Do Duy Khiem, Hirokazu Ando, Masafumi Akiyoshi

The 2nd Joint Symposium on Advanced
Mechanical Science & Technology
November 28th – December 1st, 2018

Graduate School of Engineering, Osaka Prefecture University
1-1 Gakuen-cho, Naka-ku, Sakai-shi, Osaka 599-8531, JapanINTRODUCTION

MATERIALS AND METHODSBACKGROUND
2008: The radiological education guideline has been added to theschool’s curricula by MEXT.
March, 2011: Fukushima nuclear accident occurred.
Oct., 2011: MEXT accomplished the radiation education materials.
2014: The supplemental reading documents included theaccidental information have been published (MEXT).

X-ray spectrometer

Crookes tube (3C-B,Kenis Ltd., Japan)• Crookes tube has been used in the teaching of science at a juniorand high school in Japan.
• X-ray radiation is possible exposure to a teacher who conducts thedemonstrations and experiments as well as participated students.
• It was reported in Japan that the X-ray radiated from theCrookes tube had very low energy (about 20 keV) but the dose
was very high (up to several hundred mSv/h).
• It is necessary to accomplish the radiation protection and safety
guideline that have not been evaluated sufficiently yet in Japan.

* Nominal dielectric breakdown voltage in the air
is about 1 kV at 1 mm.
* The desired output voltage can be obtained byregulating the distance of the discharge electrodes or discharge output.
* In this experiment, the discharge distance wasset at 40 mm, and variable applied voltages were controlled by change ofdischarge output from 0 to 20 in scale.

Crookes tube:
By
applyingavoltage of several tens kV between cathode and anode in thetube, cations in the evacuated tube are accelerated to hit thecathode that knockout secondary electrons. These electrons
emitted from the cold cathode are accelerated to collide theglass tube to create stopping X-ray.

OBJECTS OF THE PRESENT RESEARCHo Investigating the interrelation between the distribution of
applied high voltage and the X-ray spectrum.
o Carried out simultaneously with X-ray spectra acquisition.

PC USB Oscilloscope(6000BD, Hantek Ltd.)

0.5 mmpinhole3 mm
pinholeCollimator

X-ray
HVCZT
detector

Fixed distance (90 cm)

Estimation of transmission

Applied voltage distribution

Purpose:DPPMCA Software(Amptek Inc., USA)

Collimator:
Reducepile-up*effect and dead time
due to high X-ray
fluxinspectrum
acquisition.
* Cylinder (3mmpinhole) and thinplate(0.5mmpinhole) of Pb.

Induction coil:* High voltage power supply, spark gap of 10 – 100mm.

• Conducting an initial evaluation of the characteristics andproperties of X-ray beam radiated from the Crookes tube used in
the junior-high school for educational science.
• Developing the system that actually can be used inmeasurement of low energy X-rays.
• Submitting the results as the recommendation and guideline forradiation protection rules to prevent unwanted harmful effects
from radiation.

Pocket Multichannel(MCA8000D, Amptek Inc.,USA)Power supply and Amplifier(PX2T, Amptek Inc., USA)CZT Detector (XR-100T-CZT,Amptek Inc., USA)

Voltage divider circuit:* Reducing the magnitudeofvoltageduringmeasurement
againstdamage to oscilloscope
voltage probes due to highpulse.
* The circuit consists of
two resistors in series, oneof 500 MΩ glass resistor,and another of 100 kΩ.

Transmission of X-ray withvarious
outputappliedvoltages generated by Crookes
tube through Aluminum layers.
The transmission of X-rays
was estimated by the ambient
dose equivalent H*(0.07) using
an ionization chamber (ICS1323, Hitachi Ltd., Japan).

30 cm

RESULTS AND DISCUSSION
3. TRANSMISSION MEASURMENT

2. APPLIED VOLTAGE
MEASUREMENT

0Escape peaks
from the Cd and Te

20

1004003456PW0PW2PW4PW6PW8PW10PW12PW141000

H*(0.07) dose (µSv/h)

FWHM
410 eV

800

Voltage (kV)Counts

FWHM590 eV

2251001020Energy (keV)

3016001200

1100004059.54 keV

2000

26.34 keV

13.81 keV

1. X-RAY SPECTRUM
MEASUREMENT

15Aluminum attenuator
CZT detector

1051000102030405060-1070

0300600

Energy (keV)

1200

1500

01800

Figure 2. The high voltage pulse was observed by theoscilloscope with a buffer length of 32K, and a
Time/DIV of 20 ms.

40600

PW0 (15.8 keV)
PW2 (17.0 keV)
PW4 (18.1 keV)
Gauss Fitting

3530

PW0 (16 kV)
PW2 (17 kV)
PW4 (18 kV)
Gauss Fitting of PW0
Gauss Fitting of PW2
Gauss Fitting of PW4500400Frequency

252015300
20010100500681012141618202224262830Energy (keV)4545Voltage
X-ray energy40353530302525202015151010550002468101214161820Output Power
Figure 5. The relevant graphic of the applied voltage andspectral distribution corresponding to output voltage
distribution from PW0 to PW20.

X-ray energy (keV)

Voltage (kV)400510152025303540

Voltage (kV)

Figure 3. X-ray spectra radiated from Crookes tube
acquired by CZT detector. Each spectra corresponds tooutput power of PW0, PW2, and PW4.

1234506Al thickness (mm)Time (ms)Figure 1. 241Am spectrum measured by CZT detector

Intensity

900

Figure 4. The distribution of applied voltage shows theincrease in the output voltage of PW0, PW2, and PW4.

Correlation between applied voltage
and XX-ray energy:
There was a good correlation in thedistribution behavior between the X-ray
spectrum and applied voltage (Fig. 3&4).
Theoutput
voltage
distributed
increasingly in 23.5 ~ 38.9 kV along withincreasing output power.
A spark appeared at PW9 then theoutput voltage kept relatively consistent.
The actual average operating voltage
was about 40 kV that shows goodagreement with the nominal discharge
voltage at 40 mm of plate-needle distance.
The spectral distribution changed in
15.8 ~ 20.3 keV corresponding to theapplied voltage change.
With the consistency of applied voltage,
the X-ray energy also showed saturation
at PW9 (applied voltage reaches 40kV)
with an average energy of about 19.5 keV.

Figure 6. Transmission of X-ray with various output
applied voltages generated by Crookes tube through Al
using ionization chamber ICS-1323.

The transmission curve could be
fitted with the linear expressionof ln(I) = -µx + ln(I0).
The slope of the graph is the Al
linear attenuation coefficient (µ)
with the best fitting coefficients
rather than 0.98.
The effective energy of X-ray wasdetermined from the linear
attenuation coefficient of Al using
data from the National Instituteof Standards and Technology(NIST,USA)
andX-COMprogram.

2468Output Power101214Figure 7. X-ray energies with various output powers
obtaining by attenuation measurement and CZTdetector.

Table 1. X-ray energy estimated from Al
attenuator and CZT detector. The ambient
dose equivalent H*(0.07) measured at adistance 30 cm from the Crookes tube.
Output H*(0.07)
Energy (keV)µ (cm-1)
power (µSv/h)
Al attenuator CZT detector
PW0219
14.58
17.12
15.81
PW2
557
11.70
18.46
17.01
PW4
2064
9.12
20.13
18.11
PW6
4086
8.94
20.27
19.04
PW84182
8.62
20.53
19.26
PW105070
7.66
21.40
19.86
PW125244
8.22
20.8719.73
PW145838
8.32
20.79
19.73

Relevance of XX-ray energy between CZT detector and transmission
measurement:
The effective energy from the transmission measurement was relatively good
agreement with the spectra from CZT detector (Fig. 7).
The average percent difference between the two measurements was 7.5%, andthe average energy was about 19.5 keV for CZT detector and about 20 keV for
attenuation measurement (Table 1).
This difference caused by the effect of the filtration on an X-ray beam in Al
attenuation measurement. Added filtration caused hardening the X-ray beam
because it absorbed the lower energy photons. As a result, it produced a shift
in the effective energy of the X-ray beam.

SUMMARY
We estimated low energy X-ray from the Crookes tube with variable
voltages considered hard to perform. It was about 19.5 keV with thedischarge distance of 40 mm.
We estimated the correlation in distribution between applied voltage and
X-ray energy. The X-ray energy was shifted to higher region in the spectrum
when increasing the applied voltage.
We used the attenuation measurement as an effective approach to yield
information of low photon energy as well as reflected the change of energy
along with the change of output power. It should be considered as analternative approach of CZT detector in the estimation of low X-ray energy inthe teaching of science at junior-high school.