Dewar Attenuation of Gamma Rays: Lab Book 2014_08_21

Summary:  Initial results from the Dewar attenuation tests look odd.  They won’t be conclusively odd until all the sources have been measured for the same counting time.  At the moment, the Cs 137 32 keV line is less attenuated than the 22 keV Cd 109 line which is expected, but it also appears to be less attenuated than the Cd 109 88 keV line which is not expected.  It seems like a higher energy should have an easier time getting through the Dewar material.

To Do Today:

• .       Calculate the count rate from the Cs 137 source and compare it to the expected flux from Hirsch’s theory
• .       Run a simulation on a much smaller diameter coil looking into quenching the small YBCO superconductor.
• .       Analyze the overnight run on Cs 137

Bias	1500 V
Gate Window	0.5 uS
Threshold	1.5mV
Attenuation	0 dB
Data set	HBC_00018
Source	Cs 137 Centered in liquid helium Dewar
Start Time	~ 7:15 PM
Stop Time	9:57 AM
Date	2014_08_20 – 2014_08_21
x-y scope V/div	1, 0.5
Shielded?	Yes
Tube	Harshaw B-

Here’s the attenuation calculation done for the raw data.

time in minutes	Peak Count	Rate
Dewar
642	1235	1.923676
Window
185	14188	76.69189
attenuation		16.00618

Background

Bias	1500 V
Gate Window	0.5 uS
Threshold	1.5mV
Attenuation	0 dB
Data set	HBC_00019
Source	background
Start Time	10:04 AM
Stop Time	1:54 PM
Date	2014_08_20 – 2014_08_21
x-y scope V/div	1, 0.5
Shielded?	Yes
Tube	Harshaw B-

Bias	1500 V
Gate Window	0.5 uS
Threshold	1.5mV
Attenuation	0 dB
Data set	HBC_00020
Source	Cd 109 in Dewar
Start Time	1:59 PM
Stop Time
Date	2014_08_20 – 2014_08_21
x-y scope V/div	1, 0.5
Shielded?	Yes
Tube	Harshaw B-

The peak at 88 keV is still visible, but it’s moved over a bit to the left and sits at channel 406 instead of at channel 421. 

With background subtracted, the peak is still barely apparent.

The peak near 22 keV is completely obscured.  The run here wasn’t as long as the Cs 137 run earlier, so it will be repeated with more counting time.

The rough attenuation calculations for the Cd 109 run follow

time in minutes	Peak Count	Rate
Source in Dewar
339	81	0.238938053
Source Taped to Window
83	213243	2569.192771
attenuation		40.31511371
Predicted Background Count at Peak Channel
Peak Channel		Noise Count
59		62.29487179

time in minutes	Peak Count	Rate
Source in Dewar
339	23	0.067846608
Source Taped to Window
83	14777	178.0361446
attenuation		34.18980043
Predicted Background Count at Peak Channel
Peak Channel		Noise Count
421		10.14102564

Here’s a comparison of the peak counts to Cs 137.  Data was taken without the Dewar.

Cadmium 22 to Cs 36 count ratio 0 dB	33.50018767
Cadmium 88 to Cs 36 count ratio 0 dB	2.321446768

Plans for experiments

Pulsed Current Supply

·         Noise in scintillator output during pulse

o   Gate the detector

o   Run with source

o   Run without source

·         schematic

·         diameter of existing coil

·         simulation with existing coil

·         simulation with smaller coil

Iron Magnet

·         Need assistance for first bring-up

·         Run to half max current and check field

o   get Hall probe

·         Check heat generated by coils

Simulations

·         Heat generated by coil

·         Heat generated by eddy currents in sample

·         Discuss eddy currents and field diffusion

Proposal