富山大学水素同位体科学研究センター研究報告25 : 71‑83, 2005.

論文

高感度熱量計によるトリチウム量の絶対測定(Ⅰ)
一熱量測定システムの設計･製作及び性能試験一

松

山

政

夫

富山大学水素同位体科学研究センター〒930･8555

富山市五福3190

Absolute Measurement of Tritium by High‑Sensitivity Calorimeter (I)‑ Construction of Calorimetric Systemand its Perfわrmance Tests I

Masao Matsuyama
Hydrogen lsotope Research Center, University or Tbyama

Gofuku 3 190, Toyama 930‑8555, Japan(Received February 6, 2006; accepted March 30, 2006)
Abstract

A calorimetric system fわr evaluation or the absolute amount of tritium was designed andconstructed,and its basic performance was tested. A calorimeter canbe used to measure totalenergy of radiations as a calorific value･ The present calorimetric system consists of atwin‑type thermal conductivity calorimeter equlPPed with a vacuumghielding, a tritiumcontainer, total pressure gauges, a quadrupole mass spectrometer,and high‑vacuumsystems.
A calibration curve of the calorimeter was prepared at flrSt uSlng two Samples enclosed a

glVenam0unt Of Zr‑Ni alloy powder only,and thefollowlng linear relation was obtained: Eout
= (0･2694±0･0010) Qin, Where E｡｡t is the output (pV)from the heat sensorsand Qin is the

input power (pW) by Joule heating to the sample cell. In addition, the lower detection limit
was estimated to be O･15トLW丘om stability of the calorimeter, which corresponds to thetritium amount of O･ 16 GBq･ As an initial test, Zr‑Ni alloy powder loaded with a glVen amountof tritium was used and the amount of tritium was estimated to be 26･3 GBq, which wasslightly less than the tritium activity detemined previously by uslng a Small ionizationchamber.

71松山政夫
I. Introduction

various kinds of teclmiquesand devices are required for highly precise evaluation andcontrol of the tritiumamount in the fuel cycle of a thermonuclear fusion device from
vleWPOlntS Of safehandlingand economy of the largeamount of tritium･ Those are divided
into two groups: one is the relative measunng techniques and the other is the absolutemeasurlng OneS･ Among the fbmer techniques, 10niza血n chamber, proportional counter,βィay‑induced X‑ray counter, mass spectrometer, inorganic scintillation counter and so onplay an important role fわr quantitative measurements of tritium concentration･ On the other

hand, a pressure‑volume‑temperature methodand a calorimetric methodare ascribed to theabsolute measunng teclmiques, whereas the fTormer method additionally needsanequlPment
toanalyze a tritiumpartial pressure in the measurlng gaS･ The latter calorimetry lS a PrOmlSlng
method to detemine the absolute amount of tritium, while this technique has been mainly
applied so farto measurements of a large amount of tritium because of emission of low

energy β‑rays. Increase in the sensitivity of a calorimeter will result in extension of its

availability fわr the tritium measurements･

Although thereare a variety of chemical forms and/or physical states of tritiumspecies,
the number of P‑rays emitting from the tritiumSpecies is dependent on only the number oftritium atoms in a sample and basically independent of the chemical fb‑ and physical stateof the tritium species･ Namely, total energy emitting fTrom a tritium sample is due to the total
number oftritium atoms. This is a reason why a calorimetric me血Od is the promlSlng One f♭revaluation of the absolute amount of various kinds of tritium samplesand has high potential
as a standard system fわr the relative measurlng devices･ Some叩plications of a calorimeter

have been conducted to determine theamount of radioactive materials: fTor example,
measurements of tritium in getter materialsl1‑2]and massive carbon tiles exposed to tritium

plasmas of the D‑Tfusion experimentsinJETl3], measurements of tritium[4] and tritiated72高感度熱量計によるトリチウム量の絶対測定(Ⅰ)

waterl5], measurements of 14cl6], and so on. Kinetic energy of P‑rays emitting from tritium
atoms is as remarkably small as 5.7 keV (‑912 aJ) in average energy. For this reason absolutemeasurement of tritium by a
100000calorimeter needs ample carefulness.

Source二Tritium

0 8 6 4 2 0

3H‑‑>3He+e‑+V +Q
Maximum Energy: 18.59 keV･fNLh!suatpNleuO

Average Energy: 5.70 keV

The total energy emitting from a

Max lntensity: 2.50 keV

Total Energy: 33.8 llW/Ci

glVen amount Of tritium can be
numerically calculated uslng the

p‑ray spectrum shownin Fig. 1[7],
and

f♭r

exampletheamount

of

0

2

4

6

8

10

12

14

16

18

Energy of β‑particles, ど / keV

tritium of37

GBq (‑1.0 Ci)

Fig. 1 The calculated spectrum of P‑rays emitting fromcon●esponds to energy emission oftritium.

33.8日′W.

If the activity level of tritium is above a fTew tens Ci, it is relatively easy to measure by

us1ng a conventional calorimeter. However, this level is far beyond a detection range of theother devices as mentioned above. To make a standard system of a variety of tritium
measunng devices, lt lS necessary tO develop a calorimetric system with high reliability and･ sensitivity, which is available to an activity level below 1 Ci.
From this vleWpOint, a calodmetric system that equlpped with a high‑sensltlVlty

calorimeter was constmcted f♭r measurements of gaseous, liquid and solid tritium. In thispaper, schematic of the calorimetric systemand basic performance tests used a Zr‑Ni alloy
sample in which a glVen amount Oftritium was retained will be presented.

2･ Construction of a calorimetric system

2･ Il Schematic of the designed calorimetric system

73

松山政夫

Fig･ 2 Schematic drawlng Or a Calorimetric system designed fわr the absolute measurement oftritium･

Figure 2 shows a schematic diagram of the calorimetdc system designed f♭r the absolutemeasurement of tritium. There are three different physical states of tritium: gaseous, liquidand solid state. Among them, solid state of tritiummeans the ad/absorption states of tritium
on/in solid materials. The calorimetric part consists of vacuum pumps (TMP‑2: turbo
molecular pump, RPl2: oil‑sealed rotary pump)and the high‑sensitivity calorimeter (Model:
INC‑7200) that was purchased from Tokyo Riko Ltd. To measure gaseous tritium, devices forstorageandanalysis of tritiumwere also equlPPed. A total pressureand a partial pressure oftritiumCanbe measured by a capacitance manometer (CM)and P‑ray‑induced X‑ray
spectrometer (BIXS), respectively. As a vacuum gauge, a cold cathode gauge (CCG) was

employed in this system. Pmity of tritiumspecies canbeanalyzed by a quadrupole mass
spectrometer (QMS) equipped with a sputter ion pump (SIP). Tritiumgas diluted withhydrogen is stored in the tritiumcontainer, which was specially designed to confine safTely
tritium. An imer tube of the container consists of a stainless steel tube loaded with Zr‑Ni alloy

powderand a heater withthemocouples at the outer surface. The outer tube is connected with也e vacuum pumps (TMP‑1 and RP‑1) to avoid the increase in a temperature of the outer tube74

高感度熱量計によるトリチウム量の絶対測定(Ⅰ)

and to protect fTrom contamination of theambient air. Figure 3 shows the outlook of thecalorimetric system used in this study.

A schematic drawlng Of a speciallydesigned high sensitivity calorimeter fわrthe present study is shown in Fig. 4. The

present calorimeter is a twin type themal
conductivity calorimeter and special

improvements were made to measure quite

small caloriflC Value. Namely, main parts
such as a heat sensor, cell holder and heatFig. 3 Outlook of the calorimetric system used in thisstudy.

sink were compactly

packed into the vacuum
chamber

made

o

∫

stainless steel, which is

comected with vacuum

pumps and a pressuregauge (PG). Tb reduce
the e ffects o f atemperature change in

Fig. 4 Schematic drawlng Of a specially designed high sensitivity
c al ori meter.

ambient atmosphere as

possible, the vacuum chamber was kept in an air‑themostatic box, which was usuallyoperated at a temperature of 300.0 K. Figure 5 is the photographs of the inside arrangement of
the present calorimeter.

A themo module consisting of themo elements of 254 pairs comected in series was used
as a heat sensor of the cell holder. Themal sensitivity of two themo modules attachedbeneath the sampleand refTerence cell holders is about 52 mV/K. Calibration of the thermo

75

松山政夫

module with Joule heating was carried out uslng a heater

material fixed on the outside of each cell holder. Afine

Manganin wire was selected as the heater material,and
its resistance was controlled as to be 100.0

E2. DiffTerential output due to the temperature difference
between two thermo modules is amplified through a回'

direct current amplifier,and theamplified output was
finally recorded. Since resolution of the amplifier used is
0.1トIV, the present calorimeter is able to measure thetemperature difference as qulte Small as 2xlOl6 K･｣Sample/Reference Heat Sink VacuurTI Chamber
CeTI Holders

2.2. Design of a cell to measure solid materials Fig1 5 Photographs of the high‑sensitivity calorimeter: (A) vacuum

absorbed tritium

chamber kept in the air themostaticbox, (B) cell holders and heat sink kept
in the vacuum chamber.

Fig. 6 Detailed drawlng Of a solid cell used f♭r measurlng the tritium amount absorbed in ZトNi alloy

powder.

76

高感度熱量計によるトリチウム量の絶対測定(I)

Figure6shows the detailed

design of two cells usedformeasurement or tritium absorbed in

Zr‑Ni alloy powder (described as"solid cell"). Two solid cells wereused for measurements as reference･晋and sample cell. Tb lower heat

capacity of the solid cell, the body
Tritium‑containing Quartz Ampoule

Sample Cell Reference Ce"

and lid was made of aluminum
Fig. 7 Photographs of the solid cells before (A) and a洗er

alloy as small as possible.

(B) construction.

Photographs of the solid cells befbreand aRer construction are shownin Fig. 7. Each solidcell was cormected with a fine rod through a flne Wire in series.

3. Experimental

3. 1. Materials･ To examine basic performance of the present calorimeter, three quartz ampoules loadedwith Zr‑Ni alloy powder were prepared as test samples. One of them was loaded with a glVen
amount of tritium gas diluted with hydrogen, which was prepared using a specially designed

tritium‑handling device. The other two ampoules were loaded with the alloy powder only.

Particle sizeand weight of the powdered Zr‑Ni alloy were 300‑350い′m and 0.50 g,

respectively. Concentration of tritium gas used f♭r loading was evaluated to be 22% by uslng

a small ionization chamber that was preliminarily calibratedl8]. The totalamount of tritium
was 33 GBq (determined at April 20, 2004),and the concentration of hydrogen isotopes in

Zr‑Ni alloy powder was ZrNiQo.04 (Q‑H + T). According to the thermodynamic data of a

77

松山政夫
zrNi‑hydrogen system, it is expected that residual pressure of hydrogen isotopes is below

about 5xl0‑6 pa at 300K.

3. 2. Procedures of measurement

Asa first step, to make a calibration curve of the present calorimeter, two quartzampoules
loaded withthe alloy powder only were packed in both solid cells･ To improve thermal
conductivity in the solid cells, a glVen VOlume of liquid paraffinwas additionally introducedin each solid cell. A small hole of lids of the solid cells was connected to a fine rod using finewires a鮎r assembly of the solid cells･ Subsequently, they were placed on the sample andreference cell holders, and each fine rod of them was separately fixed to the lid of v.acuum

chamber throughhalf‑cut lids of the heat sinkand half‑cut copper disks･ About 3 cm3 0f liquidparaffin was dropped in the cell holders in advance to improve thermal conductivity between

a solid celland a cell holder. After fixing the lid of vacuumchamber, it was exhausted by
vacuum pumps below 1 ･0Ⅹ10‑2 pa･preparation of a calibration curve by means of Joule heating bias carried out after thedifference in output from two heat sensors was stable･ Applied voltage to the resistanceattached to the outside ofa sample cell holder was changed in the range of 5 to 65 mV, whichcorresponds to the input power of O･25 to 42･25トIW･

4. Results and discussion

4. 1. Preparation of the calibration curve

since the original output from the calorimeter during the tritium measurements isremarkably small,血e accuracy of calori五c measurements strongly depends on stability of a78

高感度熱量計によるトリチウム量の絶対測定(Ⅰ)

total calor血etric device including anamplifier.

Thevariations

ofabackground level measured with no^T]JtnO2‑1ndtno
瓜 札 止2 3 4

tritium ‑ c ontaining sampl e s g i ve

indication of the accuracy and stabilityof the calorimeter. Figure 8 shows an
0example of change in the background

20

40

60

80

100

120

140

160

Time, t/ minlevel with time. In this case theFig･ 8 Background level of the output measured

without tritium: both solid cells is contacting

background level was evaluated aswith the cell holders.

l0.293 ±0,014 llV. This indicates that
4 3 3 2 2 一つ 一｢ 0 00 LO 0 LO 0 Ln 0 l8 0

llfll

the present calorimeter is able toJouleHeating: appHedvoltage:36.93mV

measure precisely the calorific values if/>T]JPCZf)ndlnOres/

the output above 0.04 LIV (36‑0.042

FS｣

power:13.64ー▲W

rangeofmultipller:10pV
time:60min

I

LIV)is taken place by the net〜㌔

temperature diffTerence in both solid

cells.

20

40

60

80

100

120

140

160

180

200

Time,I/min
A calibration cuⅣe or the present
Fig･ 9 An example orthe output‑time cuⅣes with Joulecalorimeter was prepared by applying a heating･

glVen VOltage to the electric resistance fixed on the outside of the sample cell holder. An
example of the changes in the output is shown in Fig･ 9･ In this case, the input power or 13･64

LAW was supplied for 1 hour･ A rapid increase in the output appears with the input power,andthe output reached a given Saturation value after about 30 minutes. The difference between thebaseline and the saturation value is an equilibrium output depending on the present

calorimeter.

Whenthe applied voltage was cut off, the output decreased exponentially to a value of theinitial base line･ Such behavior is shown in Fig･ 10･ The linear relation is described in general

79

松山政夫

by the fbllowlng equation:

AT‑ (T2‑Tl) exp(G t/ H), ‑‑ (1)where AT is the temperature difference(^)iJtnoZ)u1〇一｢

between two heat sensors, ㌔ (n‑1 and 2)

the temperatures of the referenceandsample cell holder, G the thermal
70

80

90

conductivity of a themo module, H the

100

Time, t/ minFig. 10 Plot ofLn(E.ut) vs･ time･

effective heat capacity of a celland its
holder,and t the time. In this equation,

the reciprocal value of G / H isequivalent to a time constant (て) of a

>TlJlnO3(tndlnO

8642

calorimeter. The time constant is theelapsed time to decrease to 1/e of theequilibriumoutput, which was estimatedto be 5.0 min丘om analysis of the line

5

1

0

1

5

20

25

30

35

40

lnput,Q.n/pW
described in Fig. 10.
Fig･ ll Calibration cuⅣe fわr the solid tritium

Figure ll describes the calibration meaSurementS･

curve determined by applying a variety of input power (Qin) to the sample cell holder loadedwith a solid cell. The calibration cuⅣe was measured under the condition that a pressure of

the vacuum chamber is below 1.OxlO12 pa. As clearly seen from the figure, a good linear
relation between the inputand output power appeared,and it was found that the linear relation

canbe reproduced by the following equation in the range of O･2 to 40 pW:
E｡｡l [pV] ‑ (0.2694±0.0010) Qin lpW] ‑‑ (2)Taking account of the standard deviation obtained from the result of Fig･ 8, the lower

detection limit may be evaluated as O･1 5トLWfrom the above equation, which corresponds tothe tritium amount of 0.16 GBq (4.4 mCi).

80

高感度熱量計によるトリチウム量の絶対測定(I)4･ 2･ Measurement ofZr‑Ni alloypowder absorbed tritium

After establishment of thecalibration cuⅣe, a quartz ampoulein the solid cell or the sample cellholder was taken out, and then thetritium‑loaded quartzamPoule wasaltematively set to measure a solid
30

tritium sample･ Subsequently, thesolid cell was put on the sample cell

60

90

1

20

1

50

1

80

Time, t/min

Fig･ 12 Change in the output with time beforeand afterliRing down the tritium sample cell on the sample
cell holder.

holder,and f♭r several days it has

leftuntil the output become constant･ After this, the solid sell was liRedand separated
temporarily from the sample cell holder in the vacuum chamber f♭r one night,and then lifted

down agaln On the sample cell holder under the vacuum condition below 1 ･0Ⅹ10‑2 pa･ Figure

12 illustrates change in the output with time. The output increased sharply just a洗er the

sample cell was brought into contact with the cell holder,and then it gradually decreased to a

1 constant OutPut･ The constant value observed was 6･21 pV･ The net output due to loading withthe tritiumSample is 6･5 pV, sincethe base line was ‑0･29 pV as shownin Fig･ 8･ It was seenfTrom the Eq･ 2 that this output corresponds to 24･ 1トtW･

The present tritium sample was loaded with the tritium amount of 32 GBq, taking into
account the elapsed time a鮎r the initial tritium loading･ The output of血e present tritium

sample is therefore expected to be 29･2 pW･ Namely, the observed output was 82% of the
expected one･ It is considered that the difrTerence in output was caused by the calibration curveof the small ionization chamber and/Or changes in the base line of the calorimeter. ru血er

investigations about these polntS are required to establish a calorimetric system f♭r tritium

measurements.

81

松山政夫
5. Summary

A calorimetric system applicable to measure solid, liquidand gaseous tritium was designed
and constmcted to evaluate the absolute amount of tritium, and its basic perfbmance has beentested. A twin type themal conductivity calorimeter set in a vacuum chamber was speciallyemployed for the present purpose･ The present calorimetric system consists of a highsensitivity calorimeter, a tritium container, total pressure gauges, a quadmpole mass

spectrometer,and high vacuum systems. A calibration curve of the calorimeter has been

prepared at first uslng SOlid materials absorbed a glVen amount Of tritium,and thefollowlng
linear relation was obtained: E.uI ‑ (0.2694 ± 0.0010) Qin, Where E.ut describes the differential

output (pV) fTrom the themo modulesand Qin the input power (pW) by Joule heating to thesample cell. In addition, the lower detection limit was estimated to be O･ 15 pWfrom stabilityof the calorimeter, which corresponds to the tritiumamount of 0.1 6 GBq. As a first test, Zr‑Nialloy powder loaded with a glVen amount Of tritium was measured by the calorimeter･ The

obseⅣed output was 24.1 mW, which corresponds to 26.3 GBq. It was seen that this actlVlty

was slightly less thanthat expected from the tritiumactivity evaluated by a small ionizationchamber. The diffTerence in activity should be further investigated.

Acknowledgements

This work was supported by the Grant‑in‑Aid for Scientific Research of the Ministry of

Education, Culture, Sports, Science and Teclmology. The author is in debt to Dr. S･ Hagiwara(Tokyo Riko Co.) about helpful discussion f♭r designand construction of the high‑sensitivity

calorimeter.

82

高感度熱量計によるトリチウム量の絶対測定(Ⅰ)

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[2] R･ Lasser, C･ Caldwell‑Nichols, L. D6rr, M. Glugla, S. Grunhagen, K. Gunterand R.ID.
Penzhom, Fusion Eng. Design, 58‑59 (2001) 41 1.

【3 】 Private communication.

[4] T･ Genka, K･ Kobayashi,and S. Hagiwara, Int. J. Radiat. Appl. Instrum., Part A (1987)845.

[5]源河次雄､小林勝利､竹内紀男､石川勇､保泉澄､ RADIOISOTOPES,37(1988)

155.

[6] S･ Iwamoto, S･ Hagiwara,and T. Genka, Netsu Sokutei, 30 (2003) 106.

[7] M･ Matsuyama, K･ Watanabeand K. Hasegawa, Fusion Eng. Design, 39/40 (1998)
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[8] M･ Matsuyamaand K. Watanabe, Fusion Eng. Design, 18 (1991) 91‑96.
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27.

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