Do we need dosimetry?
The Italian group is studying this problem.
There are several options:
•
passive and rather cheap dosimeter
• active ones and rather expensive.
A possibility would be to have a test station with active ones to calibrate all the other dosimeters.
The Italian group is collecting all the necessary info in order to come to a proposal in a very short time.
What we could get (within some months)
USOP
Maybe a different mechanical support is needed.
We’ll have more on this subject soon.
Calliope fits very nicely for our tests
Conservative radiation dose assumed 10 Gy/yr
Conservative flux assumed: 5x1010 n/(yr cm2)
Alexandre comments/suggestions:
Dear Paolo,
We will effectively have 2 He-3 tubes on either side of the CDC (so 4 in
total). However those (as far as I can tell) are only used to measure
neutron fluxes at these positions, which are different than the CsI
positions. Sam de Jong (at uvic, in cc) is the expert on this system.
In the original plan, we don't have a secondary measurement of the dose near
the crystals, but having 2 CsI crystals per box provide some cross-check
capabilities. I know Claudia Cecci talked about plans to put a LYSO counter
in the CsI enclosure to measure the dose as well.
One thing that we have to keep in mind though is the cabling requirement and
rack usage of the BEAST devices. It seems to me that measuring absolute dose
in the CsI boxes is a great idea, but I would be more inclined towards the
simplest (and smallest-footprint) options. Perhaps a passive device not
relying on DAQ at all --- and _possibly_ a G-M active counter --- will
already give us all the information we need?
Cheers,
Alexandre
Obryk B. Radiation Measurements 43 (2008)
6
different
6
LiF-based
TL
detectors
was
standard
LiF:Mg,Ti (MTS-N) equivalent to TLD-100
7LiF:Mg,Ti (MTS-7) equivalent to TLD-700
LiF:Mg,Ti
(MTS-6)
equivalent
to
high sensitive LiF:Mg,Cu,P
7LiF:Mg,Cu,P
6LiF:Mg,Cu,P
LiF:Mg,Ti TLDs (100,
6Li
thank
to
the
(MCP-N)
(MCP-7)
(MCP-6)
equivalent
equivalent
equivalent
600 and 700) are used
high
cross
section
for
to
to
to
investigated:
TLD-600
TLD-100H
TLD-700H
TLD-600H
in thermal neutron fields,
6Li(n,
the
reaction
a)3H
LiF detectors are sensitive to slow neutrons, their response to neutrons being enhanced by 6Lienriched lithium or suppressed by using lithium consisting entirely of 7Li.
Comparison pf results of irradiations in the box using TLDs and Alanine
Good agreement especially at higher doses
•
The results of the experiment performed at the lateral shielding positions show that 25 cm diameter PMMA moderators enhance the response
of all types of TL detectors.
•
•
These moderators provide a 25% enhancement of the signal of MCP-6 detectors, but for MTS-6 detectors the enhancement is about 41%.
For MCP-N and MTS-N detectors the difference in the enhancement of the dose deposited due to neutron contributions is 22% and 40%,
respectively, nearly the same as in the previous case.
This results in an enhancement of the signal due to thermal neutrons (6 Li–7 Li) by 55% and 58% for the MCP- and MTS-type detectors,
respectively.
•
AT LHC MCP-N detectors (TDL-100H)
Conclusions
• In this investigation over 600 TLDs had been irradiated at the low (mGy) and at high doses (up to 150
Gy).
• The results of the high-dose experiment are compared with Monte Carlo simulations giving good
agreement for high energy mixed fields.
• In a comparison between TLDs and alanine good agreement was found at doses above a few Gy; at
lower doses TLDs appear to be more accurate.
• Our studies confirm that the efficiency for thermal and epithermal neutrons is higher for MTS than for
MCP detectors. This enhancement is almost constant for the different radiation fields available in this
experiment.
• All types of detectors used in this study show a consistent response and stable characteristics in
different fields over the high-dose range.
• Results indicate that TLDs can be successfully applied at the LHC to measure low and high doses.
While our results are very encouraging, further calibration of TLDs in high-energy mixed fields will be
of great importance.
• CaF2:Tm dosemeters (TLD-300, 200) are characterized by a
sensitivity to 60Co rays 6-10 times higher with respect to that of
Li:Mg,Ti dosemeters and they do not contain isotopes with
high cross section for thermal neutrons.
• a-Alanine by Electron spin resonance technique
What we have now
TLD700 (neutron flux LiF)
TLD(200) (photons) (CaF2) and alanina
We need a Temperature measurement, a humidity mesuarement could also help. (uSOP)
For fast neutrons a polyethylene moderator is necessary.
They are very small and can be accomodated in the foreseen mechanical support.
they can be read at ENEA Casaccia with exsisting equipment.
Electron spin resonance
Alanine
ESR dosimeter with alanine
(1Gy-500 kGy)
g
50 G
Table I V: Composition of dosimeters for low doses
Dosimeter:
AWM230
Materials:
85% wt L-α-alanine
15% wt paraffin wax
Table I V:4.8
Compos
ition of
dosimeters for low doses
Shape:
cylindrical,
mm
diameter
AWM230
andDosimeter:
10
mm
length.
Materials:
85% wt L-α-alanine
15% wt paraffin wax
Mass:
230 1% (mg)
3
cylindrical, 4.8 mm diameter
Density:
1.27Shape:
g/cm
and 10 mm length.
Dynamic dose range:
1 Gy
–
500
kGy
Mass:
230 1% (mg)
Density:
1.27 g/cm3
Detection threshold:
0.1 Gy
1 Gy – 500 kGy
0.1 Gy
Dynamic dose range:
Detection threshold:
400
400
y = -3,7+ 111,6x
y = -3,7+ 111,6x
300
Dose (Gy)
Dose (Gy)
300
200
200
100
100
0
0
0.5
1
1.5
h
2
2.5
3
3.5
4
/m [a.u.]
(peak-peak)
Figure 12: Alanine dosimeter calibration for low doses (< 500 Gy)
0
0
0.5
Alanine dos
calibration
1 1.3.3b-1.5
2 imeter
2.5
3 for high
3.5 doses4
To construct the calibration curve for high doses, Gold Bruker dosimeters were used, whose
Table V: Composition of dosimeters for high doses
Dosimeter:
Bruker, Gold (1% error mass)
Shape:
cylindrical, 4.8 mm diameter and 5 mm
height
Mass:
88±1% (mg)
Dynamic dose interval:
500 Gy – 50 kGy
Also for high doses, the dependence of the dose on the EPR signal intensity normalised to the
s linear and it can be interpolated with the following curve (Figure 13):
16