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radioactive decay

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Title: radioactive decay


1
radioactivedecay
berçincemremurat z
2
fundamental particles
?
  • electron
  • proton
  • neutron

3
fundamental particles
Family Particle Fundamental?
lepton electron yes
hadron proton neutron no
boson photongluon yes
4
leptons
  • one of the families of fundamental particles
  • first generation leptonselectrons and
    neutrinos
  • their anti-particlespositrons and antineutrinos
  • found in normal matter
  • are not affected by thestrong nuclear force

5
leptons
  • there are second and third generations, which are
    extremely short lived, so not observed in daily
    life

generation Particles Particles Anti-particles Anti-particles
1st electron electron-neutrino positron anti-neutrino
2nd muon muon-neutrino anti-muon anti-muon-neutrino
3rd tau tau-neutrino anti-tau anti-tau-neturino
6
hadrons
  • not fundamental
  • made up of even smallerparticles, quarks
  • 3 different generations of quarks

Generation Quarks Quarks
1st up down
2nd top bottom
3rd strange charm
7
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

8
1st generation quarks
Flavour Charge
up 2/3
down -1/3
updowndown
upupdown
proton
neutron
2/3 2/3 -1/3 1
-1/3- 1/3 2/3 0
9
binding the nucleus
  • the nucleus of helium contains two protons which
    are both positively charged. they should repel
    each other but they do not. why?



10
the strong force
  • an attractive force
  • has an effect over a very short range(10-15 m,
    about the size of the nucleus)
  • leptons dont feel this force, but particles in
    the quark family do.



strongnuclear force
11
b decay
  • occurs when a nucleus has either too many protons
    or neutrons. one of the neutron or protons is
    transformed to the other.

12
what causesb 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

13
b- decay
-
  • the atom has too many neutrons to be stable.
  • does it just kick out one of the neutrons?
  • but the neutrons arestuck too tightly,it cant
    do that
  • what it can do is...convert the neutroninto a
    proton!

14
b- decay
-
  • a neutron decays intoa proton, an electron (b-
    particle), and an antineutrino

1 1 0
0 1 - 1
15
how does a neutron turn into a proton?
  • one of the down quarks changeinto an up quark.

é
é
é
proton
neutron
16
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."

17
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.
18
b- decay
neutron -1, proton 1,so no change in mass number
-


¾

¾
14
14
0
b
?

N
C
e
7
6
-1
proton 1,so atomic number increases by one
19
b- decay
20
b- decay
21
b- decay
22
try on your own!
23
b decay
  • a proton decays intoa neutron, a positron (b
    particle), and a neutrino

1 1 0
1 0 1
24
b decay
neutron 1, proton -1,so no change in mass number



¾

¾
18
18
0
b

O
F
?
e
8
9
1
proton -1,so atomic number decreases by one
25
try on your own!
26
b 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

27
conservation oflepton number
leptonnumber0
leptonnumber0
leptonnumber1
leptonnumber-1
0 0 1 - 1
the leptons emitted in beta decay did not exist
in the nucleus before the decaythey are created
at the instant of the decay.
28
mass/energy conservation in b 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?

29
mass/energy conservation in b decay
  • we havent 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.

Emc2
30
mass/energy conservation in b decay
  • lets 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.

31
mass/energy conservation in b decay
  • in 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.

32
spontaneity ofb decay
  • beta 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, its
    possible to conclude that beta decay is
    spontaneous.

33
uses of b decay
  • carbon dating. carbon-14 decays by emitting beta
    particles.
  • beta particles are used for radiotheraphy

34
electron capture decay
  • Electron 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.

35
electron capture decay
  • unstable nuclei capture electrons from the K
    energy level.
  • according to theconversion, while a new
    nucleus is being formed, the atom emits photons.

36
electron capture decay
K
L
M
N
19P21N
18P22N
1
8
8
2
8
2
7
8
1
7
1s2 2s22p6 3s23p6
1s2 2s22p6 3s23p6 4s1
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