? 14 10 m Radioactivity p. 1/1 Radioactivity and Nuclear - - PowerPoint PPT Presentation

The Structure of Matter

10 m

7

10 m

1

10 m

−6

10 m

−9

10 m

−15

10 m

−14

10 m

−10

10 m

19

?

Radioactivity – p. 1/1

Radioactivity and Nuclear Decay

At the end of the nineteenth century Henri Becquerel discovers the spon- taneous emission of ‘rays’. The surprise was that no energy in- put was required. These rays carry off huge amounts of energy. Some examples of ‘rays’.

Original Photographic Plate Developed by Henri Becquerel.

Po Pb + He

212 84 208 82 2 4 212Bi 83 212 84

Pb + He (α) (β) Cs

137 55 137 56

Ba(0.0 keV) +

137 56

γ + ν (undetected) + ν (undetected)

e e

Po + e Ba(0.662 keV) + e

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The 4He − 234

90Th Potential

Blue Known Red AGuess 10 20 30 40 50 60 70 40 20 20 40 rfm VMeV

Radioactivity – p. 3/1

Rutherford Scattering

Alpha source

84 210 2 4

Po He + Pb

82 206

Microscope Alpha beam Collimator ZnS Scattered helium Thorium target

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The 4He − 234

90Th Potential

Blue Known Red AGuess 10 20 30 40 50 60 70 40 20 20 40 rfm VMeV

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Milking the Cow

This ‘clock’ ticks by producing a short-lived, radioactive material. Start with a liquid containing the ra- dioactive isotope 137Cs that decays very slowly.

137Cs→e−+137Ba(0.662 MeV)

The number “0.662 MeV” means there is still energy (0.662 MeV) stored in the Ba-137 nucleus. The excited Ba-137 then emits a high-energy photon or gamma ray to reach the stable ground state of

137Ba.

137Ba(0.662)→137Ba(0.0)+γ

137 137

γ

−

e

56 Ba

Cs

55

excited state ground state (0.662 MeV)

Decay scheme of cesium-137.

Radioactivity – p. 6/1

Using the Reduced χ2

The χ2 and reduced χ2 are defined as χ2 =

N

• i=1

((yi − f(xi))2 σ2

i

and reduced χ2 = χ2 N − d.o.f where N is the number of data points.

• R. Muto, et al., Phys. Rev. Lett., 98,

042501 (2007).

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Geiger-Muller Tube

A Geiger-Muller tube (or GM tube) is the sensing element of a Geiger counter instrument that can detect a single particle of ionizing radiation. It is a type of gaseous ionization detector with an operating voltage in the Geiger plateau.

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Poisson Statistics

P(m : n, p) = 1 m!µme−µ µ = np m - no. of events µ - average n - no. of trials p - probability of an event Probability of a discrete event occurring m times in a particular time period.

Radioactivity – p. 9/1

Poisson Statistics

P(m : n, p) = 1 m!µme−µ µ = np m - no. of events µ - average n - no. of trials p - probability of an event Probability of a discrete event occurring m times in a particular time period. Number of soldiers killed by horse-kicks each year in Prussian cavalry corp (famous example in by a book of Ladislaus Josephovich Bortkiewicz (1868-1931)). Number of yeast cells for brewing Guinness (William Sealy Gosset (1876-1937)). The number of phone calls arriving at a call center per minute. The number of deaths per year in a given age group. The number of jumps in a stock price in a given time interval. The number of mutations in a given stretch of DNA after a certain amount of radiation. The proportion of cells that will be infected at a given multiplicity of infection.

Radioactivity – p. 9/1

How Old is the Shroud of Turin?

Radioactivity – p. 10/1

Radiocarbon Dating

N

14

N

14

C

14

CO 2

14

O2 dead or buried material proton neutron loses C

14

Atmosphere Cosmic ray proton Radioactivity – p. 11/1

Radiocarbon Dating

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Radiocarbon Dating

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Radiocarbon Calibration Curve

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