Global Journal of Engineering Sciences (GJES)
Studying
the Nuclear Structure using the Naturally Occurring Radioactive Sources
Authored by MMR Chishti
Abstract
Scientists believe that that
natural radioactive sources contains the wealth of information regarding
exploring the nuclear structure as well as the search for the events during the
formation of the universe and properties and existence of matter and anti-matter.
Thorium and Uranium are radioactive sources and exist since the formation of
earth after the Big Bang. These nuclei are found abundantly on the earth and
are being been used for number different purposes including power generation,
isotopes production and studying the nuclear structure at the lowest level.
This short review explains that how these naturally occurring radioactive
sources are being studied in the laboratories to explore nuclear structure in
actinides region of nuclei and what is the scope of any potential research that
can be performed. The continuously emitted alpha, beta and gamma radiations
from these nuclei are an amazing source of information regarding the formation
of the universe and perhaps the description of the presence of matter and
anti-matter in the universe.
Thorium-232
and Uranium-238 are naturally occurring radioactive sources which are emitting
a variety of radiations with different intensities spontaneously, a phenomenon
called radioactivity. Radioactivity is described as an act of emitting
radiations spontaneously where all unstable nuclei decompose and decay into
more stable configuration. The half-lives of these radioactive nuclei are found
to be 14 billion years and 4 billion years for 232-Th and 238-Th respectively
[1,2]. A half-life is a scale in which the radioactivity of the unstable
nucleus becomes half after passage of that certain period of time or it can be
described as the time for half the radioactive nuclei in any sample to undergo
radioactive decay. This process explains how long the intensity of the
radiations will last. These two nuclei belong to the actinides regions of the
nuclear chart, the nuclei in which number of neutrons exceeds the number of
protons which results in emitting the radiations. These nuclei are highly
radioactive and only two of these are found abundantly in the universe, Uranium
and Thorium. Besides the usage of these highly radioactive nuclei in the
nuclear industry for the power generation and isotopes productions in medical
research industries, these nuclei provide a promising avenue for the nuclear
structure research. The applications of these actinides’ nuclei for the fuel
production, medical isotopes production and energy productions has been vastly
studied before [3,4]. However, scientists had been studying these nuclei in the
state-of-the-art nuclear laboratories to study the nuclear structure of the
nuclei belong to this region and to unveil the underlying mysteries in the
universe. One of the beauty of these research works is that by studying the
nucleus at extremely small level 10-15m, we can make a way to understand the
mysteries in this vast and everexpanding universe. As mentioned earlier, not
all of them are found abundantly on the earth, but the nature is too kind to provide
an opportunity to research. 232-Th and 238-U are naturally occurring
radioactive sources and it is easier to study these nuclei by using the nuclear
Physics data analysis tools and equipment i.e. detectors even in a small
laboratory. One of the promising attributes of these nuclei from Physics point
of view is their decay chains where a number of different nuclei in this region
can be studied. A decay chain is described as a number of nuclei results from
the different modes of decay from a heavier unstable nucleus. The decay chains
of these nuclei of interest is given in Figure 1 which shows the number of
nuclei is being formed on the basis of the decaying mode of radiations until
the chain goes to the stability. The mode of decaying radiations depends on the
nuclear structure of these nuclei. The nuclei belong to these chains are formed
as a result of emitted radiations due to the internal structure by and decay
modes. The mode of radiation which plays an important part in studying the
nuclear structure of these nuclei is radiation which results from the emission
of aforementioned modes of decay. The only things which differentiates between,
and decay is the emission of particles, which does not occur in case of a decay
process. The radiations, which are emitted as a result of other two decays
modes and has the higher intensity also, are examined mostly to understand the
structure of any nucleus. Much of the research has been done regarding studying
the nuclear structures of nuclei in this region through number of experiments,
however, a major breakthrough was made during studying the 224-Ra and 220-Rn
nuclei [5]. The gamma rays of interest in these nuclei were studied using the
stateof- the-art experimental setup at CERN [6] using the Coulomb excitation experimental
technique. Coulomb excitation is a technique of exciting the nucleus of
interest through inelastic collision with another nucleus through an
electromagnetic interaction [7,8]. The results based on this experiment proved
that those nuclei interest exhibit octupole deformation, a property adopted by
the nucleus with a certain internal structural attributes which results in it
having a deformed shape which resembles a pear or many scientists call it an
avocado shape as well. Since the 232-Th and 238-U are naturally occurring
sources and we do not have to populate the gamma-rays from these nuclei in any
bigger experimental facility, these nuclei can be studied in a small laboratory
by using a set of detectors. Due to the promising results from the experiment
at CERN, researches at University of the West of Scotland, United Kingdom
performed an experiment using the natural 232-Th source and observed the
radioactive decay [9,10]. The experiment was conducted using only two fast
scintillator detectors, known as LaBr3(Ce) detectors [11], the type of detector
used for gamma detection and measuring the nuclear lifetimes of the excited
states due to their optimal attributes necessary for doing such observations.
One of the important aspects of this work was to measure the enhanced electric
dipole moment in the excited states in 228-Th for the first time in actinide
region [12]. These enhanced electric dipole moments are an ambiguous sign of a
nuclear deformation, where a nucleus adapt a deformed shape like a pear. This
shape was first observed in 224-Ra nucleus from a group of nuclear scientists
mentioned above. The enhanced electric dipole moment in the nuclear excited
states found due to the distribution of the charged particles, protons, in a
nucleus due to its deformation [12]. This phenomenon of nuclear charge
distribution happens due to moment of electron which is explained in a term
called Schiff moment [13,14]. Results from the studies of 228-Th nucleus
determines the presence of such a sensitive charge distribution which exhibits
the shape deformation in this nucleus. The outstanding results from that
experiment shows that how these sources can be utilized in a small nuclear
laboratory, by using minimum resources to produce such a groundbreaking research.
Another experiment was also conducted by researchers at University of the West
of Scotland, where they are analyzing the radioactive decays in 238-U and
gathering the results regarding the nuclear structures in nuclei belong to the
decay chain in 238-U. To observe the different modes of decays as possible, a
number of different detection materials are being used to study the structure
of these nuclei in details. An important aspect of the above research regarding
presence of a deformed or pear-like shape in the 228-Th nucleus, is the
potentially an evidence of presence of anti-matter in the universe. Physics
explains that fundamental particles were created after the big-bang and each
particle has its anti-particle. These particle and anti-particle were created
in an equal amount and the whole system described as matter and anti-matter
[15]. However, only the matter has been observed in the universe where
everything is believed to be made of matter. It has been a longstanding mystery
in the universe. But, the presence of a pearshaped or a deformed nucleus shape
gives an argumentative proof of the existence of anti-matter in the universe.
In fact, these pearshaped nuclei provide an ideal system to look into the
existence of hidden mysteries of the universe in terms of exploring the studies
of dark matter and dark energy. To summarize the importance of studying these
natural radioactive sources, it can be concluded that the amount of
radioactivity information and nuclear data, not only related to the nuclear structure
and power generation, but also regarding a step forward towards unveiling the
hidden mysteries of the universe. It is a great opportunity for the students as
well as researchers who can perform the simple experiments using these natural
radioactive sources and equipment required to observe and analyse the
radiations from these sources. By looking at the decay chains of these sources,
one can reckon the amount of information that can be envisaged by analyzing the
decaying radiations.
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