433 research outputs found
Phantom study for 90Y post-treatment dosimetry with a long axial field-of-view PET/CT
Purpose: The physical properties of yttrium-90 (90Y) allow for imaging with
positron emission tomography/computed tomography (PET/CT). The increased
sensitivity of long axial field-of-view (LAFOV) PET/CT scanners possibly allows
to overcome the small branching ratio for positron production from 90Y decays
and to improve for the post-treatment dosimetry of 90Y of selective internal
radiation therapy.
Methods: For the challenging case of an image quality body phantom, we
compare a full Monte Carlo (MC) dose calculation with the results from the two
commercial software packages Simplicit90Y and Hermes. The voxel dosimetry
module of Hermes relies on the 90Y images taken with a LAFOV PET/CT, while the
MC and Simplicit90Y dose calculations are image independent.
Results: The resulting doses from the MC calculation and Simplicit90Y agree
well within the error margins. The image-based dose calculation with Hermes,
however, consistently underestimates the dose. This is due to the mismatch of
the activity distribution in the PET images and the size of the volume of
interest. Furthermore, there are likely limitations of Hermes' dose calculation
algorithm for 90Y. We found that only for the smallest phantom sphere there is
a statistically significant dependence of the Hermes dose on the image
reconstruction parameters and scan time.
Conclusion: Our study shows that Simplicit90Y's local deposition model can
provide a reliable dose estimate. On the other hand, the image based dose
calculation requires further benchmarks and verification in order to take full
advantage of LAFOV PET/CT systems
The FHI FEL Upgrade Design
Since coming on-line in November 2013, the Fritz-Haber-Institut (FHI) der Max-Planck-Gesellschaft (MPG) Free-Electron Laser (FEL) has provided intense, tunable infrared radiation to FHI user groups. It has enabled experiments in diverse fields ranging from bio-molecular spectroscopy to studies of clusters and nanoparticles, nonlinear solid-state spectroscopy, and surface science, resulting in 50 peer-reviewed publications so far. The MPG has now funded a significant upgrade to the original FHI FEL. A second short Rayleigh range undulator FEL beamline is being added that will permit lasing from 160 microns. Additionally, a 500 MHz kicker cavity will permit simultaneous two-color operation of the FEL from both FEL beamlines over an optical range of 5 to 50 microns by deflecting alternate 1 GHz pulses into each of the two undulators. We will describe the upgraded FHI FEL physics and engineering design and present the plans for two-color FEL operations in November 2020
The FHI FEL Upgrade Design
Since coming on-line in November 2013, the Fritz-Haber-Institut (FHI) der Max-Planck-Gesellschaft (MPG) Free-Electron Laser (FEL) has provided intense, tunable infrared radiation to FHI user groups. It has enabled experiments in diverse fields ranging from bio-molecular spectroscopy to studies of clusters and nanoparticles, nonlinear solid-state spectroscopy, and surface science, resulting in 50 peer-reviewed publications so far. A significant upgrade of the FHI FEL is now being prepared. A second short Rayleigh range undulator FEL beamline is being added that will permit lasing from 160 microns. Additionally, a 500 MHz kicker cavity will permit simultaneous two-color operation of the FEL from both FEL beamlines over an optical range of 5 to 50 microns by deflecting alternate 1 GHz pulses into each of the two undulators. We will describe the upgraded FHI FEL physics and engineering design and present the plans for two-color FEL operations in November 2020
The New IR FEL Facility at the Fritz-Haber-Institut in Berlin
A mid-infrared oscillator FEL has been commissioned at the Fritz-Haber-Institut. The accelerator consists of a thermionic gridded gun, a subharmonic buncher and two S-band standing-wave copper structures [1,2]. It provides a final electron energy adjustable from 15 to 50 MeV, low longitudinal (<50 keV-ps) and transverse emittance (<20 π mm-mrad), at more than 200 pC bunch charge with a micro-pulse repetition rate of 1 GHz and a macro-pulse length of up to 15 μs. Regular user operation started in Nov. 2013 with 6 user stations. Pulsed radiation with up to 100 mJ macro-pulse energy at about 0.5% FWHM bandwidth is routinely produced in the wavelength range from 4 to 48 μm. We will describe the FEL design and its performance as determined by IR power, bandwidth, and micro-pulse length measurements. Further, an overview of the new FHI FEL facility and first user results will be given. The latter include, for instance, spectroscopy of bio-molecules (peptides and small proteins) conformer selected or embedded in superfluid helium nano-droplets at 0.4 K, as well as vibrational spectroscopy of mass-selected metal-oxide clusters and protonated water clusters in the gas phase
A Mission to Explore the Pioneer Anomaly
The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep
space to date. These spacecraft had exceptional acceleration sensitivity.
However, analysis of their radio-metric tracking data has consistently
indicated that at heliocentric distances of astronomical units,
the orbit determinations indicated the presence of a small, anomalous, Doppler
frequency drift. The drift is a blue-shift, uniformly changing with a rate of
Hz/s, which can be interpreted as a
constant sunward acceleration of each particular spacecraft of . This signal has become known as the Pioneer
anomaly. The inability to explain the anomalous behavior of the Pioneers with
conventional physics has contributed to growing discussion about its origin.
There is now an increasing number of proposals that attempt to explain the
anomaly outside conventional physics. This progress emphasizes the need for a
new experiment to explore the detected signal. Furthermore, the recent
extensive efforts led to the conclusion that only a dedicated experiment could
ultimately determine the nature of the found signal. We discuss the Pioneer
anomaly and present the next steps towards an understanding of its origin. We
specifically focus on the development of a mission to explore the Pioneer
Anomaly in a dedicated experiment conducted in deep space.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020", 19-21 April 2005, ESTEC,
Noordwijk, The Netherland
Fundamental Physics with the Laser Astrometric Test Of Relativity
The Laser Astrometric Test Of Relativity (LATOR) is a joint European-U.S.
Michelson-Morley-type experiment designed to test the pure tensor metric nature
of gravitation - a fundamental postulate of Einstein's theory of general
relativity. By using a combination of independent time-series of highly
accurate gravitational deflection of light in the immediate proximity to the
Sun, along with measurements of the Shapiro time delay on interplanetary scales
(to a precision respectively better than 0.1 picoradians and 1 cm), LATOR will
significantly improve our knowledge of relativistic gravity. The primary
mission objective is to i) measure the key post-Newtonian Eddington parameter
\gamma with accuracy of a part in 10^9. (1-\gamma) is a direct measure for
presence of a new interaction in gravitational theory, and, in its search,
LATOR goes a factor 30,000 beyond the present best result, Cassini's 2003 test.
The mission will also provide: ii) first measurement of gravity's non-linear
effects on light to ~0.01% accuracy; including both the Eddington \beta
parameter and also the spatial metric's 2nd order potential contribution (never
measured before); iii) direct measurement of the solar quadrupole moment J2
(currently unavailable) to accuracy of a part in 200 of its expected size; iv)
direct measurement of the "frame-dragging" effect on light by the Sun's
gravitomagnetic field, to 1% accuracy. LATOR's primary measurement pushes to
unprecedented accuracy the search for cosmologically relevant scalar-tensor
theories of gravity by looking for a remnant scalar field in today's solar
system. We discuss the mission design of this proposed experiment.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020," 19-21 April 2005, ESTEC,
Noodrwijk, The Netherland
Development of a prototype superconducting radio-frequency cavity for conduction-cooled accelerators
The higher efficiency of superconducting radio-frequency (SRF) cavities
compared to normal-conducting ones enables the development of high-energy
continuous-wave linear accelerators (linacs). Recent progress in the
development of high-quality NbSn film coatings along with the availability
of cryocoolers with high cooling capacity at 4 K makes it feasible to operate
SRF cavities cooled by thermal conduction at relevant accelerating gradients
for use in accelerators. A possible use of conduction-cooled SRF linacs is for
environmental applications, requiring electron beams with energy of
MeV and 1 MW of power. We have designed a 915 MHz SRF linac for such an
application and developed a prototype single-cell cavity to prove the proposed
design by operating it with cryocoolers at the accelerating gradient required
for 1 MeV energy gain. The cavity has a m thick NbSn film on
the inner surface, deposited on a mm thick bulk Nb substrate and a bulk
mm thick Cu outer shell with three Cu attachment tabs. The cavity was
tested up to a peak surface magnetic field of 53 mT in liquid He at 4.3 K. A
horizontal test cryostat was designed and built to test the cavity cooled with
three Gifford-McMahon cryocoolers. The rf tests of the conduction-cooled
cavity, performed at General Atomics, achieved a peak surface magnetic field of
50 mT and stable operation was possible with up to 18.5 W of rf heat load. The
peak frequency shift due to microphonics was 23 Hz. These results represent the
highest peak surface magnetic field achieved in a conduction-cooled SRF cavity
to date and meet the requirements for a 1 MeV energy gain
Commissioning Status of the Fritz Haber Institute THz FEL
The THz Free-Electron Laser (FEL) at the Fritz Haber Institute (FHI) of the Max Planck Society in Berlin is designed to deliver radiation from 3 to 300 microns using a single-plane-focusing mid-IR undulator and a two-plane-focusing far-IR undulator that acts as a waveguide for the optical mode. A key aspect of the accelerator performance is the low longitudinal emittance, < 50 keV-psec, that is specified to be delivered at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the sponsor in October 2011 and we will describe progress in the commissioning of this device to achieve this goal. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described
First Lasing of the IR FEL at the Fritz-Haber-Institut Berlin
A new mid-infrared FEL has been commissioned at the Fritz-Haber-Institut in Berlin. The oscillator FEL operates with 15 – 50 MeV electrons from a normal-conducting Sband linac. Calculations of the FEL gain and IR-cavity losses predict that lasing will be possible in the wavelength range from less than 4 to more than 50 μm. First lasing was achieved at a wavelength of 16 μm with an electron energy of 28 MeV. At these conditions, lasing was observed over a cavity length scan range of 100 μm
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