Julia Cotter and Ethan Blitstein
Nuclear chapter 30
An atom consists of a nucleus surrounded by electrons. Within the nucleus there are
two types of subatomic particles, protons and neutrons.
The proton is a positively charged particle within the nucleus. It had a mass of
1.6726x10^-27 kg, or 1.007276u. The number of protons in a nucleus is defined by
the atomic number and if the number of protons changes in an atom it will become a
different element.
The neutron does not have a charge and has a mass of 1.6750x10^-27 kg or
1.008665u. The number of neutrons can vary within an element. Isotopes are atoms
with of the same element with different atomic masses, because they have a
different amount of neutrons inside the nucleus. When a neutron decays it becomes
a proton and an electron.
An electron is a negatively charged particle that orbits the nucleus. It has a mass of
5.486x10^-4u.
Strong nuclear forces act on a proton or a neutron and are responsible for keeping
the nucleus together. The total energy required to break this force and pull a
nucleus apart is the binding energy.
Radioactive decay
Decay mechanism
Alpha
Beta
Gama
Symbol
α
β
γ
Half Life formula:
MI/MF=(1/2)(t/h)
T= time elapsed
H=half life time
Mi= mass initial
Mf= mass final
Mass Defects
Particle
42He (with no electrons)
One electron (-e)
A photon
The actual mass of an element is less than the calculated value when adding up the
weight of the protons, neutrons, and electrons. This means that some of this mass
must be converted to energy. This energy is called binding energy.
Finding the Mass Defect:
Multiply the number of protons to the weight of one proton, and then do the
same for neutrons.
Add the protons and neutrons together
Get the difference of this number and the given mass of the element.
Finding the Binding Energy
Use E=mc2 where mass equals the mass defect and c2=931.49meV/c2
Carbon Dating is a technique used to determine to age of an organic item that had
been decaying over time.
A parent nucleus is an atom that decays and it produces a daughter nucleus.
Often times the daughter nucleus is also a radioactive isotope. If this is the case, the
daughter nucleus becomes the parent nucleus as it decays again. This continues in a
series until the atom reaches a stable isotope; it is called a decay series.
Radioactivity detectors
Geiger counter-counts the number of alpha, beta, or gamma particles absorbed.
Scintillation counter- emits photons that absorb alpha, beta, or gamma particles and
is then connected to a photomultiplier tube. This tube then emits a photon, which is
then accelerated toward a positive electrode, which will emit more electrons once
the initial electron is absorbed. The electrons continue to be absorbed by electrodes
until there is enough energy to detect a measurable current.
Cloud chamber- contains a cool gas that can detect the path of the radiation
Bubble chamber- almost boiling liquid detects the path of radiation
Four Fundamental Forces:
1) Electromagnetic force
2) Strong nuclear forces (within the nucleus)
3) Weak nuclear forces (between the nucleus and the electrons)
4) Gravitational force
A particle, thought to be like an electron but with a positive charge, or a positron. If
anti-matter were to come in contact with matter the matter would be converted to
energy. Now we know that for every particle there is a corresponding antiparticle.
Particle accelerators emit a beam of high-energy particles and make these particles
collide with a target, which can detect their energy.
With the particle accelerator scientist discovered more subatomic particles, knows
as leptons, hadrons, baryons and mesons. They then devised this classification of
matter. (see page 883 of digital textbook for masses of particles)
Baryons
(3 quarks)
Matter
Hadrons
Mesons
(A quark and an
anti-quark)
Leptons = 1 electron