HM 2014

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10/13/14

stripchart

updated rate calculation

paragraph describing percentage plots for alpha, beta, and gamma with references.


long run time shutter source
7832 6h open off
7834 35min closed off
7835 open on

10/10/14

Alpha Alpha energy percentages.png Ar alpha ionization xsection.png Alpha primaries.png
Beta Beta energy percentages.png Ar e ionization xsection.png
Gamma Gamma energy percentages.png Ar gamma ionization xsection.png 300 px


10/02/14

QDC's and Peak sensing's spectra distinguish between shutter open and shutter close as the source is on, I noticed it from yesterday's and today's measurements.

Also the spectra shows a difference in the number of count and the number of channels as the source on or off as the shutter is open. more measurements is needed to calculate the STDEV.


The oscilloscope picture is shows the gate and signal details,



date time run ended Source run number notes
10/02/14 10:45 On 7792 each run time is 20 min.
10/02/14 11:07 off 7793 22', taking the source off directly then measuring the charge does not show any difference in channel number but shows difference in counts.
10/02/14 16:30 off 7795 20', after 5 1/2 h the detector started to show a little difference again between shutter open source is on and when the source is off.
10/03/14 8:00 off 7795 20'
10/03/14 11:21 off 7795 20' equilibrium without source.
10/06/14 09:05 off 7802 20' equilibrium without source.
10/07/14 7:00 off 7806 lower charge is detected
10/07/14 11:19 off 7807 higher charge is detected (TSO's stuff were checking on the source)


GEM_HV= 2870 Volts, Drift HV = 3470 Volts

GEMoutput 10022014 A.png GEMoutput 10022014 B.pngGEMoutput 10022014 C.png

09/30/14

Plot of shutter open/closed (NO SOURCE) counter rate -vs- date


Alpha's Primaries

Alpha energy percentages.png Ar alpha ionization xsection.png Alpha primaries.png

File:Alpha primaries.xls

Plot of Number of electrons collected -vs- Energy of (alpha, beta, and gamma) from U-233

Electrons

Beta energy percentages.png Ar e ionization xsection.png


E stoppingpower MeV MeVcmg-2.png Ar e range MeV gcm-2.png


Gamma

Gamma energy percentages.png Ar gamma ionization xsection.png 300 px

09/29/14

Shutter open/close data plot for 2.87 3.48 kV GEM /Cathode

B pdaily counts.png


S pdaily counts.png


[1] The reference gives percentages of the emitted alpha particles as U-233 -> Th229 File:Alpha percentages.txt

Alpha E percent.png


Roy's detector infomation and measurements

U-233 metal deposited source is measured by Protean Instrument corporation gaseous detector, has a model number of WPC9450 (serial number: 0915723)and uses (P10) gas mixture, as shown below:

Shutter position Alpha particles /min. Beta particles /min.
Open 6879 900
Close 1 38

Alpha Secondaries.png

09/20/14

Rate of ( alpha, photon, beta) -vs- energy for U-233

Primary electron ionization -vs- (alpha,photon, beta) energy


Alpha Secondaries

U-233 decay beta energy.jpg


Photo-Absorption Secondaries


Photo-Absorption Secondaries.png

The reason that the graph started from 30 keV is the lowest gamma energy emitted by U-233 or Cf-252 is higher than that energy.


Electron Ionization


Using NIST data base [2]


we got the following data file for CO2 File:CO2 e ionization xsection.txt, For Ar, the ref. [3] that measured the ionization xsection. Ar e ionization ref p1.gif Ar e ionization ref p1.gif

Ar e ionization xsection.gif

09/20/14

The figure below shows the change in the signal as the GEM capacitor charges, at a specific fixed voltage it reaches saturation (equilibrium),

GEM signal time equilibS.png

If the capacitor does not reach equilibrium, the signal of the detector is expected to change with time. 


 What may forbid the GEM capacitor to reach the equilibrium?
  1. The circuit board voltage fluctuations.
  2. The following reference describes almost the same conditions as those of our detector when their detector is in operation to detect simultaneously photons with alpha particles.

Nuclear Instruments and Methods in Physics Research A 471 (2001) 151–155

File:Gas electron multiplier for portal imaging wallmark.pdf

The author commented in the conclusion "The studies show that GEMs can operate at extremely high rates (>10^6 Hz/mm^2) with no sign of degradation and stability loss due to radiation damage. However, it was discovered that the maximum achievable gain for all planar gaseous detectors drops with the beam intensity "

"In real clinical operation the detector can operate safely with a gain of 10^2 in the GEM closest to the collector". 

 Our detector has a rate of 100-170 Hz (without and with the source), considering  the detector age, will this rate cause an instability?
  1. High detector rate.

File:Fonte GD limitations.pdf

The gain will decrease when the count rate increases, if GEMs' voltage is at the point where gain is stable with the high rate, the detector output will be reproducible. As mentioned above, a gain of 10^2 made it enough for imaging with a well-quenched gas, I doubt we need to increase the gain more than that.

9/18/14

Determine best Cathode HV that produces the largest separation of the source ON/OFF signal.

The detector results are not reproducible, as the voltage is at 3.4 kV, the QDC spectrum is different as the source on; so QDC can not distinguish if the source is on or when it is off the detector. 

Something is wrong!!!!

We never have a reproducibility problem before using the QDC until I start using V1495, Can we borrow the older module just to test the reproducibility is still a problem. 

It is very unlikely that it is the v1495.  The V1495 only tells the DAQ to read out a module.  
You can test the DAQ by injecting a pulse with a known charge and look for it in the QDC spectrum.

It is VERY important to have scope pictures showing the difference between source ON/OFF.
Then you use scalers to check that your trigger pulse is able to see a difference between source ON/OFF
Then you do the DAQ measurements.  

If you don't follow the above proceedure then you will be building a pyramid on quicksand.

The same case when the cathode voltage increased to 3.6 kV.


Then perform a set of measurements (shutter open/closed and source ON/OFF) to establish reproduceability. Make sure you record the scaler count rates.

9/17/14

Measure the charge for several values of the Cathode HV keeping the GEM preamplifier voltage and gas flow rate constant.

CATH 3.2 KV

QDC source on off 7728 7729.png

CATH 3.1 KV

QDC source on off 7736 7737.png

All the runs have the same duration 20 min.

CATH 3.4 KV

Try to take scope picture to show difference between source on and off signal that are being measured by the QDC.

9/16/14

QDC source on off 7724 7726.png

Condition of above results

Shutter is Open

Red is Cf-252 source ON Run 7724

Green is Cf-252 source OFF run 7726

HV_GEM= -2930 Volts HV_Cathode=-3400 Volts

Gas Flow rate = 0.1 ft^3/hr

Goal
Can the Cf-252 source ON signal be changed?

Change the Cathode voltage to try and turn off the signal when the source is on.

Result

Yes, when the cathode voltage is decreased to -3100V, QDC histogram does not show any difference in the collected charge as the shutter is open with the source on it, and when the shutter is open without the source.


The figure below shows the change in the QDC spectrum when the cathode voltage is -3.2 kV. QDC source on off 7728 7729.png


Neutron_TGEM_Detector_Abdel

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