Measurement of Wood Ash Radioactivity

Introduction

I have measured, with my geiger counter, radioactivity of ashes taken from my stove. Measurements were done in my room also was monitored background activity. 

Wood ash is the residual material after combustion of various kind of woods (spruce, pine, hazel and others), as you know wood is made of carbon (that combined with oxygen give some CO2) and many other elements like: sulphur, nitrogen, phosphorus and potassium. These elements could reach the atmosphere as fly ash or as gas (like SO2). Potassium is one of the greater components of the ashes.

The isotope K-40 is pretty interesting because, as you see in fig.1, is about the 0.01% of total potassium (isotope abundance). Potassium is common in organisms (Na + /K + -ATPase for example) and  therefore it is also common in wood. Some properties of K-40 are listed below.

Natural abundance

0.0117%
Half life 1.248×10^9 years
Decay β-, γ

 

 

Materials:

Detector: Geiger counter (http://nysa.altervista.org/geiger.html) with SI-29 BG tube.
Sample mass: 700g of wood ashes
Sampling time: 30 minutes for background and 30 minutes for sample.

Enviromental conditions
T=20.7 C
P=1.012x10^5 Pa

Results:

Activity measurements are shown in Fig. 4 (sampling time 30 minutes). As you can see radioactivity of wood ashes' sample is about double of background radioactivity.