Physics 736. Experimental Methods in Nuclear-, Particle-, and Astrophysics

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1 Physics 736 Experimental Methods in Nuclear-, Particle-, and Astrophysics - Basic nuclear processes and radiation sources - Karsten Heeger heeger@wisc.edu

2 Particles & Radiation How do we observe physics interactions?

3 Particles & Radiation What are we interested in measuring?

4 Particles & Radiation What are we interested in measuring? Charged particle radiation fast electrons heavy charged particles Uncharged particles and radiation electromagnetic radiation neutrons neutrinos WIMPS?

5 Radioactivity

6 Radioactivity

7 Alpha Decay proton number (Z) neutron number (N)

Alpha Decay #-Instability bility 4 l. BasicNuclearProccsscs in RadioactivcSour particles, therefore, show a monoenergeticenergy spectrum.

daughternucleusare nevertheless nuclei, the energyspectrumshowsseveralmonoenergeticlineseachcorrespondingto decayto one of thesestates.someof the more commonlyusedsourcerare listed belo in Table 1.2.

8 Alpha Decay #-Instability bility 4 l. BasicNuclearProccsscs in RadioactivcSour particles, therefore, show a monoenergeticenergy spectrum. As well, since barri transmissionis dependenton energy,all c-sourcesare generallylimited to the ran Gamow =4-6 MeV with the higher energy sourceshaving the higher transmissionprobabili and thus the shorter half-life. For this reasonalso, most edecays are dircctly to th 1928 ground state of the daughter nucleussince this involves the highestenergy chang possible,and in su Decaysto excitedstatesof the daughternucleusare nevertheless nuclei, the energyspectrumshowsseveralmonoenergeticlineseachcorrespondingto decayto one of thesestates.someof the more commonlyusedsourcerare listed belo in Table 1.2. Gamow 1928 Text Trbh 1.2. Characteristicsof somealpha cmitters alpha energy spectrum Karsten Heeger, Univ. Wisconsin lsotope Half-life EncrgieslMcVl Branching ala- 433yrs. 2lho I 38days t5% r2.e% td)7c z2cm 163days 5.4E6 5.ut tt Experimental Nuclear Physics - PHYS741 74h 26q. alpha source 52 Becauseof its double charge, + 2e, alpha particleshavea very high rate of ener loss in matter. The range of a 5 McV a-particle in air is only a f w ccntimeters,fo example.for this reasonit is necessaryto make c sourcqras thin as posriblein order minimize energylossand particle absorption. Most esources are made,in fact, by d Karsten Heeger, Univ. of Wisconsin Physics 736, Spring positing the isotope the surfaceof a suitablebacking materialand protectingit wit on2013 Experimental Nuclear Physics - PHYS Univ. Wisconsin

9 Beta-decay Ul f J. List of pure p- crnitters h,cc Half-lifc E* [McVl t rc + i ts t ccr q6 TA trc EPD Dfl 12.26yr 5730 yr l4.2td u.4d t7.9 d!.$ x ld yr l5j d Dyt tl.7 yt/6h 2.l2xrd y 2.62yt 3.tt yr t t o.16l s2 0.() / o.xu o.76

10 Electron Capture or Auger electron

11 Annihilation Radiation intensity height thick Na-22 source

12 Internal Conversion nuclear excitation transferred to atomic electron ejection of electron looks like 2-step process classically -> single quantum process, amplitude can be calculated with pertubation theory

13 Beta-Spectrum and Internal Conversion Lines Internal Conversion Process: - information from the internal conversion electrons about the binding energies of the electrons in the daughter atom - relative intensities of these internal conversion electron peaks can give information about the electric multipole character of the nucleus. internal conversion can be useful source of monoenergetic e -

Beta-Spectrum and Internal Conversion - 203 Hg, which decays to 203 Tl by beta emission, leaving

- can proceed to the ground state by emitting a 279.190 kev gamma ray, or by internal conversion.

- internal conversion process can interact with any of the orbital electrons, the result is a

energy spectrum of the beta emission. - Energy yield of this electromagnetic transition: 279.

14 Beta-Spectrum and Internal Conversion Hg, which decays to 203 Tl by beta emission, leaving the 203 Tl in an electromagnetically excited state. - can proceed to the ground state by emitting a kev gamma ray, or by internal conversion. In this case the internal conversion is more probable. - internal conversion process can interact with any of the orbital electrons, the result is a spectrum of internal conversion electrons which will be seen as superimposed upon the electron energy spectrum of the beta emission. - Energy yield of this electromagnetic transition: kev => ejected electrons will have that energy minus their binding energy in the 203 Tl daughter atom. Electron emissions from the Hg-203 to Tl-203 decay, measured by A. H. Wapstra, et al., Physica 20, 169 (1954)

15 Auger Electrons

16 Neutron Sources spontaneous fission nuclear reactions

17 Karsten Heeger, Univ. of Wisconsin NUSS, July 13, 2009

Physics 736. Experimental Methods in Nuclear-, Particle-, and Astrophysics

Physics 736. Experimental Methods in Nuclear-, Particle-, and Astrophysics Physics 736 Experimental Methods in Nuclear-, Particle-, and Astrophysics - Basic nuclear processes and radiation sources - Karsten Heeger heeger@wisc.edu Particles & Radiation How do we observe physics