10–16 MeV proton irradiation of iron, zirconium and copper: Resistivity-dose measurements

Journal of Nuclear Materials 84 (1979) 173-182 0 North-Holland Publishing Company

lo-16 MeV PROTON IRRADIATION OF IRON, ZIRCONIUM AND COPPER: RESISTIVITY-DOSE MEASUREMENTS *

A.M. OMAR **, J.E. ROBINSON and D.A. THOMPSON Institute for Materials Research, M&aster

University, Hamilton, Ontario, Canada L8S 4iUl

Received 24 February 1979

Iron, zirconium and copper samples were irradiated at 17.5 K by 10 to 16 MeV protons. The resistivity change was measured as a function of the bombarding dose. Values of the resistivity damage rate are determined from the experimental data and are compared with the corresponding estimates obtained from a modified Kinchin-Pease model and from a vacancy-recombination model. Good agreement is found between the latter model and the experimental results. The data are also compared with other proton irradiation and d-Be neutron experiments.

able. In another experiment [S] , an iron sample was irradiated at 68 K with 16 MeV proton beam. The results of this work indicated that the number of the induced simple defects is less than the number of the same defects when estimated by applying a simple Kin&in-Pease model. In the present work, the change in electrical resistivity with dose is reported for Fe, Zr and Cu irradiated at 17.5 K, with 10, 14 and 16 MeV protons. The resistivity damage rates dApi/d@ are measured (indirectly) and compared with estimates determined using previous analytical data. A modified Kin&in-Pease model and a vacancy-recombination model are used for the theoretical evaluation of d&i/d@.

1. Introduction

In previous articles [l-3], damage parameters were calculated for Fe, Cu, Ni, Zr, Nb and Au irradiated by lo-20 MeV protons and 14 MeV neutrons. These theoretical studies indicated, for the proton bombardment case, that approximately 50% of the deposited damage energy is in the form of low-energy (
2. Experimental methods

The materials used in the present experiment were cold-drawn wires. “Marz-grade” a-iron and zirconium wires, 61 cun in diameter, were supplied by Materials Research Corporation. A high-purity * 122 cun copper wire was supplied by R.R. Coltman, Jr. of Oak Ridge National Laboratory. The specimen wires were wound on 250 cun thick anodized aluminum shee,ts to form either a target or a reference sample. Of each material, one target and one reference sainple, separated by an

* Research supported by a contract from Atomic Energy of Canada Limited. ** Present address: Westinghouse Canada Ltd., Atomic Power Division, Box 5 10, Hamilton, Ontario, Canada.

* R2&& 173

K = 1432.

174

AM. Char et al. /Proton irradrhtion @Fe, Zr, Cu - resistiviiydose

I

I

a

I

.

b

C

1

I

I

0

I

2

cm Fig. 1. Anodized ~um~um specimen sheets, (a) Reference sample sheet, (b) target sample sheet, (c) insulating sheet; (0) current lead point, (A) potential lead point, (m) target reference tap point and central potential lead point.

anodized aluminum sheet, formed a “specimen stack”. Fig. 1 displays the different sheets used for each stack. It was possible to mount two specimen stacks for the

same irradiation run. This is shown in fig. 2. Heatsinking compound was applied between all parts to provide good thermal contact. The iron and copper A

SECTION A-A

I 0

1

I

I

2

cm TARGET SIIEETS _E sHsH~;s HEATING-ELEMENT HEATING BLOCK

TUGES

Fig. 2. Sample holder assembly.

-I

175

A.M. Omar et al. /Proton irradiation of Fe, Zr, Cu - resistivitydose

samples were soldered directly to two lead-stations positioned on the sides of the target-holder body. For zirconium, brass contacts were spot-welded to the sample terminals before being soldered to the leadstations. The reference sample, mounted away from the proton beam, was soldered in series with the target. It was used to detect any variation in the base temperature. Normally, one of the Fe specimen stacks was irradiated as-received. The other stack was wound on the sheets and then annealed at 623 K for 2 h in a vacuum of 1.3 X lo-’ Pa. Such annealing conditions reduced the dislocation density in the sample without changing the grain size [6]. The copper wires were wound as-received onto two specimen stacks. One of these stacks was annealed for 2 h at 873 K [7] in a vacuum of 1.3 X lo-’ Pa in the presence of an oxygen-

gettering material. When these conditions were applied for Zr annealing, it was found that Zr wires were sig nificantly oxidized. This problem could not be avoided in the annealing facilities that we used. In choosing the sample dimensions and experimental conditions, deviations from Matthiessen’s rule [8] were kept as small as possible. The cryostat system employed in the present work has been described previously [9]. It suffices here to say that such a cryostat system comprises a two-stage helium-cooled cryocooler and a target assembly. The targets can be cooled by closing (under pressure) a thermal-contact switch using an externally controlled mechanical linkage system. The minimum temperature of the second-stage cold head of the cryocooler and of the target are lo-13 K and 13-17 K, respectively.

-ROUGH

PUMPING

\I . PROTON BEAM

I . FOUR SEGMENT APERTURE

2. FARADAY CUP 6 \I

3. CRYOCOOLER EXPANDER 4. THERMOCOUPLES FEEDTHROUGH 5. MECHANICAL REDTHROUGH 6. ION PUMP

Fig. 3. Beam alignment and irradiation setup.

I

176

A.M. Omar et al. /Proton irradiationof Fe, Zr, Cu - resistivity-dose

This compares favourably with the unloaded cryocooler temperature of 8 K. The sample temperatures were measured by two 127 I.trnchromel-gold (0.078% Fe) thermocouples [lo] calibrated against a referred GaAs temperature sensor. Preliminary measurements with such thermocouples indicated a uniform temperature distribution within 1.OK over the sample holder assembly. The lead wiies and the thermocouple leads were heat-anchored to the second stage of the cryorefrigerator to minimize heat leakage. The absolute resistance of the sample was measured using a potentiometric method. Copper wires of 127 p in diameter were used as current and potential leads. A constamcurrent of (30.00 &0.01) mA was used for the Fe and Zr samples while a current of (500.0 2’0.3) mA was employed for the Cu run. The current was applied to reference and target samples connected in series in each stack. A 10.0 CZstandard resistance was mounted in series with the specimen stack to check the value of the current employed. This showed an error in the current readings between 3 X lo-* and 6 X lo-*% as detected with a digital voltmeter. The uncertainty in the voltmeter reading was less than &1.OPV. The change in the target resistance was corrected against base temperature variations by employing the formula A& = AR + AWWrJr)

>

(1)

where A indicates a difference between the measured value at any anneal step and the pre-irradiation value; R,, R and RO are the corrected, measured and preirradiated target resistances respectively. The quantities R, and Ror, respectively, represent the measured and the pre-irradiation reference resistances. The irradiated length was measured by a microdensitometer from an x-ray photographic plate with an estimated error of 2.5%. The irradiated wire diameter was measured to +l .Opm by an optical microscope. The 9 MV terminal voltage McMaster Tandem Accelerator was used to generate a beam of 10 to 16 MeV protons. The cryostat, including the target assembly was mounted on the beam line as shown schematically in fig. 3. Following the proton beam transport to the irradiation line, the beam passed through a 4-segment aperture 0.5 cm in diameter. This circular-shaped beam then entered a 0.55 cm aperture placed in front of the target, irradiated the two target specimens, and

was collected in a Faraday cup positioned at the end of the beam line. The total current-time product could be determined from a current integrator on the Faraday cup. The area required for the dose evaluation was determined using the irradiated target before demounting. An x-ray photograph was used for this purpose in conjunction with a microdensitometer.

3. Resistivitydose measurements The target materials were irradiated with 10, 14 or 16 MeV protons to several dose-levels. The resistivity change was measured in each case as a function of dose and the resistivity damage rate was subsequently evaluated. Table 1 summarizes the specimen parameters before and after irradiation. 3.1. Iron The early runs (one to eight) were carried out using a 16.0 MeV proton beam. The change in resistivity due to irradiation, Api, with the bombarding dose was measured at several base temperatures and subsequently normalized to a base temperature of 17.5 K. For the as-received samples, the dose wasvaried from 3.8 X1016 to 1.56 X10” p/cm’, resulting in a resistivity change between 0.332 and 1.224 pS2 * cm, respectively. In addition to the asreceived specimens, run number two also included an annealed sample. After being irradiated by 1.56 X 10” p/cm’, the annealed sample featured a resistivity change of 0.884 /.LJ * cm. These early runs showed that the resistivity-dose results, which were taken with the mechanical heat switch closed, were reproducible. In runs number 9 through 12, the total dose was kept constant at approximately 3.5 X 1016 p/cm2 while the incident energy was varied from 10 to 16 MeV. The observed resistivity change was between 0.309 and 0.375 &? . cm for the as-received samples, and between 0.250 and 0.325 /,~s2* cm for the annealed cases. Run number 13 was undertaken using an incident energy of 10 MeV with a dose of 8.8 X1016 p/cm2. This yielded Apt of 0.776 and 0.700 /_~a- cm for the as-received and annealed samples, respectively. The observed resistivity changes as a function of dose are displayed for the as-received specimens in

117

A.M. Omar et al. /Proton irradhztionof Fe, Zr, Cu - resistivity-dose Table 1 Sample parameters before and after irradiation Run no.

Base temperature

Resistivity ratio a)

Eo (MeW

Maximum dose (10-16p/cmz)

APi &sL. cm)

Not rbeasured 16.40 19.80 20.25 19.95 20.11 20.64 21.28 20.46

16 16 16 16 16 16 10 14 10

1.3 15.6 1.4 1.4 3.1 3.5 3.5 3.4 8.7

0.624 1.224 0.618 0.613 0.332 0.309 0.375 0.324 0.776

(K) As-received Fe 1 2 3 3 6 9 11 12 13

Annealed Fe 2 9 11 12 13

14.1’ 12.8 16.8 16.8 17.0 17.5 14.5 17.5 17.5

12.8 17.5

16

15.6

0.884

17.5 17.5 17.5

109.29 92.82 117.23 119.55

64.20 b,

16 10 14 10

3.5 3.5 3.4 8.7

0.250 0.325 0.270 0.700

17.0 17.5 17.5 17.5

35.20 37.28 35.36 35.86

16 16 10 16

3.7 3.5 3.6 7.7

0.908 0.881 1.282 1.856

17.5

546.75

16

2.0

1.853

As received Zr 6 14 15 16

Annealed Cu 17

X lo-*

a) R296KIRBa.se temperature (K) b, Annealed at 873 K for 2 h and then wound on the sample-sheet.

fig. 4 and for the annealed targets in fig. 5. The solid curves represent a fourth-order polynomial fitted to the experimental points using a least-square approach, From figs. 4 and 5, it can be observed that for doses below approximately 2.0 X 1016 p/cm-* the experimental data are scattered along a linear least-square fit owing to a statistical error of *2.0% on the average in the resistance measurements. Above a dose of 2 X IOr p/cm2 the resistance error is less than 0.5%. However, there is an additional error of 2.5% due to the uncertainty associated with the measurements of the irradiated lengths.

3.2. Zirconium As was stated above, annealed Zr samples could not be obtained..Thus, only as-received specimens ,were employed. A beam of protons withan energy of 10 or 16 MeV was used. An integrated dose of approximately 3.6 X 1016 p/cm2 was reached in all the runs except the last in which a dose of 7.7 X 1Or6 p/cm2 was employed. The resulting resistivity change varied from 0.881 to 1.866 @la cm as summarized in table 1 and is shown as a function of dose in fig. 6.

A.M. Omar et al. /Proton irradiationof Fe, Zr, Cu - resistivity-dose

178

---

0

I

Least-squore -

Fit

Extrapolated Linear Flt

2

3

4

3 DOSE,

A,y,&m

Run No.

Eo,MeV

I 2 3

16 16 16

0.624 1.224 0.616

6 9 I I.

I6 I6 IO

0.332 o.Jo9 0.375

I2 I3

I4 IO

0.324 0.776

6

7

8

9

lOI6 ~cm-~

Fig. 4. Resistivity-dose schemes for as-received Fe.

3.3. Copper

An annealed sample was irradiated to a total dose of 2.0 X 1OL6p/cm’. This yielded a total resistivity change of 18.53 nQ - cm. The resistivity change as a function of dose is displayed in fig. 7. An error of 2.5% exists in the measurements of the absolute resistance of the target. The error bars shown in fig. 7 include this error and an error of 2.5% in measuring the irradiated length. No results are reported in the present work for as-received Cu since the change in resistivity in that cases was very small. In fig. 7, the result of Roberto et al. [ 1 l] for d-Be neutron irradiation of a similar Cu sample at 4.2 K is

also displayed. Dworschak et al. [ 121 irradiated a Cu sample with a 10 MeV proton beam at 80 K. At a dose level of 1 X 10”’ p/cm’, they observed a resistivity change of 74.0 na - cm. Since about 6% of the damage induced in Cu at 17.5 K by a 16 MeV proton beam is recovered at 70 K [ 131, and since an excess of 63% in dApr/d@ is observed in the present work (for 16 MeV proton irradiated as-received Fe at 17.5 K) over that observed previously [5] when a similar iron sample was irradiated by 16 MeV protons at 68 K, the resistivity change observed at 80 K by Dworschak et al. can be multiplied by 1.6 to determine the value that would have been observed at 17.5 K. Such a modified result is displayed in fig. 7.

A.M. Omat et al. /hoton

iwadiation of Fe, Zr, Cu - resistivitydose

119

0.7

6

-

Least-square

- ---

Extrapolated

Fit Linear Fit

0.6

G x . 2-0.5 . ii f ‘5 t: 5 5

0.4 E* 0.3

z w a

6

E.,,MeV

A,o,pficm

l

9 I I 12

16 IO I4

0.250 0.325 0.270

P

I3

IO

0.700

0

0.2

.

0

I

2

3

4

5 DOSE,

Fig. 5. Resistivitydose

4.

Run No.

Analysis and discussions

As can be seen from figs. 4 to 7, for low doses Apr varies linearly with the fluence. This is in agreement with results reported for Fe [ 141, Zr [ 151 and Cu [ 11,12,16]. A linear least-square fit was made for low doses (a.0 X 1016 p/cm2). A boundary condition was imposed on the fitted line to yield a value of zero for the intercept. Deviation from linearity was observed for fluences greater than 3.0 X 1Or6 p/cm2, independently of either the sample pre-irradiated conditions or the value of the bombarding energy. Two general features were observed from the experimental data: (i) The rate of resistivity change with dose is higher for the as-received samples than the annealed cases, and (ii) the rate of resistivity change is highest for the lowest incident energy.

6

7

8

9

lOI6 pcm-e

schemes for annealed Fe.

Experimental values of the resistivity damage rate were determined from figs. 3 to 7. The slopes of the linear part of such plots at zero dose give values for the corresponding d&t/d#t. The resistivity damage rates were also calculated using previous theoretical data [3]. This was carried out using a modified Kin&in-Pease model [ 17,181 and a vacancy-recombination model [ 181. In the modified Kinchin-Pease model, spontaneous recombination is not considered and only V-I pairs are dealt with. For such a case, the resistivity damage rate can be expressed as [ 191 KED

d&t/d@ = lo-*’ 2~

APFP 2

D

where ED is the damage energy in barn * keV, Ed is the displacement threshold energy in eV, ApFp is the

180

A.M. Omar et al. /Proton irradiation of Fe, Zr, Cu - resistivitydose

-

I .E

--

- -

Least-square

Fit

Extrapolated

Linear

Flt

EO,

Run No.

Eo, MeV

6 14

16 16 IO I6

0

0.4

0 A .

0

I

2

3

DOSE,

IX

4

5

Ap,@m 0.906 0.88 I I .262 I .056

6

7

IOU6 pcm’2

Fig. 6. Resistivity-dose schemes for as-received Zr.

resistivity due to a Frenkel pair in ps2 * cm/at%, and K is the displacement efficiency and is equal to 0.8. The vacancy-recombination model was also used to calculate values for dApt/d@t. For this purpose, the following form was developed [ 191: d&r/d#t=

&FP

?a~ *se”

@Jr) + &W?D)

@’

’ (3)

where on is the damage cross section [ 191, a(~,) and determined from computer studies [ 181, E’ is the primary recoil energy and nD

p(u,) are coefficients

is the damage efficiency. To carry out the integration, values for (ILand /I were taken from the literZ&w% VaheS for (5D, tjD and Er were obtained from previous studies [3,19]. The formula of Norgett et al. [20], which was developed originally for iron and recommended later by an IAEA committee to be used for other metals [21], was also modified to yield

P91 d&l/d$t

= 1O-27 EDAPFP ,

(4)

where ED is in barn . keV and Ap~p and ps2 * cm/at%. For the case of iron, values of ED were interpolated

A.M. Omar et al. /Proton irradiation of Fe, Zr, Cu - resistivity-dose

181

I16 MeV

Present

)-

____ --

Roberto Dworrchok

d-61

ot al.

at

al.

Protons Nautronr

IO MeV Protons (Modified for 17.5 K)

j-

DOSE,

Fig. 7. Resistivity-dose

from table 3 in ref. [3] for 10, 14 and 16 MeV protons. A value of 25 eV was assigned for Ed, while ApFp was taken as 19 @? * cm/at% [22]. Table 6 in ref. [3] was used to obtain values of ED for Zr. Values for Ed = 24 eV [23] and ApFp = 40 ~s2 * cm/at% [24] were assigned for calculations. For Cu, values of (II= 58 eV and /3= 1.3 X 10v3 were taken from the work of Robinson and Torrens [ 181. Fig. 4.8 in ref. [ 191 was used to obtain values for oo and E’. A value of bFp = 1.3 ~.cS2 * cm/at% [22] was taken. Table 5 in ref. [3] was used to determine values for ED. The experimental values of dApi/d$t were determined from figs. 4 and 5 for Fe, from fig. 6 for Zr and from fig. 7 for Cu. The theoretical estimates of the resistivity damage rate were obtained from eqs. (2) and (4) for Fe and Zr and from eqs. (2) and (3) for Cu. The present experimental and theoretical values for the resistivity damage rate are summarized in table 2 for Fe, Zr and Cu.

IO’@

p cm’*

schemes for annealed Cu.

It is of interest to point out the close agreement shown in table 2 between the experimental results and the theoretical estimates evaluated using the vacancy-recombination model for the metals under consideration. This agreement suggests that recombination of simple defects [25] is taking place in the case of lo-16 MeV proton bombardment. Another point of interest is shown in the damagerate plots presented for Fe in figs. 3 and 4. Comparison between these two plots shows that asreceived targets exhibit higher resistivity damage rates than the corresponding rates observed for annealed cases. Similar results are reported for Fe by other researchers [26-281. In the present study, this phenomenon may be related to the difference in dislocation density which exists in the as-received and annealed specimens (as indicated by the difference in the respective resistivity ratios, table 1).

182

A.M. Omar et al. /Proton iwadkation of Fe, Zr, Cu - resistivity-dose

Table 2 Resistivity damage rate, in 1O-24 s2 * cm3/particle, as estimated from theoretical and experimental data for Fe, Zr and Cu Element

Energy (MeV)

Resistivity damage rate Experiment

Theory

As-received

Annealed

MKP a)

VR b,

9.0 f 0.4 8.0 i 0.4 7.1 * 0.3

21.4 17.8 17.1

12.2 10.1 9.8

56.8 45.3

31.4 27.2

Fe

10 14 16

11.0 f 0.5 9.0 f 0.4 8.8 f 0.4

Zr

10 16

36.0 i 2.0 25.0 f 1.0

cu

16

0.95 f 0.05

1.36

1.06

a) Modified Kinchin-Pease model, eq. (2). b, Vacancy-recombination model, eqs. (3) and (4).

5. Conclusions

The present work leads to the following conclusions: (1) The vacancy recombination model is a good approximation to estimate the number of displaced atoms in proton irradiation, and (2) The resistivity damage rate increases with increase of the dislocation density in the target.

References [l] C.M. Logan, Lawrence Livermore Laboratory, Report No. UCRL-51224 (1972). [ 21 C.M. Logan, J.D. Anderson and A.K. Mukherjee, J. Nucl. Mat. 48 (1973) 223. [ 31 A.M. Omar, R.E. Robinson and D.A. Thompson, J. Nucl. Mater. 64 (1977) 121. [ 41 J.B. Mitchell, C.M. Logan and C. J. Ether, J. Nucl. Mater. 48 (1973) 139. [5] D.A. Thompson, J.E. Robinson, R.S. Walker, A.M. Omar and A.B. Campbell, in: Proc. Int. Conf. Radiation Effects and Tritium Technology for Fusion Reactors, Gatlinburg, Vol. 1 (1975) 382. [6] J.M. Wells and K.C. Russell, Radiation Effects 37 (1976) 157. [7] R.R. Coltman, Jr., Oak Ridge National Laboratory, private communication (1977). [8] J. Bass, Adv. Phys. 21 (1972) 431. 191 M. Shimotomai, A.M. Omar and J.E. Robinson, Cryogenies 17 (1977) 47. [lo] L.L. Sparks and R.L. Powell, J. Res. NBS 76A (1972) 263.

[ 111 J.B. Robertson, C.E. Klabunde, J.M. Williams, R.R. Coltman, Jr., M.J. Saltmarsh and C.B. Fulmer, Appl. Phys. Lett. 30 (1977) 509. [ 121 F. Dworschak, K. Herschbach and J.S. Koehler, Phys. Rev. 133 (1964) A293. [13] A.M. Omar, J.E. Robinson and D.A. Thompson, 1. Nucl. Mater. 84 (1979) 183. [ 141 C. Minier-Cassayre, Report No. ORNL-tr-668 (1965). [ 151 P. V&ret, F. Moreu, A. Bessis, C. Dimitrov and 0. Dimitrov, J. Nucl. Mater. 55 (1975) 83. [ 161 C.E. Klabunde, R.R. Coltman, Jr., J.K. Redman and J.M. Williams, BAPS 23 (1978) 288. [ 171 P. Sigmund, Appl. Phys. Lett. 14 (1969) 114. [ 181 M.T. Robinson and I.M. Torrens, Phys. Rev. B9 (1974) 5024. [ 191 A.M. Omar, Ph.D. Thesis, McMaster University (May 1978). [ 201 M.J. Norgett, M.T. Robinson and I.M. Torrens, Nucl. Eng. Des. 33 (1975) 50. 1211 Announcement on units, J. Nucl. Mater. 73 (1978) 2. [22] P.G. Lucasson and R.M. Walker, Phys. Rev. 127 (1962) 485. [ 231 H.H. Neely, Radiation Effects 3 (1970) 189. [ 241 M. Biget, R. Rizk a&P. Vajda, Solid State Commun. 16 (1975) 949. [25] R.S. Averback and K.L. Merkle, Phys. Rev. B16 (1977) 3860. [ 261 M. Nakagawa, K. Being, P. Rosner and G. Vogl, Phys. Lett. 56A (1976) 481. [27] S. Takamura, H. Maeta and S. Okuda, J. Phys. Sot. Japan 26 (1969) 1125. [28] J.A. Horak and T.H. Blewitt, Phys. Stat. Sol. A9 (1972) 721.