DP Physics Unit 7: Atomic, nuclear and particle physics
1. In 1897 British physicist J.J. Thomson discovered the electron, and went on to propose a ___________
model of the atom in which all of the electrons were embedded in a spherical positive charge the size of
the atom.
2. In 1911 British physicist Ernest Rutherford conducted experiments on the structure of the atom by
sending ____________________ (which we will study later) through ________________.
3. _________________ is like tin foil, but it can be made much thinner so that the alpha particles only
travel through a thin layer of atoms.
4. Rutherford proposed that alpha particles would travel more or less straight through the atom without
deflection if Thomson’s “Plum pudding” model was correct:
Here we see that the deflections are much more scattered...
Rutherford proposed that the positive charge
of the atom was located in the center, and he
coined the term _____________________.
5.
6. Only by assuming a concentration of
positive charge at the center of the
atom, as opposed to “spread out” as
in the Plum Pudding model, could
Rutherford’s team explain the results
of the experiment.
7. When a gas in a tube is subjected to a voltage, the gas ionizes, and emits light.
We can analyze that light by looking at it through a ________________________.
A spectroscope acts similar to a _______________, in that it separates the incident light into
its constituent wavelengths.
For example, heated barium gas will produce an ______________________________ that looks like
this:
An emission spectrum is an elemental fingerprint.
8. Each element also has an _____________________, caused by cool gases between a source of light
and the scope.
9. In the late 1800s a Swedish physicist by
the name of J.J. Balmer observed the
spectrum of hydrogen – the simplest of all the
elements:
His observations gave us clues as to the way the _____________________________________________.
10. In reality, there are many additional natural groupings for the hydrogen spectrum, two of which are
shown here
These groupings led scientists to imagine that the hydrogen’s single electron could occupy many
different _________________________________.
11. The first 7 energy levels for hydrogen are shown here:
The energy levels are labeled from the lowest to
the highest as ___________________________ in the picture.
n is called the _____________________ and goes all the way up to infinity ()!
In its _____________________________, hydrogen’s single electron is in the 1st
energy level (n = 1):
12. As we will see later, light energy is carried by a particle called a ________________.
If a photon of _______________________ strikes a hydrogen
atom, it is ____________ by the atom and stored by virtue of
the electron jumping to a new energy level:
The electron jumped from the n = 1 state to the n = 3 state.
We say the atom is _________________.
13. When the atom de-excites the electron jumps back down to a lower energy level.
When it does, it emits a photon of __________________________
to account for the atom’s energy loss during the
electron’s orbital drop.
The electron jumped from the ________________________ state.
We say the atom is __________________, but not quite in its ground state.
14. The graphic shown here accounts for many of the observed hydrogen emission spectra.
The excitation illustrated looked like this:
The de- excitation looked like this:
15. The human eye is only sensitive to the Balmer series of photon energies (or wavelengths):
16. The previous energy level diagram was NOT
to scale. This one is. Note that none of the energy
drops of the other series overlap those of the
Balmer series, and thus we cannot see any of them.
But we can still sense them
17. Because of ___________________ we have discovered that light not only acts like a wave, having a
wavelength _____ and a frequency _____, but it acts like a particle (called a ___________) having an
energy E given by
_____________________________________ Energy E of a photon having frequency f.
18. EXAMPLE:
An electron jumps from energy level n = 3 to energy level n = 2 in the hydrogen atom.
(a) What series is this de-excitation in?
(b) Find the atom’s change in energy in eV and in J.
(c) Find the energy (in J) of the emitted photon.
(d) Find the frequency of the emitted photon.
(e) Find the wavelength (in nm) of the emitted photon.
19. PRACTICE: Which one of the following provides direct evidence for the existence of discrete energy
levels in an atom?
A. The continuous spectrum of the light emitted by a white hot metal.
B. The line emission spectrum of a gas at low pressure.
C. The emission of gamma radiation from radioactive atoms.
D. The ionization of gas atoms when bombarded by alpha particles.
20. PRACTICE: A spectroscopic examination of glowing hydrogen shows the
presence of a 434 nm blue emission line.
(a) What is its frequency?
(b) What is the energy (in J and eV) of each of its blue-light photons?
(c) What are the energy levels associated with this photon?
20. PRACTICE: The element helium was first identified by the absorption spectrum of the sun.
(a) Explain what is meant by the term absorption spectrum.
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
(b) Show that the energy of a photon having a wavelength of 588 nm is 3.3810-19 J.
(c) Use the information in the diagram to explain how absorption at 588 nm arises.
21. In a later lecture we will discover that the most intense light reaching us from the sun is between
________________________ in wavelength.
Evolutionarily our eyes have developed in such a way that they are most sensitive to that range of
wavelengths, as shown in the following graphic:
22. Recall the ________________________, in which an atom is stripped of its electrons and accelerated
through a voltage into a magnetic field.
Scientists discovered that hydrogen nuclei had ______________________.
Since the charge of the hydrogen nucleus is e, scientists postulated the existence
of a ________________________________, which added mass without charge.
23. The proton and neutron are called _______________________.
____________________________________
Nucleons
____________________________________
For the element hydrogen, it was found that its nucleus existed in three forms:
Isotopes
__________________
__________________
__________________
A set of nuclei for a single element having different numbers of neutrons are called _________________
A particular isotope of an element is called a ________________________________________________
24. An element’s chemistry is determined by the number of ___________________________________.
The number of electrons an element has is determined by
_______________________________________.
Therefore it follows that isotopes of an element have the same chemical properties.
For example there is _______, made of hydrogen H and oxygen O, with the molecular structure _____.
But there is also __________, made of deuterium D and oxygen O, with the molecular formula ______.
Both have exactly the same chemical properties. But heavy water is slightly ____________ than water.
25. A species or nuclide of an element is described by _______________________:
The _________________________ is the total number of protons and neutrons in the nucleus.
The _______________ is the number of protons in the nucleus. It is also known as the ______________.
The ____________________ is the number of neutrons in the nucleus.
It follows that the relationship between all three numbers is just ______________ nucleon relationship.
26. In nuclear physics you need to be able to distinguish the different isotopes.
CHEMISTRY
NUCLEAR PHYSICS
27. PRACTICE: Which of the following gives the correct number of electrons, protons and neutrons in the
neutral atom 6529Cu?
28. PRACTICE: Ag-102, Ag-103 and Ag-104 are all isotopes of the element silver. Which one of the
following is a true statement about the nuclei of these isotopes?
A. All have the same mass.
B. All have the same number of nucleons.
C. All have the same number of neutrons.
D. All have the same number of protons.
29. Track X shows the deflection of a singly-charged carbon-12 ion in
the deflection chamber of a mass spectrometer. Which path best
shows the deflection of a singly-charged carbon-14 ion? Assume
both ions travel at the same speed.
30. Given that a nucleus is roughly 10-15 m in diameter it should be clear that the ___________________
between protons within the nucleus must be enormous.
Given that most ______________________________, there must be a nucleon force that acts within the
confines of the nucleus to overcome the Coulomb force.
We call this nucleon force the ________________________.
In a nutshell, the strong force…
(1) _____________________________________________________________________________
_____________________________________________________________________________
(2) is very short-range, since protons located far enough apart do, indeed, repel.
_____________________________________________________________________________
_____________________________________________________________________________
31. PRACTICE:
The nucleus of an atom contains protons. The protons are prevented from flying apart by
A. The presence of orbiting electrons.
B. The presence of gravitational forces.
C. The presence of strong attractive nuclear forces.
D. The absence of Coulomb repulsive forces at nuclear distances.
32. PRACTICE: Use Coulomb’s law to find the repulsive force between two protons in a helium nucleus.
Assume the nucleus is 1.0010-15 m in diameter and that the protons are as far apart as they can get.
33.
Range:
Force Carrier
Range:
Range:
Force Carrier
Range:
Force Carrier
34. In 1893, Pierre and Marie Curi announced the discovery of two ____________________ elements,
radium and polonium.
When these elements were placed by a radio receiver, that receiver picked up some sort of activity
coming from the elements.
35. In 1896, while studying a uranium compound, French scientist Henri Becquerel discovered
that a nearby photographic plate had somehow been exposed to some source of "light" even though it
had not been uncovered.
Apparently the darkening of the film was caused by some new type of radiation being _______________
_______________________________.
This radiation had sufficient energy to pass through the cardboard storage box and the glass of the
photographic plates.
36. Studies showed that there were three types of
radioactive particles.
If a radioactive substance is placed in a lead chamber
and its emitted particles passed through a magnetic field,
as shown, the three different types of radioactivity can be
distinguished.
Alpha particles ________________________________________.
This is identical to a helium nucleus 4He.
Beta particles ________________________________________________________________________.
Gamma rays _________________________________________________________________________.
37. When a nucleus emits an ___________________ it loses two protons and two neutrons.
All alpha particles consistently have an energy of about ___________________.
The decay just shown has the form ____________________________________
Since the energy needed to knock electrons off of atoms is just about _______, one alpha particle can
_________________________________________.
It is just this ionization process that harms ________________________________________________.
38. It turns out that the total energy of the americium nucleus will equal the total energy of the
neptunium nucleus plus the total energy of the alpha particle.
According to E = mc2 each portion has energy due to mass itself. It turns out that the right hand side is
short by about 5 MeV (considering mass only), so ___________________________________________
_________________________________________________________________.
39. In - decay, a neutron becomes a proton and an electron is emitted from the nucleus.
In + decay, a proton becomes a neutron and a positron is emitted from the nucleus.
In short, a _____________________ is either __________________ or it is ______________________.
40. In contrast to the alpha particle, it was discovered that beta particles could have a _______________
_____________________________________________________________.
In order to conserve energy it was postulated that another particle called a ____________________ was
created to carry the additional ____________________________________________.
Beta (+) decay produces neutrinos , while beta (-) decay produces anti-neutrinos .
41. Recall that electrons in an atom moving from an excited state to a de-excited state release a photon.
Nuclei can also have excited states.
When a nucleus de-excites, it also releases a photon. This process is called gamma () decay.
42. Since alpha particles are ____________________________________, they are stopped within a few
__________________________________________________________________.
The beta particles are _______________________________________. They can travel a few meters in
__________________________________________________________________.
The gamma rays are _________________________________________. They can travel a few
__________________________________________________________________.
Neutrinos can go through ____________________________________________.
43. In living organisms, _________________________________________________________________.
All three particles energize ______________________________________________________________
______________________________________.
44. Background radiation is the ionizing radiation that people are exposed to in everyday life, including
__________________________________________________________.
Average annual human exposure to ionizing radiation in millisieverts (mSv)
Artificial radiation source
World
USA
Japan
Remark
Medical
0.6
3
2.3
CT scans excludes radiotherapy
Consumer items
-
0.13
Atmospheric nuclear testing
0.005
-
0.01
peak of 0.11 mSv in 1963 and declining since
Occupational exposure
0.005
0.005
0.01
radon in mines, medical and aviation workers
Nuclear fuel cycle
0.0002
0.001
up to 0.02 mSv near sites; excludes occupational
Other
-
0.003
sub total (artificial)
0.61
3.14
cigarettes, air travel, building materials, etc.
Industrial, security, medical, educational, and
research
2.33
Average annual human exposure to ionizing radiation in millisieverts (mSv)
Natural radiation source
World
USA
Japan
Remark
Inhalation of air
1.26
2.28
0.4
mainly from radon, depends on indoor
accumulation
Ingestion of food & water
0.29
0.28
0.4
K-40, C-14, etc.
Terrestrial radiation from ground
0.48
0.21
0.4
depends on soil and building material.
Cosmic radiation from space
0.39
0.33
0.3
depends on altitude
sub total (natural)
2.4
3.1
1.5
45. Stable isotopes exist for elements having atomic numbers Z = 1 to 83.
Up to Z = 20, the neutron-to-proton ratio is close to 1.
Beyond Z = 20, the neutron-to-proton ratio is bigger than 1, and
grows with atomic number.
The extra neutrons counteract the repulsive Coulomb force
between protons by increasing the strong force but not contributing
to the Coulomb force.
46. As we have seen, some nuclides are unstable.
What this means is that an unstable nucleus may ____________________ decay into another nucleus
(which may or may not be stable).
Given many identical unstable nuclides, which precise ones __________________________________
_________________________________________________________________________________.
In other words, the ___________________________________________.
But random though the process is, if there is a large enough population of an unstable nuclide, the
probability that _______________________________________________________________________.
47. EXAMPLE: Here we have a collection of unstable Americium-241 nuclides.
We do not know which particular nucleus will decay next.
All we can say is that a certain proportion will decay in a certain amount of time.
48. Obviously the higher the population of Americium-241 there is to begin with, the more decays there
will be in a time interval.
But each decay decreases the remaining population.
Hence the decay rate _____________________________________________.
It is an __________________________________________________________.
49. Thus the previous graph had the time axis in increments of half-life.
From the graph we see that half of the original 100 nuclei have decayed
after 1 half-life.
Thus after 1 half-life, ____________________ of the original population
of 100 have retained their original form.
And the process continues…
50. Rather than measuring the amount of remaining radioactive nuclide there is in a sample (which is
extremely hard to do) we measure instead the _______________________ (which is much easier).
Decay rates are measured using various devices, most commonly the Geiger-Mueller counter.
Decay rates are measured in ___________________(Bq).
Becquerel definition: _______________________________________.
51. The decay rate or _________________A is proportional to the population of the radioactive nuclide
______ in the sample.
Activity A: ________________________
Thus if the population has decreased to half its original number, the ____________________________.
52. EXAMPLE: Suppose the activity of a radioactive sample decreases from X Bq to X / 16 Bq in 80
minutes. What is the half-life of the substance?
53. EXAMPLE: Find the half-life of the radioactive nuclide shown here. N0 is the
starting population of the nuclides.
54. EXAMPLE: Suppose you have 64 grams of a radioactive material which decays into 1 gram of
radioactive material in 10 hours. What is the half-life of this material?
55. EXAMPLE: A nuclide X has a half-life of 10 s. On decay a stable nuclide Y is formed. Initially, a sample
contains only the nuclide X. After what time will 87.5% of the sample have decayed into Y?
A. 9.0 s B. 30 s C. 80 s D. 90 s
56. PRACTICE: A sample of radioactive carbon-14 decays into a stable isotope of nitrogen. As the carbon14 decays, the rate at which nitrogen is produced
A. decreases linearly with time.
B. increases linearly with time.
C. decreases exponentially with time.
D. increases exponentially with time.
57. PRACTICE: An isotope of radium has a half-life of 4 days. A freshly prepared sample of this isotope
contains N atoms. The time taken for 7N/8 of the atoms of this isotope to decay is
A. 32 days.
B. 16 days.
C. 12 days.
D. 8 days.
58. PRACTICE:
Radioactive decay is a random process. This means that
A. a radioactive sample will decay continuously.
B. some nuclei will decay faster than others.
C. it cannot be predicted how much energy will be released.
D. it cannot be predicted when a particular nucleus will decay.
59.
60.
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63.