Gamma-ray Polarization Research Articles

Development of the multi-purpose gamma-ray detection system consisting of a double-sided silicon strip detector and a 25-segmented germanium detector

We developed a position-sensitive gamma-ray detection system consisting of a double-sided silicon strip detector (DSSD) and a 25-segmented germanium detector (25-SEGD). Two major applications of the system are gamma-ray imaging (Compton camera) and linear polarization measurement for gamma rays emitted from oriented nuclei. Customized electronics were developed in order to handle multi-channel signals of both the DSSD and the 25-SEGD. Images for a 133 Ba-based compound source in a square shape with areal dimensions of 1.5 × 1.5 mm 2 are presented. Comparison between experimental images and a Monte Carlo simulation yielded the overall imaging resolution within 1 cm for the present system.

PoGO : The polarised gamma-ray observer

A new balloon-borne instrument is proposed which will allow the polarisation of gamma-rays in the energy range 30– 200 keV to be measured. A diverse variety of astrophysical sources, such as Active Galactic Nuclei, pulsars and Galactic X-ray binaries are expected to emit polarised gamma-rays. Studies of their polarisation properties will provide a new and powerful probe of the geometry and physical conditions in these sources.

Measuring polarization of high-energy gamma rays

A method to determine the polarization of incident gamma-ray in two energy ranges is presented. The method consists basically in the determination of the asymmetry in the azimuthal distribution of the scattered radiation, in the energy range where Compton scattering dominates, and in the measurement of the asymmetric angular distribution of the e ± pair in the pair production regime. We show that the definition of the asymmetric ratio is a useful concept to determine polarization.

Spatial Distribution of Polarized Gamma Ray Generated Through Laser Compton Scattering on New SUBARU Storage Ring

Laser Compton Scattering gamma ray has been produced via a Nd:YAG laser head-on colliding the high energy electron beam of NewSUBARU storage ring by maximum energy of 17.6 MeV and flux of 1.75 × 104 counts/sec. The gamma ray can be yielded in linear polarization or circular polarization corresponding to the incoming laser light, respectively, and as is known, its spatial distribution relates to the polarization. In this paper, we report the measurement of spatial distribution of laser Compton scattering gamma ray through imaging its spot by an imaging plate. The experimental results coincide with the theoretical predictions.

The Most Probable Cause for the High Gamma-Ray Polarization in GRB 021206

The exciting detection of a very high degree of linear polarization, , in the prompt g-ray P p 80% 20% emission of the recent gamma-ray burst GRB 021206 provides strong evidence that synchrotron emission is the dominant radiation mechanism. Besides this immediate implication, there were also claims that this implies a magnetic field that is ordered on large scales within the ejecta and must therefore be produced at the source, which in turn was used as an argument in favor of magnetic fields playing an active role in the production of GRB jets. However, an alternative explanation was also suggested: a very narrow jet, of opening angle , where is the v ∼ 1/ gg 100 j Lorentz factor during the GRB, viewed slightly outside its edge, at . This explanation also works v ! v v 1/g j obs j with a magnetic field that is generated in the internal shocks and does not originate at the source. We calculate the expected degree of polarization for these two scenarios and find that it is significantly easier to produce with an ordered field. More specifically, we obtain for an ordered transverse magnetic P 50% P ∼ 43%–61% field, , whereas a shock-produced field that is random but fully within the plane of the shock, , can produce B B ord ⊥ up to for a single pulse in the GRB light curve, but the integrated emission over many pulses (as P 38%–54% measured in GRB 021206) is expected to be a factor of ∼2 lower. A magnetic field normal to the shock front, , can produce for the emission integrated over many pulses. However, polarization measurements BP ∼ 35%–62% k from GRB afterglows suggest a more isotropic configuration for the shock-produced field that should reduce P by a factor of ∼2–3. Therefore, an ordered magnetic field, , that originates at the source can produce the observed Bord polarization most naturally, while is less likely, and is the least likely of the above. BB k

New Monte Carlo method for Compton and Rayleigh scattering by polarized gamma rays

In this work we present a new Monte Carlo method for the simulation of Compton and Rayleigh scattering of polarized gamma rays. The azimuthal angle of the scattered photon and the direction of its polarization vector are described. Using the Stokes parameters formalism (Trans. Cambrige Phil. Soc. 9 (1852) 399), we show that this method reproduces the polarization process suffered by a scattered unpolarized incident beam and the depolarization effect suffered by a completely linearly polarized incident beam.

Study on polarization sensitivity of a planar-type segmented germanium detector for linearly polarized gamma rays

Study on polarization sensitivity of a planar-type segmented germanium detector for linearly polarized gamma rays

Polarization sensitivity and efficiency for a planar-type segmented germanium detector as a Compton polarimeter

We have investigated performance of a planar-type germanium detector with 25 segments as a Compton polarimeter to measure the linear polarization of gamma rays. We considered three different configurations in sampling horizontal and vertical Compton-scattering events for linearly polarized gamma rays incident on the detector. The experimental polarization sensitivity Q, coincidence efficiency ϵ coin, and figure of merit F for each configuration have been extracted for gamma rays of interest below 600 keV found in our previous in-beam spectroscopy on 155 Gd . We also obtained theoretical values for these three quantities through a Monte Carlo simulation. Experimental values were in good accord with simulation results for all the three configurations. The third configuration, sampling pairs between the segment of incidence and any off-diagonal segments in coincidence, turned out to have the largest Q as well as ϵ coin value of all the three configurations, thereby resulting in the best figure of merit F.

Linear polarization measurement of interband transitions in superdeformed 190hg: model-independent evidence for octupole vibrational structures.

The linear polarization of gamma rays between excited and yrast superdeformed (SD) states in 190Hg was measured using the four-element CLOVER detectors of the EUROBALL IV gamma-ray spectrometer. This measurement shows in a model-independent way that the interband transitions which compete with the highly collective in-band quadrupole transitions are largely enhanced electric dipoles. Not only do these results represent the first measurement of the multipolarity of transitions between different SD states, but they also provide strong evidence for the interpretation of the structures in the SD minimum of the A approximately 190 region in terms of octupole excitations.

Threshold contribution to the Gerasimov–Drell–Hearn sum rule in 3He

Measurements of the cross section, vector and tensor analyzing powers, and gamma-ray polarization in the radiative capture reactions D(p,γ)3He and p(d,γ)3He at cm. energies in the range 0–53 keV allow the determination of the reduced matrix elements (RMEs) relevant for these transitions. The RMEs provide values of the doublet and quartet Ml cross sections, as well as the asymptotic D-to-S state ratio. These quantities are in good agreement with theoretical predictions. The RMEs can also be used to compute the value of the integral which determines the Gerasimov-Drell-Hearn sum rule for 3He in the energy region of our experiment. The results are compared with the predictions of an ab initio microscopic three-body model calculation. The theoretical predictions for the value of this integral based on a ”nucleons-only” assumption are an order-of-magnitude smaller than experiment. The discrepancy is reduced to about a factor of two when meson-exchange currents are taken into account.

New photodisintegration threshold observable in3He

Measurements of the cross section, vector and tensor analyzing powers, and linear gamma-ray polarization in the radiative capture reactions $D(p,\ensuremath{\gamma}{)}^{3}\mathrm{He}$ and $p(d,\ensuremath{\gamma}{)}^{3}\mathrm{He}$ at c.m. energies in the range 0--53 keV allow the determination of the reduced matrix elements (RMEs) relevant for these transitions. From these RMEs the value of the integral which determines the Gerasimov-Drell-Hearn sum rule for ${}^{3}\mathrm{He}$ is obtained in the threshold region, corresponding to two-body breakup, and compared with the results of an ab initio microscopic three-body model calculation. The theoretical predictions for the value of this integral based on a ``nucleons-only'' assumption are an order of magnitude smaller than experiment. The discrepancy is reduced to about a factor of 2 when two-body currents are taken into account. This factor of 2 is due to an almost exact cancellation between the dominant $E1$ RMEs in the theoretical calculation. The excess $E1$ strength observed experimentally could provide useful insights into the nuclear interaction at low energies.

The 3701 keV neutron g 9/2 single-particle state in 57Ni

The neutron g(9/2) single-particle state in Ni-57 has been unambiguously identified in a combined measurement of the linear polarization, angular distribution, and angular correlation of gamma rays following the fusion-evaporation reaction Si-28(S-32,2pn)Ni-57 at a beam energy of 90 MeV. The linear polarization was measured with a EUROBALL cluster detector and a prototype of an encapsulated six-fold segmented hexaconical Ge-detector. The spin of the 3701 keV level in Ni-57 was confirmed to be I = 9/2 and its parity determined to be positive.

Gamma ray polarimetry using a position sensitive germanium detector

Imaging gamma-ray detectors make sensitive polarimeters in the Compton energy regime by measuring the scatter direction of gamma rays. The principle is to capitalize on the angular dependence of the Compton scattering cross section to polarized gamma rays and measure the distribution of scatter directions within the detector. This technique is effective in a double-sided germanium detector between roughly 50 keV and 1 MeV. This paper reviews device characteristics important to the optimization of a Compton polarimeter, and summarizes measurements we have made using a device with a 5×5 cm active area, 1 cm thickness, and strip-electrodes on a 2 mm pitch.

A method to determine the polarization of high energy gamma rays

A method to determine the polarization direction of a very high energy (50 MeV-30 GeV), linearly polarized gamma ray is analyzed and discussed. We study the differential cross section for pair production and show that the only relevant piece of information comes from the reconstruction of the pair trajectory. In particular the polarization information is coded in the azimuthal distribution of the created pair. We show that the Azimuthal Ratio (AR), defined as the ratio of produced pairs parallel to the polarization vector to pairs perpendicular to this vector, yields a very practical method to determine incoming polarization. We investigate the behavior of this function for different angular resolutions of the measuring apparatus and different energies of the incoming pairs.

Compton Polarimetry in Gamma-Ray Astronomy

The analysis of compact astronomical objects has generally dealt with the physical properties of the source within a two-parameter space, which is defined by the spectral characteristics and time variability. This approach often leads to the situation whereby two or more very different models can explain the observations successfully. Polarimetric observations have the diagnostic potential to discriminate between the different compact source models and can offer a unique insight into the geometrical nature of the emission zones. To date, however, no polarization observation in the gamma-ray energy domain has been successfully performed, due to the difficulties in making polarimetric measurements in this high-energy region of the spectrum. In this paper the polarized gamma-ray emission mechanisms are reviewed with the emphasis on their detectable characteristics. Potential astronomical sites in which these emission mechanisms may be at work are discussed. Observational results obtained in other wavebands and theoretical predications made for some of the most likely astronomical sources of polarization are reviewed. Compton polarimetry has long been used in the field of nuclear gamma-ray spectroscopy in the laboratory. The operational principle behind all generations of nuclear gamma-ray polarimeters has been to measure the asymmetry in the azimuthal distribution of the scattered photons. However none of the polarimeters designed for laboratory experiments will be sensitive enough to observe even the strongest astronomical source. In the past few years there have been a number of innovative developments aimed at the construction of astronomical gamma-ray polarimeters, either as dedicated experiments or in missions with polarimetric capability. The designs of all the polarimeters are based on either discrete or continuous position sensitive detector planes. In this paper the data analysis techniques associated with this type of polarimeter are discussed as well as methods of removing some of the systematic effects introduced by a non-ideal detector response function and observation conditions. Laboratory tests of these new polarimetric techniques are reviewed. They demonstrate the feasibility of building a suitably sensitive astronomical gamma-ray polarimeter. Optimization of the design of pixellated detector array based polarimeters is also addressed. The INTEGRAL mission, which is to be launched by ESA in the year 2001, is the most likely telescope to perform the first successful gamma-ray polarization observation. The polarimetric characteristics of the two main instruments on board INTEGRAL are evaluated and their sensitivities to a wide range of potentially polarized gamma-ray sources are estimated.

PDCO: Polarizational-directional correlation from oriented nuclei

A general formula is given for correlation between two polarized gamma rays (γ1 and γ2) emitted in a cascade from an oriented (for example, due to a heavy ion reaction) nucleus. It allows us or one to calculate the angular correlation between: (a) Linear polarizations of γ1 and γ2. (b) Polarization of γ1 and direction of γ2 or vice versa. (c) Directions of γ1 and γ2 (DCO). The formula, discussed in detail for the case (b), can be used in the analysis of data coming from the modern multidetector gamma ray spectrometers that contain new generation detectors (e.g. CLOVER) sensitive to the polarization. The analysis of polarization together with DCO ratio can lead to a unique spin/parity assignment and a mixing ratio determination.

Polarized gamma-rays with laser-Compton backscattering

Abstract Completely polarized gamma-rays can be generated by Compton backscattering of laser light. The energy of the polarized gamma-rays ranges from 1 to 10 MeV by using a Nd:YAG laser and the storage ring TERAS at Electrotechnical Laboratory. The energy spread of the gamma-rays varies from 1 to 4% according to its energy. The gamma-ray yield is measured to be 47.2 photons mA−1 W 1s−1. By using these polarized gamma-rays elastically scattered photons have been measured. The parity of the J = 1 level in 208Pb (EX = 5.514 MeV) was clearly determined to be negative and the parity of the J = 1 level in 11B (EX = 4.4451 MeV), on even-odd nucleus, was also measured to be negative. Further development in the SR-FEL will allow us to use ∼107 gamma-rays.

Gamma-Ray Bursts from Minijets

view Abstract Citations (140) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gamma-Ray Bursts from Minijets Shaviv, Nir J. ; Dar, Arnon Abstract Striking similarities exist between high-energy gamma-ray emission from active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). They suggest that GRBs are generated by inverse Compton scattering from highly relativistic electrons in transient jets. Such jets may be produced along the axis of an accretion disk formed around stellar black holes (BHs) or neutron stars (NSs) in BH-NS and NS-NS mergers and in accretion induced collapse of magnetized white dwarfs (WDs) or neutron stars in close binary systems. Such eve ts may produce the cosmological GRBs. Transient jets formed by single old magnetized neutron stars in an extended Galactic halo may produce a local population of GRBs Here we show that jet production of GRBs by inverse Compton scattering can explain quite simply the striking correlations that exist between various temporal features of GRBs, their duration histogram, the power spectrum of their complex multipeak light curves, their power-law high energy spectra and other features of GRBs. Some additional predictions are made including the expected polarization of gamma rays in the bursts. Publication: The Astrophysical Journal Pub Date: July 1995 DOI: 10.1086/175923 arXiv: arXiv:astro-ph/9407039 Bibcode: 1995ApJ...447..863S Keywords: GAMMA RAYS: BURSTS; RADIATION MECHANISMS: NONTHERMAL; STARS: NEUTRON; Astrophysics E-Print: 26 pages uuencoded compressed postscript file, TECHNION-PH-94-10 full text sources arXiv | ADS | data products SIMBAD (5) NED (1)

A new telescope for wide-band gamma-ray astronomy: The Silicon Compton Recoil Telescope (SCRT)

A new prototype gamma-ray telescope is described which is sensitive from 0.3 to 30 MeV as a Compton telescope and to 100 MeV as a pair detector. The Silicon Compton Recoil Telescope (SCRT) uses multilayers of silicon strip detectors as a Compton gamma-ray converter. Recoil electrons are tracked with the silicon strip detectors, and their energy losses and directions are measured. The direction and energy of the Compton-scattered gamma rays are measured with CsI(Tl)-photodiode detectors. Thus unique directions and energies are found for each incident gamma ray for the first time and without the background of overlapping rings. SCRT is the first Compton telescope to image the gamma-ray sky directly. It can also detect electron-positron pairs from gamma rays above 5 MeV, extending SCRT's sensitivity to above 100 MeV. Typical resolutions are 3% (FWHM) in energy at 2 MeV and 0.5 deg (1 sigma) in angle. The proposed prototype SCRT instrument has a sensitive area of 650 sq cm, a detection efficiency of 3%, a size reduction by about an order of magnitude, and a sensitivity of 15 millicrab for a typical Compton Observatory exposure. SCRT can also measure the polarization of the incident gamma rays, especially at low energies and large scattered angles. Simulation calculations and a discussion of results with a laboratory model are presented.

On the multiple scattering of linearly polarized gamma rays

A Monte Carlo method is described for the multiple scattering of linearly polarized gamma rays in non-magnetized solid state targets. An example is given for 100 keV photons scattered in aluminum. In addition, cross section and Stokes parameters for a spin-polarized target are discussed.