PePPO NaI PositronDetector 4 JLab

Detector setup for a NaI positron detector for PePPO

NaI detector

The PMT is powered by a HV supply which should have a DC ripple less than 200 mV peak-to-peak at 3kV/3mA. A DC ripple will change the gain of the PMT and cause the energy resolution to deteriorate.

The Linearity of the detector system is another way to reduce the energy resolution. The measured PMT output should be linear with the input signal when the gain is constant. This linearity can be measured using 2 radiation sources.

Input HV: +1085 V

Input Current: 2.362 mA

Running CODA: Running CODA

Measurements Using V792 QDC

Run 1979

Start Time : March 23:12:30:26

End Time: March 23: 13:10:47

Elapsed time: 2421 seconds

Run 1980

Remove Na-22 source from top of NaI crystal.

Start Time : March 23:13:11:23

End Time: March 23: 15:56:40

Elapsed Time:6317 seconds

Let's lower the gain of the Phillips 777 amplifier so the 511 peak is around channel 500. This way the 1 MeV photons may come on scale.

Run 1982

Overnight Cosmic Run

Start Time : March 23: 16:01:47

End Time: March 24: 09:41:31

Elapsed Time:63558 seconds

Run 1983

Start a run using Co-60

Start Time : March 24: 09:46:25

End Time: March 24: 10:14:24

Elapsed Time: 1679 seconds

The 1.x MeV gammas appear near channel 1200.

I'll do a long Na-22 run and think about upping the amplifier gain again to put the Co-60 peak around channel 3000.

The Co-60 source trigger rate is about 750 Hz and the Na-22 trigger rate was about 450 Hz.

Run 1984

Start a run using Na-22

Start Time : March 24: 10:16:49

End Time: March 24: 11:02:38

Elapsed Time: seconds

Run 1987

Increase gain of Phillips 777 amplifier which 
I am using on the PMT output,  We may want to adjust 
the dynode gain/discriminator to fill in the lower 
energy part of the spectrum.

Start a run using Na-22

Start Time : March 24: 11:34:35

End Time: March 24: 1 Elapsed Time: seconds

I was expecting to see a photon of energy 1.17 and one with 1.33 MeV in the above specturm. Assuming that my ability to resolve the two peaks is due to noise I will assume both are in the peak at channel [math]3158 \pm 1[/math]. Since the intensity of the above two lines are almost the same I will do a simple average.

[math]\bar{E_{\gamma}} =\frac{1.17 + 1.33}{2} =1.25 [/math] MeV

The above measurement indicates that a 1.25 MeV photon appears at channel [math]3158\pm 1[/math] in the current apparatus.

Run 1988

Start a run using Na-22

Start Time : March 24: 11:34:35

End Time: March 24: 16:21:31

Elapsed Time: 17216 seconds

The above measurement indicates that a 0.511 MeV photon appears at channel [math]1839 \pm 0.1[/math] in the current apparatus.

Run 1989

Start a run using Co-60

Start Time : March 24: 16:23:30

End Time: March 24: 16:57:00

Elapsed Time: 2010 seconds

The above measurement indicates that a 1.25 MeV photon appears at channel [math]3256 \pm 0.8[/math] previously it was at [math]3158\pm 1[/math] in the current apparatus.

The 98 channel difference is beyond the fit statistic.

Taking the average of the two give 3207 Channels.

Energy Calibration using run 1987-1989

Doing a Linear fit using the two points

1.25 MeV ,3207 Channels

0.511 MeV , 1839 Channles

gives

Channels = 893.06 + 1851.2 MeV

The energy distributions measured do not appear to have the expected structure. There is a 1.3 MeV energy gamma from the Na-22 source which was expected but only hinted at. Its intensity is 10% but it should start to show up on long runs.

The next goal will be to lower the dynode discriminator threshold so we trigger on lower energy events. Does the Compton edge become more obvious for Na-22?

Readout

F250

JLab's F250 flash ADC will be used to measure the NaI output

Na-22 source

North American Scientific Model CAL2600

Activity = 9.803 \muCi on 5/1/05

Serial Number 64236

Na-22 beta decays giving off a 215 keV KE beta and a 1.275 MeV photon.

http://atom.kaeri.re.kr/cgi-bin/decay?Na-22%20EC

Co-60 source

North American Scientific Model CAL2600

Activity = 9.641 \muCi on 5/1/05

Serial Number 64120

Co-60: decays to Ni giving 2 dominant gamma lines at 1.173237( 4) and 1.332501( 5) MeV. The Average Beta energy is 95 keV.

Co-60DecayChain.png

http://atom.kaeri.re.kr/cgi-bin/decay?Co-60%20B-

Positrons#Experiments