Typical Decay scheme II

1. Typical Decay scheme II • Nuclei can decrease their proton number by one in three ways, positron emission (the most common) • Electron capture (much more rarely; see next slide), or proton emission (very rare). • Decay rates expressed in terms of Becquerrel (1/sec) or Curies (37 GBq) http://www.nucleide.org/DDEP_WG/Nuclides/Na-22_tables.pdf

2. Absorption length for gammas(in lead and aluminum) From E. Segre, “Nuclei and Particles” 2nd ed. (1977)

3. Examples The LENS neutron source at IU creates roughly 4e4 neutrons per pC of proton charge (incident at 13MeV) through the reaction:9Be(p,n)9B in a 1mm thick target. Estimate the cross section for this reaction (Note: Fro Be r=1.85 g/cm3 and W=9.01g/mole). 2. A foil of natural In that is 1.0 mm thick is placed in a thermal neutron beam (v=2200 m/s) of flux 107n/cm2.s. In has a molecular weight of 114.8 g/mole, and a density of 7.31 g/cm3. 116In is a beta emitter and we will assume that it is only produced in a state that decays with a 54 min half life. a). What is the flux of neutrons on the back side of the foil? b). If the foil is in the beam for 1.0 min, what is the activity due to 116In? c). What is the 116In activity if the foil is in the beam for 10 hours? The information at the website on the following slide may be useful.

4. Cross Sections http://www.ncnr.nist.gov/resources/n-lengths/

5. Alpha Decay T&R Fig. 12.11 http://en.wikipedia.org/wiki/File:Alpha1spec.png

6. Lecture 23 Potential Barrier: Alpha decay The deeper the “bound” state is below the top of the barrier, the lower will be the kinetic energy of the alpha particle once it gets out, and the slower will be the rate of tunneling (and hence the longer the half-life). Figures from Rohlf “Modern Physics from a to Zo”.

7. Radiation Shielding • Different types of radiation penetrate through matter with different ranges. Alpha particles are very easily stopped (doubly charged and relatively slow), beta particles are relatively easy to stop, gamma rays need very heavy shielding, and neutrons are the hardest to shield against. • https://reich-chemistry.wikispaces.com/b.sulser+and+k.nagle+powerpoint+presentation neutron

8. Radiation Dose • Dose: • 1 Gray = 1 J/kg of whatever radiation (energy deposited per unit mass), supplants the RAD (Radiation absorbed dose) • Roentgen (older unit, radiation needed to produce a certain charge per unit mass (1 esu /cm3 of dry air). This corresponds to 0.258 mC/kg. • Equivalent Dose • 1 Sievert: absorbed dose multiplied by factors to account for relative biological effectiveness for particular radiation type (b, g, n etc.; energy etc. ) and body part involved. NOTE units are the same as the Gray, but the meaning is quite different. • REM (Roentgen Equivalent Man): 1 REM = 10 mSv

9. Radiation Dose • NOTES: • Prior to 1990 the weighting factor was referred to as the “Quality Factor and you will still see this term used. • There is some controversy over the appropriateness of the weighting factors (especially for alphas) http://www.ccohs.ca/oshanswers/phys_agents/ionizing.html

10. Effects of Radiation • “LD50/60” Dose that would result in death for 50% of the population so exposed within 60 days (Lethal Dose to 50% of the population) • LD50/60 limit for gamma radiation is roughly 450 RAD (or 4.5Gray) for whole-body exposure • Threshold lethal Dose (2 Gy, whole body exposure) • Beyond these acute dose issues, future development of cancer is also a concern • Doses at ~10 cSv appear to produce no increased risk of cancer • Occupational limits for radiation workers are set at levels below this to be conservative (typically 50 mSv/yr for radiation workers). • Typical background exposure in the US is of the order of 3.5 mSv/yr (as high as 8 mSv/yr in Colorado mountains).

11. Sources of Background Radiation • Cosmic Rays • Naturally occurring radioactive nuclei • 40K this is the most abundant radio-nuclide in your body • 14C (e.g. about 50 times/sec one C atom in the DNA of one of your cells is converted to N by beta decay). • 222R, a decay product from 238U, and a common concern in buildings • Medical tests • Man-made nuclides (fallout, waste, release etc.).

12. Sources of Background Radiation http://web.princeton.edu/sites/ehs/osradtraining/backgroundradiation/background.htm

13. Effects of Radiation • Recall: 1 rem is roughly 10mGy for gammas • Typical background radiation is 350 mrem/yr, airline travel gives roughly 0.4-1 mrem/hr (4-10 mSv/hr) • http://www.physics.isu.edu/radinf/risk.htm • See also: http://trshare.triumf.ca/~safety/EHS/rpt/rpt_4/node20.html

14. Radiation Dose • Different types of radiation at a given energy have different “Relative Biological Effectiveness”, and different parts of the body have different susceptibilities to radiation, so you have to be a bit careful about how you quote numbers. • Today medical physicists discuss dose in Gray to specific organs, rather than Sieverts etc..

15. Relative Biological Effectiveness • NOTES: • Different parts of the body have different susceptibilities to radiation (in terms of their likelihood of developing cancer after a given exposure) • This is taken into account in planning radiation treatments for cancer. http://www.ccohs.ca/oshanswers/phys_agents/ionizing.html

17. Relative Biological Effectiveness Note that a 1.5 Gy dose of Carbon ions has the same biological effect as a 4.5Gy dose of photons (for this particular cell type). http://en.wikipedia.org/wiki/Relative_biological_effectiveness

18. Applications of Radiation • Radiation and radioactive materials are used in numerous applications today, we’ll touch on only a few of these: • Nuclear Medicine • Diagnostics (x-rays, CAT scans, PET scans, etc.) • Cancer treatment (x-rays/gamma-rays, radio-nuclides, protons, heavy ions) • The key here is that rapidly reproducing cells (such as CANCER, in children/fetuses) are more susceptible to radiation damage AND CANCER cells are less able to repair the damage radiation causes (at least that is the dogma, there is some conflicting information on this). • Dating of artifacts (archeologic, organic, geologic etc.) • trace element analysis • Nuclear power

19. Proton Radiotherapy http://en.wikipedia.org/wiki/Proton_therapy http://mpri.org/science/vstreatments.php

20. KEY element (from CALM): • Large, unstable, nuclei (2) • Neutron activated dissociation (3) • These are both necessary but not sufficient: • “Chain reaction (8)” but what does that mean? • One neutron induces a reaction that produces MULTIPLE neutrons out (to sustain the reaction) (6) THIS IS THE KEY ingredient. Nuclear Fission http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fission.html

21. Fission products http://en.wikipedia.org/wiki/Fission_products http://www.euronuclear.org/info/encyclopedia/f/fissionproducts.htm

22. Nuclear Reactors (LWR’s) Pressurized water reactor (PWR) 66% of US reactors are this type Boiling water reactor (BWR) http://reactor.engr.wisc.edu/power.html

23. Yucca Mountain http://www.ocrwm.doe.gov/ymp/about/why.shtml

24. American Nuclear Plants http://www.nrc.gov/info-finder/reactor/

25. Nuclear Waste depots http://en.wikipedia.org/wiki/Radioactive_waste

26. Nuclear Decay Chains 4n chain: Thorium series 4n+2 chain Radium series 4n+1 chain Neptunium series Does not include the 4n+3 chain or Actinium series which terminates in 207Pb (Wikipedia does not have so nice a graphic for that chain; from: http://en.wikipedia.org/wiki/Decay_chain

27. About 1 part per trillion of atmospheric carbon is 14C, thanks to this mechanism. • Dates have to be calibrated to account for historic variations in the production and distribution of 14C in the atmosphere (thank goodness for the Bristlecone pine tree). Figs from: • http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/carbondating.htm • and http://en.wikipedia.org/wiki/Radiocarbon_dating

28. Various Dating schemes See article at: http://physics.info/half-life/ Note; this is really a toy example (1014 carbon atoms is only 2 ng of sample, typically you would need much more; estimate how much more)

29. Various Dating schemes See article at: http://physics.info/half-life/

30. Various Dating schemes See article at: http://physics.info/half-life/

31. Early Particle discovery: W- From E. Segre “Nuclei and Particles”, 2nd edition Particles appear as tracks (in bubble chambers in the early days, in electronic trackers of various sorts today) that are bent by a magnetic field. By measuring curvature, track length etc. things like half-life, momentum, charge etc. can be determined.

32. Early categorization of Particles Early collider experiments started to reveal more and more particles, and people started to question whether they were truly “Fundamental”, but did allow for the prediction of “missing particles that were later found. Attempts to rationalize this “zoo” of particles led Gell-Mann (and independently Zweig) to suggest more fundamental building blocks (based largely on the observation of patterns [symmetries] in the properties of the particles; they appeared in families of 1, 8, 10, 27 etc. members]:

33. The Standard Model http://newsimg.bbc.co.uk/media/images/41136000/gif/_41136526_standard_model2_416.gif