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We are a group of seven students from Tháder secondary school in
Orihuela (Alicante, Spain) who have decided to carry out this project so that we
might get to visit CERN’s facilities and have the opportunity to work with the
greatest experts in Physics.
Our group, which is led by our teacher Jesús Carnicer, likes to think we
have a great scientific spirit and we are so excited at the chance that CERN is
giving us to achieve our dream. It is not only the possibility of going to these
facilities, but also of knowing that we could realise something that many
teenagers dream of. Every day we are resigned to looking at how the biggest
problems in science have been solved, but for the first time we could be able to
contemplate them first hand and participate in their resolution. We are being
given the chance to make Science, and we do not intend to waste it without a
fight.
Travelling to Geneva and being able to use the particle accelerator would
be an unforgettable experience for us, with which we could show our abilities as
promising young scientists and furthermore, acquire knowledge that we will be
able to use in our future as scientists.
PROPOSED PROBLEM:In what way will the behaviour of alpha particles or protons colliding against either a thin plate of gold or gold nanoparticles differ depending on the speed of these particles?
Firstly, we propose to reproduce the experiment performed by Rutherford
in 1909, in which he collided alpha particles against thin plates of gold,
repeating it at the accelerator, if possible with alpha particles or otherwise
“A BEAM LINE FOR SCHOOL”
replacing them with protons. Secondly, we want to extend this experiment using
a new material as a target that was not available for Rutherford, gold
nanoparticles. Finally, we also are interested to know what will happen to the
beam of particles (alpha or protons) when it collides with gold and with gold
nanoparticles.
HYPOTHESIS: When the protons collide with the target (Au) with a small amount of energy, about the order of 6 MeV (approximately that which Rutherford used), the results will be different for the sheet of gold compared to the nanoparticles.
Because the orbital of the nanoparticles of gold is slightly different from
that for the particles of the plate, the impact parameter will be different and,
consequently, the angle of dispersion. In any case, we expect greater angles of
dispersion for alpha particles than for protons.
In contrast, when we use high energy alpha particles and protons, nuclear reactions will take place in the nucleus of the target producing the same number and types of particles.
EXPERIMENTAL DESIGN:Technical requirements of the accelerator:
1. Sinctillator Counter (Scint) – This detector is the fundamental piece of
equipment for our project. With it, we intend to measure the tiny angles at
which the particles scatter.
2. Delay Wire Chamber (DWC) - Used to check whether the trajectory of
the particles is rectilinear after crossing the gold sheet (reproducing
Rutherford's experiment).
3. Cherenkov Counter – To determine what kind of particles we get after
bombarding the gold (only in the two experiments that use high energies.
4. Halo Counter – The objective of this detector is to measure the larger
angles at which some particles will be deviated and the number of
particles with a high level of deviation (reproducing Rutherford's
experiment).
5. Absorbers – For two of the four proposed experiments (those that use a
small amount of energy), we intend to use this material to reduce the
energy of the beam even more. We would like to place the Absorber in
front of the gold plate as long as it won't interfere with our main objective.
6. MNP17 – As we know both the initial momentum that we give the beam
and the momentum of the particles produced after the collision (thanks to
this detector), we can determine the interaction between the beam and
the gold plate.
Synthesis of the Gold Nanoparticles:Our team, Los Salvadores del gato de Schrödinger (The Saviours of
Schrödinger's Cat), is supported by the Institute of Molecular Science at
Valencia University, Spain, with the researcher from this institute, Gonzalo
Abellán, who from September will work as a Marie Curie Fellow with Prof. Dr.
Andreas Hirsch in Erlangen-Nuremberg Institut für Organische Chemie II, who
has taught us how to synthesise gold nanoparticles by a seed growth strategy
kinetically controlled by reduction of tetrachloroauric acid (HAuCl4 using the
method developed by the group of Victor Puntes Landmuir, 2011, 27 (17) pp
11098-11105.
By this method we obtain aqueous dispersions of colloidal gold
nanoparticles of controlled size, monodisperse and quasi-spherical.
Experimental procedure:We begin with a sodium citrate solution in distilled water which it is
heated up while being shaken vigorously. When the mixture
starts to boil, we add the HAuCl4. The resulting particles (ca. 10
nm, ca. 3.1012 Nps/mL) are coated with negatively charged
citrate ions, so they remain well suspended in H2O.
In a second step, we can increase the size of the nanoparticles in a
controlled way, avoiding the formation of new growth seeds:
Immediately after synthesising the NPs of Au and in
the same flask, the reaction cools down
and we sequentially inject the sodium
citrate and the HAuCl4. In the end, we
obtain the NPs, the size of which can be
modulated by repeating this last addition up to 14 times,
getting a range of sizes from approximately 20nm to
180nm. If the water of the solution is evaporated, we can
obtain a dust of gold nanoparticles.
Therefore, we can have for the experiment a suspension of nanoparticles
either in water or in dust.
Having completed our experiment, it is worth mentioning that working in
such a large team supposed an added difficulty, but something that was solved
easily if we take into account the fun that we have found in every little detail,
from when we chose the group’s name to making the video that accompanies
this project; spending untold hours in the laboratory was also made enjoyable
by performing experiments that are normally forbidden, playing with helium
balloons and computer games behind the teacher's back.
Electronic microscopy image showing
quasi spherical Au nanoparticles
obtained. The scale bar represents
50nm
Histogram showing the size distribution
of the Au nanoparticles. The analysis of
more than 400NPs yields an average
size of 16.3 (±2.1) nm.gg
UV-vis Absorption spectrum of Au.
It is obvious that the work and effort that we have put into this project is
no small thing. Nevertheless, whatever the final result may be, we already
consider the mere fact of having worked together as a team, in addition to what
we have learned about nanoscience and how particle accelerators work (which
was more difficult than we expected), to be a personal and collective triumph
that we are and will be proud of in the future.
BIBLIOGRAPHY:
Tipler P. A. y Mosca G., 1997, Physics for scientists and engineers.
Puentes, V. 2011. Landmuir, 2011, 27 (17) pp 11098-11105.
web: i-cpan.es
Authors: “Los Salvadores del Gato de Schrödinger” (IES Tháder – Alicante - Spain)
Students: Abel Lidón Gloria Llor María Marco Cristina Moreno Cristian Pérez Paula Riquelme Guillermo Rocamora
Teachers: Rocío Espinosa Jesús Carnicer
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Special Thanks: Gonzalo Abellán: investigator who taught us how to
synthesize gold nanoparticles Alex Watkins: Video Narrator
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