DEFICIENCY IN READY-MADE BABY FOODS AVAILABLE IN LOCAL MARKET USING NEUTRON ACTIVATION ANALYSIS TECHNIQUE

49 Table 4.3 Description of the protective arrangement around the HPGe detector 54 Table 4.4 Sample description and identification of cereals 55 Table 4.5 Sample description and identification of milk powder 56 Table 4.6 Sample matrix, CRMs, their identification numbers and weight. 60 Table 4.7 Weight and geometry of samples for natural radioactivity 61 Table 4.8 Irradiation conditions 62 Table 5.1 Nuclear data for elements identified by the NAA technique 80 Table 5.2 Table of nuclear data for detection limit of identified elements. 82 Table 5.3 Origin and typical magnitude of uncertainties in NAA 83 Table 5.4 Measured elemental concentrations in baby foods along with.

Fig. 5.5 Al concentration in (mg/kg) in the powder milk and cereal samples 88 Fig

Introduction 1-14

Types of Radioactivity 3

Natural and Artificial Radioactivity 3

Radioactive Decay Series 5
Infant Nutritional Deficiency and Food Unconsciousness in
Health effect for Nuclear Contamination and Adulteration

N= w NA θ/A (3.5) Therefore, the number of target nuclei is proportional to the mass of the element present;. Gamma ray spectrometry allows qualitative identification and quantitative determination of radionuclides in the sample. The absolute efficiency is the ratio of the number of counts (gross counts) produced in a detector divided by the number of gamma rays actually emitted by the source in all directions [5].

Fig. 1.1 Major pathways of radionuclides to man in the event of an uncontrolled release of radioactivity [5]

Review of the Previous Studies 15-25

Review of the Previous Studies 15

Activation rate neutron flux (φ) (3.1) The activation rate is also directly proportional to the number of target nuclei present. Element activation rate measure (w) (3.6) The relationship between the activation rate, the number of target nuclei and the neutron flux is expressed by the term cross section (σ). Due to nuclear accidents such as Chernobyl, Three Miles Island, Fukushima, etc., radionuclides can be released into the environment and deposited on the ground.

Theoretical Aspects 26-42

Theory of Neutron Activation Analysis 26

Radiative Capture (n, γ) Reaction 27

Background radiation can cause extensive damage to gamma-ray spectrometry system equipment. The detector parameter measurements of the HPGe detector used in the present experiment are given below [6]. These peak areas were used to determine the concentration of radioactivity of the radionuclides present in the sample.

The average Br concentration in the milk powder samples was higher than in the cereal samples.

Fig 3.1 Different kinds of de-excitation path of compound nucleus during nuclear interaction

Neutron Activation Analysis Mechanism 28

Classification of NAA 29

In the NAA process, neutrons interact with stable isotopes of the target element and convert them into radioactive ones. In most cases, radioactive isotopes decay and emit beta particles accompanied by the emission of gamma quanta of characteristic energies, and these radiations can be used to identify and precisely quantify the elements of a sample. About 70% of elements can identify NAA, where the mode of action of DGNAA is mostly suitable [7].

Fundamental Equation for NAA Method 30

Absolute NAA Method 30
Comparative NAA Method 34

The rate of activity or decay (Ao), at the end of the irradiation time t, is then,. Wx = Weight of the element in question in the sample to be analyzed Ws = Weight of the element in the standard sample. Knowing the count rates of the standard and sample, the decay times of the standard and sample, and the mass of the element in the standard, the mass of the element in the sample can be calculated [9].

Advantages of NAA 36

However, this problem can be solved by using several certified reference materials, where the concentration of a large number of elements is certified [10].

Limitations of NAA 36

In the present work, Al2O3-based 226Ra was used as a standard material for determining the efficiency of the detectors. The uncertainty of the samples was calculated according to the 1993 ISO guide and added to the uncertainty in the measurement [10]. The uncertainty of the natural sample was calculated based on the counting statistics of the samples.

The sample uncertainty was calculated according to the 1993 ISO guidelines and added to the measurement uncertainty [4].

Fig. 3.3 The interaction mechanisms for gamma- rays in matter [19]

Theoretical Aspects of Measuring Natural Radioactivity 37

Radioactive Equilibrium 37

Secular Equilibrium 37
Transient Equilibrium 38

Radio-nuclides in Nature 38

Gamma Rays Interaction with Matter 38

Experimental Technique 43-76

Neutron Sources 43

Nuclear Reactor 44
Reactor Core 45
Fuel-Moderation Elements 46
Reflector 46
Control Rod 47
Reactor Tank 47
Reactor Shield 47

Irradiation Facilities of the Reactor 48

Pneumatic Transfer System (Rabbit) 49

Gamma Rays Spectrometry System 49

For the detection of the gamma rays emitted from the experimental samples, an experimental arrangement was established which includes a HPGe detector, a Digital Spectrum Analyzer DSA-1000 with Canberra Detector Interface Module (DIM) containing a high.

High-Purity Germanium (HPGe) Detector 50

High Voltage Unit 52
Preamplifier and Amplifier 52
Multi-Channel Analyzer (MCA) 52
Analog to Digital Converter (ADC) 52
High-Permit PC Spectroscopy Software 53

The resulting charge is integrated by a charge-sensitive preamplifier and converted into a voltage pulse with an amplitude proportional to the original photon energy. The performance of a detector depends on its depletion depth, which is inversely proportional to the net impurity concentration in the detector material. The crystal is clamped to the other end of the copper cold finger, as shown in Fig.

Because germanium has a relatively low band gap (0.74 eV), the detector must be cooled to reduce the thermal leakage current to an acceptable level, as leakage current can destroy the energy resolution of the detector. The detector is mounted in a vacuum chamber attached to or inserted into an LN2 Dewar. In addition, the detector system has a high-voltage filter with a capacitor that can deliver dangerously high current for a short time while discharged (even with the bias power supply disconnected).

The preamplifier is located as close as possible to the detector to minimize signal noise and captive loading. It also acts as an impedance match, providing a high impedance to the detector to minimize loading, while providing a low impedance output to drive downstream components. It contains a memory that stores a list of numbers corresponding to the number of pulses at each discrete voltage.

The Canberra model-8075, a single width NIM (Nuclear Instrumentation .. Module) style analog-to-digital converter was placed between the amplifier and the MCA.

Fig. 4.5 Configuration of the HPGe detector

Background Radiation Effect 53

Two types of software were used for the acquisition of gamma spectra: one is ORTEC DspecJrTM with Maestro-32 acquisition software; another is CANBERRA DSA with Genie-2000 acquisition software.

Shielding Arrangement around the HPGe Detector 53

The shielding reduces not only the background resulting from cosmic rays and from natural radioactive traces in building materials or on the Earth's surface, but also from nearby nuclear facilities and other radiation sources such as air suspected of containing traces or radioactive gases, 222Rn and 220e and so on . Due to its high density (11.4 g/cc) and large atomic number (Z=82), lead is the most commonly used material for the construction of detector shields.

Experimental Procedure 54

Sample Collection 55
Sample Preparation 56

Sample Preparation for NAA 57
Sample Preparation for Natural Radioactivity 57
Standard Preparation Using CRMs 58

Preparation for Irradiation Vial 59
Description of the Samples 59
Irradiation Conditions 61
Gamma Ray Counting and Peak Analysis 62
Optimization of Useful Parameters of the HPGe Detectors 64

Efficiency Calculation of HPGe Detector 64

Counting of Samples and Standards 68
Correction Factors of the Experiment 69

Attenuation Correction 69
Interference Correction 69

Spectrum Analysis 70
Experimental Measurements 70

Elemental Concentration 70
Quality Control 71
Detection Limit 71
Total Uncertainty Budget 73
Natural Activity 73
Dose Rate 74
Radium Equivalent Activity 75

Gamma ray counts of the standard were recorded for 5000 seconds at the surface of the detector. During the above discussion and references, it is concluded that none of the samples analyzed in the present experiments exceeded the recommended aluminum values worldwide. The maximum detection efficiency is one of the vital parameters for determining the activity concentration of radionuclides.

The average activity of 40 K in milk powder is almost twice that of cereal. After irradiation, the gamma rays of the irradiated samples were counted twice using two independent sets of gamma ray spectrometry systems. Cs content in most samples is less than the detection limit (0.46 mg/kg) except Junior Horlicks (J.H) and Marks (M.1).

Table 4.4 Sample description and identification of cereals

Result and Discussion 77-114

Toxic and Essential Elements using NAA Technique 77

Quality Control 80
Detection Limit 81
Estimation of Uncertainty Budget 82
Concentrations of Identified Elements 84

Aluminum (Al) Concentration 88
Bromine (Br) Concentration 89
Calcium (Ca) Concentration 91
Cesium (Cs) Concentration 92
Potassium (K) Concentration 93
Magnesium (Mg) Concentration 94
Manganese (Mn) Concentration 96
Sodium (Na) Concentration 97
Zinc (Zn) Concentration 98

Correlations Among the Elements 99

As can be observed from Tables 5.4-5.6, the given values of mineral content in baby foods quoted by manufacturers are somewhat lower than existing experimental values in most cases. Each of the elemental statuses in baby food and their international permissible limits are described individually below. This implies that all investigated milk powders and cereals contained trace amounts of Al which is essential for the body, but none of the samples contained levels high enough to show any toxic effects.

The main health effects that can be caused by bromine-containing organic contaminants are malfunctioning of the nervous system and disturbances in genetic materials. The average Br concentration in the powdered milk samples was found to be mg/kg. Ca deficiency is responsible for the weakness of the bones and bones are therefore more prone to fractures.

When contact with radioactive cesium occurs, a person may experience cell damage from radiation from the cesium particles. In the present experiment, the Cs content in most samples is lower than the detection limit (0.46 mg/kg), except Junior Horlicks and Marks, which contain trace amounts of 0.555 mg/kg and 0.536 mg/kg, respectively. K concentrations in most grain samples were around the allowable lower limit, indicating that grain samples were not a potassium-rich food supply for infants.

From the above analysis, it can be observed that only N.1 and L.2 samples contain a certain level of Zn concentration; in the rest of the samples the concentrations are well below the internationally permitted limit.

Fig. 5.1 Gamma ray spectrum of short irradiated Cereal-2 sample (counting duration: 300 s, decay time: 8 min)

Natural Radio-Nuclides using HPGe Detector 102

Attenuation Effects 104
Activity of Natural Radio-nuclides in Powder Milk and
Radium Equivalent Activity 111

Although the geometry of the experimental samples, CRMs and SRM were identical (packed in the same size pot, maintained at the same height), attenuation corrections were significant due to the density differences between them. The efficiency of the detectors was calibrated using Al2O3-based 226Ra standard, which was approx. 110 g. On the other hand, the average weight of the test samples was 66 g, which is somewhat less than the standard weight.

In the case of U, the milk powder contains ~ 1.7 times the activity concentration of the grains, whereas the Th content in powdered milk is approx. 1.4 times the grains. The radionuclide 137Cs is one of the tracers for identifying the radioactivity in food, including powdered milk. Although baby food samples have exposed radiation internally, the Raeq for cereal and milk powder was much lower than the maximum permissible limit (MPL) [32].

The K concentrations in most of the cereal samples were around the lower permissible limit, which indicated that cereal samples were not potassium-rich food supplies for infants. The samples, e.g. Mark's powdered milk, Cereal-3 (vegetable) and Cereal-K, contained uranium concentrations roughly within the limit of the world's permissible limit. Even a large part of the population has no idea about the radiation pollution and its harmful effects.

Milk and milk products are one of the important food items for human nutrition.

Fig. 5.15 Natural gamma ray spectrum of Marks (M.1) sample (counting time: 20000s)

Summary and Conclusion 115-120

Future Work 120

Due to the higher background effect and poor counting statistics, there were deviations in the natural activity analysis. Although the natural concentration of 238U and 232Th was higher than the world safety level, it should be checked again before warning people. BG is the background under a beam tip. The name of the element is Sodium, Na Energy = 1369 keV.