INTERACTIONS WITH THE NUCLEUSNUCLEAR DECAY PROCESSESRADIOACTIVE DECAY

The nucleus and nuclear radiationNuclear structureNuclear binding energy

Radioactive Decay

Interactions with the nucleus

A nuclide consists of an atomic species characterized by its atomic number and mass number:

XA

Z

Z = n(protons)A = n(neutrons) + Z

Potential energy

O(10-15 m = 1 fm)

(from Turner “Atoms, Radiation and Radiation Protection”)

Exercise:

What is the minimum kinetic energy that a proton must have in order to interact with a 37Cl nucleus?

Eproton > 4.37 MeV

Binding energy

(from Turner “Atoms, Radiation and Radiation Protection”)

ΔE>0 :Fusion of light elementsreleasesenergy

ΔE<0:Fission of heavyelementsreleases energy

Maximum stability

(from Turner “Atoms, Radiation and Radiation Protection”)

Nuclide data

Exercise

What is the energy released in the absorption of a termic neutron (E< 1 eV) by and Hidrogen atom?

HHn 1

2

1

1

1

0

Q = 8.0714 + 7.2890 – 13.1359 = 2.2245 MeV.

(from Turner “Atoms, Radiation and Radiation Protection”)

Nuclide data

James E. Martin, Physics for Radiation Protection, A Handbook, Wiley-VCH

http://www.nndc.bnl.gov/chart

Nuclide chart

Exercise

eeHeH 3

2

3

1

keVMeVQ daughterparent 7.180187.09313.1495.14

Q

What is the energy released?

)()(2*)( 2222cmTTQcmTTco n stTN eeeeeee

keV5112 cme

Radioactive Decay

Processes

Alpha decay

Beta decay

Gamma decay

Internal Conversion

Electronic Capture

Beta+ decay

Alpha decay

daughterparentfilhopai MMMQHeYX A

Z

A

Z

4

2

4

2

Most α emitters are heavy nuclei with com Z>83

The transfered energy, Q, is shared by the final nucleus (recoil) and the alpha particle

Alpha decay daughterparentQ 2.42 MeV

Energy-Momentum conservation (initial nucleus at rest )

QMVvm

MVvm

22

2

1

2

1

m

M

E

E

D

Mm

mQMVE

Mm

MQvmE

D

2

2

2

1

2

1

α particles kinetic energy is :

• greater then the nucleus recoil energy :

M >2 x 83 e mα=4 , então Eα >~ 40 ED

• unique for each decay ( i.e. for each “parent” nucleus).Mm

MQE

(from Turner “Atoms, Radiation and Radiation Protection”)

Nuclide data

Beta decayeepn

QEE _

__0

0

0

11 e

A

Z

A

Z eYX

)()(2*)( 2222cmTTQcmTTco n stTN eeeeeee

Increase in atomic number!

Average value of the electron kinetic energy:

3~

__ QE

Q

Qdaughterparent

Gamma decay

00 XX A

Z

Am

Z

Isomeric transition

An excited state decays for a lower energy state (may or not be the fundamental state)through the emission of a gamma with energy given by the energy difference between thetwo nuclear states.

Gamma emission follows alpha and beta decays, which, in most cases, leave the nuclei inexcited states.

Life time of excited states: typically O(10-9 s), but in some cases are of the order ofhours/days.

Qdaughterparent

Internal Conversion

The energy of the nuclear excited state is transfered to an atomic electron (K,L) that is ejected from the atom.

The electron is monoenergetic!

The IC process competes with gamma emission: IC coefficient : α = Ne-/Ngamma

α Increases with Z3 and decreases with E* -> IC prevails in heavy nucleiGamma emission dominates in light nuclei

IC is followed by the emission of X-rays due to the rearrangement of atomic orbitals

2

5

*

24

3

3 2

1~)(

L

eem

E

cm

L

L

n

ZEL

2

3

*

24

3

3 2~)(

L

eem

E

cm

n

ZML

)()( .

* eEnucEE binde*EQdaughterparent

Electric multipole Magnetic multipole

Electronic Capture

Electronic capture of an atomic electron (K) with the emission of a neutrino.

enep

0)()( eEMeEmMQ BdaughterparentdaughterBeparent

Possble if Eb < p- d

001

0

1

YeX A

Z

A

Z

Decrease in atomic number

QEC

parent

daughter

Z

E

+ decayeenp

eADAPeeADeAP mMMmmZMZmMQ 2))1((

e

A

Z

A

Z eYX 000

11

Occurs in proton rich nuclei ( above the Z vs. N stability curve)

Atomic masses:

eNDNPeNDNP mMMmMMQ

eADND

eAPNP

mZMM

ZmMM

)1(

22 cmQ eDP

A diferença de massas entre o núcleo que decai e o núcleo resultante tem de ser superior a 2*me!

Decrease in atomic number

EC vs + decay

22 cmQ eDP

)( eEQ BDPEC

Neglecting EB , the energy released by a given species in the case of EC is greater thanthe energy released in + decay by 2*me.

Beta decay

Beta decay

+ Gammadecay orInternalconversion

)()(2*)( 2222cmTTQcmTTco n stTN eeeeeee

keV5112 cme

Beta + decay

Anihilation photons

Energetic Balance