"A Crash Course in Particle Physics" by Brian Cox
[ 1 |
Hunting for Neutrinos [40:38]
by Vincenzo Cavasinni & Paola Catapano,
directed by Emanuele Angiuli
and produced, under the name "Orione", by CERN,
Istituto Nazionale di Fisica Nucleare (INFN-Pisa),
Laboratori Nazionali Gran Sasso (LNGS),
Laboratori Nazionali del Sud (LNS-Catania) and the
association for scientific culture La Limonaia (Pisa).
(2011-09-07) Radioactivity (March 1, 1896)
Henri Becquerel's great experimental discovery.
It is important to observe that this phenomenon cannot be attributed
to the luminous radiation emitted by phosphorescence. Henri Becquerel
(1852-1908; X1872; Nobel 1903)
A. Henri Becquerel belongs to one of the most famous dynasty of French physicists.
He was the grandson of Antoine
César Becquerel (1788-1878; X1806), the son of
(1820-1891) and the father of
Jean Becquerel (1878-1953; X1897)
who discovered the rotation of polarization due to a magnetic field.
Three of them studied at Polytechnique. (Edmond
as he chose to become pupil and assistant of his father instead.
In Polytechnique's own records, the remark
identifying Henri as fils de polytechnicien
is thus erroneous).
All four Becquerels held successively the same chair of applied physics,
created in 1838 at the
National d'Histoire Naturelle
(founded on 10 June 1793) and all of them became members of the French
Académie des Sciences.
Although that early discovery was duly heralded as major
at the time (1857) the World was apparently not quite ready for it yet...
By the time of Becquerel's own discovery (1896) the previous work of
Niépce de Saint-Victor had apparently been all but forgotten...
Curiously enough, one of the few noteworthy physicists who did
notice in due time was Becquerel's own father!
Edmond Becquerel (1820-1891)
fully discussed the future discovery of his son in a book he published in 1868
(La lumière, ses causes et ses effets).
At the time, the younger Becquerel was 16 and curious.
It's hard to believe he never read the book of his father.
(2011-01-19) Rutherford's Gold-Foil Experiment (1909)
This experiment was first conducted by
Hans Geiger (1882-1945)
and Ernest Marsden (1889-1970)
under the supervision of Rutherford.
It was almost as incredible as if you fired a 15-inch shell at
a piece of tissue paper and it came back and hit you. Ernest Rutherford (1871-1937)
experiment (1909) was conducted while Hans Geiger was a student of Rutherford
Ernest Marsden was still an undergraduate student there
(he was a New-Zealander, like Rutherford).
Ernest Rutherford ("Ern") had been awarded a
the previous year (1908) for his studies of radioactivity, including the concept of
half-life and the naming of alpha and beta radiations (1899).
He also coined the term gamma radiation (in 1903) for what the Frenchman
Paul Villard had discovered in 1900
while studying the decay of radium.
In spite of those early achievements, Rutherford's best work was yet to come...
In 1911, the surprising results of the Geiger-Marsden gold-foil experiment
prompted him to posit a model
of the atom consisting of a tiny heavy positively-charged nucleus orbited by electrons.
Energy of alpha particles from Po-210 decay
How close can those
approach another polonium nucleus?
Using unabbreviated notations, the nuclear decay involved can be written:
+ 5.4075 MeV
The a-particle being the bare nucleus
of helium-4 (doubly-ionized atom of helium-4)
the above is commonly written with more compact notations:
+ 5.4075 MeV
Table of Relevant (Neutral) Isotopes
Atomic weight (u)
In the main, this may be treated nonrelativistically.
As the initial polonium atom is at rest, the two outgoing particles have
opposite momenta and thus share the available total energy in inverse proportion
of their masses. So, the recoiling lead atom gets 1.9% of it and the alpha particle
(2011-01-21) Standard Decay Modes for Heavy Radioactive Nuclides
Heavy radioactive nuclei decay in the following five standard modes :
a Decay :
The alpha-decay of an atom is the emission of an
a-particle from its nucleus
(an Helium-4 nucleus consists of 2 protons and 2 neutrons).
The mass number (A) is decreased by 4 units;
the atomic number (Z) is decreased by 2 units.
With a negligible error (due to the differences in electronic binding
energies for helium-4 versus other elements), the products of
a mass not less than the combined mass of a neutral helium-4 atom
(namely 4.002603254 u) and the
(neutral) isotope of the element two steps down with
a mass number four units down.
This implies an inequality among tabulated
masses of the istopes which is a necessary
(and almost sufficient) condition for
a-decay to occur.
Translated in terms of energy, the positive difference between the
aforementioned masses is the so-called Q-value
for the a-decay reaction.
e Decay :
e decay is commonly abbreviated EC
("electron capture") in English texts.
It consists in the capture of an orbital electron
(and emission of a neutrino).
One proton of the nucleus turns into a neutron;
the mass number (A) does not change; the atomic number (Z) is decreased by one.
Besides a neutrino, whose energy can be arbitrarily low,
e decay produces
only a neutral atom of the previous element (more precisely, the isotope
of that element which has the same mass number as the isotope whose decay
is being considered).
Thus, an atom can undergo e decay
only if it is heavier than the corresponding isotope of the previous element.
b+ Decay :
b+ decay consists
in the emission of a positron (and a neutrino).
One proton of the nucleus turns into a neutron;
the mass number (A) does
not change; the atomic number (Z) is decreased by one.
The decay produces the same nuclear result as
e decay but
a positron is radiated away and an additional electron
remains in the vicinity of the nucleus (the atom produced is a negative
ion instead of a neutral atom for e+).
The binding energy of an electron is less than a few electron-volts;
(1 eV being about 0.00000000107 u).
If we neglect that,
the above means that b+ decay
can only occur for an atom whose mass exceeds that of the corresponding
isotope of the previous element by at least
two electron masses (i.e. 0.001097 u).
b- Decay :
b- decay consists in the emission
of an electron (and an antineutrino).
It used to be known simply as "b decay"
before the discovery of the positron (1932).
One neutron of the nucleus turns into
a proton; the mass number (A) does
not change; the atomic number (Z) is increased by one.
Besides the antineutrino, whose energy can be arbitrarily small,
produces only a positive ion and an electron whose combined mass is not
less than that of a neutral atom.
Thus, b- decay can occur as soon
as the decaying atom is heavier than the corresponding isotope
of the next element.
There are some (very) long lived radioisotopes like Tellurium-128 or
Tellurium-130 for which a single b- decay
is impossible but for which near-simultaneous double
(2b-) are allowed because the atom is heavier
than the corresponding isotope two elements up.
Thus, the 2b- decay of
Te-128 (resp. Te-130) into Xe-128 (resp. Te-130) is rare but
possible, whereas the b- decay of
Tellurium into Iodine is forbidden.
Other nuclides for which the same remark applies include Ca-48, Ge-76, Mo-100,
Isomeric Transition :
Isomeric Transition (IT) is the name given to the decay of a long-lived
excited state of the nucleus into an isomeric state of lower energy
(usually, but not always, the ground state).
Such long-lived metastable states
are normally marked with the suffix "m"
or, if there are several, "m1", "m2", "m3", etc.
During such a decay,
the extra energy and the extra spin (a whole number
of spin quanta)
is carried away by gamma-ray photons.
(2011-01-21) The four radioactive series of heavy nuclides:
Successive decay products of a heavy nucleus stay in one of four series.
Since the above standard decay modes
either decrease the mass number (A) by 4 units or leave it unchanged, there are
4 standard radioactive families or series.
The mass number modulo 4 is characteristic of each series.
Three of those families are natural ones which
start with a long-lived parent and end with a stable isotope of lead.
Glenn T. Seaborg was instrumental in establishing artificially the fourth series,
which was extinct :
With a half-life of only 2.14 million years,
the parent of that series (Neptunium-237) has not
maintained a native presence on Earth.
Neither has any other member of the
Neptunium series, except for the [two] final one[s]:
Bi-209 [& Tl-205].
As bismuth-209 was once believed to be the heaviest stable nuclide,
the news that it is extremely weakly radioactive made
headlines in 2003.
The line at 3.14 MeV, now attributed to
the decay of Bi-209 below, was first observed on the morning of
March 15, 2002,
during calibration of a new scintillating bolometer using bismuth germanate cooled to
Bismuth-209 decays into stable
thallium-205 with a record-breaking
half-life (about a billion times the age of the Universe)
first estimated from a total of
128 alpha disintegrations seen over a period of 5 days,
using two distinct masses of bismuth (31 g & 62 g).
The experimental value of
1.9(2) 1019 years
matched predictions around
4.6 1019 years, based on
tabulated masses and energies that have since been revised because of this discovery.
A late 1960's Homer Laughlin Fiesta Ironstone "mango red"
bowl, 6.5" in diameter, 1.75" deep.
The 0.2 mm glaze owes its color to UO3, trioxide of depleted uranium.
The Homer Laughlin Company of West Virginia used natural uranium
Depleted uranium (0.25% of U-235)
is about 60% less radioactive than the natural uranium originally used
for "Fiesta red" (1936) containing about 0.72% of U-235.
(2011-01-21) Other decay modes
Lighter isotopes commonly decay in nonstandard modes.
One reason why the above concept of radioactive series
is of little or no use for lighter elements is that their radioactive isotopes
may decay in nonstandard modes which need not preserve
the mass number modulo 4.
Such modes include the spontaneous emission of a proton or a neutron,
spontaneous fission into two nuclei [both bigger than
an alpha particle] or spallation into
three or more fragments.
(2011-09-07) Geiger-Müller Counter
The simplest device to detect ionizing radiation and quantify activity.
Interesting as it may be, that last educational film isn't part of the celebrated
"Mr Wizard" TV series and may not be completely candid...
It was deliberately produced in the educational style of the 1950s and
1960s with a grant from Southern-California Edison.
The barely-readable copyright date on the last frame
is MXMLXXIII (1973) which might indicate a specific commission to
reassure the public at that particular time... Especially dubious is the
closing comment that spending a year 5 miles from the featured nuclear plant
operated by Edison) is like watching color-tv for 8 hours... By the same reasoning,
the nuclear plant shown (photographed from a distance of about 50 yards) emits 25000 times
as much radiation, which is what you'd get by watching 30 color TVs at once.
The apparent size of the target depends on the speed of the projectile.
(2011-02-02) Critical Mass
The smallest mass that can cause a runaway chain reaction.
nuclear test (3.5 miles off Bikini Island, on July 1, 1946)
was the fourth nuclear explosion ever
(the first three were Trinity, Hiroshima and Nagasaki).
Although the test itself didn't cause any casualties, the plutonium core involved
(dubbed the Demon core) has previously claimed two lives...
Alpha (Yahoo! 2011-01-03)
Radiocarbon (C-14) allows carbon dating:
In a dead organism, carbon-14 decays with a half-life of 5730 years.
+ 156.46 keV
The above b decay occurs for
radiocarbon everywhere, including in the carbon dioxide of the air.
However, the concentration of carbon-14 in the atmosphere remains essentially constant
because it is replenished by the following action on nitrogen of neutrons that originate
from cosmic rays:
+ 625.87 keV
All told, the atmospheric concentration of radiocarbon remains fairly constant
but it may vary for several reasons
that influence the above production of radio-carbon.
Those factors, listed by increasing order of severity, include:
Radiocarbon is primarily produced in the upper atmosphere where it
gets oxidized by oxygen. Radioactive carbon dioxide then
diffuses down below (which means that the concentration of radiocarbon
varies a little bit with altitude).
The bombardment by neutrons is very sensitive to cosmic circumstances which
may vary over time. This results in some noise
which limits the precision of carbon dating for relatively
young samples, unless some calibration is
done using samples of dead things whose history is precisely known by other means.
When atmospheric nuclear tests where still allowed,
there were times when the concentration of radiocarbon was twice as
high in some locations of the Northern Hemisphere compared to
reference points in the Southern Hemisphere.
(Mixing of air through the horse latitudes
can be particularly slow at times.)
In the distant future, dead plants that grew in the wrong places during that dark period
may appear thousands of years too young if this effect is not taken into account.
... / ...
Table of Relevant Isotopes (neutral elements, unless otherwise specified)
When two new particles are produced like this,
the final release of energy is normally split between them as kinetic energy
in inverse proportion of their respective masses.
In this example, as the helion has about 3 times the mass of the neutron,
it gets 25% (817 keV)
and the neutron 75% (2.45 MeV).
Indeed, in the frame of their center of mass,
the momenta of the two particles are opposite
and their (nonrelativistic) speeds
are thus inversely proportional to their masses, which makes their kinetic energies
also inversely proportional to their masses.
Fusing heavier elements (i.e., elements heavier than Fe=iron)
requires an input of energy,
while the splitting of an heavy nucleus into several lighter pieces (fission) releases energy.
For example fission of a uranium nucleus releases energy.
The fusion of heavy nuclei into heavier ones is only possible in very violent events
(like the supernova explosion of a star)
because there is extra energy floating around which can be absorbed in the process.
This is how all elements heavier than iron were once synthesized from lighter elements
(mostly hydrogen and helium) of which the early universe was made of.
(2011-08-20) The Proton-Proton chain fusion process:
What powers the Sun and all stars colder than 15 000 000 K.
(2011-08-15) Tokamak Reactors
Igniting fusion by heating a magnetically-confined plasma.
For two positively charged atomic nuclei to fuse, they must come close
enough to each other for the attractive nuclear forces to
overcome their electric repulsion.
This can only happen if their relative speed
exceeds a certain threshold, which can be measured equivalently
either in terms of energy or temperature.
The latter is called the ignition temperature.
Temperature (K) = 11604.5 (Charges on the particle) (Voltage)
The lowest known ignition temperature
(4.5 107 K,
or about 4 keV)
is for the fusion of deuterium and tritium
(this fusion cannot occur in a natural star unless some tritium is produced
by a prior process with a higher ignition temperature).
As this "D-T fusion" seemed easiest to ignite,
it became the focus of all Tokamak experiments.
The energy of 17.6 MeV is shared between the particles
inversely as their masses: 20% (3.5 MeV)
for 4He++ and 80% (14.1 MeV)
for the neutron.
In a magnetically confined plasma, the charged helium nucleus
(alpha particle) will stay in the plasma and release its
energy in it by thermal collisions with other ions.
The neutron, on the other hand, doesn't feel the magnetic confinement and
will escape into the blanket material around the reactor,
which will get hot by absorbing it.
Useful energy from the reactor can be recovered as heat by
running a cooling fluid through that blanket.
(2011-08-15) The Farnsworth-Hirsch fusor
design (c. 1964)
A well-established way to achieve nuclear fusion on a tabletop.
The design presented below is extremely simple and works very well.
The actual construction involves substantial engineering challenges.
However, those have not stopped dozens of amateurs
(including a few high-school students)
from building homemade nuclear fusion reactors...
The core is just a spherical cavity containing deuterium
under a very low pressure between 5 and 20 microns.
Prior to receiving the deuterium, the cavity is evacuated down to
0.001 or 0.0001 microns (another possibility might be to flush the cavity
with deuterium several times using less extreme pumping).
A micron is defined either as a millitorr
(mTorr) or a micrometer of mercury
(mHg). Both definitions are used interchangeably
in practice (although the latter is preferred)
since both specify almost the same pressure.
The correct equivalence is precisely:
= 0.133322387415 Pa (exactly)
= 1.000000142466321243523316... mTorr
1 pascal (Pa) is thus very nearly equal to 7.5 microns.
A gas or plasma in that pressure range is essentially a
Inside the cavity are two concentric spherical electrodes.
The wall of the cavity can serve as the outer electrode
(it can be electrically grounded for safety).
The inner electrode, on the other hand, is kept at a large negative potential
-U of -10 000 V or -30 000 V.
That inner grid must consists of a loose mesh of wire. It is thus fairly
transparent to the positive ions that it attracts (which will go
through it most of the time, at substantial speed).
Elmore-Tuck-Watson electron accelerator :
(later, "ITT Philo Farnsworth Research Corporation")
consisted of never more than 6 engineers working on-site at the
television factory in Fort Wayne, Indiana, until ITT stopped funding the research in 1967.
The original team
(1959) working on fusors included:
Rear admiral Frederick R. Furth
VP of ITT (R&D).
In 1998, Richard Hull, the first amateur to
achieve nuclear fusion did meet with all four living members of that original team
(Hirsch, Meeks, Haak and Blasing).
Hull did it again with Paul Schatzkin around 2004.
Hull and Schatzkin are now coordinating the efforts to keep
alive among amateurs the practical knowledge gathered in that era, as explained below.
US Patent 3258402
by Philo T. Farnsworth (June 1966) for ITT
[ Virtual cathode formed by electrons ]
US Patent 3386883
by Philo T. Farnsworth (June 1968) for ITT
[ Fusor with real transparent cathode ]
US Patent 3530497
by Robert L. Hirsch and Gene A. Meeks (Sept. 1970) for ITT
[ 3 electrodes ]
(2011-08-15) Polywell design &
Wiffleball machines (WB1 ... WB8)
The brainchild of the late
Dr. Robert W. Bussard (1928-2007).
On 2006-11-09, Robert Bussard gave an inspirational
Google Tech Talk
on the fusion reactor that he had been developping since 1987, with Navy funding,
at his own company (EMC2) where
Tom Ligon had assisted him for 5 years.
Bussard passed away only 11 months later, at the age of 79.
However, his Google talk was instrumental in getting his company renewed Navy backing
a few weeks before his death.
This allowed research at EMC2 to
with a team of 5 people led by
Nebel who was on leave from
Rick Nebel retired in November 2010 and was suceeded by 41-year-old
Jaeyoung Park who gave up his position at Los Alamos to focus on the project.
As of May 2011,
EMC2 employs 8 or 9 staff members interacting with about two dozen external consultants.
If/when it becomes practical to use nuclear fusion to generate energy,
neutron radiation would become a nuisance.
would be preferred, possibly using
in a 500 keV
reaction, known as "Proton Boron-11" (p-B11)
and heralded as the Holy Grail of fusion :
11B + 1H
® 12C + 15.957 MeV
8Be + 4He + 8.590 MeV
3 4He + 8.682 MeV
A large part of the kinetic energy of the alpha particles so produced
(without any residue or harmful radiation) could be converted directly
arguments presented by
Todd H. Rider in his doctoral dissertation at
strongly indicate that any plasma outside of thermal equilibrium
cannot generate net fusion power because of
(even with gridless designs like the Polywell machines).
This applies to all known clean nuclear fuels and, most probably, to
other fuels as well. Allowing the plasma to thermalize seems
to make matters only worse. Here's how Rider saw fit to start his dissertation:
For the record, the author would like to apologize for apparently killing some of
the most attractive types of fusion reactors which have been proposed.
He advises future graduate students working on their theses to avoid accidentally
demolishing the area of research in which they plan to work after graduation.
Apparently, Bussard never considered that the Bremsstrahlung issue could be
a fundamental limitation and kept arguing that the power output of large Polywell machines
would scale as the seventh power of their linear size...
One of the above topics is the homemade fusor
(i.e., fusion reactor) built by
Jon Rosenstiel of Anaheim, California.
Jon's fusor holds the record in
nuclear fusion, with more than 10 million neutrons per second.
Such devices are arguably the most advanced type of nuclear contraptions
that have been successfully duplicated by independent amateurs.
The amateur fusion movement began in 1997 when Tom Ligon,
the assistant of Robert Bussard, decided to
stir up interest in nuclear fusion among the
Tesla Coil Builders Of Richmond (TCBOR) at a Teslathon
organized by Richard Hull in Richmond, VA.
In a matter of weeks, Hull had built his own fusor
and other amateurs weren't far behind...
With Paul Schatzkin ("The Perfesser")
Richard Hull now runs fusor.net,
where all fusioneers congregate (including Tom Ligon).
Hull maintains a
of known experimenters at various stages of their own
fusor projects :
Scroungers who have declared their intentions to gather components.
Plasma Club members have obtained preliminary functionality.
Members of the Neutron Club have achieved fusion and measured it.
As of June 2013,
about 50 hobbyists have reached that last stage
(dubbed Star in a Jar in some popular articles).
They almost always use a plasma of deuterium as nuclear fuel in a traditional
which can be built at low cost (albeit beyond Hull's low estimate of $50-$400).
According to the aforementioned records, Mark Suppes
(who has worked as a Web designer for Gucci)
became the 37-th hobbyist to achieve nuclear fusion,
in 2010 (in a Brooklyn warehouse, at a cost of about $39000).
Suppes was investigating Bussard's
Polywell design, but he apparently settled
for a standard Farnsworth-Hirsch fusor instead.
The amateurs are not even trying to produce the net output of energy that
is aiming for.
Their fusors serve exclusively as artificial sources of neutrons
based on deuterium-deuterium (D-D) fusion:
(2011-08-08) The Radioactive Boyscout
& misguided endeavors:
Poor experiments attract more media attention than great investigations.
The best known case of radioactivity experimentations gone astray is surely that of
David Charles Hahn
(born Oct. 30, 1976) who conducted misguided experiments on radioactivity
in a potting shed at his mother's house, until 1994 (he was then a 17-year old boyscout who
had earned a merit badge for atomic energy in 1991 and had already attained the rank of
After being discharged from the U.S. Navy, David Hahn returned to his
home state of Michigan, still obsessed with radioactivity.
On August 1st 2007, at age 31, Hahn was arrested in Detroit for stealing 16
His face was covered with open sores, hastily attributed to radiation exposure.
No hazardous materials were found in Hahn's appartment.
Subsequently, Hahn was sentenced to a treatment facility where he had Internet access
and would make weird posts on
about his story,
using the handle Thumper235 or Thumper23598
David Charles Hahn /
Eagle Scout / Former U.S. Navy /
Former U.S. Marine Corps (Retired) /
Time Travel Institute Member /
American Legion Member /
Associates Of Applied Science /
"The Radioactive Boyscout".
A Swedish rad-freak who made the news :
In May 2011, Richard Handl
(a 31 year old unemployed man from
Ängelholm, southern Sweden)
chronicled in his blog his own attempts at reproducing the misguided efforts of David Hahn.
On 2011-05-20, he quoted some hilarious
for building a "nuclear reactor"
as if it had been some kind of inspirational documentary...
The very next day, Handl reported a
after trying to cook (on his stovetop) americium, radium and beryllium
in 96% sulfuric acid,
seemingly unaware of the dangerous propensity of concentrated sulfuric acid
to burp when improperly heated.
He had been fooling around with his samples of radioactive elements
"to easier get them blended" [sic!] in the naive way mocked by the aforementioned spoof video...
Richard Handl alerted the
Radiation Safety Authority himself to make sure he wasn't doing anything illegal...
He was questioned by police, who confiscated his radioactive samples and his computer.
He readily admitted that his experiments were crazy
but (rightly) argued that they were
"not so dangerous" (well, boiling concentrated sulfuric acid
is just about as dangerous with or without radioactive samples in it).
Following his arrest, Handl announced on his blog the "cancelation"
of his project
that he attracted, starting with a 2011-08-02
News preliminary report (from a
NewsCore story) and culminating with a
BBC news interview on