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X-Ray Astronomy Lab X-rays Why look for X-rays? –High temperatures –Atomic lines –Non-thermal processes X-ray detectors X-ray telescopes The Lab.

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Presentation on theme: "X-Ray Astronomy Lab X-rays Why look for X-rays? –High temperatures –Atomic lines –Non-thermal processes X-ray detectors X-ray telescopes The Lab."— Presentation transcript:

1 X-Ray Astronomy Lab X-rays Why look for X-rays? –High temperatures –Atomic lines –Non-thermal processes X-ray detectors X-ray telescopes The Lab

2 X-rays Measure X-ray energies in energy units (eV or keV) or wavelength units (Angstroms) Soft X-rays = keV Medium (“standard”) X-rays = 2-10 keV Hard X-rays keV

3 Photons Energy of photon is set by frequency/wavelength Unit is electon-volt (eV or keV) 1 eV = 1.6  J = 1.6  erg

4 Thermal Radiation Thermal spectrum peaks at 2.7 kT, falls off sharply at higher and lower energies. Wien’s Law: Peak of radiation = 2.9  10 7 Å/ T(K) = (0.43 keV)  (T/10 6 K)

5 Black holes make X-rays BH of 10 solar masses can have a luminosity of 100,000 times the Sun’s emitted from a region ~ 200 km in radius Use Stefan-Boltzman law to find temperature, L = 4  R 2  T 4 T A = 1000  5700 K ~ 6,000,000 K Peak at 4.8 Å = 2.6 keV

6 Atomic lines Link to tables of line energies Photons emitted from transitions to inner electron shells are in the X-ray band

7 Non-thermal processes Particle acceleration in magnetic fields Supernova remnants Corona of black hole accretion disks Radiation from pulsars Jet acceleration by black holes

8 X-Ray Detectors Usually detect each individual photon Wish to measure photon properties –Energy –Number –Time of arrival –Position –Polarization

9 Solid State X-ray Detectors X-ray interacts in material to produce photoelectrons which are collected by applying a drift field

10 Energy Resolution Number of initial photoelectrons N = E/w, where E = energy of X- ray, w = average ionization energy (3.62 eV for Si) Creation of photoelectrons is a random process, number fluctuates Variance of N:  N 2 = FN, where F is the “Fano” factor, fluctuations are lower than expected from Poisson statistics (F = 0.17 for Ar, Xe) Energy resolution (FWHM) is For silicon, F = 0.115, w = 3.62 eV. Energy resolution is often degraded by electronic noise.

11 Quantum Efficiency To be detected, X-ray must pass through window without being absorbed and then be absorbed in gas T w is geometric open fraction of window, t is window thickness, d is gas depth, ’s are absorption length for window/gas (energy dependent)

12 Charge Coupled Devices

13 Pixelated Detectors CCDs have small pixel sizes, good energy resolution, and a single readout electronics channel, but are slow, thin (< 300 microns), and only made in Si. Pixelated detectors have larger pixel sizes, require many electronics channels, but are fast and can be made thick and of various materials – therefore can be efficient up to higher energies

14 X-Ray Reflectivity

15 Grazing Incidence Optics

16 The Lab 1.Shine X-rays on sample 2.Measure energies of fluorescent X-rays 3.Determine elements in sample

17 Silicon X-Ray Detector X-Ray Generator

18 Setup Preamp Multichannel analyzer X-ray source Target Si X Xe-e- 1. Calibrate MCA eV/channel: Measure spectra of known targets 2. Determine composition of unknown target: Measure spectrum and identify lines.


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