Nuclear reaction analysis
Encyclopedia
Nuclear reaction analysis (NRA) is a nuclear method in materials science
to obtain concentration vs. depth distributions for certain target chemical element
s in a solid thin film.
If irradiated with select projectile nuclei
at kinetic energies
Ekin these target elements can undergo a nuclear reaction under resonance
conditions for a sharply defined resonance energy. The reaction product is usually a nucleus in an excited state which immediately decays, emitting ionizing radiation
.
To obtain depth information the initial kinetic energy of the projectile nucleus (which has to exceed the resonance energy) and its stopping power
(energy loss per distance traveled) in the sample has to be known. To contribute to the nuclear reaction the projectile nuclei have to slow down in the sample to reach the resonance energy. Thus each initial kinetic energy corresponds to a depth in the sample where the reaction occurs (the higher the energy, the deeper the reaction).
For example, a commonly used reaction to profile hydrogen
is
with a resonance at 6.385 MeV. The energetic emitted γ ray is characteristic of the reaction and the number that are detected at any incident energy is proportional to the concentration at the respective depth of hydrogen in the sample. The H concentration profile is then obtained by scanning the 15N incident beam energy.
Hydrogen is an element inaccessible to RBS due to its low mass, although it is often analysed by elastic recoil detection
.
NRA can also be used non-resonantly. For example, deuterium
can easily be profiled with a 3He
beam without changing the incident energy by using the
reaction. The energy of the fast proton detected depends on the depth of the deuterium atom in the sample.
at http://www-nds.iaea.org/ibandl/.
The energy released in nuclear reactions (the "Q value") can easily be calculated (from E=mc2): see http://nucleardata.nuclear.lu.se/database/masses/.
NRA at JSI Microanalytical center in Ljubljana, Slovenia
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
to obtain concentration vs. depth distributions for certain target chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
s in a solid thin film.
If irradiated with select projectile nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
at kinetic energies
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
Ekin these target elements can undergo a nuclear reaction under resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
conditions for a sharply defined resonance energy. The reaction product is usually a nucleus in an excited state which immediately decays, emitting ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
.
To obtain depth information the initial kinetic energy of the projectile nucleus (which has to exceed the resonance energy) and its stopping power
Stopping power (particle radiation)
In passing through matter, fast charged particles ionize the atoms or molecules which they encounter. Thus, the fast particles gradually lose energy in many small steps. Stopping power is defined as the average energy loss of the particle per unit path length, measured for example in MeV/cm...
(energy loss per distance traveled) in the sample has to be known. To contribute to the nuclear reaction the projectile nuclei have to slow down in the sample to reach the resonance energy. Thus each initial kinetic energy corresponds to a depth in the sample where the reaction occurs (the higher the energy, the deeper the reaction).
For example, a commonly used reaction to profile hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
is
- 15NNitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
+ 1HHydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
→ 12CCarbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
+ αAlpha particleAlpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
+ γGamma rayGamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
(4.965MeV)
with a resonance at 6.385 MeV. The energetic emitted γ ray is characteristic of the reaction and the number that are detected at any incident energy is proportional to the concentration at the respective depth of hydrogen in the sample. The H concentration profile is then obtained by scanning the 15N incident beam energy.
Hydrogen is an element inaccessible to RBS due to its low mass, although it is often analysed by elastic recoil detection
Elastic recoil detection
Elastic Recoil Detection, also referred to as forward recoil scattering, is a nuclear technique in materials science to obtain elemental concentration depth profiles in thin films. An energetic ion beam is directed at the sample to be depth profiled and there is an elastic nuclear interaction...
.
NRA can also be used non-resonantly. For example, deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...
can easily be profiled with a 3He
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
beam without changing the incident energy by using the
- 3He + D = α + pProtonThe proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
+ 18.353 MeV
reaction. The energy of the fast proton detected depends on the depth of the deuterium atom in the sample.
External links
Details of many known reactions are hosted by the IAEAInternational Atomic Energy Agency
The International Atomic Energy Agency is an international organization that seeks to promote the peaceful use of nuclear energy, and to inhibit its use for any military purpose, including nuclear weapons. The IAEA was established as an autonomous organization on 29 July 1957...
at http://www-nds.iaea.org/ibandl/.
The energy released in nuclear reactions (the "Q value") can easily be calculated (from E=mc2): see http://nucleardata.nuclear.lu.se/database/masses/.
NRA at JSI Microanalytical center in Ljubljana, Slovenia