Nuclear RadiationThe Chart of Nuclides

Experiment 10-Physics Lab. 2120

Younes Sina

To become familiar with the use of the Chart of Nuclides

Objective

XAZ

An up quark has a mass of 0.0047 u and a down quark has a mass of 0.0074 u.

up down

The decay modes are -, + and electron capture (EC).

n p

Electron Capture (EC)

+

→ →

Cross Sections

Probability of a neutron interaction with a nucleus is depend on the kind of nucleus and the energy of the neutron.

In fission reactors thermal neutrons can be absorbed easier than fast neutrons.

H20 is an excellent moderator because of the hydrogen nuclei (protons) in the water. As a moderator, D20 is almost as good as normal water and has the added advantage that its neutron absorption cross section is small. Graphite also slows neutrons well, is inexpensive, but burns .

A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (speed of 14,000 km/s)

A thermal neutron is a free neutron with a kinetic energy of about 0.025 eV (speed of 2.2 km/s)

How Do Reactors Work?

U-235 + 1 neutron =======> Fragment A + Fragment B + 200 MeV of energy

Critical Mass For a chain reaction of nuclear fission, such as that of uranium-235, is to sustain itself, then at least one neutron from each fission must strike another U-235 nucleus and cause a fission. If this condition is just met, then the reaction is said to be "critical" and will continue. The mass of fissile material required to achieve this critical condition is said to be a critical mass. The critical mass depends upon the concentration of U-235 nuclei in the fuel material as well as its geometry. As applied for the generation of electric energy in nuclear reactors, it also depends upon the moderation used to slow down the neutrons. In those reactors, the critical condition also depends upon neutrons from the fission fragments, called delayed neutrons.

The neutrons emitted in nuclear fission reactions have high energies, typically in the range of 1 MEV. But the cross section for neutron capture leading to fission is greatest for neutrons of energy around 1 eV, a million times less. Neutrons with energies less than 1 eV are commonly referred to as "thermal neutrons" since they have energies similar to what particles have as a result of ordinary room-temperature thermal energy.

Thermal reactorsMost fission reactors are thermal reactors that use a neutron moderator to slow down, or thermalize the neutrons produced by nuclear fission. Moderation substantially increases the fission cross section for fissile nuclei such as uranium-235 or plutonium-239. In addition, uranium-238 also has a much lower capture cross section for thermal neutrons, allowing more neutrons to cause fission of fissile nuclei and continue the chain reaction, rather than being captured by 238U. The combination of these effects allows light water reactors to use low-enriched uranium.

Guide for using the Chart of the Nuclides

1 day to 10 days

10 days to 100 days

100 days to 10 years

10 years to 5E8 years

> 5E8 years or stable

Colors used for half lives(Appear in upper half of nuclide block)

10 barns to 100 barns

Colors used for neutron absorption properties(Appear in lower half of nuclide block)

100 barns to 500 barns

500 barns to 1000 barns

> 1000 barns

H1.0079

Hydrogen

σa .333, .150

Chemical Element

Symbol

Atomic Weight (Carbon-123 Scale)

Thermal Neutron Absorption Cross Section in Barns, followed by Resonance Integral, in Barns

Gray shaded square: (Stable Nuclide)

Pd 108

26.46

107.903894

σγ (.19+8),(5+24E1)

Stable

Symbol, Mass Number

Atom Percent Abundance

Thermal Neutron Activation Cross Section in Barns, Leading to( Isomeric+ Ground State),followed by Resonance Integrals Leading to( Isomeric+ Ground State)

Even Z, Even N

Fission Product, Slow Neutron Fission of U235, U233 or Pu239

Isotopic Mass (Carbon-123 Scale)

White or "color" square: ( Artificially Produced Radioactive Nuclide)

S382.84 h

E 2.94

β- .99,…, γ 1941.9,…

Artificially Radioactive

Half-Life

Beta Disintegration Energy in Mev

Modes of Decay with Energy of Radiation in Mev for Alpha and Beta; kev for gammas

Symbol, Mass Number

Black rectangles across the top of square

a. On gray-shaded square: Radioactive nuclide with long half life (Considered Stable)

b. On white square: Radioactive nuclide found in nature with relatively short half life

La 138

5+

Two Isomeric States Both Radioactive

Beta Disintegration Energy Followed by Isotopic Mass

Spin and Parity

Modes of Decay in order of Prominence with Energy of Radiation in Mev for alpha and Beta, Kev for gamma

Thermal Neutron Capture Cross Section, followed by Resonance Integral

Half-Life

Symbol, Mass Number

0.090 1.05 E11 a

ϵ, β- .25 γ 1435.8,788.7 σγ ~57,4E2 E 1.04 137.90711

Atom Percent Abundance

Smaller black rectangle near top of square

Nuclide is a member of a natural radioactive decay chain

Po 2183.10 m

218.oo8965

α 6.0024γ 510β- ω

Member of Naturally Radioactive Decay Chain

Half-Life

Isotopic Mass

Modes of Decay and Energy in Mev for Alpha and Beta; kev for gammasω Indicates Decay Mode Intensity

Symbol, Mass Number

RaA

Historical Symbol

Black triangle at bottom corner of square: Refer to item 1 above. This indicates nuclide is formed by fission of U-235 or Pu-239

6. Vertically divided square

Two isomeric states, one stable

Two isomeric states, both radioactive

Sn 117 1/+11/-

13.69 d7.68

IT 156.0, e-γ158.6

116.902953

σγ 1.3,~ 15

Isotopic Mass

Fission Product, Slow Neutron Fission of U235, U233 or Pu239

Two Isomeric States One Stable Spin and Parity of

Ground State, ½+

Spin and Parity of Metastable State, 11/2-

Atom Percent Abundance

Modes of Decay with Energy of Radiation in Mev for Alpha and Beta; kev for gammas

Thermal Neutron Capture Cross Section in Barns, followed by Resonance Integral in Barns

Radioactive Isomer Stable Ground State

Co 602+ 5+

10.47 m 5.271 a

IT 58.6, e-β-1.6 ω,γ1332.5 ωσγ 60,2.3E2

β- .318,…γ 1332.5,1173.2,…..σγ 2.0,4

E 2.824

Two Isomeric States Both Radioactive

Spin and Parity of Ground State, ½+

Spin and Parity of Metastable State

Modes of Decay and Energy in order of Intensity, … Indicates (Where Shown) Range of Energies Included.

Thermal Neutron Activation Cross Section in Barns, followed by Resonance Integral in Barns

Radioactive m-State Isomer Radioactive Ground State Isomer

Half-Life

Symbol, Mass Number

Beta Disintegration Energy in Mev

Other useful information

The age of the Earth is 4.54 × 109 years ± 1%

Form of Energy Released Amount of Energy Released (MeV)

Kinetic energy of two fission fragments 168Immediate gamma rays 7

Delayed gamma rays 3-12Fission neutrons 5

Energy of decay products of fission fragments ...Gamma rays 7

Beta particles 8Neutrons 12

Average total energy released 215 MeV

Energy From Uranium Fission

Plutonium

Mahabad- Iran