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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

The quest for solvable multistate Landau-Zener models

Recently, integrability conditions (ICs) in mutistate Landau-Zener (MLZ) theory were proposed. They describe common properties of all known solved systems with linearly time-dependent Hamiltonians. Here we show that ICs enable efficient computer assisted search for new solvable MLZ models that span complexity range from several interacting states to mesoscopic systems with many-body dynamics and combinatorially large phase space. This diversity suggests that nontrivial solvable MLZ models are numerous. Additionally, we refine the formulation of ICs and extend the class of solvable systems to models with points of multiple diabatic level crossing.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

UNCOVERING THE DEEPLY EMBEDDED ACTIVE GALACTIC NUCLEUS ACTIVITY IN THE NUCLEAR REGIONS OF THE INTERACTING GALAXY Arp 299

We present mid-infrared (MIR) 8-13 μm spectroscopy of the nuclear regions of the interacting galaxy Arp 299 (IC 694+NGC 3690) obtained with CanariCam (CC) on the 10.4 m Gran Telescopio Canarias (GTC). The high angular resolution (∼0.''3-0.''6) of the data allows us to probe nuclear physical scales between 60 and 120 pc, which is a factor of 10 improvement over previous MIR spectroscopic observations of this system. The GTC/CC spectroscopy displays evidence of deeply embedded active galactic nucleus (AGN) activity in both nuclei. The GTC/CC nuclear spectrum of NGC 3690/Arp 299-B1 can be explained as emission from AGN-heated dust in a clumpy torus with both a high covering factor and high extinction along the line of sight. The estimated bolometric luminosity of the AGN in NGC 3690 is 3.2 ± 0.6 × 10{sup 44} erg s{sup –1}. The nuclear GTC/CC spectrum of IC 694/Arp 299-A shows 11.3 μm polycyclic aromatic hydrocarbon emission stemming from a deeply embedded (A{sub V} ∼ 24 mag) region of less than 120 pc in size. There is also a continuum-emitting dust component. If associated with the putative AGN in IC 694, we estimate that it would be approximately five times less luminous than the AGN in NGC 3690. The presence of dual AGN activity makes Arp 299 a good example to study such phenomena in the early coalescence phase of interacting galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

PAIR-DOMINATED GeV-OPTICAL FLASH IN GRB 130427A

We show that the light curve of the double GeV+optical flash in GRB 130427A is consistent with radiation from the blast wave in a wind-type medium with density parameter A = ρr {sup 2} ∼ 5 × 10{sup 10} g cm{sup –1}. The peak of the flash is emitted by copious e {sup ±} pairs created and heated in the blast wave; our first-principle calculation determines the pair-loading factor and temperature of the shocked plasma. Using detailed radiative transfer simulations, we reconstruct the observed double flash. The optical flash is dominated by synchrotron emission from the thermal plasma behind the forward shock, and the GeV flash is produced via inverse Compton (IC) scattering by the same plasma. The seed photons for IC scattering are dominated by the prompt MeV radiation during the first tens of seconds, and by the optical to X-ray afterglow thereafter. IC cooling of the thermal plasma behind the forward shock reproduces all GeV data from a few seconds to ∼1 day. We find that the blast wave Lorentz factor at the peak of the flash is Γ ≈ 200, and the forward shock magnetization is ε{sub B} ∼ 2 × 10{sup –4}. An additional source is required by the data in the optical and X-ray bands at times >10{sup 2} s; we speculate that this additional source may be a long-lived reverse shock in the explosion ejecta.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Cherenkov Telescope Array sensitivity to the putative millisecond pulsar population responsible for the Galactic Centre excess

ABSTRACT The leading explanation of the Fermi Galactic Centre γ-ray excess is the extended emission from an unresolved population of millisecond pulsars (MSPs) in the Galactic bulge. Such a population would, along with the prompt γ-rays, also inject large quantities of electrons/positrons (e±) into the interstellar medium. These e± could potentially inverse-Compton (IC) scatter ambient photons into γ-rays that fall within the sensitivity range of the upcoming Cherenkov Telescope Array (CTA). In this article, we examine the detection potential of CTA to this signature by making a realistic estimation of the systematic uncertainties on the Galactic diffuse emission model at TeV-scale γ-ray energies. We forecast that, in the event that e± injection spectra are harder than E−2, CTA has the potential to robustly discover the IC signature of a putative Galactic bulge MSP population sufficient to explain the Galactic Centre excess for e± injection efficiencies in the range of ≈2.9–74.1 per cent, or higher, depending on the level of mismodelling of the Galactic diffuse emission components. On the other hand, for spectra softer than E−2.5, a reliable CTA detection would require an unphysically large e± injection efficiency of ${\gtrsim} 158{{\ \rm per\ cent}}$. However, even this pessimistic conclusion may be avoided in the plausible event that MSP observational and/or modelling uncertainties can be reduced. We further find that, in the event that an IC signal were detected, CTA can successfully discriminate between an MSP and a dark matter origin for the radiating e±.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Insights into the origin of halo mass profiles from machine learning

ABSTRACT The mass distribution of dark matter haloes is the result of the hierarchical growth of initial density perturbations through mass accretion and mergers. We use an interpretable machine-learning framework to provide physical insights into the origin of the spherically-averaged mass profile of dark matter haloes. We train a gradient-boosted-trees algorithm to predict the final mass profiles of cluster-sized haloes, and measure the importance of the different inputs provided to the algorithm. We find two primary scales in the initial conditions (ICs) that impact the final mass profile: the density at approximately the scale of the haloes’ Lagrangian patch RL ($R\sim 0.7\, R_L$) and that in the large-scale environment (R ∼ 1.7 RL). The model also identifies three primary time-scales in the halo assembly history that affect the final profile: (i) the formation time of the virialized, collapsed material inside the halo, (ii) the dynamical time, which captures the dynamically unrelaxed, infalling component of the halo over its first orbit, (iii) a third, most recent time-scale, which captures the impact on the outer profile of recent massive merger events. While the inner profile retains memory of the ICs, this information alone is insufficient to yield accurate predictions for the outer profile. As we add information about the haloes’ mass accretion history, we find a significant improvement in the predicted profiles at all radii. Our machine-learning framework provides novel insights into the role of the ICs and the mass assembly history in determining the final mass profile of cluster-sized haloes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Relativistic turbulence with strong synchrotron and synchrotron self-Compton cooling

Many relativistic plasma environments in high-energy astrophysics, including pulsar wind nebulae (PWN), hot accretion flows on to black holes, relativistic jets in active galactic nuclei and gamma-ray bursts, and giant radio lobes, are naturally turbulent. The plasma in these environments is often so hot that synchrotron and inverse-Compton (IC) radiative cooling becomes important. In this paper, we investigate the general thermodynamic and radiative properties (and hence the observational appearance) of an optically thin relativistically hot plasma stirred by driven magnetohydrodynamic (MHD) turbulence and cooled by radiation. We find that if the system reaches a statistical equilibrium where turbulent heating is balanced by radiative cooling, the effective electron temperature tends to attain a universal value θ=kT e /m e c 2 ~ 1/√τ T , where τT = n e σT L « 1 is the system's Thomson optical depth, essentially independent of the strength of turbulent driving and hence of the magnetic field. This is because both MHD turbulent dissipation and synchrotron cooling are proportional to the magnetic energy density. We also find that synchrotron self-Compton (SSC) cooling and perhaps a few higher order IC components are automatically comparable to synchrotron in this regime. The overall broad-band radiation spectrum then consists of several distinct components (synchrotron, SSC, etc.), well separated in photon energy (by a factor ~τ T -1 ) and roughly equal in power. The number of IC peaks is checked by Klein–Nishina effects and depends logarithmically on τT and the magnetic field. We also examine the limitations due to synchrotron self-absorption, explore applications to Crab PWN and blazar jets, and discuss links to radiative magnetic reconnection.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Particle acceleration in relativistic magnetic reconnection with strong inverse-Compton cooling in pair plasmas

Particle-in-cell (PIC) simulations have shown that relativistic collisionless magnetic reconnection drives non-thermal particle acceleration (NTPA), potentially explaining high-energy (X-ray/γ-ray) synchrotron and/or inverse Compton (IC) radiation observed from various astrophysical sources. The radiation back-reaction force on radiating particles has been neglected in most of these simulations, even though radiative cooling considerably alters particle dynamics in many astrophysical environments where reconnection may be important. We present a radiative PIC study examining the effects of external IC cooling on the basic dynamics, NTPA, and radiative signatures of relativistic reconnection in pair plasmas. We find that, while the reconnection rate and overall dynamics are basically unchanged, IC cooling significantly influences NTPA: the particle spectra still show a hard power law (index ≥ -2) as in non-radiative reconnection, but transition to a steeper power law that extends to a cooling-dependent cut-off. The steep power-law index fluctuates in time between roughly -3 and -5. The time-integrated photon spectra display corresponding power laws with indices ≈-0.5 and ≈-1.1, similar to those observed in hard X-ray spectra of accreting black holes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Free-electron laser inverse-Compton interaction x-ray source

Free-electron lasers (FEL) and synchrotron sources of high brilliance x-rays have been confirmed to be of tremendous value in basic and applied research. Inverse-Compton sources (ICS) can achieve brilliance matching the requirements of many applications pioneered at those FEL and synchrotron facilities—including phase contrast imaging, macromolecular x-ray crystallography, and x-ray microscopy—but with size, cost, and complexity compatible with a small laboratory. The free-electron laser inverse-Compton interaction compact x-ray source at the University of Hawaii at Manoa is a unique approach to an ICS which employs an FEL as the laser source. We have measured a total average flux of 3.0 × 10 5 photons / second with an average brilliance of 2.0 × 10 7 photons / s mm 2 mrad 2 0.1% of bandwidth (BW) with a peak energy of 10.9 keV from the source. While these results are modest in comparison to the standards set by other IC sources, upgrades to the system have the potential to increase the total average flux to 9.2 × 10 11 photons / second with an average brilliance of 1.9 × 10 12 photons / s mm 2 mrad 2 0.1% BW: comparing more favorably to other sources. We discuss the scientific program, the progress made in design and development, and the achievements of the source to date. We also outline future upgrades and integration needed to yield an enabling source for emerging high brilliance x-ray applications.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Highly dispersive magnons with spin-gap-like features in the frustrated ferromagnetic S = 1 2 chain compound Ca 2 Y 2 Cu 5 O 10 detected by inelastic neutron scattering

In this paper, we report inelastic neutron scattering experiments in Ca 2 Y 2 Cu 5 O 10 and map out the full one-magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO 2 chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT) reproduces well the observed strong dispersion along the chains and a weak one perpendicularly. The ratio α=| J a 2 / J a 1 | of the FM NN and the AFM NNN couplings is found as ~0.23, close to the critical point α c =1/4 which separates ferromagnetically and antiferromagnetically correlated spiral magnetic ground states in single chains, whereas α c >0.25 for coupled chains is considerably upshifted even for relatively weak IC. Although the measured dispersion can be described by homogeneous LSWT, the scattering intensity appears to be considerably reduced at ~11.5 and ~28 meV. The gaplike feature at 11.5 meV is attributed to magnon-phonon coupling whereas based on density matrix renormalization group simulations of the dynamical structure factor the gap at 28 meV is considered to stem partly from quantum effects due to the AFM IC. Another contribution to that gap is ascribed to the intrinsic superstructure from the distorting incommensurate pattern of CaY cationic chains adjacent to the CuO 2 ones. It gives rise to nonequivalent CuO 4 units and Cu-O-Cu bond angles Φ and a resulting distribution of all exchange integrals. The J 's fitted by homogeneous LSWT are regarded as average values. The record value of the FM NN integral J 1 =24 meV among FFESC cuprates can be explained by a nonuniversal Φ(≠90°) and Cu-O bond length dependent anisotropic mean direct FM Cu-O exchange $\overline{K}_{pd}$~120 meV, similar to a value of 105 meV for Li 2 CuO 2 , in accord with larger values for La 2 CuO 4 and CuGeO 3 (~110 meV) reported by Braden et al . [Phys. Rev. B 54, 1105 (1996)] phenomenologically. Lastly, enhanced $K_{pd}$ values are also needed to compensate a significant AFM J dd ≥ 6 meV from the dd channel, generic for FFESC cuprates but ignored so far.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Spin-lattice coupling mediated multiferroicity in (ND 4 ) 2 FeCl 5 • D 2 O

In this paper, we report a neutron diffraction study of the multiferroic mechanism in (ND 4 ) 2 FeCl 5 • D 2 O, a molecular compound that exhibits magnetically induced ferroelectricity. This material exhibits two successive magnetic transitions on cooling: a long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at T N = 7.3 K, followed by a second transition to an IC cycloidal spin state at T FE = 6.8 K, the latter of which is accompanied by spontaneous ferroelectric polarization. The cycloid structure is strongly distorted by spin-lattice coupling, as evidenced by the observations of both odd and even higher-order harmonics associated with the cycloid wave vector, and a weak commensurate phase that coexists with the IC phase. The second-order harmonic appears at T FE , thereby providing unambiguous evidence that the onset of the electric polarization is accompanied by a lattice modulation due to spin-lattice interaction. The neutron results, in conjunction with the negative thermal expansion and large magnetostriction observed, indicate that spin-lattice coupling plays a critical role in the ferroelectric mechanism of (ND 4 ) 2 FeCl 5 • D 2 O.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Field-induced magnetic phase transitions and metastable states in Tb 3 Ni

In this study we report the detailed study of magnetic phase diagrams, low-temperature magnetic structures, and the magnetic field effect on the electrical resistivity of the binary intermetallic compound ${\mathrm{Tb}}_{3}\mathrm{Ni}$. The incommensurate magnetic structure of the spin-density-wave type described with magnetic superspace group $P{112}_{1}/a{1}^{{'}}(ab0)0ss$ and propagation vector ${\mathbf{k}}_{\mathrm{IC}}=\left[0.506,0.299,0\right]$ was found to emerge just below Néel temperature ${T}_{\mathrm{N}}=61$ K. Further cooling below 58 K results in the appearance of multicomponent magnetic states: (i) a combination of ${\mathbf{k}}_{1}=\left[\frac{1}{2},\frac{1}{2},0\right]$ and ${\mathbf{k}}_{\mathrm{IC}}$ in the temperature range 51 < T < 58 K; (ii) a mixed magnetic state of ${\mathbf{k}}_{\mathrm{IC}}, {\mathbf{k}}_{1}$, and ${\mathbf{k}}_{2}=\left[\frac{1}{2},\frac{1}{4},0\right]$ with the partially locked-in incommensurate component in the temperature range 48 < T < 51 K; and (iii) a low-temperature magnetic structure that is described by the intersection of two isotropy subgroups associated with the irreducible representations of two coupled primary order parameters (OPs) ${\mathbf{k}}_{2}=\left[\frac{1}{2},\frac{1}{4},0\right]$ and ${\mathbf{k}}_{3}=\left[\frac{1}{2},\frac{1}{3},0\right]$ and involves irreducible representations of the secondary OPs ${\mathbf{k}}_{1}=\left[\frac{1}{2},\frac{1}{2},0\right]$ and ${\mathbf{k}}_{4}=\left[\frac{1}{2},0,0\right]$ below 48 K. An external magnetic field suppresses the complex low-temperature antiferromagnetic states and induces metamagnetic transitions towards a forced ferromagnetic state that are accompanied by a substantial magnetoresistance effect due to the magnetic superzone effect. Finally, the forced ferromagnetic state induced after application of an external magnetic field along the $b$ and $c$ crystallographic axes was found to be irreversible below 3 and 8 K, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Inverse Compton emission from millisecond pulsars in the Galactic bulge

Analyses of Fermi Gamma-Ray Space Telescope data have revealed a source of excess diffuse gamma rays towards the Galactic center that extends up to roughly ±20 degrees in latitude. The leading theory postulates that this GeV excess is the aggregate emission from a large number of faint millisecond pulsars (MSPs). The electrons and positrons (e ± ) injected by this population could produce detectable inverse-Compton (IC) emissions by up-scattering ambient photons to gamma-ray energies. In this work, we calculate such IC emissions using galprop. A triaxial three-dimensional model of the bulge stars obtained from a fit to infrared data is used as a tracer of the putative MSP population. This model is compared against one in which the MSPs are spatially distributed as a Navarro-Frenk-White squared profile. We show that the resulting spectra for both models are indistinguishable, but that their spatial morphologies have salient recognizable features. Furthermore, the IC component above ~TeV energies carries information on the spatial morphology of the injected e ± . Such differences could potentially be used by future high-energy gamma-ray detectors such as the Cherenkov Telescope Array to provide a viable multiwavelength handle for the MSP origin of the GeV excess.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Method for Assessment of Security-Relevant Settings in Anomaly-Based Intrusion Detection for Industrial Control Systems

Ensuring the integrity of Ethernet-based networks is a challenging and constantly evolving domain. This problem is exacerbated for those operational technology (OT) networks supporting industrial control systems (ICS) since much of that equipment was originally designed to be on a network that was isolated and generally considered free of malefactors. Increasing pressure to bridge these systems with traditional information technology (IT) networks has introduced a bevy of new threats. In response, both academia and industry have responded with security solutions tailored to ICS environments. Deploying these protection systems often involves several configuration choices. While some of these choices are clear (e.g., block/enable protocol X) others are far more subjective (e.g. alert threshold == 3.43). Further complicating the situation, while often similar to IT networks, OT networks have unique challenges and characteristics that make the task of protecting them simultaneously more difficult and straight forward.Extant solutions for quantifying the relative security of intrusion detection systems fail to effectively support the operators of said systems with understanding the impact of various configuration changes. Further, they assume that the attacks are static and not subject to manipulation or alteration in the face of defenses. In this paper, we present a threat-based method for quantifying the relative impact of various security settings for intrusion detection systems (IDSs) within ICS environments. This method provides operational staff with a clear understanding of the relative impact of their settings and assumes that the attacks levied against them are dynamic. The model is described in detail, we apply the model to a synthetic data set, and discuss the inferences that can be made and what types of decisions they could be used to support.

Gillen, Rob↗
DOE OSTI2020

NDX: Neutron Dose Rate Meters with Extended Capabilities

Particle accelerators, irradiation facilities, and nuclear power plants would benefit from using neutron dose rate meters featuring improved energy response covering full range of expected neutron energies, improved dynamic range of measured dose rates while providing the real-time data, and improved ability to operate in harsh radiation environments including heavy photon backgrounds and pulsed beams. The novel design of the neutron moderator for the NDX dose rate meter implements a layer of a Beryllium-loaded medium Z material which, similar to the earlier known WENDI detectors, allows the device to detect higher energy neutron flux and convert it to dose. Using Beryllium helps to fill the known dip in the response functions around 5-50 MeV. Optimized design parameter set, obtained using FLUKA Monte Carlo simulations, features the NDX moderator made of polyethylene embedding a layer of BeCu alloy inside, with the dose rate response constant within ±10% in the neutron energy range from about 100 keV to 500 MeV, and ±25% essentially in the full energy range above thermal. A new sensor technique implemented in the NDX is based on using the Ionization Chamber (IC) filled with 3He gas to capture the moderated neutron fluence, and includes a symmetric IC filled with regular 4He to evaluate the contributions due to the non-neutron ionizing radiation. Advantages of the method include large accessible dynamic range, relative insensitivity of the IC probes to photon radiation fields, and the ability to subtract their contribution. Two prototype NDX detectors were built, calibrated, and operated in various conditions at the CEBAF 12 GeV electron accelerator at JLab. The first results showed reliable neutron dose rate measurements in the presence of overwhelming photon radiation fields, and at practical high dose rate levels of up to approximately 10 Sv/h. Detector design, operation, first results, and further development plans are presented.

Degtiarenko, Pavel V.↗
DOE OSTI2020

An electric-circuit model on the inter-tape contact resistance and current sharing for REBCO cable and magnet applications

REBCO coated conductor has demonstrated high current capacity that can enable high-field magnets for high energy physics and fusion applications. However, quench protection is still one of the main challenges to be addressed for these applications. In addition, Ic and n value variations along the length of REBCO tapes exist in commercial production. The inter-tape contact resistance plays a key role to develop the self protection capability in cables and magnets by enabling current sharing and suppressing excessive eddy currents. Here we propose an electric-circuit model to describe the inter-tape contact resistance and its impact on the current sharing between REBCO tapes. We report the experiments on a 2-stacked tape REBCO cable with local Ic drop to validate the model. With the developed model, we study the upper limit of the contact resistance which allows current sharing between tapes. We also study the impact of variation in Ic and n values in tapes on the cable performance. Finally, our model is expected to provide useful insight into the current sharing and target values for inter-tape contact resistance in REBCO cables and magnets for various applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Assessing Anomaly-Based Intrusion Detection Configurations for Industrial Control Systems

To reduce cost and ease maintenance, industrial control systems (ICS) have adopted Ethernetbased interconnections that integrate operational technology (OT) systems with information technology (IT) networks. This integration has made these critical systems vulnerable to attack. Security solutions tailored to ICS environments are an active area of research. Anomalybased network intrusion detection systems are well-suited for these environments. Often these systems must be optimized for their specific environment. In prior work, we introduced a method for assessing the impact of various anomaly-based network IDS settings on security. This paper reviews the experimental outcomes when we applied our method to a full-scale ICS test bed using actual attacks. Our method provides new and valuable data to operators enabling more informed decisions about IDS configurations.

Gillen, Rob↗
DOE OSTI2023

Immune checkpoint analysis of T‐cell responses to pp65 and IE‐1 antigens in end‐stage lung diseases

Abstract Lung transplant (LTX) patients are at high risk of cytomegalovirus (CMV) infection, which is often associated with high mortality and morbidity. Reactivation of CMV causes cell injury due to the cytopathic effect of viral replication and triggering of T cell immunity. The aim of this study was to compare expression of immune checkpoints (ICs) (PD‐1, CTLA‐4, LAG‐3 and TIGIT) in CD4, CD8 and CD56 and activation markers CD137, CD154 and CD69 of end‐stage patients awaiting lung transplant. Eighteen pre‐LTX positive for anti‐CMV IgG titres and 18 healthy subjects were enrolled. IC and activation markers have been evaluated through flow cytometric analysis in HC and pre‐LTX patients. Reactive (QF+) and unreactive (QF−) patients were stratified according to QuantiFERON‐CMV assays. ICs' and activation markers' expression were determined before and after in vitro stimulation with pp‐65 and IE‐1 antigens. Lower expression of PD‐1 was observed in CD4 and CD8 cells of pre‐LTX patients than controls, whereas CTLA4 appeared upregulated in CD56 and CD8 cells. TIGIT is increased on the surface of CD4, CD8 and NK cells after peptide stimulation in QF‐negative patients and PD‐1 is only downregulated after stimulation in the QF‐positive patients. This study provides new evidence of immune dysregulation in patients with end‐stage lung disorders, particularly in relation to immune checkpoint cell biology. The change in QF+ mostly happens on cytotoxic cells NK and CD8, while the changes in QF− were observed in adaptive immune cells, including CD4 and CD8.

Bergantini, Laura↗
DOE OSTI2014

SU-E-T-96: Demonstration of a Consistent Method for Correcting Surface Dose Measurements Using Both Solid State and Ionization Chamber Detectors

Purpose: To compare the surface dose (SD) measured using a PTW 30-360 extrapolation chamber with different commonly used dosimeters (Ds): parallel plate ion chambers (ICs): RMI-449 (Attix), Capintec PS-033, PTW 30-329 (Markus) and Memorial; TLD chips (cTLD), TLD powder (pTLD), optically stimulated (OSLs), radiochromic (EXR2) and radiographic (EDR2) films, and to provide an intercomparison correction to Ds for each of them. Methods: Investigations were performed for a 6 MV x-ray beam (Varian Clinac 2300, 10x10 cm{sup 2} open field, SSD = 100 cm). The Ds were placed at the surface of the solid water phantom and at the reference depth dref=1.7cm. The measurements for cTLD, OSLs, EDR2 and EXR2 were corrected to SD using an extrapolation method (EM) indexed to the baseline PTW 30-360 measurements. A consistent use of the EM involved: 1) irradiation of three Ds stacked on top of each other on the surface of the phantom; 2) measurement of the relative dose value for each layer; and, 3) extrapolation of these values to zero thickness. An additional measurement was performed with externally exposed OSLs (eOSLs), that were rotated out of their protective housing. Results: All single Ds measurements overestimated the SD compared with the extrapolation chamber, except for Attix IC. The closest match to the true SD was measured with the Attix IC (− 0.1%), followed by pTLD (0.5%), Capintec (4.5%), Memorial (7.3%), Markus (10%), cTLD (11.8%), eOSL (12.8%), EXR2 (14%), EDR2 (14.8%) and OSL (26%). The EM method of correction for SD worked well for all Ds, except the unexposed OSLs. Conclusion: This EM cross calibration of solid state detectors with an extrapolation or Attix chamber can provide thickness corrections for cTLD, eOSLs, EXR2, and EDR2. Standard packaged OSLs were not found to be simply corrected.

60 APPLIED LIFE SCIENCES↗