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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: "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 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 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 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 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 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 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 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 Introduction

9 Introduction Cargo scanning using linear accelerators

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

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 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 (T1/2>10-9s)

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

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

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 > 5x109 years (or decay products of these long-lived nuclides) 238U, 232Th, 235U (Actinium) series Laboratory produced Most stable nuclei have N=Z True for small N and Z For heavier nuclei, N>Z

17 Valley of Stability

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 Valley of Stability

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) = {ZMH + NMn - M(Z,N)} M(Z,N) is the mass of the neutral atom MH is the mass of the hydrogen atom One can also define proton, neutron, and alpha separation energies Sp = B(Z,N) - B(Z-1,N) Sn = B(Z,N) - B(Z,N-1) Sα = B(Z,N) - B(Z-2,N-2) - B(4He) Similar to atomic ionization energies

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<0 => 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 Example Is 238U stable wrt to α decay?
Sα = B(238U) - B(234Th) - B(4He) Sα = – – (keV) Sα = MeV => Unstable and will decay

23 Radioactivity Radioactive decay law Nomenclature τ in sec = lifetime
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 Radioactivity t1/2 = time for ½ the nuclei to decay

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 << t1/2 Consider t1/2=1s, measurements of A at 1 minute and 1 hour give the same number of counts

26 Radioactivity Activity units bequerel (Bq) curie (C)
1 Bq = 1 disintegration / s Common unit is MBq curie (C) 1 C = 3.7 x 1010 disintegrations / s Originally defined as the activity of 1 g of radium Common unit is mC or μC

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 = ∑Γi where Γi are called the partial widths The branching fraction or ratio for channel or state i is simply Γi/Γ

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

29 Radioactivity We have (assuming N1(0)=N0 and N2(0)=0)

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

31 Radioactivity Transient equilibrium A2/A1=l2/(l2-l1)
Example is 99Mo decay (67h) to 99mTc decay (6h) Daughter nuclei effectively decay with the decay constant of the parent

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

33 Radioactivity Secular equilibrium A1=A2
Daughter nuclei are decaying at the same rate they are formed

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

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

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

39 Electromagnetic Spectrum
Photon energy is given by

40 Constants and Conversions


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