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Karlsruhe Nuclide Chart – The New Edition in 2015

Zs. Sóti1, J. Magill2

1 European Commission, Joint Research Centre, Institute for Transuranium Elements,Postfach 2340, 76125 Karlsruhe, Germanyhttps://ec.europa.eu/jrc/

2 Nucleonica GmbH, 76344 Eggenstein-Leopoldshafen, Germanyhttp://www.nucleonica.com

Karlsruhe Nuclide Chart

The first edition was published in 1958.The 9th edition was printed in 2015.

Atoms with different numbers of protons and neutrons intheir nucleus are generally known as nuclides.The Karlsruhe Nuclide Chart shows all known nuclides in aclear two dimensional co-ordinate system of nuclide boxesdepicting the number of protons and neutrons in the atomicnucleus. A nuclide box in the chart contains the elementsymbol, the mass number and other nuclear data on thenuclide characterised by the position in theneutron-proton co-ordinate system.

Z

NNumber of neutrons

Number of protons

The colours of the nuclide boxes representthe different radioactive decay modes ofthe radionuclides.

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Karlsruhe Nuclide Chart

Nuclides with approximately equal numbers of protonsand neutrons are stable and marked in black.Nuclides with an excess of protons have the colour redor yellow whereas those with an excess of neutronshave the colour blue.Each horizontal row on the Chart starts with a boxdescribing the element and it is followed by the isotopesof this chemical element. (Z is constant)If N is constant - IsotonesIf A=N+Z is constant - Isobars

These nuclides are continuously produced instars and supernovae explosions.On Earth, they are also producedin particles accelerators andnuclear reactors. Z

N

IsotopesZ=constant

IsotonesN=constant

IsobarsN+Z=A=constant

Z

N

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New 9th Edition in 2015

The Karlsruhe Nuclide Chart isprinted in three different standardformats: Fold-out Chart, WallChart and Auditorium Chart(0.43 x 3.16 m).

The accompanying bookletprovides a detailed explanationof the nuclide box structure usedin the Chart. The sectionReduced Decay Schemescontains about 50 nuclide decayschemes to aid the user tointerpret the highly condensedinformation in the nuclide boxes.

The colour blue indicates that the nucleus decays by ߯ emission.

Ar 41 is characterised by the emission of several beta particleswith different endpoint energies. In the case of ß decay the nuclidebox contains a maximum of two ß endpoint energies. The firstnumber corresponds to the strongest transition whereas thesecond corresponds to the highest ß endpoint energy. Additionaltransitions are indicated by dots. The excited states of thedaughter nuclide K 41 release their energy through gammaemissions.

Theoretical background

The colours indicate various modes of radioactive decay:

߯decay

ec/ß+ decay

α decay neutron decay

proton decay

spontaneous fission

isomeric transition

stable nuclide

The mass number in a nuclide box is the number of protons plus the number ofneutrons: A = Z + N. The number of protons defines the chemical element,the number of neutrons: N = A – ZA nuclide position in the chart is defined by co-ordinates (N,Z).

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Alpha ( α) DecayIn alpha decay, the parent atom (A,Z)P emits an alpha particle (4,2)α and results in adaughter nuclide (A-4,Z-2)D. Immediately following the alpha particle emission, thedaughter atom still has the Z electrons of the parent – hence the daughter atom has twoelectrons too many and should be denoted by [A-4,Z-2]D2-. These extra electrons are lostsoon after the alpha particle emission leaving the daughter atom electrically neutral. Inaddition, the alpha particle will slow down and lose its kinetic energy. At low energies thealpha particle will acquire two electrons to become a neutral helium atom. The alpha decayprocess is described by:

Z

N

Z

N

Gamma Spectrum Characteristics

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Beta-minus ( β¯ ) Decay

߯ radioactivity occurs when a nucleus emits a negative electron from an unstable radioactive nucleus. Thishappens when the nuclide has an excess of neutrons. Theoretical considerations (de Broglie wavelength ofMeV electrons is much larger than nuclear dimensions), however, do not allow the existence of a negativeelectron in the nucleus. For this reason the beta particle is postulated to arise from the nucleartransformation of a neutron into a proton through the reaction

where ν is an anti-neutrino. The ejected high energy electron from the nucleus denoted by β¯ to distinguish itfrom other electrons denoted by e–. Beta emission differs from alpha emission in that beta particles have acontinuous spectrum of energies between zero and some maximum value, the endpoint energy,characteristic of that nuclide. The β¯ decay process can be described by:

Z

N

Gamma Spectrum – Peak at 1294 keV

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Beta-plus ( β+) Decay (Positron Emission)

In nuclides where the neutron to proton ratio is low, and alpha emission is notenergetically possible, the nucleus may become more stable by the emission of apositron (a positively charged electron). Within the nucleus a proton is converted into aneutron, a positron, and a neutrino i.e.

Similarly to the β¯, the positron β+ is continuously distributed in energy up to acharacteristic maximum energy. The positron, after being emitted from the nucleus,undergoes strong electrostatic attraction with the atomic electrons. The positron andnegative electrons annihilate each other and result in two photons (gamma rays) eachwith energy of 511 keV moving in opposite directions.

Z

N

Annihilation Peak511 keV

Gamma Spectrum – Annihilation Peak

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Electron Capture ( ε)

Neutron deficient nuclides can also attain stability by capturing an electron from theinner K or L shells of the atomic orbits. As a result, a proton in the nucleus transforms toa neutron i.e.

The process is similar to β+ decay in that the charge of the nucleus decreases by 1. Theelectron capture decay process can be described by:

and the daughter is usually produced in an excited state. The resulting nucleus isunstable and decays by the ejection of an neutrino (ν) and the emission of an X-raywhen the electron vacancy in the K or L shell is filled by outer orbital electrons.

Z

N

N

Gamma Spectrum

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Isomeric Transition, ITAfter a radioactive nucleus undergoes an isobaric transition (beta emission, positronemission, or electron capture), it usually contains too much energy to be in its finalstable or daughter state. Nuclei in these intermediate and final states are isomers, sincethey have the same atomic and mass numbers. Nuclei in the intermediate state willundergo an isomeric transition by emitting energy and dropping to the ground state.

In contrast to normal gamma emission, isomeric transitions occur on a longer time-scale. If the lifetime for gamma emission exceeds about one nanosecond, the excitednucleus is defined to be in a metastable or isomeric state. The decay process from thisexcited state is known as an isomeric transition (IT) e.g.

The letter m after the mass number denotes the metastable state.

Gamma Spectrum

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Internal Conversion, e -

The excess energy of radioactive nuclei in excited states is usually relieved through gamma emission.However, if the wave function of the orbital electron is such that it can exist close to or in the nucleus, theexcess energy can be transferred directly to the orbital electron. Hence, as an alternative to gammaemission, the excited nucleus may return to the ground state by ejecting an orbital electron. This is knownas internal conversion and results in an energetic electron and X-rays due to electrons cascading to lowerenergy levels.Following the internal conversion, outer orbital electrons fill the deeper energy levels and result incharacteristic X-ray emission.

The ratio of internal conversion to gamma emission photons is known as the internal conversion coefficientdenoted as αT = αK + αL + …. .Consider the decay of the isomeric state 60mCo. This excited nuclide state can lose its energy (59 keV)either by gamma emission or by the emission of a conversion electron. Since αT = 47, the state de-excitesmainly via internal conversion.

Spontaneous Fission (sf)

Actinides and trans-actinides can undergo radioactive decay by spontaneous fission. In thisprocess the nucleus splits into two fragment nuclei, with mass and charge roughly half that ofthe parent, and several neutrons. The spontaneous fission decay process can be describedqualitatively by:

A “parent” nuclide splits into two “daughter” nuclides and together with the release of nprompt neutrons and energy E*. Typically n ranges from 2 – 4 and E* is approximately 200MeV. The daughter nuclides or fission products have in general different mass numbers A andatomic numbers Z.

Colour green denotes the spontaneous fission

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Multiple Decay Modes and Branching Ratios

When a nuclide has more than one mode of decay, the use of colouredtriangles gives an indication of the branching rati os of the different decay modes.

Left: The large triangles in I-126 indicates that the branching ratios for electron capture and beta emission are ≥ 5 %, but ≤ 95 %.

Notice that the order of the branching ratios in th e text box indicates the most important ,second most important etc.

Right: The small triangle in Tc-100 indicates that εεεε branching ratio ≤ 5 % is. The corresponding value for ß - emission ≥ 95 %.

Example

The colour blue indicates that the nucleusdecays by ߯ emission. Cs 137 is characterizedby the emission of three ߯ particles withdifferent endpoint energies. The most probable߯ emission is at 0.5 MeV whereas the highestenergy emission occurs at 1.2 MeV. Additionalbeta particles are also emitted indicated by thedots. The box entry m indicates that the main ߖdecay is to the metastable state (94.7%) Ba137m. The gamma transition from thismetastable state is found in the nuclide box Ba137m. The use of the symbol g indicates thatthe direct transition to the ground state has abranching greater than 5%. Actually in this caseit is 5.3%. Decay to an excited state of thedaughter Ba 137 is less probable (less than 1%)and gives rise to the weak gamma emission at284 keV indicated by the entry (284).

Neutron capture in Cs 137 leads to theformation of Cs138m (cross section 0.20 barn)and Cs 138g (cross section 0.07 barn)

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Only Cs 137

Example

Special Editions of KNC

Some special editions have been produced in the previous three years

for various institutes and organisations.

Nuclide Carpet (CERN), the Contour Chart (European Dialogue Centre)

and the Ceramic Tiles version of Karlsruhe Nuclide Chart (Institute for

Transuranium Elements)

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For almost 60 years, the Karlsruhe Nuclide Chart has provided scientists and students with structured,accurate information on the half-lives and decay modes of radionuclides, as well as the energies ofemitted radiation.An important characteristic of the Chart is its great didactic value for education and training in the nuclearsciences. It has been used in training programs worldwide and is a valuable addition to many books onnuclear science including school physics textbooks.The Karlsruhe Nuclide Chart shows all known nuclides in a two dimensional co-ordinate system depictingthe number of protons Z and neutrons N in the atomic nucleus.Nuclides with approximately equal numbers of protons and neutrons are stable and marked in black.Nuclides with an excess of protons have the colour red or yellow whereas those with an excess ofneutrons have the colour blue.Each horizontal row on the Chart starts with a box describing the element and is followed by the isotopesof this chemical element.

Overview

The End