radioactive decay

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radioactivedecay
berçincemremurat z
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fundamental particles
?

• electron
• proton
• neutron

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fundamental particles
Family Particle Fundamental?
lepton electron yes
hadron proton neutron no
boson photongluon yes
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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

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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
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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
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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

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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
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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?

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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
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b decay

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

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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

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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!

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b- decay
-

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

1 1 0
0 1 - 1
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how does a neutron turn into a proton?

• one of the down quarks changeinto an up quark.

é
é
é
proton
neutron
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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."

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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.
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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
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b- decay
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b- decay
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b- decay
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try on your own!
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b decay

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

1 1 0
1 0 1
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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
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try on your own!
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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

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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.
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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?

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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
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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.

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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.

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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.

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uses of b decay

• carbon dating. carbon-14 decays by emitting beta
  particles.
• beta particles are used for radiotheraphy

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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.

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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.

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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