MEASUREMENT OF ALPHA-DECAY PROBABILITY OF POLONIUM-212
IMPLANTED INTO SUBSTANCES CONTAINING LEAD-208
V.L. Mikheev1, V.A. Morozov2, N.V. Morozova2
1
2
Flerov Laboratory of Nuclear Reactions, JINR, 141980 Dubna, Russia
Dzhelepov Laboratory of Nuclear Problems, JINR, 141980 Dubna, Russia
One of the paradigms of nuclear science is
the general understanding that the decay
constant of a radioactive substance is
independent of extranuclear considerations
[1]. But all scientific laws are valid only
within the definite limits. The search for the
ways to influence and control the decay rate
of atomic nuclei is a very important and
complex problem. All of the methods realized
up to now can be characterized as dynamic
based on the change of energetic balance of
radioactive decay. One can mention the
creation of isomeric states, variations of
chemical binding energy within molecules
including radioactive atoms, bound-state betadecay. The results of the change of
Mössbauer isomers decay rates through
electromagnetic interference in the system of
decaying atoms and environment including
atoms identical to decay products are very
intriguing.
We made an attempt to observe the change
of nuclear decay rate due to interference of
quantum-mechanical wave function of
decaying nuclear system and wave functions
of nuclei identical to decay products and
forming the solid state environment. As a
motivation, we used the ideas of macroscopic
nonlocality of quantum-mechanical wave
functions and the possibility of not only
dynamical but low perturbing information
control of microscopic processes through the
interference of quantum waves [3, 4]. In the
case of 212Po α-decay, there is a possibility to
implant initial nuclei in the solid state
medium (for example, metal) including 208Pb
nuclei identical to the daughter 208Pb nuclei
forming via 212Po α-decay. One can suppose
the rise of the interference of wave functions
of 208Pb nuclei forming in a process of 212Po
α-decay and wave functions of lead
environment. Due to this interference the
amplitude of the resulting wave function will
change and the corresponding quantum
probability of the α-decay process will
change also. We decided to make the
comparison of the decay rates of 212Po
implanted into natural lead and collected on
the nickel backing as the first step of
investigations.
In our experiments the sources of 212Po
nuclei were prepared by electrostatic
collection of ionized 220Rn decay products in
the emanator with the powder of 232Th oxide
of ~10 grams in weight. Ni-collectors were
made from 50 μm polished foil. Pb-collectors
were made from ~2 mm metal film, which
was freshly mechanically cleaned from oxides
to mirror appearance surface. After one day
collection, the 212Po α-activity on the
collector was ~ 103 1/sec due to the decay
chain: 232Th (T1/2 = 1.4⋅1010 y) Æ 228Ra (5.7
y) Æ 228Ac (6.13 h) Æ 228Th (1.9 y) Æ 224Ra
(3.64 d) Æ 220Rn (55.6 sec) Æ216Po (0.15
sec)Æ 212Pb (10.6 h) Æ 212Bi (60.6 min) Æ
212
Po (0.3μsec) Æ 208Pb. The 212Po position in
the collector is determined by the position of
212
Pb due to small recoil effects in beta-decay.
Due to the collecting mechanism in Themanator, one half of 212Pb is implanted into
the collector in a depth down to 24 μg/cm2 in
the lead equivalent because of 212Pb recoil in
α-decay of 216Po. This is ~200 atomic layers.
Another half of 212Pb ions is absorbed at the
collector surface. In the experiment with the
lead collector we performed thermo-vacuum
evaporation of an additional lead layer ~500
μg/cm2 in thickness onto the surface of the
collector after its exposition in the emanator
to ensure the full immersion of all the 212Po
atoms into the lead medium.
The measurements of decay curves of 212Po
were performed with the scintillation
spectrometer
of
delayed
beta-alpha
coincidences with the NE104 plastic
scintillator [5]. The results of the first
measurements are shown in Fig.1. We have
100000
212Po→208Pb
1. Pb
2. Pb
3. Ni
4. Ni
10000
ChW = 1.99 ns
1
Counts
1000
100
3
4
2
10
1
0
1000
2000
3000
4000
Channel number
Fig. 1. Decay curves of 212Po implanted into natural lead without (1) and with the additional
evaporated lead layer (2) and collected on Ni-foils (3, 4)
obtained the difference of the measured halflives of 212Po implanted into natural lead and
collected on the nickel backing the value of
T1/2 ( Pb ) –T1/2 ( Ni ) = -0.70 ± 0.34 ns
The statistical significance of the obtained
result is 95%, and it must be improved
undoubtedly. The half-life table value for the
alpha-decay of 212Po is 299 ± 2 ns.
Accordingly, the relative difference in decay
rates measured by us is ~2·10-3. The possible
effect of electromagnetic interactions via
change of the Coulomb part of potential
barrier for α-decay is ~10-7. It is important to
continue measurements with the collectors
made from lead compounds with crystalline
structure and enriched with 208Pb. The
interference of any waves (including the
quantum-mechanical wave functions) from
the system of identical equidistant radiators
can form high intensity amplitude maxima.
The work in this direction is very complex
and must include methods of nuclear physics,
solid state physics and great theoretical
efforts. The new experimental possibilities are
accessible now with the beams of radioactive
ions. One can mention the study of 6He decay
in 6Li medium.
References:
1. G.T. Emery, Ann. Rev. of Nucl. Sci., v.
22, 1972, p. 165.
2. S.K. Godovikov, Izv. AN Russia, ser. fiz.,
v. 65, 2001, p. 1063.
3. B.B.
Kadomtsev,
Dynamics
and
Information, ed. by Uspekhi Fiz. Nauk,
Moscow, 1999.
4. Control of molecular and quantum
systems, ed. by A.L. Fradkov and O.A.
Yakubovski, Moscow-Izhevsk, 2003.
5. V.A. Morozov, N.V. Morozova, Yu.V.
Norseev, Zh. Sereeter, V.B. Zlokazov,
NIM, v. A484, 2002, p. 225.