radioactivedecay

berçincemre

murat z

fundamental particles

electron proton neutron ?

fundamental particles

Family Particle Fundamental?

lepton electron yes

hadronprotonneutron

no

bosonphotongluon

yes

leptons one of the families of

fundamental particles first generation leptons:

electrons and neutrinos; their anti-particles:

positrons and antineutrinos found in normal matter

are not affected by thestrong nuclear force

leptons there are second and third

generations, which are extremely short lived, so not observed in daily lifegener

ationParticles Anti-particles

1stelectron electron-

neutrinopositron anti-

neutrino

2ndmuon muon-

neutrinoanti-muon anti-muon-

neutrino

3rdtau tau-

neutrinoanti-tau anti-tau-

neturino

hadrons not fundamental made up of even smaller

particles, quarks 3 different generations of quarks

Generation

Quarks

1st up down

2nd top bottom

3rd strange charm

hadrons

the combination of these 6 types of quarks make up hundreds of hadrons

1st generation quarks (up/down)found in the proton and the neutron, the nucleons of normal matter

other quarks are found in experiments, not in daily life

1st generation quarks

proton neutron

Flavour Charge

up +2/3

down -1/3

2/3+ 2/3 -

1/3 = +1

upupdown

updowndown

-1/3- 1/3 +

2/3 = 0

binding the nucleusthe nucleus of helium contains two protons which are both positively charged. they should repel each other but they do not. why?

the strong force an attractive force has an effect over a very short range

(10-15 m, about the size of the nucleus)

leptons don’t feel this force, but particles in the quark family do.

strongnuclear force

decay occurs when a nucleus has

either too many protons or neutrons. one of the neutron or protons is transformed to the other.

what causes decay?it cannot be the strong nuclear force because this has no effect on electrons and the beta particle is an electron. neither, as physicists know, can it be the electromagnetic force. in order to explain it, we need to identify a new force called the weak force. the weak force is very short range and, as the name implies, it is not at all strong. its effects are felt by all fundamental particles - quarks and leptons

the atom has too many neutrons to be stable. does it just kick out one of the neutrons? but the neutrons are

stuck too tightly,it can’t do that

what it can do is...convert the neutroninto a proton!

decay

a neutron decays intoa proton, an electron ( particle), and an antineutrino

e00

01

11

10 νepn

1 = 1 + 0

0 = 1 - 1

decay

how does a neutron turn into a proton?one of the down quarks changeinto an up quark.

neutronproton

neutrinos same exact beta decay produced an electron

with variable energies.

Li-8 becoming Be-8 Each atom of Li-8 produces an electron the theory says all should have the same

energy. this was not the case.

the electrons were coming out with any old value they pleased up to a maximun value, characteristic of each specific decay.

Pauli suggested the energy was being split randomly between two particles - the electron and an unknown light particle that was escaping detection. Enrico Fermi suggested the name "neutrino," which was Italian for "little neutral one."

neutrinos discovered because

momentum and charge didn't seem to be conserved in nuclear reactions

neutrinos have some mass, maybe about one ten-millionth the mass of an electron.

Wolfgang Pauli suggested the existence of a neutrino.

ν NC e147

146

neutron -1, proton +1,so no change in mass number

proton +1,so atomic number increases by one

0-1

decay

ν YX eA

Z+1AZ

0-1

decay

decay

decay

try on your own!

He62

O198

Cs13755

Li83

a proton decays intoa neutron, a positron ( particle), and a neutrino

e00

01

10

11 νenp

1 = 1 + 0

1 = 0 + 1

decay

+ OF e188

189

neutron +1, proton -1,so no change in mass number

proton -1,so atomic number decreases by one

01

decay

ν

+ ν YX eA

Z-1AZ

0 1

try on your own!

Si2714

O158

Cs13755

Cu6029

Dy15566

decay all reactions occur because in

different regions of the Chart of the Nuclides, one or the other will move the product closer to the region of stability

these particular reactions take place because conservation laws are obeyed

conservation oflepton number

leptonnumber

0

leptonnumber

0

leptonnumber

1

leptonnumber

-1

0 = 0 + 1 - 1

e00

01

11

10 νepn

the leptons emitted in beta decay did not exist in the nucleus before the decay–they are created at the instant of the decay.

the mass of an electron is very small

neutrons are a little heavierthan protons

keeping the same mass number doesn't necessarily mean you end up with exactly the same mass

but we have just converted a neutron to a proton- how does it happen?

mass/energy conservation in decay

mass/energy conservation in decaywe haven’t talked about relativity, but last year we studied the famous equation of Einstein:

which means that mass (m) and energy (E) are really the same thing, and that you can convert one into the other using the speed of light.

if you add up all the mass and energy that's around before and after a nuclear reaction, you'll find that the totals come out exactly the same.

E=mc2

mass/energy conservation in decay

let’s take this as an example.the proton has slightly less mass than the neutron. the mass of the electron makes up for this somewhat, but if you do the math, you'll see that there's still some mass "missing" from the right side of the reaction. energy takes up the slack: the electron comes out moving very fast, i.e., with lots of kinetic energy.

e00

01

11

10 νepn

mass/energy conservation in decayin other reactions, the "leftover" energy sometimes shows itself in different ways. for example, the nucleus that comes out is sometimes in an excited state--the remaining protons and neutrons have more energy than usual. The atom eventually gets rid of this extra energy by giving off a gamma ray.

spontaneity of decaybeta decay satisfies the minimum energy condition because the nucleus tends to give off energy after becoming more stable.

beta decay also satisfies the maximum randomness condition because after decay, a beta particle and an anti/neutrino is given out, so the number of particles, therefore possible micro states increase.

satisfying both of these tendencies, it’s possible to conclude that beta decay is spontaneous.

uses of decay

carbon dating. carbon-14 decays by emitting beta particles.

beta particles are used for radiotheraphy

electron capture decayElectron capture is not like any other decay –

alpha or beta, All other decays shoot something out of the nucleus. In electron capture, something ENTERS the nucleus.

An electron from the closest energy level falls into the nucleus, which causes a proton to become a neutron.

A neutrino is emitted from the nucleus. Another electron falls into the empty energy

level and so on causing a cascade of electrons falling. The atomic number goes DOWN by one and mass number remains unchanged.

νKeK 00

4018

01

4019

unstable nuclei capture electrons from the K energy level.

according to the

conversion, while a new nucleus is being formed, the atom emits photons.

electron capture decay

npe 10

11

01

electron capture decay

unstableK40

19 19P19P21N21N19P19P21N21N

K L M N

2

1s2 2s22p6 3s23p6 4s1

18P18P22N22N18P18P22N22N

8 8 11 72 78 8stableK40

18

1s2 2s22p6 3s23p6