Fertilizer and photopeak identification

Equipment:

SP5630EN/ENP – Enviromental Kit 
Beta Radioactive Source

Purpose of the experiment:

Record the energy spectrum of Fertilizer sample and identify the Potassium peak. The experience will guide the user to select a ROI and perform a Gaussian fit on the peak. This sample can be used also as a reference for the spectrum calibration.

Fundamentals:

Potassium is a natural element whose radioactive isotope ⁴⁰K is widely available on Earth, especially in food and in human bodies. It plays a key role in geologic fields for the dating samples and rocks. Indeed, one of the main decay is in ⁴⁰Ar, which remains locked up in minerals. Knowing the decay time of ⁴⁰K into ⁴⁰Ar, and measuring the ratio between the two elements, it is possible to give a precise estimate about the origin of that material.

Another interesting application is the so-called Banana Equivalent Dose (BED), a “user-friendly” unit to measure radioactivity. Bananas naturally contains ⁴⁰K and 1 BED corresponds to 0.1 mSi of equivalent dose. To understand the proportions, consider that a dental X-ray corresponds to eating 50 bananas, an average daily dose of natural background is 100 BED, a fatal dose is 100 million bananas. This quantity has been introduced to get users familiar with natural low-radioactive objects.

Experimental setup block diagram.

Requirements:

No other tool is needed

Carrying out the experiment:

Put the i-Spector digital into the base and place the Fertilizer box into the place-holder. Power on the i-Spector and connect the Ethernet cable. Wait until the temperature is stable from the web interface (it can take half an hour from power on).

Check the waveform, modify the threshold and gate width, if needed, then start the measurement of the energy spectrum.

Take 30 minutes of acquisition with the Fertilizer.

NOTE: in case of background measurement, settings and acquisition time must be the same. Lead blocks could help in distinguish a clearer peak but they must be used if just employed in background measurement only.

Results:

Several steps can be done in this experiment. First, the background subtraction by saving the .csv of the two and by making a bin-by-bin subtraction of the two spectra. A small portion of the ⁴⁰K peak can be seen in the background spectrum too. The ⁴⁰K peak can be then selected through a ROI and fitted by means of a Gaussian function. The peak can be used together with the LYSO crystal for the energy calibration of the system (ID.6140)

Fertilizer sample: total contribution and background on the left; background subtracted on the right with a Gaussian fit on the ⁴⁰K peak. The mean value is in agreement with the expected value of 1460.8 keV