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1 Introduction  A more general title for this course might be “Radiation Detector Physics”  Goals are to understand the physics, detection, and applications.

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Presentation on theme: "1 Introduction  A more general title for this course might be “Radiation Detector Physics”  Goals are to understand the physics, detection, and applications."— Presentation transcript:

1 1 Introduction  A more general title for this course might be “Radiation Detector Physics”  Goals are to understand the physics, detection, and applications of ionizing radiation The emphasis for this course is on radiation detection and applications to radiological physics However there is much overlap with experimental astro-, particle and nuclear physics And examples will be drawn from all of these fields

2 2 Introduction  While particle and medical radiation physics may seem unrelated, there is much commonality Interactions of radiation with matter is the same Detection principals of radiation are the same Some detectors are also the same, though possibly in different guises  Advances in medical physics have often followed quickly from advances in particle physics

3 3 Introduction  Roentgen discovered x-rays in 1895 (Nobel Prize in 1901)  A few weeks later he was photographing his wife’s hand  Less than a year later x-rays were becoming routine in diagnostic radiography in US, Europe, and Japan  Today the applications are ubiquitous (CAT, angiography, fluoroscopy, …)

4 4 Introduction  Ernest Lawrence invented the cyclotron accelerator in 1930 (Nobel Prize in 1939)  Five years later, John Lawrence began studies on cancer treatment using radioisotopes and neutrons (produced with the cyclotron)  Their mother saved from cancer using massive x- ray dose

5 5 Introduction  Importance and relevance Radiation is often the only observable available in processes that occur on very short, very small, or very large scales Radiation detection is used in many diverse areas in science and engineering Often a detailed understanding of radiation detectors is needed to fully interpret and understand experimental results

6 6 Introduction  Applications of particle detectors in science Particle physics  ATLAS and CMS experiments at the CERN LHC  Neutrino physics experiments throughout the world Nuclear physics  ALICE experiment at the CERN LHC  Understanding the structure of the nucleon at JLAB Astronomy/astrophysics  CCD’s on Hubble, Keck, LSST, …, amateur telescopes  HESS and GLAST gamma ray telescopes  Antimatter measurements with PAMELA and AMS Condensed matter/material science/ chemistry/biology  Variety of experiments using synchrotron light sources throughout the world

7 7 Introduction  Applications of radiation/radiation detectors in industry Medical diagnosis, treatment, and sterilization Nuclear power (both fission and fusion) Semiconductor fabrication (lithography, doping) Food preservation through irradiation Density measurements (soil, oil, concrete) Gauging (thickness) measurements in manufacturing (steel, paper) and monitoring (corrosion in bridges and engines) Flow measurements (oil, gas) Insect control (fruit fly) Development of new crop varieties through genetic modification Curing (radiation curing of radial tires) Heat shrink tubing (electrical insulation, cable bundling)  Huge number of applications with hundreds of billions of $ and millions of jobs

8 8 Introduction

9 9  Cargo scanning using linear accelerators

10 10 Radiation  Directly ionizing radiation (energy is delivered directly to matter) Charged particles  Electrons, protons, muons, alphas, charged pions and kaons, …  Indirectly ionizing radiation (first transfer their energy to charged particles in matter) Photons Neutrons  Biological systems are particularly sensitive to damage by ionizing radiation

11 11 Electromagnetic Spectrum  Our interest will be primarily be in the region from 100 eV to 10 MeV

12 12 Electromagnetic Spectrum  Note the fuzzy overlap between hard x-rays and gamma rays  Sometimes the distinction is made by their source X-rays  Produced in atomic transitions (characteristic x-rays) or in electron deacceleration (bremsstrahlung) Gamma rays  Produced in nuclear transitions or electron-positron annihilation  The physics is the same; they are both just photons

13 13 Nuclear Terminology  Nuclear species == nuclide A nucleons (mass number), Z protons (atomic number) N neutrons (neutron number) A = Z+N  Nuclides with the same Z == isotopes  Nuclides with the same N == isotones  Nuclides with the same A == isobars  Identical nuclides with different energy states == isomers Metastable excited state (T 1/2 >10 -9 s)

14 14 Table of Nuclides  Plot of Z vs N for all nuclides  Detailed information for ~ 3000 nuclides

15 15 Table of Nuclides  Here are some links to the Table of Nuclides which contain basic information about most known nuclides

16 16 Table of Nuclides  ~3000 nuclides but only ~10% are stable  No stable nuclei for Z > 83 (bismuth)  Unstable nuclei on earth Naturally found if τ > 5x10 9 years (or decay products of these long-lived nuclides)  238 U, 232 Th, 235 U (Actinium) series Laboratory produced  Most stable nuclei have N=Z True for small N and Z For heavier nuclei, N>Z

17 17 Valley of Stability

18 18 Valley of Stability  Table also contains information on decays of unstable nuclides Alpha decay Beta (minus or plus) decay Isomeric transitions (IT) Spontaneous fission (SF)

19 19 Valley of Stability

20 20 Binding Energy  The binding energy B is the amount of energy it takes to remove all Z protons and N neutrons from the nucleus B(Z,N) = {ZM H + NM n - M(Z,N)}  M(Z,N) is the mass of the neutral atom  M H is the mass of the hydrogen atom  One can also define proton, neutron, and alpha separation energies S p = B(Z,N) - B(Z-1,N) S n = B(Z,N) - B(Z,N-1) S α = B(Z,N) - B(Z-2,N-2) - B( 4 He)  Similar to atomic ionization energies

21 21 Binding Energy  Separation energies can also be calculated as Q, the energy released, is just the negative of the separation energy S  Q>0 => energy released as kinetic energy  Q kinetic energy converted to nuclear mass or binding energy  Sometimes the tables of nuclides give the mass excess (defect) Δ = {M (in u) – A} x MeV Note these are atomic masses

22 22 Example  Is 238 U stable wrt to α decay? S α = B( 238 U) - B( 234 Th) - B( 4 He) S α = – – (keV) S α = MeV => Unstable and will decay

23 23 Radioactivity  Radioactive decay law  Nomenclature λ in 1/s = decay rate λ in MeV = decay width (h-bar λ) τ in sec = lifetime You’ll also see Γ = λ

24 24 Radioactivity  t 1/2 = time for ½ the nuclei to decay

25 25 Radioactivity  It’s easier to measure the number of nuclei that have decayed rather than the number that haven’t decayed (N(t))  The activity is the rate at which decays occur Measuring the activity of a sample must be done in a time interval Δt << t 1/2  Consider t 1/2 =1s, measurements of A at 1 minute and 1 hour give the same number of counts

26 26 Radioactivity  Activity units bequerel (Bq)  1 Bq = 1 disintegration / s  Common unit is MBq curie (C)  1 C = 3.7 x disintegrations / s  Originally defined as the activity of 1 g of radium  Common unit is mC or μC

27 27 Radioactivity  Often a nucleus or particle can decay into different states and/or through different interactions The branching fraction or ratio tells you what fraction of time a nucleus or particle decays into that channel  A decaying particle has a decay width Γ Γ = ∑ Γ i where Γ i are called the partial widths The branching fraction or ratio for channel or state i is simply Γ i /Γ

28 28 Radioactivity  Sometimes we have the situation where  The daughter is both being created and removed

29 29 Radioactivity  We have (assuming N 1 (0)=N 0 and N 2 (0)=0)

30 30 Radioactivity  Case 1 (parent half-life > daughter half-life) This is called transient equilibrium

31 31 Radioactivity  Transient equilibrium A 2 /A 1 = 2 /( ) Example is 99 Mo decay (67h) to 99m Tc decay (6h) Daughter nuclei effectively decay with the decay constant of the parent

32 32 Radioactivity  Case 2 (parent half-life >> daughter half-life) This is called secular equilibrium Example is 226 Ra decay

33 33 Radioactivity  Secular equilibrium A 1 =A 2 Daughter nuclei are decaying at the same rate they are formed

34 34 Radioactivity  Case 3 (parent half-life < daughter half-life) What happens?

35 35 Units  Sometimes I will slide into natural units used in particle physics  Then at the end of the calculation or whatever we’ll insert h-bar’s and c’s to make the answer dimensionally correct  And while it might not come up so often

36 36 Electromagnetic Spectrum  What part of the EM spectrum has a physiological effect on the human body?

37 37 Radioactivity  Case 3 (parent half-life < daughter half-life) What happens?  Parent decays quickly away, daughter activity rises to a maximum and then decays with its characteristic decay constant

38 38 Electromagnetic Spectrum  What part of the EM spectrum has a physiological effect on the human body?

39 39 Electromagnetic Spectrum  Photon energy is given by

40 40 Constants and Conversions


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