ASSESSING THE ENVIRONMENTAL POLLUTION USING

NEUTRON ACTIVATION ANALYSIS – K0 METHOD

ON MOSSES

Adrian Florinel BUCSA

Institute for Nuclear Research, Pitesti, ROMANIA

adrian.bucsa@yahoo.com

1. INTRODUCTION

• The problem of toxic pollutant agents that exists in environment was and still is a main interest subject for nowadays health protection

issues.

• Evaluating the impact of these agents on human health can influence major decisions that are to be taken by the authorities

concerning the industrial activities developed in the inhabited areas or from the surrounding areas that directly impact the

environment and inferentially the man.

• Precise measurements of toxic particles in the environment at the level of microelements are essential for an efficient assessment of

the pollution degree.

• In order to determine the elements’ concentration in the samples, it was employed as analysis method the Neutron Activation using

k0 standardization (NAA-k0).

• The Neutron Activation Analysis is an analytic technique based on measuring the number and energy of gamma radiation emitted by

the radioactive isotopes produced in the sample matrix by irradiation with neutrons in a nuclear reactor.

• In the urban areas, the air’s quality is strongly influenced by many

human activities. The high population density, the heavy traffic and the

house heating system in winter and various industrial activities influence

the concentration of trace radionuclide elements in the atmosphere.

• Consequently, the population is exposed to potential adverse effects of

changes in the composition of urban air. Thus, monitoring of air quality

has become a standard of quality control procedure in the urban

environment.

• The purpose of this paper is to determine the concentrations of the

chemical elements that affect the human health – toxic agents that are

present in the air and that are retained through fallout in the ground

mosses – a genuine pollution indicator.

• This plant has the ability to retain in the vegetative tissue the chemical

elements precipitated from the atmosphere – (acts as a sponge –, because

the cuticle that would stop the penetration of elements in the cells lacks

totally and they don’t have roots (they present rhizoids that anchor them

to their substrate)

Figure 1. Different types of ground mosses

• Moss samples were picked-up from certain locations (the locations considered with a higher degree regarding environment pollution),

and then these were processed (dried in oven) and finally they were inserted in polypropylene vial and ready to be irradiate in neutron

flux.

• For the experimental part of this research work there have taken a total of 9 samples from different locations of the city of Pitesti. Out

of the total samples we chose to analyze only 4 samples due to the lack of time.

• After collecting the samples, they were stored in polyethylene bags at room temperature for 10 days after which they were weighed

and then placed in an oven at a temperature of 40oC. There were made regular measurements of the masses and then the work

continued with drying them in the oven until the ground moss’s mass became constant.

• This step was made for the following reasons:

- Water vaporization from the vegetative tissue of the mosses;

- To obtain homogeneous and concentrated samples.

2. SAMPLING

Figure 2. Mosses masses evolution from sampling to ready to irradiation state

Table 1. Samples selected for irradiation in TRIGA ACPR

Sample

no. Sampling location

Initial mass 40oC dry

[g] [g]

1* TRIGA Reactor stack 5,887 3,065

2 Rad-waste treatment plant 3,055 2,785

3 Water purification plant 8,378 4,021

4* PITESTI SOUTH Train Station 3,115 2,984

5 TRIVALE Forrest 3,298 2,902

6* ARPECHIM petrochemical

refinery

3,921 1,732

7* ROLAST S.A. rubber factory 5,426 3,136

8 Pitesti Downtown 8,862 3,990

9 GH. DOJA neighborhood 5,573 2,166

Figure 3. Satellite map of Pitesti with sampling location

• For irradiation, we have chosen a quantity approximately equal from the all four samples; these were weighted in polypropylene vials

with small dimensions and then were sealed.

• The samples irradiation was conducted in the TRIGA ACPR reactor in the rabbit (D10 location). The study was conducted on a total of

four samples of ground moss from the environment (rough samples) because of lack of time.

• The samples together with neutron flux monitor (foil of Au-197) were irradiated in TRIGA ACPR reactor’s rabbit for 4142 seconds.

During the entire irradiation period, the presence of the sample in the irradiation location did not disturb the average value of the

thermal neutron flux.

• The calculus made after irradiation showed that the mean value of neutron thermal flux was about 9.47E+11 neutrons / (cm2*sec).

• It should be mentioned that the short irradiation period of time did not allow the activation of heavy metals elements. Hence, in 4142

seconds of irradiation we succeed to activate short life-time isotopes: 55Mn, 41K, 45Sc, 121Sb, 139La, 151Eu, 75As, 81Br, 58Fe.

3. IRRADIATION PREPARATION

• For this experiment it were used the following samples, devices and installations:

ground mosses samples, polypropylene vials, TRIGA ACPR reactor (rabbit) and

detection system consisted of bin and power supply, high resolution germanium γ-ray

detector, amplifier, detector bias supply, pulsating source, multichannel analyzer

(MCA) and personal computer, Figure 4.

• The detection system was delivered with a software specially used for radiation

spectrum analysis (GENIE 2000).

• The high resolution gamma ray detector is shown in the Figure 5.

4. MEASUREMENTS

Figure 5. HPGe Gamma ray detector scheme Figure 4. Block diagram for high resolution gamma ray analysis

HPGe detector main characteristics: 2 calibration curves:

a) Energy calibration curve;

b) Efficiency calibration curve.

These calibration curves were obtain by using 5 certified sources of Am241, Co60, Cs137, Ba133 and Eu152

a) b)

• TRIGA ACPR Research Reactor – It is an annular core pulsed reactor produced by

General Atomics.

• ACPR reactor can operate in pulsed mode of 20.000 MW.

• It has only one central irradiation channel used for fuel rod irradiation and other

structural materials in pulsed mode.

Irradiation facilities

• C6 Capsule (Max temperature 290 C; Pmax: 6 bar) is an irradiation device used for

irradiation tests in transient regime of experimental fuel rods;

• Neutronography installation;

• PGA (Prompt gamma analysis);

• Pneumatic rabbit for NAA;

• Due to modernization process finalized in 2011, TRIGA Reactor’s lifetime has

been extent until 2030.

Figure 6. TRIGA ACPR Research reactor at NRI Pitesti

TRIGA ACPR REACTOR (ANNULAR CORE PULSED REACTOR)

Neutron flux measurements TRIGA ACPR rabbit (D-10) by Au-197 monitor foil irradiation

Irradiation date: 11/8/2016

Start: 11:07:14

Stop: 12:16:16 Tiradiere(sec) 4142

Pter (MW) 63kW

Monitor Au 0,1% Φmonitor 4 mm

M(g) 4.59E-03

σ0 (cm^2) 9.88E-23

Counting no. T(h) (cooling) R (decay/(nucl*s)) Rcd Thermal flux (n/cm^2*s) R (average)

(decay/(nucl*s)) Std dev (n-1) (rate)

Average thermal flux

(n/cm^2*s) Std dev (n-1) (flux)

1 23.55 1.7790E-10 2.10 9.432E+11

1.7862E-10 1.4677E-12 9.470E+11 7.78E+09

2 28.58 1.8020E-10 2.10 9.554E+11

3 53.58 1.7653E-10 2.10 9.359E+11

4 67.66 1.7679E-10 2.10 9.373E+11

5 145.83 1.7930E-10 2.10 9.506E+11

6 151.07 1.8030E-10 2.10 9.559E+11

7 163.7 1.7830E-10 2.10 9.453E+11

8 168.78 1.7960E-10 2.10 9.522E+11

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- Reactor’s parameters: f and α ( Høgdahl Convention, well-described)

- Irradiation and measurement aspects: neutron self-absorbtion in sample, dead time,

counting time, coincidence correction, etc.

- Detection efficiency calculated for absorption in sample (according with Moens)

- k0 nuclear data and decay correction scheme (all are available in open literature)

NAA-K0 standardization method

NAA-k0 Analysis results uncertities

Induced by Contribution

k0

Q0

α

f

εp – measurement and conversion

Real coincidence correction

~ 1%

~ 1 %

~ 1,5%

~ 1%

~ 2%

~ 1,5%

Total (quadratic summation ) ~ 3,5%

Elemental concentration

Label

Mn K Br Eu La As Sc Sb Fe

[ppm] ± [%] ± [ppm] ± [ppm] ± [ppm] ± [ppm] ± [ppm] ± [ppm] ± [%] ±

Sample 1 890,17 55,7 2,39 2,04E-03 123,1 3,29 0,76 0,106 24,99 4,57 5,74 0,799 5,87 0,599 5,47 1,1 1,97 4,23E-03

Sample 2 807,75 9,55 1,68 5,41E-04 76,36 5,92 0,61 8,33E-02 25,43 2,29 7,33 1,25 5,29 0,824 7,23 0,773 2,05 7,71E-03

Sample 3 762,5 46,2 1,66 1,09E-03 51,03 9,32 0,65 0,148 22,25 3,05 4,88 0,561 7,78 1,2 1,1 0,318 2,07 3,46E-03

Sample 4 704,5 26,87 1,2 7,00E-04 31,01 4,69 0,82 7,87E-02 25,36 3,01 5,35 0,551 6,09 0,43 3,21 0,358 1,78 1,25E-03

• In K0 standardization method the precision depends on a number of parameters like

Q0, f şi α, measurement geometry and real coincidence effects.

• Uncertities values (for NAA) are:

5. RESULTS

Fe

The discussion related to iron toxicity is limited to

ingestion and exposure through environmental pathway.

Target organs are liver, cardiovascular system and

kidneys.Iron affects usually the myocardium and liver

cells and provokes coma, metabolic acidosis, shock, liver

malfunction, coagulopathy, long term affection of organs

and might cause death too.A dose between 0 mg and 60

mg per each mass kg is considered lethal for human

body.

Eu

There are no clear evidences of toxicity property of

europium comparing to the other heavy metals.

Europium chloride indicates a limit intake value for

intraperitoneal area of 550 mg/kg and 5000 mg/kg for

ingestion. Europium nitride shows a slightly smaller

limit intake value for intraperitoneal area of 320 mg/kg,

while the severe toxicity for ingestion is reached at

around 5000 mg/kg.

Sb

Antimony dust inhalation is very dangerous and in

some cases might be lethal; in small doses level, it

provokes headache, dizziness and depression. In case

of prolonged contact with skin surface in provokes

dermatitis; it also affects kidneys and liver, causing

severe nausea and might lead to death in several days.

As

Arsenic might be found in every source of water from

the globe and involves the exposure of both fish and

shellfish. Other exposure pathways are from dyes,

fungicide and from substances that inhibit the wood

aging. Target organs are blood, kidneys, CNS, digestive

system and skin. The ability of arsenic to involve in

redox conversion between As(III) and As(V) makes him

available and more abundant in environment.

Mg

Manganese compounds are less toxic than any other

spreader metals like nickel and copper. However,

exposure to manganese dust should not exceed the limit

value of 5 mg/m3 even for short periods of time

because of his toxicity. Manganese poisoning was

linked to malfunction of locomotive system of human

body and to some cognitive malfunctions.

Br

Bromism – this state of CNS depression is caused by

the moderate toxicity of bromide in several grams dose

level for humans and other animals. The long half-life

of bromide ions (approximate 12 days) provokes the

poisoning of vital fluids. Bromine ingestion can cause a

skin hives similar to acne.

Sc

Elemental scandium is considered a non-toxic

element. The average lethal dose for scandium

chloride (III) for mice was determined to be 4

mg/kg for intraperitoneal area and 755 mg/kg for

ingestion. Due this, the scandium compounds must

be handled similar to the compounds which shows

moderate toxicity.

K

Because of its strong reactive behavior,

potassium must be carefully handled with skin

and eyes protection. Large potassium quantities

ingestion might lead to hyperkalemia strongly

affecting the cardiovascular system.

La

Lanthanum shows a moderate level of toxicity and

must be handled with care. It produces

hyperglycemia, it implies the decreasing of blood

pressure, spleen degeneration and liver

malfunctions.

NAANAA