Development of an Active Electron Polarized Target
1) Material properties
Magnetic susceptibility is depicted on pic.1.
Picture 1. Suscettivita’ magnetica a 100 Oe (unita’ emu per mole Gd2SiO5 Oe-1)
Inverted magnetic susceptibility is given at pic.2.
Picture 2. Fitting Curie. Misurati 8.02 B /at Gd (previsti 7.94 B /at Gd).
Picture 3. Assenza di anisotropia magnetocristallina. Suscettivita’ a 100 Oe per H parallelo ai
tre assi di un campione a forma cubica.
M (emu/mol GSO)
SQUID_0527 scheggia 0.0030 g M(H)
8.000 10
4
7.000 10
4
6.000 10
4
5.000 10
4
4.000 10
4
3.000 10
4
2.000 10
4
1.000 10
4
0.000 10
0
M teo
M (emu/mole)
0
10000
20000
30000
40000
50000
60000
B (Oe)
Picture 4. M(H) curva sperimentale confrontata con quella teorica corrispondente a
momenti Gd liberi.
M (emu/mol GSO)
M teo con B
SQUID_0521 18.36.00 07/03/2011
12000.00
M (emu/mol GSO)
10000.00
8000.00
6000.00
4000.00
2000.00
0.00
0
10000
20000
30000
40000
50000
B=H-0.26 4pai M+M (Oe)
Picture 5. M(B) per GSO confrontata con la curva prevista per Gd liberi a 77 K.
2) GSO behavior at cold under magnetic field made by PMT
Spectral measurements of 511 keV source (22Na) with PMT under different conditions were
done. Measurements were held at room temperature (299 K) without and with magnetic field
(B  1 Tl) and at cold temperature (13.3 K) with and without magnetic field. The scheme of this
measurements is given at pic. 6.
H.V.
-1125 V
Amplifier
MCA
PC
Light
pulser
PMT
Quartz
bar
Magnetic
shields
Fiber optics
Quartz bar
magnet
22
GSO
Na
Magnet
Picture 6. The schematic view of experimental set-up
(left) and it’s photo with opened metallic cover (right).
All measurements were done with high voltage on PMT equal to -1125V, shaping time of the
amplifier equal to 6 microseconds, fine gain and coarse gain of the amplifier are 1.5 and 2000
respectively. Also the pulse was given to PMT to check the gain under different conditions. Each
time 2 measurements were done: the spectrum of 511 keV source and the PMT response to a light
pulse.
Room temperature measurements without and with magnetic field

Results for measurements at room temperature without magnetic field are following:
a
Counts
Counts
1340
30
1590
20
0
b
15
0
1000
2000
1000
2000
Channel
Channel
Picture 7. Measurements at 299 K without B-field; a) spectrum of 22Na, b) PMT response to a
light pulse.

Results for measurements at room temperature with magnetic field (1 Tl) are following:
20
250
a
1600
b
1460
Counts
Counts
200
10
150
100
50
0
0
0
1000
2000
Channel
0
1000
2000
Channel
Picture 8. Measurements at 300 K with B  1 Tl; a) spectrum of 22Na, b) PMT response to a
light pulse.
The position of the pulse has changed and this means that the gain of PMT has slightly
changed too. If to take this change into account we can renormalize the position of the source.
When this renormalization is done it turns that the spectrum of 22Na moved to lower channel
number by factor 1.08.
Result: Magnetic field makes no changes in the system and the light output of GSO
scintillator doesn’t change.
Cold temperature measurements without and with magnetic field

Results for measurements at cold temperature without magnetic field are following:
a
200
b
640
1390
Counts
Counts
40
100
20
0
0
0
500
1000
1000
Channel
2000
Channel
Picture 9. Measurements at 13.7 K without B-field; a) spectrum of 22Na, b) PMT response to
a light pulse.

Results for measurements at cold temperature with magnetic field (1 Tl) are following:
120
60
a
680
1790
b
Counts
Counts
90
30
60
30
0
0
0
500
1000
Channel
1500
0
1000
2000
Channel
Picture 10. Measurements at 13.4 K with B  1 Tl; a) spectrum of 22Na, b) PMT response to a
light pulse.
When all renormalizations like for room temp measurements are done it turns that the
spectrum of 22Na moved to lower channel number by factor 1.21. This is a minor movement so…
Results:
a) Magnetic field makes no changes in the system at room and at cold temperature and the
light output of GSO scintillator doesn’t change;
b) Spectrum moves because emission spectrum of GSO goes red [M. Sekita and others,
Optical studies of Ce-doped Gd2SiO5 single crystals]
PMT time response:

at room temperature with B-field
70
60
Amp, mV
50
40
30
20
10
0
1
2
3
4
5
Time, s
Picture A. Inverted PMT signal at 300 K.
Approximate decay time observed at room temperature is 200 ns. But it is not a decay time of
GSO scintillator. Really observed = 0.2µs = (2sci + 2system), sci  56ns.
This means that we can calculate that system = 192 ns.

at cold temperature with B-field
120
100
Amp, mV
80
60
40
20
0
0
1
2
3
4
5
Time, s
Picture B. Inverted PMT signal at 13.4 K.
Approximate decay time observed at room temperature is 900 ns.
Now we can calculate that sci@cold = 880 ns.
We also report no observable changes (in 10% level) in PMT response without magnetic field.
Result: Response signal became longer because of decreasing temperature.
4) APD Measurements: A) 6 keV cold testing + B) GSO spectral measurements
A) Spectral measurements of 6 keV source with APD under different conditions were done.
Measurements were held at room temperature (300 K) without magnetic field and at cold
temperature (13.3 K) without magnetic field. The scheme of measurements that were held at
room temperature is given at pic. 11.
6keV source
APD
PC
MCA
H.V.
1800 V
Pre Amp
Selective
Amp
Fast filter
Amp
Picture 11. The schematic view of experimental set-up and it’s photo with opened metallic
cover.
Measurement at room temperature was done with APD voltage equal to 1800 V, integration
time (ORTEC Fast filter amplifier) equal to 500 ns, fine gain and coarse gain of this amplifier are 1
and 250 respectively. Also the pulse was given to Preamplifier to check the gain of the system.

Result for measurement at room temperature is following:
Counts
60
440
Source (6 keV)
Peak 440ch:
height = 38.24
center = 440
HWHM = 67.64
3029
Pulse:
f = 20 Hz
t = 1 s
A = 200 mV
30
0
0
1000
2000
3000
Channel
Picture 12. Spectrum of 6 keV source at 300 K with APD.
Measurements with APD at cold temperature (13.8 K) were held with a small integration
device between selective amplifier and fast filter amplifier. It is shown on pic. 13.
6keV source
APD
PC
MCA
H.V.
Pre Amp
Selective
Amp
Fast filter
Amp
1800 V
Picture 13. The schematic view of experimental set-up used for measurements at 13.8 K.
Spectral measurements of 6 keV source were done for different APD voltages: from 1250 V
to 1325 V with a step in 25 V. Resulting curve (Channel number VS APD voltage) is given at pic. 14.
Channel number
2000
1750
Data: Data1_B
Model: ExpGro1
Equation: y = A1*exp(x/t1) + y0
Weighting:
y
No weighting
1500
Chi^2/DoF
= 770.759
R^2
= 0.99899
1250
y0
A1
t1
162.2659
8.5093E-13
37.52909
±30.68923
±1.6362E-12
±2.03496
1000
750
500
250
1200
1225
1250
1275
1300
1325
APD Voltage
Picture 14. Channel number VS APD voltage at 13.8 K.
Also measurements with a pulse were done. Pulse’s frequency was 100 Hz, it’s width was 5
ms and it’s amplitude was (10-35) mV with 5 mV step. Such measurements were done also for
coarse gain of fast filter amplifier equal to 50. The resulting plot (Channel number VS Pulse
amplitude) is given here:
coarse gain 100
coarse gain 50
2250
2000
y = 56.3x - 4.7
y = 23.5x + 2.9
Channel number
1750
1500
1250
1000
750
500
250
5
10
15
20
25
30
35
40
Pulse amp, mV
Picture 15. Channel number VS Pulse amplitude at 13.8 K for coarse gain = 100 (red one)
and coarse gain = 50 (green one).
This measurements with pulse allowed us to check the APD gain, so channel numbers could
be renormalized to gain. Resulting curve (Gain VS APD voltage) is given at pic. 16.
800
700
6 keV source
APD at cold: Tplate = 13.8 K
Integr.time = 500 ns
coarse gain = 100
fine gain = 1
Gain
600
Data: Data1_B
Model: ExpGro1
Equation: y = A1*exp(x/t1) + y0
Weighting:
y
No weighting
500
400
Chi^2/DoF
= 26408.65802
R^2
= 0.99339
300
y0
A1
t1
131.14148
1.3357E-14
33.4475
±121.77834
±5.794E-14
±3.58888
200
100
1200
1225
1250
1275
1300
1325
1350
APD Voltage
Picture 16. Gain VS APD voltage at 13.8 K.
Also the Gain of the preamplifier was calculated.
GPreAmp = 0.8 mV/fC
Result: APD works reliably well at low temperature with Gain ≈ 1000 but at voltage higher
than 1400 V starts to have some problem we did not understand yet.
B) APD+GSO spectral Measurements
Spectral measurements of 662 keV source with a GSO crystal which was on top of APD were
done. No optical grease connection between GSO crystal and APD.
source
Coarse g = 5
Fine g = 0.84
Sh.time = 500ns
GSO
APD
H.V.
1800 V
Coarse g = 250
Fine g = 1
Int.time = 500ns
Diff.time = 500ns
Pre Amp
Fast filter
Amp 1
PC
MCA
Amplifier 2
Picture 17. The schematic view of experimental set-up for APD+GSO measurements.
Measurement was done at room temperature with APD voltage equal to 1800 V, shaping
time1 (ORTEC Fast filter amplifier 1) equal to 500 ns, fine gain and coarse gain of this amplifier are
1 and 250 respectively; integration time2 (Amplifier 2) equal to 500 ns, fine gain and coarse gain of
this amplifier are 0.84 and 5 respectively. Also the pulse was given to Preamplifier to check the
gain of the system.

Result for measurement spectrum of 662 keV source at room temperature is following:
662 keV source
is about 1190 channel
APD Volt = 1800V
sh.time1=500 ns
600
Counts
sh.time2=500 ns
400
200
0
0
500
1000
1500
Channel
Picture 18. Spectrum of 662 keV source at 298 K with APD+GSO. APD voltage = 1800V
Measurements at cold temperature were done with the same settings as one at room
temperature (except APD voltage).

Result for measurement spectrum of 662 keV source at cold temperature is following:
30
Source is about 1680 channel
APD Volt = 1325V,
coarse gain1 = 250
25
Counts
20
15
10
5
0
0
1000
2000
Channel
Picture 19. Spectrum of 662 keV source at 15 K with APD+GSO. APD voltage = 1325V
If to make a necessary renormalization of the position of the peak it turns that peak moves almost
300 channels to the lower channel number!
Result: At low temperature spectrum moves 300 channels (25%) to the lower channel
number. This means that the APD Gain decreases. But we also have to take into account that GSO
spectrum is going red at cold [M. Sekita and others, Optical studies of Ce-doped Gd2SiO5 single
crystals]. The quantum efficiency of APD for 400 nm is about 80%, and for 800 nm it is about 60%.
So this mean that we lose approximately 20% of quantum efficiency of APD when moving to red
emission. This can explain why the gain of the APD decreases about 25% at cold.
Magnetization signal estimation
We couple an inductance around the GSO crystal to measure the flux variation caused by a laser
light pulse onto the crystal at cold ( 4 Kelvin )under magnetic field ( 1 T ).
Our attempts to estimate an electric current:
  L  i , where L is an inductance of a coil and i is an electric current.
At the same time
 
 0  

, where  - changing of magnetization of GSO sample, H – height of the sample.
Thus we can say that i 
0 1
L 
Next we can write that  
 .

 
 

, where  is an energy of laser pulse that we provide

 C
to the sample and C is a heat capacitance of GSO sample.
Further we can say that
    const


  
.



So for i we can assume that
i 
 0   
L  C 
.
2
We use   1Tl ,   1mJ ,   2.5  10 m ,
C ~ 10
2
J
(at temperature = 10K). But we do not know exactly the Debye temperature of this crystal
mol  K

1
 2 emu
at 10K we estimated from your data as 10
,

mol Oe  K
4
We have to measure an inductance L but we estimate it as 10 H .