Transcript Man-Made Nuclides - Beverley High School

Man-Made Nuclides
Early Work
• During the 1930s,
• Irène and Frédérick Joliot-Curie made the
first artificial radioactive nuclides by
bombarding boron (5B) and aluminum (
13Al) with α particles to form radioactive
isotopes of nitrogen
• ( 7N) and phosphorus (15P).
New isotopes of existing elements
11
5
B   N
26
13
4
2
15
7
Al    P
4
2
30
15
Whereas the isotope Nitrogen-15 is stable ( a percentage
abundance of 0.38% in the air)
phosphorus-30 has a half life of 2.25min and is a β+ emitter.
30
15
P Si    e
30
14

Making transuranic elements
Protons are positively charged and tend
repel one another
(they are held in the nucleus against this
repulsion by the strong nuclear force).
Atoms whose nuclei have more than 92
protons tend to be unstable.
None are found naturally on Earth
The First Transuranic Element
It was found that by exposing uranium and
other elements to neutron radiation a
neutron would occasionally be
absorbed.
This increases the nucleon number but not
the proton number.
However if the larger nucleus is subject to
beta decay ( in which a neutron turns
into a proton) an atom with a higher
atomic number is formed:
•
•
•
This meant that the nucleus now had
93 protons and was a new element, of
atomic number 93, which was
christened neptunium, Np.
This was actually done by
Edwin McMillan and Philip Abelson
n
p
U  n U
238
92
1
0
239
92
U  Np 1 
239
92
239
93

Quick Question
•
(a) It might seem easier to make an atom of
atomic number 93 by firing protons at uranium
(atomic number 92) and hoping they would
‘stick’ rather than firing neutrons, hoping that one
would ‘stick’ and then hoping that one would
then turn into a proton and an electron. Explain
the problem involved with a proton sticking to a
uranium nucleus.
• (b) If an alpha particle is fired at an atom of
uranium-238 and it ‘sticks’, what new atom will
be formed (give the name, symbol, number
of neutrons and number of protons)?
Seaborg
• The nuclear chemist
Glen T Seaborg
discovered many
transuranic elements
• Element 106
seaborgium was
named in his honour
plutonium
94
americium
95
curium
96
berkelium,
97
californium
98
einsteinium
99
fermium
100
mendelevium
101
Nobelium (produced by
102
bombarding curium with carbon
nuclei)
The properties of man-made
radioactive nuclides
• The nuclides which do not exist in nature
have relatively short half lives which
explains their rarity.
• The sheer number of man made nuclides
means that many have found applications
in industry and medicine:
• Medical traces including iodine 131 (
positron emitter half life of 8 days)
Accelerators and nuclear reactors may also produce
manmade radioactive elements that emit radiation.
Many manmade nuclides are used in medicine,
industry, and research.
For example, moisture-density gauges
use the manmade sources:
cesium-137 (gamma source), Cf-252 (neutron source),
and americium-241:beryllium (neutron source).