction for high energy gamma rays has made it possible to develop crystals that have both high diffraction efficiency and a relatively broad energy bandwidth. These crystals have near perfect crystal structure, except that the crystalline planes are slightly curved. This new type of crystal can be produced in 3 different ways. First, they can be grown as a two component crystal where the relative concentration of the two components is varied as the crystal is grown, second, they can be produced by applying a thermal gradient to a near perfect crystal and third, they can be produced by bending a near perfect crystal. A series of experiments have been performed using crystal made with all 3 approaches, using high energy x-ray beams from the Advanced Photon Source, a large synchrotron facility located at the Argonne National Laboratory, and with gamma rays from radioactive sources. One of the advantages of using the synchrotron beams to test these crystals is that as sources they look very much like the flux coming from a distant super nova source. The radiation is collimated to a few arc sec and has a narrow but finite energy bandwidth. The thermal gradient approach has demonstrated that one can have crystals with 90 percent diffraction efficiency and an angular bandwidth of 50 arc sec. At 100 keV this corresponds to an energy bandwidth of 1,27 keV and at 500 keV, a bandwidth of 6.33 keV, when using the [111] crystalline planes of silicon. These energy widths correspond to Doppler shifts of 3800 km per sec. This paper will compare the 3 approaches as applied to the construction of a crystal diffraction lens. There is a potential of increasing both the diffraction efficiency and the bandwidth by a factor of 5 as compared to what can be done with mosaic crystals.
Ulmer Melville
Progress Toward Light Weight High Angular Resolution Multilayer Coated Optics
We have been working on 3 separate projects that together will give us the ability to make 1 arc second, light weight Wolter I optics that work above 40 keV. The three separate tasks are:
(a) coating of the inside of Wolter I mirrors,
(b) actuator designs for improving figure quality;
(c) plasma spraying of metal-coated micro-balloons. We will give a progress report on our work on all three areas.top
Program
Update : September 2005
Questions and comments : Peter von Ballmoos