Alejandro Algora (CSIC-Univ. of Valencia, Spain)

51 Pages·2017·14.82 MB·English

Total absorption
spectroscopy applications to
reactor neutrino physics

Alejandro Algora
IFIC (CSIC-Univ. Valencia, Valencia), Spain
MTA ATOMKI, Hungary

γ
1 γ
2

Solvay Workshop, Nov.-Dec. 2017
Fission process energy balance
Energy released in the fission of 235U
Energy distribution MeV
Kinetic energy light fission fragment 100.0
Kinetic energy heavy fission fragment 66.2
Prompt neutrons 4.8
Prompt gamma rays 8.0
Beta energy of fission fragments 7.0
Gamma energy of fission fragments 7.2
Subtotal 192.9
Each fission is
Energy taken by the neutrinos 9.6
approximately followed by
Total 202.7
6 beta decays (sizable
amount of energy)
James, J. Nucl. Energy 23 (1969) 517
A reactor (1 GW thermal)
produces 1020 ν/s
Example of reactor neutrino oscillation experiment:
Double Chooz, Θ (also: Daya Bay, Reno)
13
Determination of the primary antineutrino spectrum

•  “Pure conversion procedure”: using the beta spectrum measured
by Schreckenbach et al. from different fissile nuclides (235U,239,241Pu)
and more recently 238U (Haag et al.), which requires complex
conversion procedures

•  “Pure” summation calculations (next slide), for many years the only
posibility for 238U
•  “Mixed” solution (Huber-Mueller model)
Antineutrino and decay heat summation
calculations
Beta decay (β-) Spectrum for each transition
J ,π J ,π → J ,π
i i i i f f
A I S(Q − E , J π , J π )
Z N k
k i i f f
J ,π
f f ν spectrum for the decay (n)
S (E) = ∑ I S(Q − E , J π , J π )
(cid:0)
n k k i i f f
(cid:0)
k
A
Z+1 N-1 (cid:0)
(cid:0)
Anti-neutrino rate per fission (Vogel, 1981)
(cid:0)
∑ ∑
S(E) = λ N S (E) / r = CFY S (E)
n n n n n
n n
Decay heat summation calculation
∑
f (t) = E λN (t)
i i i
i
(cid:0)
Example: 60Co decay from http://www.nndc.bnl.gov/
feeding:=I = P *100
β f
Comparative half-life: ft

A way introduced by Fermi
to compare the different
decays (Q, Z’)
p
max T
f (Z′,Q) = const ⋅ ∫ F(Z′, p)p2(Q − E )2 dp, t = 1/2
e f
P
0 f
1
ft = const′ ln(2)
f 2 T = =τln(2)
M 1/2
λ
if
(cid:0)
(cid:0)
The problem of measuring the β-feeding

β
A
Z N
2
γ
2
Real
situation
E E
γ γ
1 2
f = I
1
2 γ
2
γ
f = 0 1
1 •(cid:0)  G e(cid:0) detectors are conventionally
(I = I )
used to construct the level scheme
γ γ
2 1
populated in the decay
A
Z+1 N-1
• From the γ intensity balance we
deduce the β-feeding
(cid:0)
Experimental perspective:
the problem of measuring the β- feeding
β
A
Z N
2
γ
2
Apparent
situation
E E
γ γ
1 2
f = 0 1
2
γ
f = I 1
1 γ •(cid:0)  W (cid:0)h at happens if we miss some
1
intensity
A Single γ ~ ε
Z+1 N-1
(cid:0)
Coinc γ γ ~ εε
1 2 1 2
(cid:0)
Pandemonium (The Capital of Hell)
introduced by John Milton (XVII) in his epic poem Paradise Lost
John Martin (~ 1825), presently at Louvre Hardy et al., Phys. Lett. 71B (1977) 307
TAGS measurements
Since the gamma detection is the only
reasonable way to solve the problem, we need
a highly efficient device:
A TOTAL ABSORTION SPECTROMETER
But if you built such a detector instead of
detecting the individual gamma rays you can
sum the energy deposited by the gamma
cascades in the detector.
A TAS is like a calorimeter!
Big crystal, 4π
d = R(B) ⋅ f