Transcript RADIOACTIVITY

RADIOACTIVITY
Pierre Curie was already a famous scientist before he married Marie
Sklodowska in 1895. This famous couple did not only find true love, they also
discovered radium and polonium. For their groundbreaking research in
radioactivity, the couple were awarded the 1903 Nobel Prize in physics. It was
Marie Curie who coined the term "radioactivity", and in her honor, the 1910
Radiology Congress chose the curie as the basic unit of radioactivity. Pierre
died from being run over by a horse drawn wagon, but Marie continued their
research, and was eventually awarded a second Nobel Prize, the 1911 prize for
Chemistry. She died in 1934, suffering from pernicious anemia which had
undoubtedly been the result of years of radiation exposure.
RADIOACTIVITY ?
The atoms making up matter are generally stable, but some of them
are spontaneously transformed by emitting radiations which release
energy. This is called radioactivity.
There are three types of radiations corresponding to three types of
radioactivity.
alpha radioactivity corresponds to the emission of a helium nucleus, a
particularly stable structure consisting of two protons and two neutrons,
called an a particle.
beta radioactivity corresponds to the transformation, in the nucleus:
- either of a neutron into a proton, beta- radioactivity, characterised by the
emission of an electron e- or of a proton into a neutron, beta+ radioactivity, characterised by the
emission of an anti-electron or positron e+. It only appears in artificial
radioactive nuclei produced by nuclear reactions.
gamma radioactivity, unlike the other two, is not related to a
transmutation of the nucleus. It results in the emission, by the nucleus, of
an electromagnetic radiation, like visible light or X-rays, but more
energetic.
gamma radioactivity can occur by itself or together with alpha or beta
radioactivity
When we talk about the alpha decay then it means that a twice positive charged
heliumion (helium atomic nucleus) is emited from the atomic nucleus. Then we find
two protons ans two neutrons less in this atomic nucleus, so it is lighter. The alpha
radiation is the most dangerous of the three types of radiation, but a sheet of paper is
enough to protect oneself. The skin protects us also from alpha radiation
There are two types of the beta decay. The one is the beta minus decay and the other is
the beta plus decay. When we talk about the beta minus decay a neutron decays into a
proton, an electron and an antineutrino. The electron and the antineutrino are emited.
The radioactive particle is the electron. The number of nucleons do not change, but we
have got one proton more than before the decay. 2 or 3 cm of wood are enough to
protect oneself.
When we talk about the beta plus decay a proton decays into a neutron, a positron (the
antiparticle of the electron) and a neutrino. The positron and the neutrino are emited.
The radioactive particle is the positron
When we talk about the gamma decay high-energy electromagnetic waves are emited
from the atomic nucleus. This waves are photons, which have got a higher frequency
and less wave long than light. A gamma decay can happen after an alpha decay or a beta
decay, because the atomic nucleus is very energitic.
X-rays come fromELECTRON CLOUD
DIFFERENCE BETWEEN XRAYS & GAMMA RAYS
ORIGIN!!!
RADIATION & ITS ORIGIN
RADIATION TYPE
•
•
•
•
•
ALPHA
BETABETA+
GAMMA
X-RAYS
ORIGIN
•
•
•
•
•
NUCLEUS
NUCLEUS
NUCLEUS
NUCLEUS
ELECTRON CLOUD
(SPACE CHARGE)
RADIATION AND ITS
CHARGE
--
http://images.google.com/imgres?i
mgurl=http://www.sutree.com/uplo
ad/eysvcgzrkvccfqgflfvoh/captured.
jpg&imgrefurl=http://www.sutree.c
om/how-to/3434/Chapter-21--RadioactiveDecay&usg=__d4UymD6LWmUL
4aOVrHw8c_EsYUo=&h=407&w
=501&sz=40&hl=en&start=35&u
m=1&tbnid=1vxkwojb3NHnNM:&
tbnh=106&tbnw=130&prev=/imag
es%3Fq%3Dradioactive%2Bdecay
%26ndsp%3D18%26hl%3Den%26
rlz%3D1R2ADRA_enUS339%26s
a%3DN%26start%3D18%26um%3
D1
RADIATION AND ITS
CHARGE
•
•
•
•
•
ALPHA
BETA –
BETA+
GAMMA
X-RAYS
•
•
•
•
•
+2
-1
+1
0
0
RADIATION PENETRATION
Radiation is absorbed by the material through which it passes. During radioactive decay the alpha
or beta particles, and the gamma rays that are given off can all penetrate matter, although alphaparticles can be stopped by a piece of paper or the human skin, whereas beta-particles require a
few millimetres of metal to absorb them. Gamma-rays, on the other hand, are very penetrating and
require lead shields or a metre of concrete to stop them. The dose of radiation received is the
amount of energy absorbed per unit mass of matter. Exposure to ionizing radiation can be harmful
as the radiation can cause cancers in the living population and genetic changes that may produce
heritable defects in future generations
Alpha particles can usually be stopped by a very thin barrier. Radioisotopes emitting alpha
particles are usually not hazardous outside the body, but they can cause damage if ingested.
Betas (streams of electrons) can pass through a hand, but are usually stopped by a modest
barrier such as a few millimeters of aluminum, or even a layer of clothing. As with alphas,
beta particles are more hazardous if inhaled or ingested.
Gammas can be very penetrating and can pass through thick barriers. Several feet of concrete
would be needed to stop some of the more energetic gammas. A natural gamma source found
in the environment (and in the human body) is 40K, an isotope of potassium.
Neutrons are also very penetrating. Some elements, like hydrogen, capture and scatter
neutrons. Water is commonly used as a neutron radiation shield.
THE
HALF
LIFE
of
a
radioisotope is the time that it
takes for half the atoms in the
sample to decay. Although we
cannot predict when a particular
nucleus will decay, no matter
how many atoms there are, the
halving of the number always
takes the same time
HALF-LIFE
A decay chain
Uranium-238 has a half life of 4½
million years and emits alphaparticles. It decays to produce
thorium-234 which has a half life of
24 days and produces beta-particles,
to protactinium-234 with a half life of
7 hours emitting beta-particles, to
uranium-234 with a half life of a
quarter of a million years which
decays by emitting alpha-particles...
and so on until it finally creates the
stable isotope lead-206.
DECAY CHAIN
HALF-LIFE AND
RADIOACTIVITY REMAINING
HALF-LIFE #
•
•
•
•
•
•
•
1
2
3
4
5
6
7
RADIOACTIVITY REMAINING
•
•
•
•
•
•
•
50%
25%
12.5%
6.25%
3.12%
1.56%
0.78%
http://www.loncapa.org/~mmp/applist/decay/deca
y.htm
USES FOR RADIOACTIVITY
CARBON DATING
The rate at which 14C decays is absolutely constant. Given any set of 14C
atoms, half of them will decay in 5730 years. Since this rate is slow relative
to the movement of carbon through food chains (from plants to animals to
bacteria) all carbon in biomass at earth's surface contains atmospheric levels
of 14C. However, as soon as any carbon drops out of the cycle of biological
processes - for example, through burial in mud or soil - the abundance of 14C
begins to decline. After 5730 years only half remains. After another 5730
years only a quarter remains. This process, which continues until no 14C
remains, is the basis of carbon dating
NUCLEAR MEDICINE
NUCLEAR ENERGY
FISSION
Splitting the Uranium Atom:
Uranium is the principle element used in nuclear reactors and in certain types of
atomic bombs. The specific isotope used is 235U. When a stray neutron strikes a
235U nucleus, it is at first absorbed into it. This creates 236U. 236U is unstable and
this causes the atom to fission
CHAIN REACTION
NUCLEAR-ENERGY
POWER PLANTS
In a nuclear reactor, however, the last thing you
(and the rest of the world) want is all your
atoms splitting at once. But the reactor core
needs to be slightly supercritical so that plant
operators can raise and lower the temperature of
the reactor. The control rods give the operators a
way to absorb free neutrons so operators can
maintain the reactor at a critical level.To turn
nuclear fission into electrical energy, the first
step for nuclear power plant operators is to be
able to control the energy given off by the
enriched uranium and allow it to heat water into
steam