Chapter 32, Problem 32.21QAP

Interpretation Introduction

(a)

Interpretation:

The differences in terms of instrumental and radiochemical between prompt gamma ray neutron activation and delayed gamma ray neutron activation is to be found by using internet search engine or by using reference on NAA.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

Answer to Problem 32.21QAP

The differences in terms of instrumental and radiochemical between prompt gamma ray neutron activation is that in the instrumental prompt gamma ray neutron activation is directly applied to the irradiated sample while in radiochemical prompt gamma ray neutron activation is used to remove the interference or concentrating one for the radioisotope chemical separation.

Explanation of Solution

The measurement of neutron irradiation gamma rays or gamma ray neutron activation analysis is checked by the NAA technique. The irradiation of the beam of neutrons continuously on the sample results in the method of the Prompted Gamma Ray Neutron Activation Analysis. The detection of the gamma rays emitted by the elements of the sample is done by the Gamma rays spectrometer and the determination of the electron capture element is done by the energies of gamma rays. The intensities of peak obtained during the experiment will be used to determine the concentration of the elements. The analysis of the elements that produce radioactive nuclide is done by the Delayed Gamma Ray Neutron Activation Analysis.

The reduction sensitivity is defined as the improvement in the sensitivity of short-lived nuclide by the reduction in the irradiation time of long-live radionuclide and it is the advantage of the Delayed Gamma Ray Neutron Activation Analysis over analytical method.

The NAA method is also called as the Instrumental Neutron Activation Analysis when it is directly applied to the irradiated sample.

The Radio Chemical Neutron Activation Analysis is used to remove the interference or concentrating one for the radioisotope chemical separation.

Interpretation Introduction

(b)

Interpretation:

The type of elements which prompt gamma ray activation analysis is to be determined.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

Answer to Problem 32.21QAP

The types of elements which prompt gamma ray activation analysis are boron, cadmium, samarium and gadolinium.

Explanation of Solution

The high area of neutron capture is exhibit by the elements such as boron, cadmium, samarium and gadolinium which are irradiated by Prompted Gamma Neutron Activation Analysis (PGNAA) technique. This technique is also used for the elements which have stable isotopes with weak decay gamma ray intensities, whereas the elements which have high decay rate will use Delayed Gamma Ray Neutron Activation Analysis (DGNAA).

Interpretation Introduction

(c)

Interpretation:

The reason for the delayed gamma ray emission used most often in NAA is to be determined.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

Answer to Problem 32.21QAP

The reason for the delayed gamma ray emission used most often in NAA is that it is independent of the time and the sensitivity of longer-lived nuclide will improve by the decaying of irradiation time of short-live nuclide and vice-versa.

Explanation of Solution

The elements which produce radioactive nuclides will use Delayed Gamma Ray Neutron Activation Analysis (DGNAA) also called as Neutron Activation Analysis (NAA). This technique is independent of time and the sensitivity of longer-lived nuclide will improve by the decaying of irradiation time of short-live nuclide. Similarly, the reduction sensitivity is defined as the improvement in the sensitivity of short-lived nuclide by the reduction in the irradiation time of long-live radionuclide.

Interpretation Introduction

(d)

Interpretation:

The reason for that NAA is very sensitive and selective method is to be determined.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

Answer to Problem 32.21QAP

The reason for that NAA is very sensitive and selective method is that the value of accuracy and precision are 5% and 0.1% respectively and it is used to determine the amount of trace present in the sample and it is also useful to determine ppb-ppm range for trace amounts.

Explanation of Solution

Neutron Activation Analysis (NAA) is defined as the formation of radioactive nuclei from stable atomic nuclei using irradiation with neutrons as well as due to the continuous detection of gamma rays which are emitted by the decay of radioactive nuclei. This technique is used to determine the amount of trace present in the sample and it is also useful to determine ppb-ppm range for trace amounts.

The technique NAA can perform non-destructive analysis for samples such as solids, liquids, suspensions, slurries gases. For this technique the value of accuracy and precision are 5% and 0.1% respectively and this method also sensitive in comparison of others.

Interpretation Introduction

(e)

Interpretation:

The following table represents the nature or behavior of the naturally occurring isotopes of crystal.

100%	${}_9^{19}F{(n,\gamma )}_9^{20}F$	$\stackrel{t_{1/2}=11s}{\to }$	${}_{10}^{20}Ne+{\beta }^{-}+\overline{\nu }$
93%	${}_{19}^{39}K{(n,\gamma )}_{19}^{40}K$
0.01%	${}_{19}^{40}K{(n,\gamma )}_{19}^{41}K$
7%	${}_{19}^{41}K{(n,\gamma )}_{19}^{42}K$	$\stackrel{t_{1/2}=12.4h}{\to }$	${}_{20}^{42}Ca+{\beta }^{-}+\overline{\nu }$

The elements ${}^{19}F{,}^{20}Ne{,}^{39}K{,}^{41}K{,}^{42}Ca$ are stable and it is also considered that ${}^{40}K$ is also stable as the half-time of this crystal is 1.3×10⁹ years. The method for the irradiation and detection sequence is to be determined for the analysis of the fluorine.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

Answer to Problem 32.21QAP

The method for the irradiation and detection sequence is irradiation of the sample of each element called as Fast Rabbit method for the analysis of the fluorine.

Explanation of Solution

The short lived nuclide analyzed first in neutron activation analysis method. The value of half-life for nuclei of fluorine element is 11 seconds and because of this it will analyze first. In the Fast Rabbit method, the sample of each element will be irradiated for 10 to 30 seconds at the electron flux of 10¹⁷m²s-1. Just after the irradiation the value of the half life of the element fluorine is 11 seconds and 20 mins later of this sample and comparator of this element will measured separately.

Interpretation Introduction

(f)

Interpretation:

The method for the irradiation and detection sequence is to be determined for the analysis of the potassium.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

Answer to Problem 32.21QAP

The method for the irradiation and detection sequence is the irradiation of the long −live radionuclide and short-live radionuclide for the analysis of the potassium.

Explanation of Solution

The analysis of the long-lived nuclide happened after the completion of the analysis of the short-lived nuclide. The value of the half-time of the potassium is K is 12.4 hr. in this analysis, packed samples are depends on the materials which are irradiated for 1 to 4 hrs at neutron flux of $5\times {10}^{16}{m}^{-2}{s}^{-1}$. The analysis of medium lived radionuclide will be done after 3 to 5 days of irradiation and in case of long-lived radionuclide it will be measured after three weeks.

Interpretation Introduction

(g)

Interpretation:

The amount of the pure potassium fluoride sample 50-mg which is irradiated for 60s. By refereeing the section (e) the activity due to ${}^{20}F$ and ${}^{42}K$ in the sample is to be determined. The cross section are for the ${}^{20}F$ and ${}^{42}K$ are $0.0090\times {10}^{-24}c{m}^2$ and $1.1\times {10}^{-24}c{m}^2$ respectively and it is considered that flux density is $1.0\times {10}^{13}$ neutrons.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

The formulas that will be used-

$A=N\varphi \sigma \left[1-e^{\left(\frac{-0.693t}{t_{1/2}}\right)}\right]$

Answer to Problem 32.21QAP

The value of activity of the fluorine = $A_F=1.3\times {10}^{6}cpm$

The value of the activity of potassium = $A_K=4.796\times {10}^{9}cpm$

Explanation of Solution

The formula is −

$A=N\varphi \sigma \left[1-e^{\left(\frac{-0.693t}{t_{1/2}}\right)}\right]$ ………………….. (1)

Where,

A= activity

$\varphi$ = neutron flux

$\sigma$ = cross section area

N = number of stable target atoms

$\left(\frac{t}{t_{1/2}}\right)$ = ratio for irradiation time

The value of N_F is calculated as-

$N_F=\frac{58\times {10}^{-3}\times 6.022\times {10}^{23}\times \left(20/58\right)\times 0.007}{58}$

$N_F=1.45\times {10}^{19}atoms$

Now, the activity of fluorine is calculated as-

Given that-

$\varphi$ = $1.0\times {10}^{13}$ neutrons

$\sigma$ = $0.0090\times {10}^{-24}c{m}^2$

$N_F=1.45\times {10}^{19}atoms$

$\left(\frac{t}{t_{1/2}}\right)$ = 60s

$A_F=1.45\times {10}^{19}\times 0.0090\times {10}^{-24}\times 1.0\times {10}^{13}\left[1-e^{\left(-0.693\times 60\right)}\right]$

$A_F=1.3\times {10}^{6}cpm$

Similarly, for potassium-

Given that-

$\varphi$ = $1.0\times {10}^{13}$ neutrons

$\sigma$ = $1.1\times {10}^{-24}c{m}^2$

$N_K=4.36\times {10}^{20}atoms$

$\left(\frac{t}{t_{1/2}}\right)$ = 60s

$A_K=4.36\times {10}^{20}\times 1.1\times {10}^{-24}\times 1.0\times {10}^{13}\left[1-e^{\left(-0.693\times 60\right)}\right]$

$A_K=4.796\times {10}^{9}cpm$

Interpretation Introduction

(h)

Interpretation:

The disadvantage and advantage of NAA method over analytical method is to be determined.

Concept introduction:

The NAA method or neutron activation analysis method is defined as the process in which conversion of analyte element to the radioactive isotopes occurs because of the use of neutron irradiation.

Answer to Problem 32.21QAP

In the terms of the advantage of NAA method, it has high sensitivity, easy calibration, good agreements result and requires minimum sample preparation.

In terms of disadvantage of NAA method, requires large instruments, special facility, it is expensive and difficulty in the deposition of radioactive elements.

Explanation of Solution

In the freshwater ecosystem selenium is determined by using the non-destructive method and this is element which shows only gamma-decay.

In this process, samples and standards will be irradiated with the neutrons. The irradiation time is depending on the various factor and the period of the irradiation time is varies from few minutes to several hours.

• The advantages of the NAA method in comparison of analytical method are written below-
• The NAA method ahs high sensitivity
• The NAA method requires minimum sample preparation.
• The process of calibration is easy in this method.
• The results produce by this method are good in agreements
• The NAA method is applicable for the analysis of the minute quantity of analyte.

The disadvantage of NAA method is also given below-

• This method requires large instruments.
• The NAA method is very expensive in comparison of the analytical method.
• This process or technique requires special facility for the experiment.
• In this method there is difficulty for the deposition of the radioactive materials.