Er is onderzocht of bij de teelt van andijvie er een verschil in opbrengsteffect was bij het geven van een stikstofstartgift of -bemesting 3 weken na planten

Alon Osovizky

Dimitry Ginsburg

Eugene Paperno

Max Ghelman

Tzahi Mazor

Yossi Cohen

Ruijter, F.J., de

Name not available

Stikstofbemesting bij andijvie : startgiften en bijbemesting

a b s t r a c t A novel spectroscopic personal radiation device (SPRD) with sub-milliwatt power consumption is proposed. The SPRD is based on a compact, low-power, high-gain silicon photomultiplier (SiPM) coupled to a high-light-yield CsI(Tl) scintillator. The SiPM is operated in a special mode, in which its output is voltage rather than charge. In this mode, the SiPM output becomes higher and rises more slowly than in the charge amplification mode. Such a mode allows us to use a lower-frequency frontend amplifier with a lower gain and lower power consumption. Moreover, the very beginning of the slower, large-amplitude pulses is easier to detect with a comparator. At each detection event, the rest of the SPRD circuitry is activated only for the time needed for the pulse-processing. Because at background the radiation count rate is very low, some tens per second, and the duration of the signal-processing is very short, about 10 ms, the power-demanding SPRD circuitry is not activated most of the time, and its average power consumption is very low. Proper matching of the scintillator and the SiPM helps us to achieve the required gain from the radiation sensor with a relatively low-power, low-gain front-end amplifier. Optimizing the input impedance of the front-end amplifier helps us to obtain the required SiPM output amplitude and shape. Because it takes some time for the signal processing circuit to be activated, an additional passive delay and shaping circuit is used. An experimental model of this device is built, and tested. It is superior to other devices due to its very low power consumption, its portability, and its non-sensitivity to microphonics. The power consumption of the SPRD is about 0.3 mW by the radiation sensor and about 0.3 mW by the electronics (for a total of 0.6 mW as compared to above 20 mW consumed by conventional spectroscopic radiation devices). The power consumption has been measured at count rates up to a few hundreds per second, which are much higher than expected in practice

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Nuclear Instruments and Methods in Physics Research A ] (]]]]) ]]]–]]]Contents lists available at ScienceDirectNuclear Instruments and Methods in
Physics Research A0168-90
doi:10.1
n Corr
E-m
Pleasjournal homepage: www.elsevier.com/locate/nimaSub-milliwatt spectroscopic personal radiation device based
on a silicon photomultiplierMax Ghelman a,n, Eugene Paperno b, Dimitry Ginsburg c, Tzahi Mazor a, Yossi Cohen a, Alon Osovizky c
a Electronics & Control Laboratories, Nuclear Research Center, Negev, P.O. Box 9001, Beer-Sheva, Israel
b Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
c Health Physics Instrumentation Department, Rotem Industries Ltd., Israela r t i c l e i n f o
Keywords:
Silicon photomultiplier (SiPM)
Spectroscopic portable radiation device
(SPRD)
Scintillator
Low power02/$ - see front matter & 2010 Elsevier B.V. A
016/j.nima.2010.08.062
esponding author. Tel.: +972 548358669.
ail address: MaxGhelman@gmail.com (M. Ghe
e cite this article as: M. Ghelman, ea b s t r a c t
A novel spectroscopic personal radiation device (SPRD) with sub-milliwatt power consumption is
proposed. The SPRD is based on a compact, low-power, high-gain silicon photomultiplier (SiPM)
coupled to a high-light-yield CsI(Tl) scintillator. The SiPM is operated in a special mode, in which its
output is voltage rather than charge. In this mode, the SiPM output becomes higher and rises more
slowly than in the charge amplification mode. Such a mode allows us to use a lower-frequency front-
end amplifier with a lower gain and lower power consumption. Moreover, the very beginning of the
slower, large-amplitude pulses is easier to detect with a comparator. At each detection event, the rest of
the SPRD circuitry is activated only for the time needed for the pulse-processing. Because at background
the radiation count rate is very low, some tens per second, and the duration of the signal-processing is
very short, about 10 ms, the power-demanding SPRD circuitry is not activated most of the time, and its
average power consumption is very low. Proper matching of the scintillator and the SiPM helps us to
achieve the required gain from the radiation sensor with a relatively low-power, low-gain front-end
amplifier. Optimizing the input impedance of the front-end amplifier helps us to obtain the required
SiPM output amplitude and shape. Because it takes some time for the signal processing circuit to be
activated, an additional passive delay and shaping circuit is used. An experimental model of this device
is built, and tested. It is superior to other devices due to its very low power consumption, its portability,
and its non-sensitivity to microphonics. The power consumption of the SPRD is about 0.3 mW by the
radiation sensor and about 0.3 mW by the electronics (for a total of 0.6 mW as compared to above
20 mW consumed by conventional spectroscopic radiation devices). The power consumption has been
measured at count rates up to a few hundreds per second, which are much higher than expected in
practice.
& 2010 Elsevier B.V. All rights reserved.1. Introduction
The homeland security market requires advanced spectro-
scopic personal radiation devices (SPRDs) for both radioactivity
detection and radionuclide identification to target malicious
activities. The requirements for SPRDs are given in the latest
ANSI 42.48 [1].
Conventional radiation identification devices (RIDs), [2] being
traditionally based on photomultiplier tubes (PMTs), are cumber-
some, need a high bias voltage, and consume high power [3].
Alternative light detectors, such as PIN diodes and avalanche
photo diodes, also require high-power, low-noise amplifiers
(LNAs) [3].ll rights reserved.
lman).
t al., Nucl. Instr. and Meth.To render conventional RIDs portable, their power consumption
should be substantially decreased. In conventional RIDs, the power
consumption is about 10 mW for the radiation sensor and about
10 mW for the electronics. To substantially decrease the total
power consumption, both these components should be minimized.
In this work, we minimize the first component (to 0.3 mW) by
employing a new type of radiation sensor based on a low-power
light-sensing device: a silicon photomultiplier (SiPM).
To minimize the power consumption of the electronics, we
operate the pulse-processing part of it in a power-gating mode
(see Fig. 1): The power is enabled only when gamma-photon
interactions with the radiation sensor occur. These events are
detected by the comparator, and the logic block synchronizes
the power gating and the integrator operation. The power
gating of the pulse-processing electronics allows us to make
its power consumption negligible compared to that of the rest of
the electronics.A (2010), doi:10.1016/j.nima.2010.08.062
Fig. 1. Spectroscopic portable radiation device based on an SiPM. Schematic and
time diagrams (the outputs of the device components as a function of time). The
dashed lines show the pulse shapes that would obtained for a charge front-end
amplifier.
A
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(a
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ts
)
0
0
In
te
ns
ity
 (a
rb
. u
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ts
)
SiPM manufacturers
Photonunique
Hamamatsu
SensL
Bialkali PMT
LYSO
CsI (Na)
Nal (Tl)
CdWO4
BGO
CsI (Tl)
0.4
0.3
0.2
0.1
1.0
0.8
0.6
0.4
0.2
100 200 300
Wavelength (nm)
400 500 600 700 800
Fig. 2. Wavelength matching between the scintillators and SiPMs. Emission
spectrums of scintillators (top). Absorption spectrums of SiPMs (bottom). For
comparison, the absorption spectrum of a Bialkali PMT is shown as the dashed
line.
M. Ghelman et al. / Nuclear Instruments and Methods in Physics Research A ] (]]]]) ]]]–]]]2To reduce (to 0.1 mW) the power consumption of the front-
end amplifier, we minimize its speed. We use a voltage rather
than a charge front-end amplifier, and this increases both the
width and the amplitude of the pulses at its input (see Fig. 1). As a
result, it becomes possible to use a front-end amplifier with a
lower gain–bandwidth product and, hence, with lower power
consumption.
The remaining major power consumer (0.2 mW) is the
comparator; thus, the total power consumption of the electronics
(0.3 mW) matches that of the radiation sensor (0.3 mW).
The low power consumption of the developed SPRD allows a
month-long operation from a single AAA battery compared to a
few hours operation of a RID based on a PMT. This is not only
because of a greater power consumption of the PMT but also
because of the much lower efficiency of the voltage converter thatPlease cite this article as: M. Ghelman, et al., Nucl. Instr. and Meth.converts the low batteries voltage into a very high bias voltage of
the PMT.2. Radiation sensor
2.1. Selecting the scintillator and SiPM couple
To integrate an SiPM into the radiation sensor, we have
analyzed the matching between commercially available scintilla-
tors and SiPMs. Fig. 2 shows the wavelength correspondence
between the scintillators and SiPMs, and Table 1 lists the
parameters of the scintillators.
The wavelength correspondence and the light yields of the
scintillators (see Table 1) give us the signal yields for different
types of SiPMs (see Table 2). Table 2 shows that the CsI(Tl)–SensL
couple provides the maximum signal yield. Considering the
CsI(Tl) scintillator density given in Table 1, a 8830 mm3
crystal has been selected to meet the sensitivity requirements of
the ANSI 42.48 standard.
The three commercially available SensL’s SiPMs have sizes of
11, 33, and 66 mm2. Their power consumption increases
with size. To minimize the power consumed by the radiation
sensor, we have chosen an SiPM of the SPM3035 [7] type with a
size of 33 mm2. These are the minimal dimensions that provide
low enough noise (see Fig. 3). The selected SiPM consumes about
0.3 mW.
2.2. Temperature stability
As seen from the above, we have modified the radiation sensor
and the electronics to reduce the SPRD’s total power consump-
tion. In the radiation sensor, the conventional PMT has been
replaced with an SiPM. The SiPM noise and gain are high enough
to neglect the contribution of the subsequent electronic stages toA (2010), doi:10.1016/j.nima.2010.08.062
Table 1
Properties of scintillators.
Scintillation crystal Density (g/cm3) Light yield (ph/MeV) Decay time, t (ms) Hygroscopicity Intrinsic radioactivity
BGO 7.13 9000 0.3 None None
CdWO4 7.90 13,500 14.0 None None
CsI(Tl) 4.51 54,000 1.0 Low None
LYSO 7.10 32,000 0.041 None Present
NaI(Tl) 3.67 38,000 0.25 High None
CsI(Na) 4.51 41,000 0.63 High None
The hygroscopicity of the CsI(Tl) scintillator is considered to be low enough for practical purposes.
Table 2
Relative signal yields of different types of radiation sensors compared to an NaI(Tl) scintillator coupled to a Bialkali PMT.
Scintillation crystal Signal yield of different types of light detectors
Bialkali PMT SiPMs
Hamamatsu MPPC SensL SPM Photonique SSPM
BGO 0.17 0.21 0.27 0.19
CdWO4 0.23 0.29 0.38 0.29
CsI(Tl) 0.60 0.94 1.44 1.41
LYSO 0.81 0.87 0.89 0.48
NaI(Tl) 1.00 1.04 0.69 0.30
CsI(Na) 1.10 1.14 0.85 0.40
The relative signal yields include only the wavelength correspondence and the number of initially produced photons.
0
0
C
ou
nt
s
Noise
241Am
1500
1250
1000
750
500
250
100 200 300
Energy (keV)
400 500 600 700 800 900 1000
137Cs
Fig. 3. Energy spectra of the selected scintillator and the light sensor: CsI(Tl) and
SPM3035.
M. Ghelman et al. / Nuclear Instruments and Methods in Physics Research A ] (]]]]) ]]]–]]] 3the device total noise. Moreover, the SiPM is more temperature
sensitive than the electronics. For these reasons, we have
addressed only the effect of the radiation sensor modification on
the device’s precision, neglecting the effect of the electronics
modification.
Temperature affects the gain [4], the avalanche initiation
probability (AIP) [5], and the SiPM noise. Both the gain and the AIP
are functions of the over-voltage VOV that equals the difference
between the bias voltage VB and the SiPM breakdown voltage VBR:
VOV ¼ VBVBR ð1Þ
VBR ¼ V0þaDT ð2Þ
where V0 is the breakdown voltage at a given temperature T, a is
the temperature coefficient, and DT is the temperature change.
As seen from Eqs. (1) and (2), for VB ¼ a DT + VB0, where VB0 is
the bias voltage at T, VOV¼VB0 V0. Thus, both the SiPM gain and
the AIP become temperature insensitive. For the SPM3035, a has
been measured to be 21 mV/1C, and VOV was set at 1.5 V.
To be sure that the identification functionality is not disrupted
by the SiPM noise, we have measured the 137Cs resolutionPlease cite this article as: M. Ghelman, et al., Nucl. Instr. and Meth.(see Fig. 3) at the highest temperature (50 1C), required by
standards. The full width at half maximum (FWHM) resolution at
50 1C is 15%, which is only by 2% worse than at room temperature.3. Electronics
3.1. Power gating of the signal-processing electronics
Direct application of power gating to the pulse-processing
electronics of conventional RIDs is not effective due to the short
duration of the radiation pulses at the front-end amplifier output
(see Fig. 1); the processing electronics does not activate quickly
enough to catch the radiation pulse.
To make the radiation pulses longer, we use a voltage rather
than a charge front-end amplifier and optimize its input
impedance to increase the radiation pulse duration without
significantly increasing the noise (see Section 3.2). We also use
a delay and shaping circuit to further increase the radiation pulse
width (see Fig. 1). These increases provide enough time (about
2 ms) for the integrator to wake up. Due to the long memory of the
integrator, its output can be read by the microcontroller mC,
which activates in about 5 ms.
Employing the integrator helps us to avoid decreasing the
signal-to-noise ratio (SNR), because, delaying the radiation pulse
with the analog shaper by 5 ms instead of 2 ms would collect more
noise.
Selecting a scintillator with a decay constant shorter than 1 ms
would shorten the radiation pulse. A front-end amplifier with a
higher gain and higher power consumption should be used in that
case to compensate for the higher reduction of shorter pulses by
the delay and shaping circuit.
A CdWO4 scintillator, with a very long decay constant, would
allow us to simplify the electronics by omitting the delay and
shaping circuit. We have not selected, this type of scintillator,
however, because radiation sensor pulses that too long would
gather too much SiPM noise.A (2010), doi:10.1016/j.nima.2010.08.062
Fig. 4. SiPM time response to a single microcell activation. The input impedance of
the front-end amplifier is shown as a parameter.
Firing microcell Other microcells
I
RQ CQ
CD CD(N−1)
CG
RQ
RS
RLS
CQ(N−1)N−1
Stray output
impedance
Input resistance of the front-end amplifier
SiPM
Fig. 5. Equivalent electrical circuit of the SiPM.
M. Ghelman et al. / Nuclear Instruments and Methods in Physics Research A ] (]]]]) ]]]–]]]43.2. Front-end amplifier
As mentioned above, employing a voltage rather than a current
front-end amplifier increases the radiation pulse duration. More-
over, this also increases the magnitudes of the radiation pulses. As
a result, it is possible to use a front-end amplifier with a lower
speed and, hence, lower power consumption.
To optimize the input resistance of the front-end amplifier, we
have analyzed its effect on the shape of the radiation sensor’s
output. This output is a superposition of the SiPM’s microcell
activations. Fig. 4 shows the SiPM time response to a single
microcell activation in accordance with the SiPM’s characteristics
[6] and its equivalent electrical circuit [7] (see Fig. 5).
I in Fig. 5 is the equivalent current source that injects an
electrical charge generated by a microcell discharge. CD is the
parasitic capacitance of the microcell, RQ is the quenching resistor,
CQ is the parasitic capacitance of the quenching resistor, CG is the
parasitic capacitance between the SiPM output terminal and the
SiPM gage, RLS is the series parasitic resistance of the SiPM, and RS
is the input resistance of the front-end amplifier. We neglect the
input capacitance (about 10 pF) of the front-end amplifier
compared to CG (about 100 pF).
One can see from Fig. 4, that increasing the input resistance of
the front-end amplifier increases both the amplitude of the SiPM
time response and its duration. One can also see that for relatively
high values of RS, the time-response amplitude grows insignif-
icantly, whereas its decay time continues to increase. As a result,Please cite this article as: M. Ghelman, et al., Nucl. Instr. and Meth.more noise is integrated at the moment when the pulses reach
their maxima, and the SPRD’s SNR decreases. Hence, a tradeoff is
necessary between increasing the SiPM’s output pulse amplitude
and decreasing the SNR. Our simulations and experiments have
shown that the optimum value of the input resistance is 2.6 kO.4. Summary and conclusion
A new low-power SPRD has been developed, built, and tested.
The power consumption has been reduced by more than an order
of magnitude (to 0.6 mW) compared with that of conventional
devices (above 20 mW). Such a significant power reduction has
been obtained by replacing the PMT in the radiation sensor with a
new, and much more power-efficient type of light sensor: the
SiPM. In addition, the power consumption of the electronics has
been reduced to match the power consumption of the SiPM.
The SiPM is operated in a special mode, where its output is
voltage rather than charge. In this mode, the SiPM output
becomes higher and rises more slowly. This has allowed us to
use a lower-frequency front-end amplifier with a lower gain and
lower power consumption.
To maximize the radiation sensor efficiency, we have selected
the CsI(Tl)–SPM3035 couple, after considering the wavelength
correspondence, light yield, the scintillator density, and SiPM size.
We have selected the CsI(Tl) scintillator with a 1-ms decay
constant, because longer radiation pulses would collect more
SiPM noise. For shorter radiation pulses, a front-end amplifier
with a higher gain and higher power consumption should be used
to compensate for more significant reduction of shorter pulses by
the delay and shaping circuit.
A temperature-dependent bias voltage has been used to reduce
the temperature sensitivity of the SiPM.
An experimental prototype has been built and tested. Due to
the integration of the SiPM into the radiation sensor and also due
to the modification of the electronics, the prototype has become
low-power and compact enough to meet the standards for SPRD.
Integrating the SiPM into the radiation sensor also provides
additional advantages such as low bias voltage, robustness, and
insensitivity to microphonics and ambient magnetic fields [8].
The newly developed device provides a 40 keV noise level and
13% FWHM resolution for the 137Cs. It could be used in homeland
security applications to target malicious activities by detecting
radioactivity and identifying radionuclides.
References
[1] ANSI N42.48-2008 Standard for spectroscopic personal radiation device
(SPRD).
[2] ANSI N42.34-2006 Standard for spectroscopic for hand-held instruments for
the detection and identification of radionuclides.
[3] D. Renker, Nucl. Instr. and Meth. A 571 (2007) 1.
[4] Naser Faramarpour, et al., IEEE Trans. Electron Devices 55 (3) (2008).
[5] N. Otte, The silicon photomultiplier—a new device for high energy physics,
Astroparticle physics, industrial and medical Applications, in: SNIC Sympo-
sium, Stanford, CA, 3–6 April 2006, p. 18.
[6] SensL, private letters on the parameters of the SPMmicro3035.
[7] F. Corsi, et al., Electrical characterization of silicon photo-multiplier detectors
for optimal front-end design, IEEE NSS Conference Record, San Diego, USA,
October 2006, pp. 1276–1280.
[8] R. Hawkes, Silicon photomultiplier performance tests in magnetic resonance
pulsed fields, IEEE NSS M18-118 2007.A (2010), doi:10.1016/j.nima.2010.08.062


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