Gamma-rays produced by muon
capture on Al, Si, Ca, I, Au and
Bi (& Fe and Ni)
David F. Measday
Department of Physics and Astronomy
University of British Columbia
Vancouver, B.C.
Canada V6T 1Z1
Muon capture at TRIUMF
●
Ph. D. thesis of Trevor Stocki
–Muon capture in 14N
–Detected gamma-rays with a
–Nucl.Phys. A697, 55 (2002)
HPGE detector
Background check using Al, Si, Ca, Fe, Ni, I, Au,
& Bi
●
Motivation
●
●
Muon capture as a test of the Weak
Interactions
Test of transition strengths in various nuclei,
useful for comparison to beta decay and
especially double beta decay
●
Comparison to knockout reactions
●
Background in high-energy experiments
Experiment at TRIUMF
HPGe
Muon beam line
HPGe
Muon Capture
40
Ca
40
HPGe
K
X-ray
(prompt)
Gamma-ray studies
Advantages
●
●
Good resolution and definition of transition
Easy normalization to μ-mesic x-rays
Disadvantages
●
●
No information on ground-state transition
Vulnerable to background γ-rays
General spectrum
HPGe Efficiency
Recoilling ion causes Doppler broadening of the emitted γrays, but for long-lived states the ion stops
Stopped 28Si(π– ,γ)28Al with pair spectrometer at PSI
Comparison of 28Si(p,n)28P with 28Si(d,2He )28Al, which is
similar to 28Si(n,p)28Al and to 28Si(μ―,ν )28Al
Comparison of our data on 40Ca(μ―,ν)40K, with the
40Ca(p,n)40Sc data of Chittrakarn et al. from IUCF.
Comparison on 40Ca(γ,p)40K for 60 MeV γ-rays with our own
data on 40Ca(μ―,νn)40K.
We do not observe a line in 38Cl that was seen by Igo-Kemenes
et al., with a limit a factor of three smaller
Yields in
Reaction
40
40
Ca(
K
40
39
Ca(
K
40
38
Ca(
K
40
39
Ca(
Ar
40
38
Ca(
Ar
40
36
Ca(
Cl etc
TOTAL
40
Ca
Yield
Total
13 + 0+12 =
25
25 + 8+10 =
43
0.3+0.3+ 2 =
3
6+ 4 + 1 =
11
7+ 5+1=
13
5+0=
5
52 +22+ 26 = 100
Yields in
56
Fe
Line IDs increased from 5 to ~22
Reaction
Yield
Total
56
56
Fe(
Mn
0 + 0 + 15 =
15
56
55
60
Fe(
Mn 38 + 12 + 10 =
56
54
14
Fe(
Mn 6 + 4 + 4 =
56
53
5
Fe(
Mn 3 + 1 + 1 =
56
55
4
Fe(
Cr etc 3 + 0 + 1 =
56
52
2
Fe(
V etc 0 + 1 + 1 =
Total
49 + 18 + 32 = 100
Yields in
nat
Ni
Line IDs increased from 3 to 12
●
●
●
nat
Ni is 68% 58Ni and 26% 60Ni plus 6% from
3 other less abundant isotopes.
We observe 8 lines from 58Ni(μ―,νn)57Co and
4 lines from 60Ni(μ―,νn)59Co; other reactions
are too low in yield.
The 58Ni(μ―,νn)57Co reaction closely
resembles the (γ,pγ) reaction, but does not
follow the spectroscopic factors.
Conclusions
●
●
●
●
●
We have significantly expanded the identifications
for muon capture in Ca, Fe, Ni, (and also Al, Si, I,
Au, Bi)
The (μ―,ν) is observed up to Ca, but not for heavier
nuclei
The (μ―,νn) reaction excites levels similar to those
in the (γ,p) reaction but not to the spectroscopic
factors from knock-out reactions.
The (μ―,ν2n) and (μ―,ν3n) reactions become more
important for heavier nuclei
We do NOT observe the reactions (μ―,ν2p) and
(μ―,ν2pn) reactions
E.Caurier et al., Nucl. Phys. A653, 439 (1999)
Calculations of the (n,p) reaction at 0°
mainly GT, i.e. 1+, ΔT = 1, transitions