soil analysis with different techinques.

NEUTRON ACTIVATION
NEUTRON ACTIVATION
ANALYSIS
ANALYSIS
DR HARSH MOHAN
DR HARSH MOHAN
DEPARTMENT OF PHYSICS
DEPARTMENT OF PHYSICS
M.L.N.COLLEGE
M.L.N.COLLEGE
YAMUNA NAGAR
YAMUNA NAGAR

What is Neutron Activation Analysis
What is Neutron Activation Analysis
(NAA)?
(NAA)?
 NAA
NAA is a method for qualitative and
is a method for qualitative and
quantitative determination of elements based
quantitative determination of elements based
on the measurement of characteristic radiation
on the measurement of characteristic radiation
from radionuclide formed directly or indirectly
from radionuclide formed directly or indirectly
by neutron irradiation of the material.
by neutron irradiation of the material.
INTRODUCTION
INTRODUCTION

HISTORICAL PROSPECTIVE
HISTORICAL PROSPECTIVE
1936 HEVESY AND LEVI
1936 HEVESY AND LEVI
RARE EARTH ELEMENTS
RARE EARTH ELEMENTS
EMPLOY NUC. REACTION
EMPLOY NUC. REACTION
MEASURED GAMMA RAY
MEASURED GAMMA RAY

BASIC PRINCIPAL
BASIC PRINCIPAL

NAA Categories
NAA Categories
 According to type of emitted
According to type of emitted γ
γ-ray measured
-ray measured
 If the Prompt
If the Prompt γ
γ-ray is the measured radiation
-ray is the measured radiation
Prompt
Prompt γ
γ -ray neutron activation analysis
-ray neutron activation analysis
(PGNAA)
(PGNAA)
 The measurements take place during irradiation.
The measurements take place during irradiation.
 If Delayed
If Delayed γ
γ-ray is the measured radiation.
-ray is the measured radiation.
 Delayed
Delayed γ
γ -ray neutron activation analysis
-ray neutron activation analysis
(DGNAA)
(DGNAA)
The measurements take place after a certain decay
The measurements take place after a certain decay
period
period.
.
 (DGNAA) is more common.
(DGNAA) is more common.

I. PGNAA
I. PGNAA
 The PGNAA technique is generally performed by using a beam of
The PGNAA technique is generally performed by using a beam of
neutrons extracted through a reactor beam port.
neutrons extracted through a reactor beam port.
 detectors are placed very close to the sample compensating for
detectors are placed very close to the sample compensating for
much of the loss in sensitivity due to flux.
much of the loss in sensitivity due to flux.
 The PGNAA technique is most applicable to elements with
The PGNAA technique is most applicable to elements with
extremely high neutron capture cross-sections (B, Cd, Sm, and
extremely high neutron capture cross-sections (B, Cd, Sm, and
Gd); elements which decay too rapidly to be measured by
Gd); elements which decay too rapidly to be measured by
DGNAA; elements that produce only stable isotopes; or elements
DGNAA; elements that produce only stable isotopes; or elements
with weak decay gamma-ray intensities.
with weak decay gamma-ray intensities.

II. DGNAA
II. DGNAA
 DGNAA (sometimes called conventional NAA)
DGNAA (sometimes called conventional NAA)
is useful for the
is useful for the vast majority of elements
vast majority of elements that
that
produce radioactive nuclides.
produce radioactive nuclides.
 The technique is flexible with respect to time
The technique is flexible with respect to time
such that the sensitivity for a long-lived
such that the sensitivity for a long-lived
radionuclide that suffers from an interference by
radionuclide that suffers from an interference by
a shorter-lived radionuclide can be improved by
a shorter-lived radionuclide can be improved by
waiting for the short-lived radionuclide to decay
waiting for the short-lived radionuclide to decay.
.
 This selectivity
This selectivity is a key advantage of DGNAA
is a key advantage of DGNAA
over other analytical methods.
over other analytical methods.

Prompt vs. Delayed NAA
 The PGNAA technique is generally performed by
The PGNAA technique is generally performed by
using a beam of neutrons extracted through a
using a beam of neutrons extracted through a
reactor beam port. Fluxes on samples irradiated in
reactor beam port. Fluxes on samples irradiated in
beams are on the order of one million times lower
beams are on the order of one million times lower
than on samples inside a reactor but detectors can
than on samples inside a reactor but detectors can
be placed very close to the sample compensating
be placed very close to the sample compensating
for much of the loss in sensitivity due to flux. The
for much of the loss in sensitivity due to flux. The
PGNAA technique is most applicable to elements
PGNAA technique is most applicable to elements
with extremely high neutron capture cross-
with extremely high neutron capture cross-
sections B, Cd, Sm, and Gd
sections B, Cd, Sm, and Gd

 DGNAA (sometimes called conventional
DGNAA (sometimes called conventional
NAA) is useful for the vast majority of
NAA) is useful for the vast majority of
elements that produce radioactive nuclides.
elements that produce radioactive nuclides.
The technique is flexible with respect to
The technique is flexible with respect to
time such that the sensitivity for a long-
time such that the sensitivity for a long-
lived radionuclide that suffers from an
lived radionuclide that suffers from an
interference by a shorter-lived radionuclide
interference by a shorter-lived radionuclide
can be improved by waiting for the short-
can be improved by waiting for the short-
lived radionuclide to decay
lived radionuclide to decay

Instrumental vs. Radiochemical
NAA
NAA
 The application of purely instrumental
The application of purely instrumental
procedures is commonly called instrumental
procedures is commonly called instrumental
neutron activation analysis (INAA)
neutron activation analysis (INAA)
If chemical separations are done to samples after
irradiation to remove interferences or to
concentrate the radioisotope of interest, the
technique is called radiochemical neutron
activation analysis (RNAA). The latter technique is
performed infrequently due to its high labor cost.

NAA
NAA
 It is generally possible to simultaneously measure more
It is generally possible to simultaneously measure more
than thirty elements in most sample types without
than thirty elements in most sample types without
chemical processing.
chemical processing.
 The application of purely instrumental procedures is
The application of purely instrumental procedures is
commonly called instrumental neutron activation analysis
commonly called instrumental neutron activation analysis
(INAA) and is one of NAA's most important advantages
(INAA) and is one of NAA's most important advantages
over other analytical techniques.
over other analytical techniques.
 If chemical separations
If chemical separations are done to samples after
are done to samples after
irradiation to remove interferences or to concentrate the
irradiation to remove interferences or to concentrate the
radioisotope of interest, the technique is called
radioisotope of interest, the technique is called
radiochemical neutron activation analysis (RNAA).
radiochemical neutron activation analysis (RNAA).

NAA
NAA procedure
procedure
 Sampling;
Sampling;
 Pre-irradiation sample treatment (such as cleaning,
Pre-irradiation sample treatment (such as cleaning,
drying or ashing, pre-concentration of elements of
drying or ashing, pre-concentration of elements of
interest or elimination of interfering elements, sub-
interest or elimination of interfering elements, sub-
sampling and packing);
sampling and packing);
 Irradiation (and prompt gamma-ray counting in
Irradiation (and prompt gamma-ray counting in
PGNAA);
PGNAA);
 Radiochemical separation (
Radiochemical separation (only in RNAA
only in RNAA);
);
 Radioactivity measurement;
Radioactivity measurement;
 Elemental concentration calculation;
Elemental concentration calculation;
 Critical evaluation of results and preparation of the
Critical evaluation of results and preparation of the
NAA report.
NAA report.

Irradiation
Irradiation
 There are several types of neutron sources: reactors,
There are several types of neutron sources: reactors,
accelerators, and radioisotopic neutron emitters.
accelerators, and radioisotopic neutron emitters.
 Nuclear reactors with their
Nuclear reactors with their high fluxes of neutrons
high fluxes of neutrons
offer the highest available sensitivities for most
offer the highest available sensitivities for most
elements.
elements.
 Most neutron energy distributions are quite broad and
Most neutron energy distributions are quite broad and
consist of three principal components
consist of three principal components (thermal,
(thermal,
epithermal, and fast).
epithermal, and fast).

NEUTRON SOURCES
NEUTRON SOURCES
 NEUTRON GENERATORS
NEUTRON GENERATORS
 Accelerators
Accelerators
 14 MeV Neutrons
14 MeV Neutrons
NUCLEAR REACTORS
NUCLEAR REACTORS
maximum thermal power region of 100 kW-10 MW

NEUTRON SOURCES
NEUTRON SOURCES
ISOTOPIC NEUTRON SOURCES
ISOTOPIC NEUTRON SOURCES
Neutron emitter
Neutron emitter Average Neutron energy
Average Neutron energy
Ac
Ac 4 MeV
4 MeV
Ra
Ra 3.6MeV
3.6MeV
Pu
Pu 4.5 MeV
4.5 MeV
Po
Po 4.3 MeV
4.3 MeV

NEUTRON ENERGY
NEUTRON ENERGY
DISTRIBUTION
DISTRIBUTION

NEUTRON ENERGY
NEUTRON ENERGY
 THERMAL NEUTRON
THERMAL NEUTRON
 EPI-THERMAL NEUTRON
EPI-THERMAL NEUTRON
 FAST NEUTRON
FAST NEUTRON

I. Thermal Flux
I. Thermal Flux
 The thermal neutron component consists of low-
The thermal neutron component consists of low-
energy neutrons (energies below 0.5 eV) in
energy neutrons (energies below 0.5 eV) in
thermal equilibrium with atoms in the reactor's
thermal equilibrium with atoms in the reactor's
moderator.
moderator.
 At room temperature, the energy spectrum of
At room temperature, the energy spectrum of
thermal neutrons is best described by a Maxwell-
thermal neutrons is best described by a Maxwell-
Boltzmann distribution with a mean energy of
Boltzmann distribution with a mean energy of
0.025 eV
0.025 eV and a most probable velocity of
and a most probable velocity of 2200
2200
m/s
m/s.
.
 In most reactor irradiation positions,
In most reactor irradiation positions, 90-95%
90-95% of
of
the neutrons that bombard a sample are thermal
the neutrons that bombard a sample are thermal
neutrons.
neutrons.

II. Epithermal Flux
II. Epithermal Flux
 The epithermal neutron component consists of neutrons
The epithermal neutron component consists of neutrons
(energies from 0.5 eV to about 0.5 MeV) which have been only
(energies from 0.5 eV to about 0.5 MeV) which have been only
partially moderated.
partially moderated.
 A
A cadmium foil 1 mm thick
cadmium foil 1 mm thick absorbs all thermal neutrons but
absorbs all thermal neutrons but
will allow epithermal and fast neutrons above 0.5 eV in energy
will allow epithermal and fast neutrons above 0.5 eV in energy
to pass through.
to pass through.
 In a typical unshielded reactor irradiation position, the
In a typical unshielded reactor irradiation position, the
epithermal neutron flux represents about 2% the total neutron
epithermal neutron flux represents about 2% the total neutron
flux.
flux.
 Both thermal and epithermal neutrons induce (n,gamma)
Both thermal and epithermal neutrons induce (n,gamma)
reactions on target nuclei.
reactions on target nuclei.
 An NAA technique that employs only epithermal neutrons to
An NAA technique that employs only epithermal neutrons to
induce (n,gamma) reactions by irradiating the samples being
induce (n,gamma) reactions by irradiating the samples being
analyzed inside either cadmium or boron shields is called
analyzed inside either cadmium or boron shields is called
epithermal neutron activation analysis (ENAA).
epithermal neutron activation analysis (ENAA).

III. Fast Flux
III. Fast Flux
 The fast neutron component of the neutron spectrum
The fast neutron component of the neutron spectrum
(energies above 0.5 MeV) consists of the primary
(energies above 0.5 MeV) consists of the primary
fission neutrons which still have much of their original
fission neutrons which still have much of their original
energy following fission.
energy following fission.
 Fast neutrons
Fast neutrons contribute very little to the (n,gamma)
contribute very little to the (n,gamma)
reaction, but instead induce nuclear reactions where the
reaction, but instead induce nuclear reactions where the
ejection of one or more nuclear particles - (n,p), (n,
ejection of one or more nuclear particles - (n,p), (n,α
α),
),
and (n,2n) - are prevalent.
and (n,2n) - are prevalent.
 In a typical reactor irradiation position, about 5% of
In a typical reactor irradiation position, about 5% of
the total flux consists of fast neutrons.
the total flux consists of fast neutrons.
 An NAA technique that employs nuclear reactions
An NAA technique that employs nuclear reactions
induced by fast neutrons is called
induced by fast neutrons is called fast neutron
fast neutron
activation analysis (FNAA).
activation analysis (FNAA).

Radioactivity Measurement
Radioactivity Measurement
 The instrumentation used to measure
The instrumentation used to measure
gamma rays from radioactive samples
gamma rays from radioactive samples
generally consists of a semiconductor
generally consists of a semiconductor
detector, associated electronics, and a
detector, associated electronics, and a
computer-based, multi-channel analyzer
computer-based, multi-channel analyzer
(MCA/computer).
(MCA/computer).
 Most NAA labs operate one or more
Most NAA labs operate one or more hyper
hyper
pure germanium detector (HPGe).
pure germanium detector (HPGe).

Gamma-Spectroscopy System
Gamma-Spectroscopy System

Calibration
Calibration
 Energy Calibration
Energy Calibration
 FWHM Calibration
FWHM Calibration
 Efficiency Calibration
Efficiency Calibration

Measurement of Gamma Rays
 . Other characteristics to consider are peak
. Other characteristics to consider are peak
shape, peak-to-Compton ratio, crystal
shape, peak-to-Compton ratio, crystal
dimensions or shape, and price.
dimensions or shape, and price.

 The detector's resolution is a measure of its ability
The detector's resolution is a measure of its ability
to separate closely spaced peaks in a spectrum. In
to separate closely spaced peaks in a spectrum. In
general, detector resolution is specified in terms of
general, detector resolution is specified in terms of
the full width at half maximum (FWHM) of the
the full width at half maximum (FWHM) of the
122-keV photopeak of Co-57 and the 1332-keV
122-keV photopeak of Co-57 and the 1332-keV
photopeak of Co-60. For most NAA applications,
photopeak of Co-60. For most NAA applications,
a detector with 1.0-keV resolution or below at 122
a detector with 1.0-keV resolution or below at 122
keV and 1.8 keV or below at 1332 keV is
keV and 1.8 keV or below at 1332 keV is
sufficient.
sufficient.

 Detector efficiency depends on the energy
Detector efficiency depends on the energy
of the measured radiation, the solid angle
of the measured radiation, the solid angle
between sample and detector crystal, and
between sample and detector crystal, and
the active volume of the crystal. A larger
the active volume of the crystal. A larger
volume detector will have a higher
volume detector will have a higher
efficiency
efficiency
 As detector volume increases, the detector
As detector volume increases, the detector
resolution gradually decreases
resolution gradually decreases

Gamma-ray spectrum from an
Gamma-ray spectrum from an
irradiated pottery specimen
irradiated pottery specimen

Gamma-ray spectrum from 0 to 800 keV
Gamma-ray spectrum from 0 to 800 keV
showing medium- and long-lived elements
showing medium- and long-lived elements
measured in a sample
measured in a sample

Kinetics of activation
 R = N (
R = N (φ
φth
th·
·σ
σth
th +
+ φ
φe
e · I
· I0
0 )
)
R= reaction rate
R= reaction rate
 σ
σth
th:
: conventional thermal neutron flux [in cm
conventional thermal neutron flux [in cm2
2
]
]
 φ
φth
th :
: effective thermal neutron cross-section [in
effective thermal neutron cross-section [in
cm
cm2
2
]
]
 φ
φe
e:
: conventional epithermal neutron flux [in cm
conventional epithermal neutron flux [in cm-2
-2
s
s-
-
1
1
eV]
eV]
I
Io
o:
: resonance integral cross section (in epithermal
resonance integral cross section (in epithermal
region), for 1/E epithermal spectrum [in cm
region), for 1/E epithermal spectrum [in cm2
2
]
]


 The activity (A) of the isotopes depends on
The activity (A) of the isotopes depends on
time. During irradiation the activity of the
time. During irradiation the activity of the
radioactive isotope produced grows
radioactive isotope produced grows
according to a saturation characteristic
according to a saturation characteristic
governed by a saturation factor S=1-e
governed by a saturation factor S=1-e-
-λ
λt
t
i
i.
.
Subsequent to the irradiation the isotope
Subsequent to the irradiation the isotope
decays according to the exponential law:
decays according to the exponential law:
D=e
D=e-
-λ
λ t
t
d
d:
:
 Where t
Where ti
i : time of irradiation; t
: time of irradiation; td
d : time of
: time of
decay;
decay; λ
λ : decay constant
: decay constant

 A=
A= I
e
th
th ⋅
+
⋅ ϕ
σ
ϕ
D
S
A
N
f
m
rel
Av
i
⋅
⋅
⋅
⋅
NAv
= Avogadro number
fi
= isotopic abundance
m = the mass of the irradiated element
Arel
= atomic mass of target element

 The intensity of the measured gamma line is
The intensity of the measured gamma line is
proportional to the activity. The measured
proportional to the activity. The measured
parameter is the total energy peak area (N
parameter is the total energy peak area (NP
P)
)
at a particular energy given by the
at a particular energy given by the
following equation (x)
following equation (x)
N A f t
P m
= ⋅ ⋅ ⋅
γ γ
ε

 The efficiency (
The efficiency (ε
εγ
γ) of a semiconductor
) of a semiconductor
detector varies with gamma energy. The
detector varies with gamma energy. The
emission probability of a gamma photon at
emission probability of a gamma photon at
a given energy is the f
a given energy is the fγ
γ, t
, tm
m is the measuring
is the measuring
time.
time.

Measurement and evaluation
Measurement and evaluation
 The modern gamma measuring systems consist of
The modern gamma measuring systems consist of
a gamma detector, usually a HPGe type and
a gamma detector, usually a HPGe type and
sometimes NaI(Tl) scintillation crystals. The
sometimes NaI(Tl) scintillation crystals. The
detectors are connected to a multichannel analyzer
detectors are connected to a multichannel analyzer
(MCA) by an appropriate electronic system
(MCA) by an appropriate electronic system
(preamlifier, spectroscopy amplifier, etc.).
(preamlifier, spectroscopy amplifier, etc.).
Nowadays, the MCAs are computer based systems
Nowadays, the MCAs are computer based systems
with the ability of an automatic spectrum
with the ability of an automatic spectrum
evaluation.
evaluation.

Analysis of the gamma spectra
 The usual objective of the measurements
The usual objective of the measurements
by gamma ray spectrometers is the
by gamma ray spectrometers is the
determination of the number and energy
determination of the number and energy
of the photons emitted by the source.
of the photons emitted by the source.
The peak location and the peak area in
The peak location and the peak area in
the spectra have to be determined. The
the spectra have to be determined. The
peak location is a measure of the gamma
peak location is a measure of the gamma
energy, while the peak area is
energy, while the peak area is
proportional to the photon emission rate
proportional to the photon emission rate

 For the energy measurement the pulse
For the energy measurement the pulse
height scale must be calibrated with
height scale must be calibrated with
standard sources emitting photons of
standard sources emitting photons of
known energies
known energies
 In order to calculate the activities, the full-
In order to calculate the activities, the full-
energy-peak efficiencies of the source-
energy-peak efficiencies of the source-
detector system have to be determined by
detector system have to be determined by
using sources of known activities.
using sources of known activities.

 For the determination of the peak areas the
For the determination of the peak areas the
background under the peak interval has to be
background under the peak interval has to be
subtracted. The net count (Np) results from N
subtracted. The net count (Np) results from NP
P =
=
N
Nint
int - N
- NB
B, (N
, (Nint
int integral under the peak and N
integral under the peak and NB
B refers
refers
to the background).
to the background).
 The peak area can also be calculated by computer
The peak area can also be calculated by computer
programs which fit an analytical function to the
programs which fit an analytical function to the
peak. The shape is described basically by a
peak. The shape is described basically by a
Gaussian function, modified by suitable auxiliary
Gaussian function, modified by suitable auxiliary
functions. Thus all the peaks including also the
functions. Thus all the peaks including also the
multiplets can be automatically analysed.
multiplets can be automatically analysed.

Quantitative Analysis
 Absolute method
Absolute method
 The quantitative measurement can be
The quantitative measurement can be
effected by determining the neutron flux
effected by determining the neutron flux
and counting the absolute gamma rays.
and counting the absolute gamma rays.
The direct calculation of concentration is
The direct calculation of concentration is
made by applying nuclear constants
made by applying nuclear constants
according to Eq
according to Eq (x)
(x)

 Classic relative method
Classic relative method
 The method is based on the simultaneous
The method is based on the simultaneous
irradiation of the sample with standards of known
irradiation of the sample with standards of known
quantities of the elements in question in identical
quantities of the elements in question in identical
positions, followed by measuring the induced
positions, followed by measuring the induced
intensities of both the standard and the sample in a
intensities of both the standard and the sample in a
well known geometrical position.
well known geometrical position.
 A relative standardisation can be performed by
A relative standardisation can be performed by
means of individual monoelement standards, or
means of individual monoelement standards, or
by using synthetic or natural multielement
by using synthetic or natural multielement
standards.
standards.

 The equation used to calculate the mass of
The equation used to calculate the mass of
an element in the unknown sample relative
an element in the unknown sample relative
to the comparator standard
to the comparator standard

 Where A = activity of the sample (sam) and
Where A = activity of the sample (sam) and
standard (std),
standard (std),
M = mass of the element,
M = mass of the element,
= decay constant for the
= decay constant for the
isotope and =
isotope and =
decay time
decay time

 When performing short irradiations, the
When performing short irradiations, the
irradiation, decay and counting times are
irradiation, decay and counting times are
normally fixed the same for all samples and
normally fixed the same for all samples and
standards such that the time dependent
standards such that the time dependent
factors cancel. Thus the equation
factors cancel. Thus the equation
simplifies into
simplifies into

 Where C = concentration of the element
Where C = concentration of the element
W= weight of the sample and standard
W= weight of the sample and standard

Counting statistics
Counting statistics
 The nuclear decay processes occur at random, and
The nuclear decay processes occur at random, and
follow a Poisson distribution, where the standard
follow a Poisson distribution, where the standard
deviation (
deviation (σ)
σ) equals to N
equals to N1/2
1/2
(N is the observed
(N is the observed
number of events). In gamma spectrometry, the
number of events). In gamma spectrometry, the
peak area is the measured parameter. The standard
peak area is the measured parameter. The standard
deviation is:
deviation is: σ
σ = (N+2N
= (N+2NB
B)
)1/2
1/2
where the
where the
confidence level is 68%.
confidence level is 68%.
 The counting statistic is only one of the possible
The counting statistic is only one of the possible
sources of errors in NAA, the overall value
sources of errors in NAA, the overall value
depending on a number of different factors (e.g.
depending on a number of different factors (e.g.
sample preparation, weighing, and uncertainty of
sample preparation, weighing, and uncertainty of
standardisation).
standardisation).

Equipment and materials
Equipment and materials
 - sample for analysis hair sample, soil or
- sample for analysis hair sample, soil or
steel etc.
steel etc.
 - analytical balance
- analytical balance
 - micropipette
- micropipette
 - reactor for irradiation
- reactor for irradiation
 - HPGe detector, spectrometer
- HPGe detector, spectrometer

Procedure
Procedure
 1 .Choose the proper -nuclear reaction
1 .Choose the proper -nuclear reaction
-analytical gamma
-analytical gamma
line
line
-irradiation, decay
-irradiation, decay
and measuring time
and measuring time

Procedure
Procedure
 2.
2. Sample preparation:
Sample preparation:
 - weigh the samples into polyethylene
- weigh the samples into polyethylene
bags using analytical balance
bags using analytical balance
 - prepare standards using micropipettes
- prepare standards using micropipettes

Procedure
Procedure
 3.
3. Irradiation of the samples using pneumatic
Irradiation of the samples using pneumatic
system of the reactor
system of the reactor
 4.
4. Measure the gamma-spectra, evaluate the
Measure the gamma-spectra, evaluate the
spectra (determine the peak areas at the given
spectra (determine the peak areas at the given
gamma-lines)
gamma-lines)
 5.
5. Identify the isotopes in the spectra using
Identify the isotopes in the spectra using
gamma library. Determine the elemental
gamma library. Determine the elemental
concentrations and their uncertainties using
concentrations and their uncertainties using
standard method
standard method

Sensitivities Available by NAA
Sensitivities Available by NAA
 The sensitivities for NAA are dependent upon the
The sensitivities for NAA are dependent upon the
irradiation parameters (i.e., neutron flux,
irradiation parameters (i.e., neutron flux,
irradiation and decay times), measurement
irradiation and decay times), measurement
conditions (i.e., measurement time, detector
conditions (i.e., measurement time, detector
efficiency), nuclear parameters of the elements
efficiency), nuclear parameters of the elements
being measured (i.e., isotope abundance, neutron
being measured (i.e., isotope abundance, neutron
cross-section, half-life, and gamma-ray
cross-section, half-life, and gamma-ray
abundance). The accuracy of an individual NAA
abundance). The accuracy of an individual NAA
determination usually ranges between 1 to 10
determination usually ranges between 1 to 10
percent of the reported value.
percent of the reported value.

Detection Limits
Detection Limits
 The detection limit represents the ability of a
The detection limit represents the ability of a
given NAA procedure to determine the
given NAA procedure to determine the
minimum amounts of an element reliably.
minimum amounts of an element reliably.
 The detection limit depends on the:
The detection limit depends on the:
(1)The amount of material to be irradiated and to be counted.
(1)The amount of material to be irradiated and to be counted..
.
(2)
(2) The neutron fluxes.
The neutron fluxes.
(3)
(3) The duration of the irradiation time.
The duration of the irradiation time.
(4)
(4) The total induced radioactivity that can be
The total induced radioactivity that can be
(5)The duration of the counting time
(5)The duration of the counting time
(6)
(6) The detector size, counting geometry and background
The detector size, counting geometry and background
shielding.
shielding.

Advantages of NAA
Advantages of NAA
 Very low detection limits for 30–40 elements,
Very low detection limits for 30–40 elements,
 Significant matrix independence,
Significant matrix independence,
 The possibility of non-destructive analysis
The possibility of non-destructive analysis
(instrumental NAA or INAA),
(instrumental NAA or INAA),
 The use of radiochemical separation to overcome
The use of radiochemical separation to overcome
interference in complex gamma-ray spectra
interference in complex gamma-ray spectra
(radiochemical NAA or RNAA),
(radiochemical NAA or RNAA),
 An inherent capability for high levels of accuracy
An inherent capability for high levels of accuracy
compared to other trace element analysis
compared to other trace element analysis
techniques.
techniques.

NAA Applications
NAA Applications
 Archaeology
Archaeology
 Biomedicine
Biomedicine
 Environmental science and related fields
Environmental science and related fields
 Geology and geochemistry
Geology and geochemistry
 Industrial products
Industrial products
 Nutrition
Nutrition
 Quality assurance of analysis and reference
Quality assurance of analysis and reference
materials
materials

Applications for NAA
 1.
1. Archaeology
Archaeology
 The use of neutron activation analysis to
The use of neutron activation analysis to
characterize archaeological specimens (e.g.,
characterize archaeological specimens (e.g.,
pottery, obsidian, chert, basalt and
pottery, obsidian, chert, basalt and
limestone) and to relate the artifacts to
limestone) and to relate the artifacts to
sources through their chemical signatures is
sources through their chemical signatures is
a well-established application of the
a well-established application of the
method.
method.

Neutron activation of paintings
Neutron activation of paintings

 Geological science
Geological science
 Analysis of rock specimens by neutron activation
Analysis of rock specimens by neutron activation
analysis assists geochemists in research on the
analysis assists geochemists in research on the
processes involved in the formation of different
processes involved in the formation of different
rocks through the analysis of the rare earth
rocks through the analysis of the rare earth
elements (REEs) and other trace elements. About
elements (REEs) and other trace elements. About
thirty elements can be measured routinely in
thirty elements can be measured routinely in
almost any geological sample. An additional 15-
almost any geological sample. An additional 15-
20 elements can be measured by applying
20 elements can be measured by applying
specialized procedures
specialized procedures

 Semiconductor materials and other high-purity
Semiconductor materials and other high-purity
materials
materials
 Neutron Activation Analysis (NAA)
Neutron Activation Analysis (NAA) is used to
is used to
measure trace- and ultra trace-element
measure trace- and ultra trace-element
concentrations of impurities and/or dopants in
concentrations of impurities and/or dopants in
semiconductors and other high-purity materials.
semiconductors and other high-purity materials.
The behavior of semiconductor devices is strongly
The behavior of semiconductor devices is strongly
influenced by the presence of impurity elements
influenced by the presence of impurity elements
either added intentionally (doping with B, P, As,
either added intentionally (doping with B, P, As,
Au, etc.) or contaminants remaining due to
Au, etc.) or contaminants remaining due to
incomplete purification of the semiconductor
incomplete purification of the semiconductor
material during device manufacture.
material during device manufacture.

 Soil Science
Soil Science
 Many agricultural processes and their
Many agricultural processes and their
consequences, such as fertilization and herbicidal
consequences, such as fertilization and herbicidal
and pesticidal control, are influenced by surface
and pesticidal control, are influenced by surface
and sub-surface movement, percolation and
and sub-surface movement, percolation and
infiltration of water. Stable activatable tracers,
infiltration of water. Stable activatable tracers,
such as bromide, analyzed by NAA, have allowed
such as bromide, analyzed by NAA, have allowed
the soil scientist to quantify the distribution of
the soil scientist to quantify the distribution of
agricultural chemicals under a wide variety of
agricultural chemicals under a wide variety of
environmental and land use influences
environmental and land use influences

Obtain plant sample. Wash the sample to
Obtain plant sample. Wash the sample to
remove possible contaminants
remove possible contaminants

Dehydrate the sample.
Dehydrate the sample.
 Dehydration methods
Dehydration methods
use heat or freeze-
use heat or freeze-
drying.
drying.
 A lyophilizer is frequently
A lyophilizer is frequently
used for the freeze-dry
used for the freeze-dry
method.
method.
 A plant sample is then
A plant sample is then
placed in the chamber
placed in the chamber
atop the lyophilizer to the
atop the lyophilizer to the
right.
right.

The dehydrated sample is then prepared for
The dehydrated sample is then prepared for
testing. A small amount of dehydrated plant
testing. A small amount of dehydrated plant
material is removed from this bag.
material is removed from this bag.

A portion of the dried plant material is ground into a powder
A portion of the dried plant material is ground into a powder
using a mortar and pestle. Sterile technique is required
using a mortar and pestle. Sterile technique is required
to avoid cross contamination
to avoid cross contamination.
.

Bag the sample. Some of the ground plant powder
Bag the sample. Some of the ground plant powder
is bagged into a small plastic envelope. The sample
is bagged into a small plastic envelope. The sample
is double-bagged and labeled
is double-bagged and labeled.
.

Select a standard for comparison.
Select a standard for comparison.
 When looking for arsenic in
When looking for arsenic in
plant material, you would need
plant material, you would need
to prepare a sample of a
to prepare a sample of a
standard containing arsenic.
standard containing arsenic.
 The “standard” contains a
The “standard” contains a
known quantity of the element
known quantity of the element
you are looking for.
you are looking for.
 Containers of certified
Containers of certified
standards are pictured.
standards are pictured.

Place packages of both the prepared sample and
Place packages of both the prepared sample and
standard sample in a capsule.
standard sample in a capsule.

Take sample to the rabbit system apparatus.
Take sample to the rabbit system apparatus.
 The rabbit system works much
The rabbit system works much
like the system used by banks at
like the system used by banks at
drive-through windows. A
drive-through windows. A
canister carries items back and
canister carries items back and
forth between the customer and
forth between the customer and
teller.
teller.
 The sample is sent through the
The sample is sent through the
wall in a mini canister into the
wall in a mini canister into the
nuclear reactor located behind the
nuclear reactor located behind the
wall.
wall.
 Once inside the reactor, the
Once inside the reactor, the
sample is irradiated with
sample is irradiated with
neutrons.
neutrons.

After irradiation of the sample in the capsule, and before removing
After irradiation of the sample in the capsule, and before removing
it from the reactor site, it must be determined if the capsule is safe
it from the reactor site, it must be determined if the capsule is safe
for transfer. A Geiger counter is used to assess whether the
for transfer. A Geiger counter is used to assess whether the
radioactive decay has reached low enough levels to be safe.
radioactive decay has reached low enough levels to be safe.

The prepared sample and standard sample are placed
The prepared sample and standard sample are placed
in a “detector” one at a time.
in a “detector” one at a time.
 The detector system
The detector system
counts and records
counts and records
gamma radiation
gamma radiation
emissions for a period
emissions for a period
of time.
of time.
 Time varies, but is
Time varies, but is
usually in the range of 5
usually in the range of 5
minutes to an hour.
minutes to an hour.

Counts recorded by the detector system is sent
Counts recorded by the detector system is sent
to a computer.
to a computer.

12. Specialized software analyzes radiation peaks.
12. Specialized software analyzes radiation peaks.
Peak data is correlated to specific elements for
Peak data is correlated to specific elements for
identification and quantification.
identification and quantification.

Computer data is compared to a nuclide chart
Computer data is compared to a nuclide chart
to evaluate the results.
to evaluate the results.

soil analysis with different techinques.

soil analysis with different techinques.

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