pdf 2.3 seeking stability

7/28/2019 PDF 2.3 Seeking Stability

1/19

A Look at NuclearScience and Technology

Larry Foulke

Atomic and Nuclear Physics The Einstein Connection

2.3 Seeking Stability


2/19

Nuclear Stability (Proton Rich)

2

p

n

p

p

n

nn

pp

p

pp

p

Too many protons-or- nucleus too large

Long-range repulsive

Coulomb forcesoverpower short-range attractivenuclear forces.

Nucleus is unstable.Nuclear Force (Attractive)

Coulomb Force (Repulsive)


3/19

Nuclear Stability (Neutron Rich)

3

n

n

nn

pp

p

p

Too many neutrons

Significant asymmetry betweenthe number of protons andnumber of neutrons creates an

imbalance in the internalenergy levels of the two types ofnucleons.

Excess neutrons cause thenucleus to be at a higher thandesired energy state.

Nucleus is unstable.

nn

n

n

n


4/19

Nuclear Stability

Too many protons Unstable

Too many neutrons Unstable

1< neutrons / protons


5/19

Chart of the Nuclides

UNSTABLE Proton Rich

UNSTABLE Neutron Rich

Too many

NucleonsSolution: Emit particle orbreak apart.

Too many

ProtonsSolution: convertprotonsto neutrons

Too manyNeutrons

Solution: convert neutronsto protons.

Image Source: See Note 1


6/19

Nuclear Stability

6

n

p Nature will always force

unstable nuclei to DECAY intoa more stable form.

Three mechanisms for a nucleusto stabilize

Break apart

Emit a particle

Change a neutron into aproton (or vice versa),usually accompanied by an

emitted particle

n

n

n

p

n

n

n

p

n

n

n

p

nn

pn

nn

p

p

n

n


7/19

Nuclear Decay Modes

Decay Mode 1: Break apart.

Affects large nuclei that are unstable due toCoulomb forces within nucleus

7

Spontaneous Fission Heavy nuclei spontaneously

break apart into two smallernuclei.

Only occurs for nuclei with

Z2/A 45 Frequently observed in

isotopes of Pu and Cf.

Low probability relative toAlpha decay.


8/19

Nuclear Decay Modes

Decay Mode 2: Emit a nucleon(s)

Affects large nuclei that are unstable due to

Coulomb forces within nucleus Possible types of nucleon emission decay:

Proton emission (rare)

Double proton emission (rare)

Neutron emission (rare)

Alpha decay (common)

Cluster decay (rare)8


9/19

Alpha Decay

Alpha Decay

Large, unstable, nuclei emit an alpha particle

9Image Source: See Note 2

Alpha particles

Mass = 4 amu, charge +2

Helium nucleus

Decay mechanism forlarge, unstable atoms

Most common decay modefor nuclei with Z > 90


10/19

Nuclear Decay Modes Decay Mode 3: Change nucleon flavor

Most common type of decay for nuclei withZ < 90.

All processes that change nucleon flavor are referred toasbeta decay.

Two basic modes of beta decay

Negative Turns a neutron into a proton

Beta-Negative decay, double Beta-Negative Decay

Positive Turns a proton into a neutron

Positron emission, electron capture, double positron

emission, double electron capture10


11/19

Negative Beta Decay

Beta Decay (Negative) Affects unstable nuclei with more neutrons than protons.

Nuclei changes neutron to proton and emits a beta particle

and an antineutrino.

11

Beta particles

Mass


12/19

Positive Beta Decay

Positron Emission (Beta-Positive Decay) Affects unstable nuclei with more protons than neutrons.

Nuclei changes proton to neutron and emits a positron and aneutrino.

12

Positron

Mass


13/19

e

Positive Beta Decay Electron Capture (Beta-Positive Decay)

Affects unstable nuclei with more protons than neutrons.

Nuclei captures an orbiting electron and changes a proton to

neutron and emits a neutrino.

13

Does not emit a nucleon duringdecay process.

+

p

n

Image Source: See Note 4


14/19

Nuclear Decay Modes

Nuclear Decay modes that you shouldknow: Alpha Decay(Z,A)(Z2, A4).

Spontaneous Fission (Z,A)(Z1, A1) + (Z2, A2).

Beta Decay(Z,A)(Z+1, A).

Positron Emission (Z,A)(Z1, A).

Always remember:

Nuclear decay must conserve mass, charge, totalenergy and angular momentum (spin).

14


15/19

Nuclear Decay Balance Eqns. Shorthand notation for writing nuclear decay events

Similar to chemical balance equations

Equation must always conserve mass and charge

Typically dont list energy or momentum in thesebalance equations

15

4

2

231

90

235

92+

ThU

Examples

HeThU

4

2

231

90

235

92+

or 0

0

0

1

239

94

239

93++

PuNp

Alpha Decay:

Beta Decay:

Positron Emiss.: 0

0

0

1

11

5

11

6++

+

BC


16/19

Nuclear Decay Balance Eqns. -

Example Given Bi-210, write the balance

equations for the following decays:

Alpha

Beta

16


17/19


ExampleBi-210 =

Alpha

Beta

17

Bi21083

He+XBi 42AZ

21083

00AZ01-21083 +X+Bi


18/19


ExampleBi-210 =

Alpha

Beta

18

Bi21083

He+XBi 42AZ

21083

00AZ01-21083 +X+Bi


19/19

1. Image adapted from DOE Fundamental Handbook:Nuclear Physics and Reactor Theory, Volume 1 of 2.(1993). U. S. Department of Energy. DOE-HDBK-1019/1-93.

http://www.hss.energy.gov/nuclearsafety/techstds/docs/handbook/h1019v1.pdf

2. Public domain:http://en.wikipedia.org/wiki/File:Alpha_Decay.svg

3. Public domain: http://en.wikipedia.org/wiki/File:Beta-

minus_Decay.svg4. Adapted from public domain image at

http://en.wikipedia.org/wiki/File:Beta-minus_Decay.svg

Image Source Notes
http://www.hss.energy.gov/nuclearsafety/techstds/docs/handbook/h1019v1.pdfhttp://www.hss.energy.gov/nuclearsafety/techstds/docs/handbook/h1019v1.pdfhttp://www.hss.energy.gov/nuclearsafety/techstds/docs/handbook/h1019v1.pdfhttp://en.wikipedia.org/wiki/File:Alpha_Decay.svghttp://en.wikipedia.org/wiki/File:Beta-minus_Decay.svghttp://en.wikipedia.org/wiki/File:Beta-minus_Decay.svghttp://en.wikipedia.org/wiki/File:Beta-minus_Decay.svghttp://en.wikipedia.org/wiki/File:Beta-minus_Decay.svghttp://en.wikipedia.org/wiki/File:Beta-minus_Decay.svghttp://en.wikipedia.org/wiki/File:Beta-minus_Decay.svghttp://en.wikipedia.org/wiki/File:Alpha_Decay.svghttp://www.hss.energy.gov/nuclearsafety/techstds/docs/handbook/h1019v1.pdfhttp://www.hss.energy.gov/nuclearsafety/techstds/docs/handbook/h1019v1.pdf

pdf 2.3 seeking stability

Documents