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u S DEPOS y L'
U S DEPOSITORY
ATOMIC ENERGY COMMISSION
RADIOACTIVITY OF Cu60
C. E. Leith
B. J. Moyer
University of California
RADIOACTIVITY OF Cu60
By C. E. Leith, A. Bratenahl and B. J. Moyer
A positron activity with a half-life of 24.6 .3 minutes has been assigned to Cu60
If radiation associated with this decay has an energy of 1.50 .05 Mev, and the upper
limit positron energy is 2.50 .25 Mev.
This activity has been produced in three ways, using separated isotopes of Ni. These
are listed with the cyclotron and particle energies used, as follows:
Ni60 (p,n) 37" frequency modulated cyclotron 5-15 Mev p
60" cyclotron 9 Mev p (18 Mev H2 )
Ni60 (d,7n) 60' cyclotron 18 Mev d
Ni58 (a ,pn) 60' cyclotron 36 Mev d
In the 37 "frequency modulated cyclotron, the Ni60 sample was mounted on a probe;
hence it could be bombarded at an arbitrary distance from the cyclotron center. The
threshold energy observed for the Ni60(p,n) reaction was 5 Mev.
The decay of the activity was observed, using an ionization chamber and Ryerson-
Lindemann electrometer. By exciting the activity with 5.5 Mev protons the decay was meas-
ured through six half-lives with no evidence of a foreign activity.
TYPE OF RADIATION
That the particles emitted were positrons was determined by bending them in a magnet-
ic field into a counter. Penetrating f radiation was also observed.
ASSIGNMENT OF ISCTOPE
Chemical separation of normal nickel targets after bombardment with 15 Mev protons
into Cu, Ni, and Co fractions showed in each case that more than 99 per cent of the 24.6 min
activity followed the Cu separation chemistry.
The 20 mg Ni target was dissolved in 1 mc of boiling concentrated HNO3, which was then
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2 MDDC 1065
driven off by several additions of HCt. 5 mg of Co and 5 mg of Cu as chlorides were added
as carriers. Cu was reduced to cuprous state with .5 ml NH4HSO3 and Cu SCN was precipi-
tated with .5 ml of 10 per cent NH4SCN to be removed by centrifuging. The Cu SCN precipi-
tate was washed twice with a solution of 1 ml 10 per cent NH4 SCN and 5 drops NH4 H803 in
100 ml water. The washed precipitate was dissolved in concentrated HNO3 and dried on a
platinum disc for counting. This separation was accomplished within one hour of the end of
Mass separation in a calutron accomplished within one hour of the end of A p bombarl-
ment showed without question that this activity belonged to Cu60 .
1 ENERGY MEASUREMENT
The energy of "1 radiation was measured by absorption in lead, using the absorption of
Co60, 1.1 and 1.3 Mev 7 radiation for calibration of the geometry. The geometry was simi-
lar to that of Cork and Pidd.1 The active sample was surrounded by at least 2 inches of
lead, except down a collimating hole 8 inches long in lead. The counter tube was 40 inches from
the sample and the lead absorbers were placed directly in front of the collimating hole.
The effective absorption coefficient in lead of the two cascade -y's of Co60 was .640
.010 cm-l, in good agreement with results of Cork and Pidd. The absorption coefficient 1i
lead for the l radiation of Cu60Ni60 was .546 .013 cm-1, corresponding to an energy of
1.50 .5 Mev.
From consideration of the positron energy expected on the basis of (p,n) threshold
energy, it may be that the p + spectrum is complex, consisting of two groups with energies
of 1.0 and 2.5, the 1.5 Mev 1 following the 1.0 Mev P +i Thus the disintegration scheme
0 i60 Cu60
PREVIOUSLY REPORTED ACTIVITIES
The 81 sec and 7.9 min positron activities produced by proton bombardment of Ni ob-
served by Delsasso et al., 2 and tentatively assigned to either Cu58 or Cu60, correspond
1 Physical Review 66, 227 '(1944)
2 Physical Review 55, 113, (1939)
to 81 sec and 10 min activities observed after bombarding Ni with protons in the 37 inch
cyclotron. These are tentatively assigned to Cu59 and Cu58, respectively, on the basis of
threshold and excitation considerations. The longer life was shown to be a Cu activity by
The 3.4 hour half-life activity assigned 3 to Ca61 was verified by being produced in a
Ni61 (p,n) reaction.
The 10.5 min half-life activity assigned4 to Cu62 was also verified, but the half-life
was found to be 10.1 .1 min in measurements made through 6 half-lives.
Acknowledgement is due to Dr. E. H. Huffman and Robert Lilly, of the Radiation Lab-
oratory, for the chemical separations. The mass separations on the calutron were perform-
ed by Keith Pierce.
3 Ridenour and HendersonPhysical Review52 889, (1937)
4 Heyn, Physica 4, 1224, (1937)
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HALF THICKNESS :.500": 1.27 CM
2 3 4
PB THICKNESS IN INCHES
ABSORPTION OF CU60 Io
1000 1500 2000
AL THICKNESS IN MG/CM2
- 5 -
1000 --- MDDC
HALF LIFE v 24.6 MINUTES
DECAY OF ACTIVITY IN
Ni60 AFTER BOMBARDMENT
WITH 5.5 MEV. PROTONS
TIME IN MINUTES
UNIVERSITY OF FLORIDA
III II 111111111111111ill
3 1262 08907 9684
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