Kapiti gaigakaunta

bias

I've increased the photomultiplier voltage from 478 Volts to 725 Volts, measured with a 10MΩ input meter. Still digging for the high voltage probe.
Latest spectrum 24Aug2011

Increasing the voltage resulted in higher count rates, especially when testing samples, which overwhelmed the computer. I disabled the logging of every count and all seems well.

index

	Am241 v2.0 - smoke alarm redux: hot	28 April 2011
	Am241 - smoke alarm false start	22 April 2011
	bias - increased voltage from 478 to 725V	21 April 2011
	prejudice - snapshot of record before voltage increase	21 April 2011
	perspective - tritium in local waterways	21 April 2011
	spectra - gallery of spectra 30Mar-17Apr	17 April 2011
	fall - southerlies eat radiation	5 April 2011
	top model - Norwegian atmospheric projector	5 April 2011
	rain - it's hot up north	27 March 2011
	bulk bins - fiddling with PRA	25 March 2011
	links	24 March 2011
	production - just another plot of background	24 March 2011
	dimension++ - first 10½ hour run	23 March 2011
	forth - a better regulator, discovering PRA	22 March 2011
	the third day - looking at pulses	21 March 2011
	tutu - rock is cold	20 March 2011
	guff - te ahi kaa	19 March 2011

guff

This is a scintillation detector sitting on a workbench on the Kapiti coast north of Wellington, New Zealand.
It consists of an NaI(Tl) (Thallium doped Sodium Iodide) crystal, I kid you not, under a tinfoil hat. When ionising radiation hits the crystal, scintillation, flashes of light, happens. The crystal peak emission wavelength is 430nm ("super blue").
This is faced up against a photomultiplier tube to complete the detector.
A power supply and interface came with the detector. This runs on 24VDC and generates the high voltage for the photomultiplier. The various electrodes in the photomultiplier tube are connected to a resistive divider in the power supply. A BNC connector carries the electrical output pulses.
These pulses are tee-ed off to a sound card line in, which is used for spectrographic analysis, and to a buffer and an RS232 driver which is used to make the Counts Per Minute graphs.
This all makes a highly sensitive, somewhat unstable, γ (gamma) ray detector capable of broadband spectrographic operation, with peak sensitivity around 210 keV.
Gamma rays have energies of 124 keV or more.
Uncalibrated and subject to change.
Kia kaha Christchurch.
Kia kaha Japan.
Kia kaha katoa.